The 2010–11 South-West Indian Ocean cyclone season was the least active cyclone season on record in the basin, tied with 1982–83, producing only three systems of gale intensity. This was due to cooler than normal water temperatures and the Walker circulation – a broad atmospheric circulation – causing unusually moist conditions in the eastern Indian Ocean and unusually dry conditions in the western Indian Ocean. The basin includes the waters of the ocean south of the equator and west of 90o E to the eastern coast of Africa.

There were nine tropical or subtropical cyclones during the season, including five weak tropical disturbances or depressions, mostly in the northeastern portion of the basin or to the east of Madagascar. The first of these systems developed on 25 October 2010, which had its origins in the northeastern portion of the basin. On 29 November, the first named storm – Abele – also formed in the same area, strengthening to become one of the season's two tropical cyclones – storms with maximum sustained winds of at least 120 km/h (75 mph). The strongest system of the season was Cyclone Bingiza, which attained peak winds of 160 km/h (100 mph) off the northeastern coast of Madagascar in February. Bingiza was also the only storm to cause severe effects on land, causing heavy damage and 34 fatalities across Madagascar. Moderate Tropical Storm Cherono developed in March and traversed much of the ocean, only brushing by the island of Rodrigues. The final system was a subtropical depression that intensified south of Madagascar, becoming extratropical on 16 April to end the season.

## Season forecast and summary

On 22 October 2010, the MMS released their seasonal outlook and predicted that there would be 8–10 named storms within the basin during the season. At the end of December, the MMS issued an updated seasonal outlook, predicting that only 6–8 named storms would develop.

As the season began, strong La Niña conditions persisted across the Pacific and Indian oceans, causing an increase in cyclonic flow near the equator over the Indian Ocean. However, atmospheric conditions over the basin significantly decreased tropical cyclogenesis. The Walker circulation – a broad atmospheric circulation – caused unusually moist conditions in the eastern Indian Ocean while producing an increase in subsidence and unusually dry conditions in the western Indian Ocean. In addition, sea surface temperatures were below normal from 5°–15° S and west of 90° E, which limited storm formation near the Chagos Archipelago, typically a common area of formation. By the end of the season, there were only three named storms, the fewest in 50 years, although there was also a subtropical cyclone with gale-force winds that could have been named. In terms of total days in which cyclones were active, the season was slightly behind the 1982–83 season, thus making the 2010–11 season the second-quietest on record. The season also marked a global trend of decreasing tropical cyclone activity over the preceding five years, although the basin experienced a sudden shift toward increased activity in the subsequent season.

Météo-France's meteorological office in Réunion (MFR) – the official Regional Specialized Meteorological Center for the South-West Indian Ocean – tracked and named all tropical cyclones from the east coast of Africa to 90° E. The Joint Typhoon Warning Center (JTWC), which is a joint United States Navy – United States Air Force task force that issues tropical cyclone warnings for the region, also issued advisories for storms during the season.

## Systems

### Tropical Depression 01

For two days toward the end of October, an area of convection persisted within the equatorial trough, east-southeast of the Chagos Archipelago. With a ridge to the south, the system moved generally southwestward. Initially, strong wind shear exposed the circulation, although the system had good inflow from the south. At 12:00 UTC on 25 October, the MFR designated the system as Tropical Disturbance 01, and on the next day upgraded it to a tropical depression, estimating winds of 55 km/h (35 mph). Also on 26 October, the JTWC classified the system as Tropical Cyclone 01S about 1,575 km (980 mi) east-southeast of Diego Garcia, estimating peak winds of 65 km/h (40 mph), or a minimal tropical storm. This followed a decrease in wind shear and an increase in convection over the center. Persistent wind shear prevented the system from organizing, causing the thunderstorms to be removed from the center. The JTWC discontinued advisories on the cyclone on 27 October, and on the same day the MFR downgraded it to a tropical disturbance. On 29 October, the MFR issued their final advisory on the system. The remnants continued to the west-southwest, occasionally producing thunderstorms through early November.

### Tropical Cyclone Abele

On 23 November, an area of convection persisted southwest of Sumatra within the Intertropical Convergence Zone (ITCZ), accompanied by a poorly-defined circulation. Initially the system remained nearly stationary, although it began drifting to the southwest due to a weakness in the subtropical ridge. Decreasing wind shear and improved inflow favored further development. On 28 November, the MFR designated the system as a zone of disturbed weather in the far northeastern portion of the basin. Early the next day, the agency upgraded the system to Tropical Disturbance 02 after the convection organized further. Also on 29 November, the TCWC Perth classified the disturbance as Tropical Low 02U, and the JTWC designated it as Tropical Cyclone 03S about 1,295 km (805 mi) west of the Cocos (Keeling) Islands.

After the storm's development, the convection pulsed around the circulation, and was initially disrupted by wind shear in the region. Despite the circulation being exposed from the thunderstorms, the MFR upgraded the disturbance to a depression on 30 November, and further to Moderate Tropical Storm Abele on 1 December. By that time, the convection had consolidated over the center, which developed an eye amid lower wind shear. The MFR upgraded Abele to a severe tropical storm and later a tropical cyclone on 2 December, estimating peak 10 minute winds of 130 km/h (80 mph). The JTWC assessed 1 minute winds of 150 km/h (95 mph). By that time, Abele had turned to the south and southeast ahead of an approaching trough. Cooler water temperatures and increased wind shear caused the convection to weaken, and the winds dropped accordingly. Late on 2 December, Abele crossed 90°E into the Australian region; the storm continued weakening and later became extratropical on 4 December, dissipating the next day.

### Tropical Depression 03

On December 28, the ITCZ spurred an increase in convection in the northeastern portion of the basin. An elongated low-pressure area developed by 31 December, accompanied by intermittent thunderstorms. The system slowly consolidated, and the circulation center was exposed but well-defined. Despite moderate wind shear, the convection organized into rainbands on the system's southern periphery. On 2 January, the MFR classified the system as Tropical Disturbance 03, and later that day upgraded it to a tropical depression. However, persistent shear caused the convection to diminish on 3 January, which exposed the circulation. As a result, the MFR discontinued advisories on the system that day. The remnants produced scattered convection while moving west-southwestward. By 10 January, the circulation was still observed, although it was difficult to track. Two days later, the system turned southward, and by 15 January, the convection became more persistent as the system approached northeastern Madagascar. That day, the JTWC issued a Tropical Cyclone Formation Alert based on the improved appearance on satellite imagery. At around 05:00 UTC on 16 January, the remnants of the depression struck Madagascar near Fenoarivo Atsinanana, and the system rapidly dissipated over land.

### Tropical Cyclone Bingiza

A zone of disturbed weather developed on 6 February well northeast of Madagascar. For the next few days, the system meandered southwestward, becoming Tropical Disturbance 05 on 8 February. By late the next day, the system had intensified into Moderate Tropical Storm Bingiza, and the JTWC classified it as Tropical Cyclone 13S. After two days of meandering without strengthening, the storm turned to the southwest on 12 February due to a ridge to the south building toward Madagascar, Later that day an eye became apparent on satellite imagery, and Bingiza intensified to tropical cyclone status. Early on 13 February, the cyclone attained peak 10 minute winds of 155 km/h (95 mph), and the JTWC estimated peak 1 minute winds of 185 km/h (115 mph). The cyclone moved ashore in northeastern Madagascar on 14 February and quickly weakened as it crossed the country. It emerged into the Mozambique Channel as a weak tropical disturbance, but almost immediately turned southward and moved ashore western Madagascar. The storm again reached open waters on 16 February, and briefly reintensified into a tropical storm. On 17 February, Bingiza made its final landfall near Morondava, and once again weakened over land. Late on 18 February the system reached open waters, which became extratropical two days later.

Cyclone Bingiza was the only main storm to affect Madagascar during the season. It dropped heavy rainfall, peaking at 276.3 mm (10.88 in), in addition to the strong winds near the landfall point. In Vinanivao, located along the Masoala peninsula, the cyclone destroyed half of the buildings as well as the roads and bridges, leaving it only accessible by boat. The high winds caused heavy crop damage, including to rice and banana, which left minimal food supplies in some areas. Overall, the cyclone destroyed 405.23 km2 (156.46 mi2) of rice fields, as well as 101.67 km2 (39.26 mi2) of other crops. Across its path, Bingiza destroyed 25,464 houses and damaged 36 schools, and caused 34 deaths in the country. The storm's outer circulation also dropped heavy rainfall in the Comoros, peaking at 770 mm (30 in) in the capital Moroni, and increased moist air over Malawi, Mozambique, and Tanzania.

### Moderate Tropical Storm Cherono

On 10 March, Tropical Low 23U developed in the Australian basin southwest of Sumatra, and proceeded to move west. After crossing 90oE, the MFR classified the system as a zone of disturbed weather late on 13 March, followed by an upgrade to Tropical Disturbance 07 on 14 March. The system had a poorly-defined circulation but persistent convection, despite strong easterly wind shear. By 16 March however, the shear had relaxed, allowing the convection to organize as the circulation became better defined. Good outflow and warm waters favored further intensification. At 00:00 UTC on 17 March, the MFR upgraded the system to a tropical depression, and a few hours later, the JTWC initiated advisories on the system as Tropical Cyclone 18S about 925 km (575 mi) southeast of Diego Garcia, an island in the central Indian Ocean.

Gradually intensifying, the system moved steadily to the west-southwest, steered around the northern periphery of a ridge. Late on March 17, the MFR upgraded the depression to Moderate Tropical Storm Cherono. This marked the latest date for the third named storm of a season. On March 18, Cherono attained peak 10 minute winds of 75 km/h (45 mph) according to the MFR, and 1 minute winds of 85 km/h (55 mph) according to the JTWC. After that time, the circulation became exposed from the convection, affected by dry air in the region, as well as increased wind shear. On 19 March, the JTWC discontinued advisories, and operationally the MFR downgraded the system to a tropical depression that day, although a post-season analysis indicated Cherono remained a moderate tropical storm for two more days. At 21:00 UTC on 19 March, the storm passed about 40 km (25 mi) south of Rodrigues island, producing winds of 31 km/h (20 mph). The storm continued producing pulsing convection, increasing over the center on 20 March due to a temporary increase in wind shear. However, the shear returned and the convection weakened on 21 March due to an approaching upper-level trough, and Cherono weakened to tropical depression status. The same trough turned the storm to the south and southeast. On 23 March, the system became extratropical as it curved eastward. The low weakened further the next day, dissipating on 25 March.

### Subtropical Depression 09

A low-pressure area moved eastward from Mozambique over open waters on 9 April. Two days later, convection increased over the center while located about 40 km (25 mi) southeast of Tôlanaro, Madagascar, which recorded a drop in atmospheric pressure. Located in a baroclinic environment, the system was located beneath an upper-level low, resulting in an unusual structure. However, warm waters and low wind shear favored development. Late on 11 April, the MFR classified the system as a zone of disturbed weather, and soon after designated it as a tropical disturbance. On 13 April, the MFR reclassified the system as Subtropical Depression 09, about 360 km (220 mi) southeast of Fort Dauphin. The system's asymmetric structure – the strongest winds were located in a convective rainband to the south of the center – resulted in the subtropical designation.

Late on 13 April, the system attained gale-force winds, although it remained an unnamed subtropical depression. The MFR later noted that the storm could have been named, but the agency decided against it due to the structure and the location. After moving clockwise, the storm began moving southwestward, steered by a ridge. The storm gradually intensified, and the convection increased around the center, although the wind field remained very large. Despite decreasing water temperatures, the storm attained peak 10 minute winds of 95 km/h (60 mph) on 15 April. That day, the system also developed a warm thermal core, similar in structure to a tropical cyclone. Increased wind shear disrupted the convection, causing the storm to transition into an extratropical cyclone on 16 April. The system turned to the southeast and was absorbed by an approaching cold front on 17 April.

### Other systems

The monsoon spawned a mesoscale convective system near Réunion on 28 January, with a weak circulation forming near the south coast of the island. The system dropped heavy rainfall over the island, reaching 400 mm (16 in) in mountainous areas. The circulation moved southward away from Réunion, becoming increasingly defined. On January 30, the MFR classified the system as Tropical Disturbance 04. However, the system soon weakened after it encountered cooler waters and stronger wind shear, and the MFR discontinued advisories early on 31 January. By 2 February, the remnants of the disturbance became extratropical while accelerating to the southeast.

On 14 February, a weak low was present north of Rodrigues island with disorganized convection due to easterly wind shear. By the following day, the convection had become more persistent, accompanied by a broad circulation. At 18:00 UTC on 15 February, the MFR classified the system as Tropical Disturbance 06 to the northeast of Réunion. Continued wind shear prevented significant development, and the system moved southward, developing intermittently strong convection. On 18 February, the MFR discontinued advisories, although the remnant circulation persisted for several more days.

Toward the end of March, the ITCZ produced an increase in convection in the Australian basin, accompanied by a disorganized center. The system moved westward over an area of warm water temperatures, and after crossing 90oE into the basin, the MFR classified it as Tropical Disturbance 08 on 29 March after the convection organized more. The circulation became better defined, and the MFR anticipated that the system would eventually intensify into a severe tropical storm. However, poor inflow and unfavorable wind shear prevented the system from organizing, and the MFR discontinued advisories on March 31 after the circulation remained exposed from the convection. The circulation persisted for a few more days before becoming poorly defined on 4 April.

## Storm names

Within the South-west Indian Ocean Tropical Depressions and Subtropical Depressions that are judged to have 10-minute sustained windspeeds of 65 km/h, (40 mph) by the Regional Specialized Meteorological Center on La Réunion Island, France (RSMC La Réunion) are usually assigned a name. However it is the Sub-Regional Tropical Cyclone Advisory Centers in Mauritius and Madagascar who name the systems. The Sub-Regional Tropical Cyclone Advisory Center in Mauritius names the storm should it intensify into a moderate tropical storm between 55°E and 90°E, if the storm should intensify into a moderate tropical storm between 30°E and 55°E then the Sub-Regional Tropical Cyclone Advisory Center in Madagascar assigns the appropriate name to the storm. Tropical Cyclones moving into this region from the Australian Region are renamed by the Sub-Regional Tropical Cyclone Advisory Center in Mauritius, however tropical cyclones moving into the Australian region do not get renamed. New name lists are used every year, whilst a name is normally only used once so thus no names are retired.

## Season effects

This table lists all of the tropical cyclones and subtropical cyclones that were monitored during the 2010–2011 South-West Indian Ocean cyclone season. Information on their intensity, duration, name, areas affected, primarily comes from RSMC La Réunion. Death and damage reports come from either press reports or the relevant national disaster management agency while the damage totals are given in 2010 or 2011 USD.

\|- \| 01 \|\| 25–29 October \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| None \|\| None \|\| None \|\| \|- \| Abele \|\| 28 November – 3 December \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| None \|\| None \|\| None \|\| \|- \| 03 \|\| 2–3 January \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| Madagascar \|\| None \|\| None \|\| \|- \| 04 \|\| 30–31 January \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| Réunion \|\| None \|\| None \|\| \|- \| Bingiza \|\| 9–17 February \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| Comoros, Madagascar \|\| Unknown \|\| 34 \|\| \|- \| 06 \|\| 15–18 February \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| None \|\| None \|\| None \|\| \|- \| Cherono \|\| 13–23 March \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| Rodrigues Island \|\| None \|\| None \|\| \|- \| 08 \|\| 29–31 March \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| None \|\| None \|\| None \|\| \|- \| 09 \|\| 13–16 April \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| bgcolor=#\| \|\| None \|\| None \|\| None \|\| \|-

## See also

- Tropical cyclones in 2010 and 2011
- South-West Indian Ocean tropical cyclone
- List of Southern Hemisphere cyclone seasons
- Atlantic hurricane seasons: 2010, 2011
- Pacific hurricane seasons: 2010, 2011
- Pacific typhoon seasons: 2010, 2011
- North Indian Ocean cyclone seasons: 2010, 2011
- South Atlantic tropical cyclone

Cyclone season in the Southwest Indian Ocean

Articles which contain graphical timelines


Saturn

Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth, but is over 95 times more massive.

Saturn's interior is thought to be composed of a rocky core, surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium, and finally, a gaseous outer layer. Saturn has a pale yellow hue due to ammonia crystals in its upper atmosphere. An electrical current within the metallic hydrogen layer is thought to give rise to Saturn's planetary magnetic field, which is weaker than Earth's, but which has a magnetic moment 580 times that of Earth due to Saturn's larger size. Saturn's magnetic field strength is around one-twentieth of Jupiter's. The outer atmosphere is generally bland and lacking in contrast, although long-lived features can appear. Wind speeds on Saturn can reach 1,800 kilometres per hour (1,100 miles per hour).

The planet has a prominent ring system, which is composed mainly of ice particles, with a smaller amount of rocky debris and dust. At least 146 moons are known to orbit the planet, of which 63 are officially named; this does not include the hundreds of moonlets in its rings. Titan, Saturn's largest moon and the second largest in the Solar System, is larger (while less massive) than the planet Mercury and is the only moon in the Solar System to have a substantial atmosphere.

## Name and symbol

Saturn is named after the Roman god of wealth and agriculture and father of Jupiter. Its astronomical symbol () has been traced back to the Greek Oxyrhynchus Papyri, where it can be seen to be a Greek kappa-rho ligature with a horizontal stroke, as an abbreviation for Κρονος (Cronus), the Greek name for the planet (). It later came to look like a lower-case Greek eta, with the cross added at the top in the 16th century to Christianize this pagan symbol.

The Romans named the seventh day of the week Saturday, Sāturni diēs ("Saturn's Day"), for the planet Saturn.

## Physical characteristics

Saturn is a gas giant composed predominantly of hydrogen and helium. It lacks a definite surface, though it is likely to have a solid core. Saturn's rotation causes it to have the shape of an oblate spheroid; that is, it is flattened at the poles and bulges at its equator. Its equatorial radius is more than 10% larger than its polar radius: 60,268 km versus 54,364 km. Jupiter, Uranus, and Neptune, the other giant planets in the Solar System, are also oblate but to a lesser extent. The combination of the bulge and rotation rate means that the effective surface gravity along the equator, 8.96 m/s2, is 74% of what it is at the poles and is lower than the surface gravity of Earth. However, the equatorial escape velocity of nearly 36 km/s is much higher than that of Earth.

Saturn is the only planet of the Solar System that is less dense than water—about 30% less. Although Saturn's core is considerably denser than water, the average specific density of the planet is 0.69 g/cm3 due to the atmosphere. Jupiter has 318 times Earth's mass, and Saturn is 95 times Earth's mass. Together, Jupiter and Saturn hold 92% of the total planetary mass in the Solar System.

### Internal structure

Despite consisting mostly of hydrogen and helium, most of Saturn's mass is not in the gas phase, because hydrogen becomes a non-ideal liquid when the density is above 0.01 g/cm3, which is reached at a radius containing 99.9% of Saturn's mass. The temperature, pressure, and density inside Saturn all rise steadily toward the core, which causes hydrogen to be a metal in the deeper layers.

Standard planetary models suggest that the interior of Saturn is similar to that of Jupiter, having a small rocky core surrounded by hydrogen and helium, with trace amounts of various volatiles. Analysis of the distortion shows that Saturn is substantially more centrally condensed than Jupiter and therefore contains a significantly larger amount of material denser than hydrogen near its centre. Saturn's central regions contain about 50% hydrogen by mass, while Jupiter's contain approximately 67% hydrogen.

This core is similar in composition to Earth, but is more dense. The examination of Saturn's gravitational moment, in combination with physical models of the interior, has allowed constraints to be placed on the mass of Saturn's core. In 2004, scientists estimated that the core must be 9–22 times the mass of Earth, which corresponds to a diameter of about 25,000 km. However, measurements of Saturn's rings suggest a much more diffuse core with a mass equal to about 17 Earths and a radius equal to around 60% of Saturn's entire radius. This is surrounded by a thicker liquid metallic hydrogen layer, followed by a liquid layer of helium-saturated molecular hydrogen that gradually transitions to a gas with increasing altitude. The outermost layer spans 1,000 km and consists of gas.

Saturn has a hot interior, reaching 11,700 °C at its core, and radiates 2.5 times more energy into space than it receives from the Sun. Jupiter's thermal energy is generated by the Kelvin–Helmholtz mechanism of slow gravitational compression, but such a process alone may not be sufficient to explain heat production for Saturn, because it is less massive. An alternative or additional mechanism may be generation of heat through the "raining out" of droplets of helium deep in Saturn's interior. As the droplets descend through the lower-density hydrogen, the process releases heat by friction and leaves Saturn's outer layers depleted of helium. These descending droplets may have accumulated into a helium shell surrounding the core. Rainfalls of diamonds have been suggested to occur within Saturn, as well as in Jupiter and ice giants Uranus and Neptune.

### Atmosphere

The outer atmosphere of Saturn contains 96.3% molecular hydrogen and 3.25% helium by volume. The proportion of helium is significantly deficient compared to the abundance of this element in the Sun. The quantity of elements heavier than helium (metallicity) is not known precisely, but the proportions are assumed to match the primordial abundances from the formation of the Solar System. The total mass of these heavier elements is estimated to be 19–31 times the mass of the Earth, with a significant fraction located in Saturn's core region.

Trace amounts of ammonia, acetylene, ethane, propane, phosphine, and methane have been detected in Saturn's atmosphere. The upper clouds are composed of ammonia crystals, while the lower level clouds appear to consist of either ammonium hydrosulfide (NH4SH) or water. Ultraviolet radiation from the Sun causes methane photolysis in the upper atmosphere, leading to a series of hydrocarbon chemical reactions with the resulting products being carried downward by eddies and diffusion. This photochemical cycle is modulated by Saturn's annual seasonal cycle. Cassini observed a series of cloud features found in northern latitudes, nicknamed the "String of Pearls". These features are cloud clearings that reside in deeper cloud layers.

#### Cloud layers

Saturn's atmosphere exhibits a banded pattern similar to Jupiter's, but Saturn's bands are much fainter and are much wider near the equator. The nomenclature used to describe these bands is the same as on Jupiter. Saturn's finer cloud patterns were not observed until the flybys of the Voyager spacecraft during the 1980s. Since then, Earth-based telescopy has improved to the point where regular observations can be made.

The composition of the clouds varies with depth and increasing pressure. In the upper cloud layers, with the temperature in the range 100–160 K and pressures extending between 0.5–2 bar, the clouds consist of ammonia ice. Water ice clouds begin at a level where the pressure is about 2.5 bar and extend down to 9.5 bar, where temperatures range from 185 to 270 K. Intermixed in this layer is a band of ammonium hydrosulfide ice, lying in the pressure range 3–6 bar with temperatures of 190–235 K. Finally, the lower layers, where pressures are between 10 and 20 bar and temperatures are 270–330 K, contains a region of water droplets with ammonia in aqueous solution.

Saturn's usually bland atmosphere occasionally exhibits long-lived ovals and other features common on Jupiter. In 1990, the Hubble Space Telescope imaged an enormous white cloud near Saturn's equator that was not present during the Voyager encounters, and in 1994 another smaller storm was observed. The 1990 storm was an example of a Great White Spot, a short-lived phenomenon that occurs once every Saturnian year, roughly every 30 Earth years, around the time of the northern hemisphere's summer solstice. Previous Great White Spots were observed in 1876, 1903, 1933 and 1960, with the 1933 storm being the best observed. The latest giant storm was observed in 2010. In 2015, researchers used Very Large Array telescope to study Saturnian atmosphere, and reported that they found "long-lasting signatures of all mid-latitude giant storms, a mixture of equatorial storms up to hundreds of years old, and potentially an unreported older storm at 70°N".

The winds on Saturn are the second fastest among the Solar System's planets, after Neptune's. Voyager data indicate peak easterly winds of 500 m/s (1,800 km/h). In images from the Cassini spacecraft during 2007, Saturn's northern hemisphere displayed a bright blue hue, similar to Uranus. The color was most likely caused by Rayleigh scattering. Thermography has shown that Saturn's south pole has a warm polar vortex, the only known example of such a phenomenon in the Solar System. Whereas temperatures on Saturn are normally −185 °C, temperatures on the vortex often reach as high as −122 °C, suspected to be the warmest spot on Saturn.

#### Hexagonal cloud patterns

A persisting hexagonal wave pattern around the north polar vortex in the atmosphere at about 78°N was first noted in the Voyager images. The sides of the hexagon are each about 14,500 km (9,000 mi) long, which is longer than the diameter of the Earth. The entire structure rotates with a period of (the same period as that of the planet's radio emissions) which is assumed to be equal to the period of rotation of Saturn's interior. The hexagonal feature does not shift in longitude like the other clouds in the visible atmosphere. The pattern's origin is a matter of much speculation. Most scientists think it is a standing wave pattern in the atmosphere. Polygonal shapes have been replicated in the laboratory through differential rotation of fluids.

HST imaging of the south polar region indicates the presence of a jet stream, but no strong polar vortex nor any hexagonal standing wave. NASA reported in November 2006 that Cassini had observed a "hurricane-like" storm locked to the south pole that had a clearly defined eyewall. Eyewall clouds had not previously been seen on any planet other than Earth. For example, images from the Galileo spacecraft did not show an eyewall in the Great Red Spot of Jupiter.

The south pole storm may have been present for billions of years. This vortex is comparable to the size of Earth, and it has winds of 550 km/h.

### Magnetosphere

Saturn has an intrinsic magnetic field that has a simple, symmetric shape—a magnetic dipole. Its strength at the equator—0.2 gauss (μT)—is approximately one twentieth of that of the field around Jupiter and slightly weaker than Earth's magnetic field. As a result, Saturn's magnetosphere is much smaller than Jupiter's. When Voyager 2 entered the magnetosphere, the solar wind pressure was high and the magnetosphere extended only 19 Saturn radii, or 1.1 million km (712,000 mi), although it enlarged within several hours, and remained so for about three days. Most probably, the magnetic field is generated similarly to that of Jupiter—by currents in the liquid metallic-hydrogen layer called a metallic-hydrogen dynamo. This magnetosphere is efficient at deflecting the solar wind particles from the Sun. The moon Titan orbits within the outer part of Saturn's magnetosphere and contributes plasma from the ionized particles in Titan's outer atmosphere. Saturn's magnetosphere, like Earth's, produces aurorae.

## Orbit and rotation

The average distance between Saturn and the Sun is over 1.4 billion kilometers (9 AU). With an average orbital speed of 9.68 km/s, it takes Saturn 10,759 Earth days (or about 29+1⁄2 years) to finish one revolution around the Sun. As a consequence, it forms a near 5:2 mean-motion resonance with Jupiter. The elliptical orbit of Saturn is inclined 2.48° relative to the orbital plane of the Earth. The perihelion and aphelion distances are, respectively, 9.195 and 9.957 AU, on average. The visible features on Saturn rotate at different rates depending on latitude, and multiple rotation periods have been assigned to various regions (as in Jupiter's case).

Astronomers use three different systems for specifying the rotation rate of Saturn. System I has a period of (844.3°/d) and encompasses the Equatorial Zone, the South Equatorial Belt, and the North Equatorial Belt. The polar regions are considered to have rotation rates similar to System I. All other Saturnian latitudes, excluding the north and south polar regions, are indicated as System II and have been assigned a rotation period of (810.76°/d). System III refers to Saturn's internal rotation rate. Based on radio emissions from the planet detected by Voyager 1 and Voyager 2, System III has a rotation period of (810.8°/d). System III has largely superseded System II.

A precise value for the rotation period of the interior remains elusive. While approaching Saturn in 2004, Cassini found that the radio rotation period of Saturn had increased appreciably, to approximately . An estimate of Saturn's rotation (as an indicated rotation rate for Saturn as a whole) based on a compilation of various measurements from the Cassini, Voyager and Pioneer probes is . Studies of the planet's C Ring yield a rotation period of  .

In March 2007, it was found that the variation of radio emissions from the planet did not match Saturn's rotation rate. This variance may be caused by geyser activity on Saturn's moon Enceladus. The water vapor emitted into Saturn's orbit by this activity becomes charged and creates a drag upon Saturn's magnetic field, slowing its rotation slightly relative to the rotation of the planet.

An apparent oddity for Saturn is that it does not have any known trojan asteroids. These are minor planets that orbit the Sun at the stable Lagrangian points, designated L4 and L5, located at 60° angles to the planet along its orbit. Trojan asteroids have been discovered for Mars, Jupiter, Uranus, and Neptune. Orbital resonance mechanisms, including secular resonance, are believed to be the cause of the missing Saturnian trojans.

## Natural satellites

Saturn has 146 known moons, 63 of which have formal names. It is estimated that there are another 100±30 outer irregular moons larger than 3 km (2 mi) in diameter. In addition, there is evidence of dozens to hundreds of moonlets with diameters of 40–500 meters in Saturn's rings, which are not considered to be true moons. Titan, the largest moon, comprises more than 90% of the mass in orbit around Saturn, including the rings. Saturn's second-largest moon, Rhea, may have a tenuous ring system of its own, along with a tenuous atmosphere.

Many of the other moons are small: 131 are less than 50 km in diameter. Traditionally, most of Saturn's moons have been named after Titans of Greek mythology. Titan is the only satellite in the Solar System with a major atmosphere, in which a complex organic chemistry occurs. It is the only satellite with hydrocarbon lakes.

On 6 June 2013, scientists at the IAA-CSIC reported the detection of polycyclic aromatic hydrocarbons in the upper atmosphere of Titan, a possible precursor for life. On 23 June 2014, NASA claimed to have strong evidence that nitrogen in the atmosphere of Titan came from materials in the Oort cloud, associated with comets, and not from the materials that formed Saturn in earlier times.

Saturn's moon Enceladus, which seems similar in chemical makeup to comets, has often been regarded as a potential habitat for microbial life. Evidence of this possibility includes the satellite's salt-rich particles having an "ocean-like" composition that indicates most of Enceladus's expelled ice comes from the evaporation of liquid salt water. A 2015 flyby by Cassini through a plume on Enceladus found most of the ingredients to sustain life forms that live by methanogenesis.

In April 2014, NASA scientists reported the possible beginning of a new moon within the A Ring, which was imaged by Cassini on 15 April 2013.

## Planetary rings

Saturn is probably best known for the system of planetary rings that makes it visually unique. The rings extend from 6,630 to 120,700 kilometers (4,120 to 75,000 mi) outward from Saturn's equator and average approximately 20 meters (66 ft) in thickness. They are composed predominantly of water ice, with trace amounts of tholin impurities and a peppered coating of approximately 7% amorphous carbon. The particles that make up the rings range in size from specks of dust up to 10 m. While the other gas giants also have ring systems, Saturn's is the largest and most visible.

There are two main hypotheses regarding the origin of the rings. One hypothesis is that the rings are remnants of a destroyed moon of Saturn, for which a research team at MIT has proposed the name "Chrysalis". The second hypothesis is that the rings are left over from the original nebular material from which Saturn was formed. Some ice in the E ring comes from the moon Enceladus's geysers. The water abundance of the rings varies radially, with the outermost ring A being the most pure in ice water. This abundance variance may be explained by meteor bombardment.

Beyond the main rings, at a distance of 12 million km from the planet is the sparse Phoebe ring. It is tilted at an angle of 27° to the other rings and, like Phoebe, orbits in retrograde fashion.

Some of the moons of Saturn, including Pandora and Prometheus, act as shepherd moons to confine the rings and prevent them from spreading out. Pan and Atlas cause weak, linear density waves in Saturn's rings that have yielded more reliable calculations of their masses.

## History of observation and exploration

The observation and exploration of Saturn can be divided into three phases: (1) pre-modern observations with the naked eye, (2) telescopic observations from Earth beginning in the 17th century, and (3) visitation by space probes, in orbit or on flyby. In the 21st century, telescopic observations continue from Earth (including Earth-orbiting observatories like the Hubble Space Telescope) and, until its 2017 retirement, from the Cassini orbiter around Saturn.

### Pre-telescopic observation

Saturn has been known since prehistoric times, and in early recorded history it was a major character in various mythologies. Babylonian astronomers systematically observed and recorded the movements of Saturn. In ancient Greek, the planet was known as Φαίνων Phainon, and in Roman times it was known as the "star of Saturn". In ancient Roman mythology, the planet Phainon was sacred to this agricultural god, from which the planet takes its modern name. The Romans considered the god Saturnus the equivalent of the Greek god Cronus; in modern Greek, the planet retains the name Cronus—Κρόνος: Kronos.

The Greek scientist Ptolemy based his calculations of Saturn's orbit on observations he made while it was in opposition. In Hindu astrology, there are nine astrological objects, known as Navagrahas. Saturn is known as "Shani" and judges everyone based on the good and bad deeds performed in life. Ancient Chinese and Japanese culture designated the planet Saturn as the "earth star" (土星). This was based on Five Elements which were traditionally used to classify natural elements.

In ancient Hebrew, Saturn is called Shabbathai. Its angel is Cassiel. Its intelligence or beneficial spirit is 'Agȋȇl (Hebrew: אגיאל, romanized: ʿAgyal), and its darker spirit (demon) is Zȃzȇl (Hebrew: זאזל, romanized: Zazl). Zazel has been described as a great angel, invoked in Solomonic magic, who is "effective in love conjurations". In Ottoman Turkish, Urdu, and Malay, the name of Zazel is 'Zuhal', derived from the Arabic language (Arabic: زحل, romanized: Zuhal).

### Telescopic pre-spaceflight observations

Saturn's rings require at least a 15-mm-diameter telescope to resolve and thus were not known to exist until Christiaan Huygens saw them in 1655 and published about this in 1659. Galileo, with his primitive telescope in 1610, incorrectly thought of Saturn's appearing not quite round as two moons on Saturn's sides. It was not until Huygens used greater telescopic magnification that this notion was refuted, and the rings were truly seen for the first time. Huygens also discovered Saturn's moon Titan; Giovanni Domenico Cassini later discovered four other moons: Iapetus, Rhea, Tethys and Dione. In 1675, Cassini discovered the gap now known as the Cassini Division.

No further discoveries of significance were made until 1789 when William Herschel discovered two further moons, Mimas and Enceladus. The irregularly shaped satellite Hyperion, which has a resonance with Titan, was discovered in 1848 by a British team.

In 1899 William Henry Pickering discovered Phoebe, a highly irregular satellite that does not rotate synchronously with Saturn as the larger moons do. Phoebe was the first such satellite found and it takes more than a year to orbit Saturn in a retrograde orbit. During the early 20th century, research on Titan led to the confirmation in 1944 that it had a thick atmosphere – a feature unique among the Solar System's moons.

### Spaceflight missions

#### Pioneer 11 flyby

Pioneer 11 made the first flyby of Saturn in September 1979, when it passed within 20,000 km of the planet's cloud tops. Images were taken of the planet and a few of its moons, although their resolution was too low to discern surface detail. The spacecraft also studied Saturn's rings, revealing the thin F-ring and the fact that dark gaps in the rings are bright when viewed at high phase angle (towards the Sun), meaning that they contain fine light-scattering material. In addition, Pioneer 11 measured the temperature of Titan.

#### Voyager flybys

In November 1980, the Voyager 1 probe visited the Saturn system. It sent back the first high-resolution images of the planet, its rings and satellites. Surface features of various moons were seen for the first time. Voyager 1 performed a close flyby of Titan, increasing knowledge of the atmosphere of the moon. It proved that Titan's atmosphere is impenetrable in visible wavelengths; therefore no surface details were seen. The flyby changed the spacecraft's trajectory out from the plane of the Solar System.

Almost a year later, in August 1981, Voyager 2 continued the study of the Saturn system. More close-up images of Saturn's moons were acquired, as well as evidence of changes in the atmosphere and the rings. Unfortunately, during the flyby, the probe's turnable camera platform stuck for a couple of days and some planned imaging was lost. Saturn's gravity was used to direct the spacecraft's trajectory towards Uranus.

The probes discovered and confirmed several new satellites orbiting near or within the planet's rings, as well as the small Maxwell Gap (a gap within the C Ring) and Keeler gap (a 42 km-wide gap in the A Ring).

#### Cassini–Huygens spacecraft

The Cassini–Huygens space probe entered orbit around Saturn on 1 July 2004. In June 2004, it conducted a close flyby of Phoebe, sending back high-resolution images and data. Cassini's flyby of Saturn's largest moon, Titan, captured radar images of large lakes and their coastlines with numerous islands and mountains. The orbiter completed two Titan flybys before releasing the Huygens probe on 25 December 2004. Huygens descended onto the surface of Titan on 14 January 2005.

Starting in early 2005, scientists used Cassini to track lightning on Saturn. The power of the lightning is approximately 1,000 times that of lightning on Earth.

In 2006, NASA reported that Cassini had found evidence of liquid water reservoirs no more than tens of meters below the surface that erupt in geysers on Saturn's moon Enceladus. These jets of icy particles are emitted into orbit around Saturn from vents in the moon's south polar region. Over 100 geysers have been identified on Enceladus. In May 2011, NASA scientists reported that Enceladus "is emerging as the most habitable spot beyond Earth in the Solar System for life as we know it".

Cassini photographs have revealed a previously undiscovered planetary ring, outside the brighter main rings of Saturn and inside the G and E rings. The source of this ring is hypothesized to be the crashing of a meteoroid off Janus and Epimetheus. In July 2006, images were returned of hydrocarbon lakes near Titan's north pole, the presence of which were confirmed in January 2007. In March 2007, hydrocarbon seas were found near the North pole, the largest of which is almost the size of the Caspian Sea. In October 2006, the probe detected an 8,000 km diameter cyclone-like storm with an eyewall at Saturn's south pole.

From 2004 to 2 November 2009, the probe discovered and confirmed eight new satellites. In April 2013 Cassini sent back images of a hurricane at the planet's north pole 20 times larger than those found on Earth, with winds faster than 530 km/h (330 mph). On 15 September 2017, the Cassini-Huygens spacecraft performed the "Grand Finale" of its mission: a number of passes through gaps between Saturn and Saturn's inner rings. The atmospheric entry of Cassini ended the mission.

#### Possible future missions

The continued exploration of Saturn is still considered to be a viable option for NASA as part of their ongoing New Frontiers program of missions. NASA previously requested for plans to be put forward for a mission to Saturn that included the Saturn Atmospheric Entry Probe, and possible investigations into the habitability and possible discovery of life on Saturn's moons Titan and Enceladus by Dragonfly.

## Observation

Saturn is the most distant of the five planets easily visible to the naked eye from Earth, the other four being Mercury, Venus, Mars and Jupiter. (Uranus, and occasionally 4 Vesta, are visible to the naked eye in dark skies.) Saturn appears to the naked eye in the night sky as a bright, yellowish point of light. The mean apparent magnitude of Saturn is 0.46 with a standard deviation of 0.34. Most of the magnitude variation is due to the inclination of the ring system relative to the Sun and Earth. The brightest magnitude, −0.55, occurs near in time to when the plane of the rings is inclined most highly, and the faintest magnitude, 1.17, occurs around the time when they are least inclined. It takes approximately 29.4 years for the planet to complete an entire circuit of the ecliptic against the background constellations of the zodiac. Most people will require an optical aid (very large binoculars or a small telescope) that magnifies at least 30 times to achieve an image of Saturn's rings in which clear resolution is present. When Earth passes through the ring plane, which occurs twice every Saturnian year (roughly every 15 Earth years), the rings briefly disappear from view because they are so thin. Such a "disappearance" will next occur in 2025, but Saturn will be too close to the Sun for observations.

Saturn and its rings are best seen when the planet is at, or near, opposition, the configuration of a planet when it is at an elongation of 180°, and thus appears opposite the Sun in the sky. A Saturnian opposition occurs every year—approximately every 378 days—and results in the planet appearing at its brightest. Both the Earth and Saturn orbit the Sun on eccentric orbits, which means their distances from the Sun vary over time, and therefore so do their distances from each other, hence varying the brightness of Saturn from one opposition to the next. Saturn also appears brighter when the rings are angled such that they are more visible. For example, during the opposition of 17 December 2002, Saturn appeared at its brightest due to a favorable orientation of its rings relative to the Earth, even though Saturn was closer to the Earth and Sun in late 2003.

From time to time, Saturn is occulted by the Moon (that is, the Moon covers up Saturn in the sky). As with all the planets in the Solar System, occultations of Saturn occur in "seasons". Saturnian occultations will take place monthly for about a 12-month period, followed by about a five-year period in which no such activity is registered. The Moon's orbit is inclined by several degrees relative to Saturn's, so occultations will only occur when Saturn is near one of the points in the sky where the two planes intersect (both the length of Saturn's year and the 18.6-Earth year nodal precession period of the Moon's orbit influence the periodicity).

## See also

- Statistics of planets in the Solar System

Sixth planet from the Sun

Astronomical objects known since antiquity


Doctor Who (season 1)

The first season of British science fiction television programme Doctor Who was originally broadcast on BBC TV between 1963 and 1964. The series began on 23 November 1963 with An Unearthly Child and ended with The Reign of Terror on 12 September 1964. The show was created by BBC Television head of drama Sydney Newman to fill the Saturday evening timeslot and appeal to both the younger and older audiences of the neighbouring programmes. Formatting of the programme was handled by Newman, head of serials Donald Wilson, writer C. E. Webber, and producer Rex Tucker. Production was overseen by the BBC's first female producer Verity Lambert and story editor David Whitaker, both of whom handled the scripts and stories.

The season introduces William Hartnell as the first incarnation of the Doctor, an alien who travels through time and space in his TARDIS, which appears to be a British police box on the outside. Carole Ann Ford is also introduced as the Doctor's granddaughter Susan Foreman, who acts as his companion alongside her schoolteachers Ian Chesterton and Barbara Wright, portrayed by William Russell and Jacqueline Hill, respectively. Throughout the season, the Doctor and his companions travel throughout history and into the future. Historical stories were intended to educate viewers about significant events in history, such as the Aztec civilisation and the French Revolution; futuristic episodes took a more subtle approach to educating viewers, such as the theme of pacifism with the Daleks.

The first eight serials were written by six writers: Whitaker, Anthony Coburn, Terry Nation, John Lucarotti, Peter R. Newman, and Dennis Spooner. Webber also co-wrote the show's first episode. The show was developed with three particular story types envisioned: past history, future technology, and alternative present; Coburn, Lucarotti, and Spooner wrote historical episodes, Nation and Newman penned futuristic stories, and Whitaker wrote a "filler" serial set entirely in the TARDIS. The serials were mostly directed by junior directors, such as Waris Hussein, John Gorrie, John Crockett, Henric Hirsch, Richard Martin, Christopher Barry, and Frank Cox; the exception is experienced director Mervyn Pinfield, who directed the first four episodes of The Sensorites. Filming started in September 1963 and lasted for approximately nine months, with weekly recording taking place mostly at Lime Grove Studios or the BBC Television Centre.

The first episode, overshadowed by the assassination of John F. Kennedy the previous day, was watched by 4.4 million viewers; the episode was repeated the following week, and the programme gained popularity with audiences, particularly with the introduction of the Daleks in the second serial, which peaked at 10.4 million viewers. The season received generally positive reviews, with praise particularly directed at the scripts and performances. However, many retrospective reviewers noted that Susan lacked character development and was generally portrayed as a damsel in distress, a criticism often echoed by Ford. Several episodes were erased by the BBC between 1967 and 1972, and only 33 of a total of 42 episodes survive; all seven episodes of Marco Polo and two episodes of The Reign of Terror remain missing. The existing serials received several VHS and DVD releases as well as tie-in novels.

## Serials

`Episode is missing`

## Production

### Conception

In March 1963, BBC Television's Controller of Programmes Donald Baverstock informed Head of Drama Sydney Newman of a gap in the schedule on Saturday evenings between the sports showcase Grandstand and the pop music programme Juke Box Jury. Baverstock figured that the programme should appeal to three audiences: children who had previously been accustomed to the timeslot, the teenage audience of Juke Box Jury, and the adult sports fan audience of Grandstand. Newman decided that a science fiction programme should fill the gap. Head of Serials Donald Wilson and writer C. E. Webber contributed heavily to the formatting of the programme, and co-wrote the programme's first format document with Newman; the latter conceived the idea of a time machine larger on the inside than the outside, as well as the central character of the mysterious "Doctor", and the show's name Doctor Who. Production was initiated several months later and handed to producer Verity Lambert and story editor David Whitaker to oversee, after a brief period when the show had been handled by a "caretaker" producer, Rex Tucker.

### Casting and characters

William Hartnell portrayed the first incarnation of the Doctor (referred to as "Dr. Who") in this season. The role was originally offered to Hugh David, Leslie French, Cyril Cusack, Alan Webb and Geoffrey Bayldon; David, Cusack and Webb turned down the role as they were reluctant to work on a series, while Bayldon wished to avoid another "old man" role. Lambert and director Waris Hussein invited Hartnell to play the role; he accepted after several discussions, viewing it as an opportunity to take his career in a new direction. Hartnell had always wished to play an older character in his work, but failed to do so, becoming typecast as a "tough" actor due to his roles in Carry On Sergeant (1958) and The Army Game (1957–61). Although portrayed as grumpy and antagonistic in early episodes, the Doctor warms to his companions as the show progresses.

The Doctor's granddaughter Susan Foreman was portrayed by Carole Ann Ford, a 23-year-old who typically played younger roles. Lambert was originally in talks with actress Jacqueline Lenya for the role, and several actresses auditioned for the part, including Christa Bergmann, Anne Castaldini, Maureen Crombie, Heather Fleming, Camilla Hasse, Waveney Lee, Anna Palk and Anneke Wills. Ford felt that the character of Susan deteriorated throughout the series; although the show's initial pitch depicted Susan as a strange alien creature, she often played the damsel in distress role, panicking at minor events. Susan's school teachers Ian Chesterton and Barbara Wright were played by William Russell and Jacqueline Hill, respectively. Russell was the only actor considered by Lambert for the role of Chesterton. While Sally Home, Phyllida Law and Penelope Lee were considered for Barbara, Lambert chose Hill, her friend, for the role.

### Writing

Three particular story types were envisioned for the show: history of the past, technology in the future, and alternatives of the present. Historical stories were intended to educate viewers about significant events in history, such as the Aztec civilisation and the French Revolution; futuristic episodes took a more subtle approach to educating viewers, such as the theme of pacifism in The Daleks.

The programme was originally intended to open with a serial entitled The Giants, written by Webber, but was scrapped by June 1963 as the technical requirements of the storyline—which involved the leading characters being drastically reduced in size—were beyond the technical capabilities, and the story itself lacked the necessary impact for an opener. Due to the lack of scripts ready for production, the untitled second serial from Coburn was moved to first in the running order. The order change necessitated rewriting the opening episode of Coburn's script to include some introductory elements of Webber's script for the first episode of The Giants. Coburn also made several significant original contributions to the opening episode, most notably that the Doctor's time machine should resemble a police box, an idea he conceived after seeing a real police box while walking near his office.

The second serial of Doctor Who was always planned to be futuristic due to the historical nature of the first. Comedy writer Terry Nation had written a 26-page outline for a story entitled The Survivors at his home, influenced by the threat of racial extermination by the Nazis and the concerns of advanced warfare, as well as taking influences from H. G. Wells' novel The Time Machine (1895). Newman and Wilson were unhappy with the serial, having wanted to avoid featuring "bug-eyed monsters"; however, with no other scripts prepared, they were forced to accept the serial for production. Due to other sudden commitments, Nation quickly wrote the scripts for the serial at the rate of one per day. Nation also wrote the show's fifth serial, The Keys of Marinus, to replace Dr Who and the Hidden Planet by Malcolm Hulke, which was deemed problematic and required rewrites. Nation and Whitaker decided to base the serial around a series of "mini-adventures", each with a different setting and cast; Nation was intrigued by the idea of the TARDIS crew searching for parts of a puzzle. Nation was also set to write the show's eighth serial, Doctor Who and the Red Fort, a seven-part story set during the Indian Rebellion of 1857, but other commitments prevented him from doing so.

Newman suggested writer John Lucarotti to the production team during the show's early development. Lucarotti, who had recently worked on the 18-part radio serial The Three Journeys of Marco Polo (1955), penned a seven-part serial about the Italian merchant and explorer Marco Polo titled Dr Who and a Journey to Cathay. Later known as Marco Polo, the serial was moved from its placement in the running order to accommodate The Edge of Destruction. Lucarotti was approached to write The Aztecs while Marco Polo was in production. Having lived in Mexico, Lucarotti was fascinated by the Aztec civilisation and their obsession with human sacrifice. The show's eighth serial, The Reign of Terror, is also a historical story, though writer Dennis Spooner was initially interested in writing a science fiction story. Whitaker gave Spooner four possible historical subjects, and he ultimately selected the French Revolution.

The show's third serial, The Edge of Destruction, was written as a "filler" in case the show was not renewed beyond 13 episodes. Since the serial had no budget and minimal resources, Whitaker took the opportunity to develop an idea conceived during the show's formative weeks: a character-driven story exploring the facets of the TARDIS. He wrote the script in two days, drawing upon influences of ghost stories and haunted houses. Peter R. Newman wrote the show's sixth serial, The Sensorites, inspired by 1950s films set during World War II that explore the notion of soldiers who continued to fight after the war.

### Filming

An Unearthly Child was provisionally scheduled to begin recording on 5 July, but was delayed to 19 July. Production was later deferred for a further two weeks while scripts were prepared. The show's pilot recording was finally scheduled for 27 September and regular episodes made from 18 October. Tucker was originally selected as the serial's director, but the task was assigned to Hussein due to Tucker's unavailability after the rearranging of production dates. Some of the pre-filmed inserts for the serial, shot at Ealing Studios in September and October 1963, were directed by Hussein's production assistant Douglas Camfield. The first version of the opening episode was recorded at Lime Grove Studios on the evening of 27 September 1963, following a week of rehearsals. However, the recording was bedevilled with technical errors, including the doors leading into the TARDIS control room failing to close properly. After viewing the episode, Newman ordered that it be mounted again. During the weeks between the two tapings, changes were made to costuming, effects, performances, and scripts. The second attempt at the opening episode was recorded on 18 October, with the following three episodes being recorded weekly on 25 October, 1 November and 8 November.

Tucker was initially appointed to direct The Daleks, but was later replaced by Christopher Barry. A week of shooting for The Daleks took place from 28 October, consisting mostly of inserts of the city and models. Weekly recording began on 15 November; it was later discovered that the first recording was affected by induction—an effect in which the voices from the production assistants' headphones was clearly audible. The episode was re-recorded on 6 December, pushing the weekly recordings of episodes 4–7 back by one week. The final episode was recorded on 10 January 1964. The re-recording forced Paddy Russell to forego directing The Edge of Destruction due to other commitments; junior director Richard Martin was later handed the role, and the first episode was recorded on 17 January. Frank Cox directed the second episode on 24 January, as Martin was unavailable. Filming for Marco Polo was preceded by a week of insert shooting of locations and props for the montage sequences. The serial was recorded weekly from 31 January to 13 March, directed by Hussein; John Crockett directed the fourth episode in Hussein's absence.

Weekly recording for The Keys of Marinus, directed by John Gorrie, took place from 20 March to 24 April; Hartnell was absent for the third and fourth episodes, as he was on holiday. The Aztecs, directed by Crockett, was filmed from 1 to 22 May; Ford appeared in pre-filmed inserts for the second and third episodes, shot on 13 April, due to her holiday. Experienced director Mervyn Pinfield was chosen to direct the first four episodes of The Sensorites, while Cox directed the final two episodes. Recording took place from 29 March to 3 July; Hill was absent for the fourth and fifth episodes due to her holiday. The Reign of Terror featured the show's first outdoor filming in Denham, Buckinghamshire, led by cameraman Peter Hamilton on 15 June 1964. Hungarian director Henric Hirsch directed the serial, which was recorded from 10 July to 19 August; in preparation for his holiday, William Russell recorded inserts for the second and third episodes from 16–17 June. Hirsch collapsed during the filming of the third episode. Lambert placed production assistant Tim Combe in charge until a replacement director could be found; documentation indicates that Gorrie oversaw production of the third episode, though Gorrie has no memory of the event. Hirsch returned to direct the final three episodes, splitting some of the workload with Combe.

## Release

### Promotion

Doctor Who was announced as a year-long series by Controller of BBC Television Stuart Hood on 12 September 1963, described by Television Mail as "a serial of stories to entertain the whole family". Trade newspaper Kinematograph Weekly devoted its TV column to the show on 24 October; journalist Tony Gruner described the show as "a somewhat mysterious type of programme consisting in part of fantasy and realism". A trailer for the show was broadcast on the BBC on 16 November. The first serial was given a half-page preview in Radio Times on 21 November, outlining the show's main characters and upcoming settings. On the same day, the main cast and production team attended the show's launch at Room 222 of the BBC's Broadcasting House. Hartnell hosted a radio trailer for the show on the BBC Light Programme. The BBC Home Service programme Today hosted a one-minute piece about the show's "space music" on 22 November, and a second trailer for the show was screened on BBC in the evening.

Hartnell taped a radio interview for Northern View on 17 December to promote the show's second serial. To increase the profile of the Daleks, the BBC sent two Dalek models—operated by Kevin Manser and Robert Jewell—to interact with the public at the Shepherd's Bush Market on 23 December. Hartnell recorded an appearance for Junior Points of View on 8 January, broadcast the following day, at Television Centre Presentation Studio A. In character as the Doctor, Hartnell spoke about the Daleks, based on dialogue written by Nation. A promotional image of Marco Polo was featured on the cover of Radio Times on 20 February 1964, with a half-page introduction to the serial inside. The Voord creatures from The Keys of Marinus were featured in several stories the Daily Express and Daily Mail in April 1964, while the titular creatures from The Sensorites were featured in similar press pieces in June. Lucarotti provided a syndicated interview with the press regarding The Aztecs, published in various papers such as the North-Western Evening Mail on 9 May. On 20 June, Ford opened the East Ham Town Show at the Central Park in East Ham, with 20,000 people in attendance. Radio Times ran a half-page interview with Hartnell on 16 July to promote the fourth episode of The Sensorites.

### Broadcast

The first episode of An Unearthly Child was transmitted on BBC TV at 5:16 p.m. on Saturday 23 November 1963; the following three episodes were transmitted at 5:15 p.m. over the next three weeks. The serial has been repeated twice on the BBC: on BBC Two in November 1981 as part of the repeat season The Five Faces of Doctor Who, and on BBC Four as part of the show's 50th anniversary on 21 November 2013. The Daleks was broadcast across seven weeks from 21 December 1963 to 1 February 1964, and has been repeated twice on the BBC: the final episode was broadcast on BBC Two late in the evening on 13 November 1999 as part of "Doctor Who Night"; and the serial was shown in three blocks from 5–9 April 2008 on BBC Four, as part of a celebration of the life and work of Lambert following her death in November 2007. The Edge of Destruction was transmitted across two weeks, from 8 to 15 February 1964, and Marco Polo was broadcast over seven weeks from 22 February to 4 April. From the sixth episode of Marco Polo, the show's broadcast time was pushed a further fifteen minutes, from 5:15 p.m. to 5:30 p.m., overlapping with competitor programme ITV News. Marco Polo was erased by the BBC on 17 August 1967; the entire serial is missing as a result. It is one of three stories of which no footage whatsoever is known to have survived, though tele-snaps (images of the show during transmission, photographed from a television) of episodes 1–3 and 5–7 exist, and were subsequently released with the original audio soundtrack, which was recorded "off air" during the original transmission.

The Keys of Marinus was transmitted across six weeks from 11 April to 16 May; the third episode became the first Doctor Who episode to be transmitted on BBC1, following its renaming from BBC TV due to the launch of BBC2, and the show's broadcast time returned to its original slot of 5:15 p.m. from the fifth episode. The Aztecs was broadcast weekly from 23 May to 13 June. The first two episodes of The Sensorites were broadcast on 20 and 27 June; the second episode aired 25 minutes late due to an overrun of the previous programme Summer Grandstand. Due to extended coverage of the Wimbledon tennis championships and Ashes Test match on 4 July, the third episode was replaced by Juke Box Jury and postponed to the following week. The final three episodes were broadcast weekly from 18 July to 1 August; episodes 3–5 were erased by the BBC on 17 August 1967, while the remaining three were erased on 31 January 1969. BBC Enterprises retained negatives of the original 16 mm film with soundtracks made in 1967; these were returned to the BBC Archives in 1978. The Reign of Terror was transmitted weekly from 8 August to 12 September; the second and third episodes were shifted to the later time of 5:30 p.m., the fourth episode was broadcast at 5:15 p.m. (due to coverage of the Royal Edinburgh Military Tattoo), and the final two episodes again shifted to 5:30 p.m. The original prints of The Reign of Terror were wiped by BBC Enterprises in 1972. The sixth episode was returned to the BBC by a private collector in May 1982, and the first three episodes were located in Cyprus in late 1984; the fourth and fifth episodes remain missing, existing only as off-air recordings from 1964. The existing episodes were screened as part of the National Film Theatre's Bastille Day schedule on 14 July 1999, with links between the episodes by Ford.

### Home media

#### VHS releases

#### DVD releases

### Books

## Reception

### Ratings

The assassination of John F. Kennedy the day preceding the launch of Doctor Who overshadowed the first episode; as a result, it was repeated a week later, on 30 November, preceding the second episode. The first episode was watched by 4.4 million viewers (9.1% of the viewing audience), and it received a score of 63 on the Appreciation Index; the repeat of the first episode reached a larger audience of six million viewers. Across its four episodes, An Unearthly Child was watched by an average of 6 million (12.3% of potential viewers). Mark Bould suggests that a disappointing audience reaction and high production costs prompted the BBC's chief of programmes to cancel the series until the Daleks, introduced in the second serial, were immediately popular with viewers. The first two episodes of The Daleks received 6.9 and 6.4 million viewers, respectively. By the third episode, news about the Daleks had spread, and the episode was watched by 8.9 million viewers. An additional million viewers watched for the following two weeks, and the final two episodes reached 10.4 million; by the end of the serial, the show's overall audience had increased by 50%. The following two serials retained these high viewing figures, with The Edge of Destruction receiving 10.4 and 9.9 million viewers, and Marco Polo maintaining an average of 9.47 million viewers.

The fourth episode of The Keys of Marinus received 10.4 million viewers, but saw a drop of 2.5 million viewers the following week, and an additional drop of one million for the sixth episode. The drop in viewers for the sixth episode was attributed to the absence of Juke Box Jury, the programme that followed Doctor Who. The Aztecs maintained these figures, with an average of 7.5 million viewers across the four episodes; the third episode became the first episode of the show to place in the top 20 of the BBC's audience measurement charts. The fourth and fifth episodes of The Sensorites dropped to 5.5 and 6.9 million viewers, respectively, but were nonetheless the highest-rated BBC show in the BBC North region for their respective weeks. The Reign of Terror received smaller audiences than previous serials due to the warmer weekends, with an average of around 6.7 million viewers, but still maintained a position within the top 40 shows for the week.

### Critical response

Doctor Who's first season received generally positive responses. For An Unearthly Child, Variety felt that the script "suffered from a glibness of characterisations which didn't carry the burden of belief", but praised the "effective camerawork", noting that the show "will impress if it decides to establish a firm base in realism". Mary Crozier of The Guardian was unimpressed by the first serial, stating that it "has fallen off badly soon after getting underway". Conversely, Marjorie Norris of Television Today commented that if the show "keeps up the high standard of the first two episodes it will capture a much wider audience". The following serial, The Daleks, was widely praised, described by the Daily Mirror's Richard Sear as "splendid children's stuff". The serial's villains, the Daleks, became a cultural phenomenon, and have been closely associated with the show since. The Edge of Destruction was criticised at a BBC Programme Review Board Meeting in February 1964 by controller of television programmes Stuart Hood, who felt that the serial's sequences in which Susan uses scissors as a weapon "digressed from the code of violence in programmes"; Lambert apologised for the scenes.

Marco Polo was positively received; Philip Purser of The Sunday Telegraph noted that Mark Eden impersonated Marco Polo "with sartorial dash", but felt that the main characters were poorly written, describing Barbara as "a persistent drip". The Keys of Marinus was criticised by Bob Leeson of the Daily Worker, who felt that the fifth episode of the serial was the show's low point, noting that the introduction of a trial scene represented a rushed script. The following serial, The Aztecs, received high praise and is retrospectively seen as one of the show's greatest stories. Television Today's Bill Edmunds praised the serial's villains, but felt that Barbara should have "a chance to look beautiful instead of worried", and Leeson of the Daily Worker felt that the serial had "charm", applauding the "painstaking attempts for historical accuracy" and noting a "much tighter plot" than previous serials. The Reign of Terror was criticised for its historical inaccuracies, described by Daily Worker's Stewart Lane as a "half-baked royalist adventure".

Retrospective reviews of the season were positive. Kimberley Piece of Geek Girl Authority felt that, while the season started slowly, it "managed to find its footing" and "developed quickly into a popular ratings favorite". Simbasible found that most serials are memorable, though many feature repetitive and "silly" storytelling. Richard Gray of The Reel Bits praised the imagination and perseverance of the show's producers. Reviewing the first serial in 2008, Radio Times reviewer Patrick Mulkern praised the casting of Hartnell, the "moody" direction and the "thrilling" race back to the TARDIS. For The Daleks, Mulkern praised the strength of Nation's scripts, particularly the first three cliffhangers, but felt that "the urgency and claustrophobia dissipate towards the end", describing the final battle as "a disappointingly limp affair". Reviewing The Edge of Destruction, Mulkern described David Whitaker as "a master of dialogue, characterisation and atmosphere", but felt he struggled with plot logic, as evidenced by the fast return switch explanation.

Mark Braxton of Radio Times praised Marco Polo, stating that "the historical landscape was rarely mapped with such poetry and elegance", though noted inconsistencies in the foreign characters' accents. Mulkern wrote that "standards slip appreciably" in The Keys of Marinus, and Arnold T. Blumberg of IGN described the serial as "a clichéd premise ... handled poorly and with no spark at all apart from Hartnell's late-hour rally". Christopher Bahn of The A.V. Club described The Aztecs as "a classical tragedy infused with just enough hope toward the end to keep it from being unbearably bleak", and Ian Berriman of SFX described the serial as "Jacqueline Hill's finest hour". DVD Talk's John Sinnott considered The Sensorites "well constructed" with impressive set design and an expanded role for Susan, but felt that there was "nothing special" about the serial. Mulkern wrote positively of the humour and Hartnell's increased role in The Reign of Terror, but felt that Susan was "at her weakest".

Season of British television series

Black-and-white British television shows