The planet Venus crossed in front of the sun at a slow pace on Tuesday, marking the final visible transit from Earth for 105 years. Transits of Venus occur in pairs eight years apart, separated by more than a century. During this recent transit, Venus appeared as a small black dot moving gradually across the sun's northern hemisphere. Many amateur astronomers watched the event online through various websites offering live video feeds. Detailed views from the Prescott Observatory in Arizona, streamed on Slooh.com, showed a minor solar flare forming just below Venus' silhouette. The transit that took place on Tuesday marked the end of a pair of transits that occurred between 2004 and 2012. The event began at 6:09 p.m. EDT (2209 GMT) and was visible to skywatchers on all seven continents, including Antarctica. Even astronauts on the International Space Station were able to witness at least part of the transit. Don Pettit, a flight engineer on the space station, had been looking forward to this event and had brought a solar filter with him in preparation. The focus is not solely on beautiful images. Various scientific experiments were arranged, including research that could aid in the discovery of habitable planets outside of our solar system. Telescopes like NASA's Kepler space telescope are being utilized to locate extrasolar planets that pass in front of their respective stars, similar to Venus passing in front of the sun. During Venus' transit, astronomers aimed to analyze the planet's dense atmosphere in order to develop methods for studying atmospheres of other planets. By examining Venus' atmosphere, researchers could gain insight into why Earth and Venus, despite being nearly identical in size and orbiting at a similar distance from the sun, are so dissimilar. Venus has an extremely thick atmosphere, mainly composed of carbon dioxide, which is 100 times denser than Earth's atmosphere. The planet's surface temperature reaches a scorching 900 degrees Fahrenheit (480 degrees Celsius) and high-speed clouds of sulfuric acid move around Venus at 220 miles per hour, causing acid rain. Despite being known as the goddess of love, Venus is not a planet you would want to get close to, according to an astronomer on a webcast. Scientists are studying Venus' climate to gain insight into potential changes in Earth's atmosphere. In past transits of Venus, scientists determined the size of the solar system and the distance between the sun and the planets. Tuesday's transit, only the eighth since the telescope was invented, is the last one until December 10-11, 2117. This transit is unique as it is the first to occur with a spacecraft at Venus. Observations from Europe's Venus Express probe will be compared to data collected by various ground and space-based telescopes, such as NASA's Solar Dynamics Observatory, the US-European Solar and Heliospheric Observatory, and Japan's Hinode spacecraft.