Hertzsprung-Russell Diagram
Hertzsprung-Russell Diagram
Expanded Hertzsprung-Russell Diagram [A scatter plot is shown, with the x-axis labeled Effective Temperature (in kelvins), and the y-axis Luminosity (watts).] [Circled items in the top left (high temperature and high luminosity):] Supergiants Giants Main sequence White dwarfs Brown dwarfs [Items shown as points and their values:] Betelgeuse: 	3200 K, 	1.6 × 10 31 W Vega: 	10,000 K, 	1.8 × 10 28 W Sun: 	5800 K, 	3.6 × 10 26 W Proxima Centauri: 	2700 K, 	2.0 × 10 23 W HD 189733 b: 	2100 K, 	4.8 × 10 21 W Interior of a hydrogen bomb during detonation: 	~108 K, 	~10 20 W Jupiter: 	285 K, 	1.2 × 10 18 W Venus: 	330 K, 	5.0 × 10 17 W Earth: 	300 K, 	3.0 × 10 17 W Mars: 	255 K, 	2.0 × 10 16 W Moon: 	300 K, 	1.2 × 10 16 W Nuclear Fireball: 	8000 K, 	2.0 × 10 14 W France: 	300 K, 	2.0 × 10 14 W Europa: 	90 K, 	3.5 × 10 14 W Lightning Bolt: 	30,000 K, 	30 GW Ivanpah Solar Plant Salt Tank: 	1200 K, 	1.2 GW Medium-sized Lava Lake: 	800 K, 	32 MW Cruise Ship: 	325 K, 	30 MW Campfire: 	870 K, 	7.0 kW Blue whale: 	280 K, 	78 kW Arc lamp: 	6500 K, 	150 W Lightbulb: 	4800 K, 	75 W LED Bulb: 	5800 K, 	8 W Astronomer: 	310 K, 	100 W

The Hertzsprung–Russell diagram is a scatterplot showing absolute luminosities of stars against its effective temperature or color. It's generally used to understand a star's age.
The axes are labeled in Kelvin (degrees Celsius above absolute zero ) for effective temperature and, unlike many Hertzsprung–Russell diagrams, Watts for luminosity . While most Hertzsprung–Russell diagrams are labelled in units of solar luminosity or absolute magnitude , all three are perfectly valid measures of luminosity , which refers to the total power emitted by the star (or other body). Effective temperature refers to temperature of a blackbody with the same surface area and luminosity. This is meant to provide an estimate of the surface temperature of the object.
Roughly speaking, the luminosity (i.e. total power radiated) by an object is proportional to (1) the total surface area of the object, multiplied by (2) the (absolute) temperature raised to the fourth power. So a high luminosity generally results from either a very hot or a very large object, or a combination of the two. The surface-area dependence explains why the whale and the cruise ship are more luminous than the hotter campfire.
Regular Hertzsprung–Russell diagrams cover ranges of about 1,000K to 30,000K, and what is labeled on this diagram as 10 21 to 10 33 watts—i.e. the upper-left corner. Extended diagrams increase the luminosity range only to include the "Brown Dwarfs". This diagram has been extended to much lower magnitudes on both axes. The joke comes from the absurdity of a diagram meant for stars including much smaller objects, such as planets ... and astronomers.
Though not included in the diagram, the title text notes that the diagram itself would probably be plotted somewhere in the lower right corner due to its (relatively) low power output and temperature. On its face this is nonsensical - the diagram itself, being mere information, possesses neither power output nor temperature - but one can read this as the power output and temperature of a typical screen displaying the diagram. Bigger screens have a higher total output (in terms of luminosity) and are thus positioned further towards the diagram's top. An "unusually big screen" would have to be something like a JumboTron or a projector for its luminosity or temperature to put it outside of the lower right corner.
Expanded Hertzsprung-Russell Diagram [A scatter plot is shown, with the x-axis labeled Effective Temperature (in kelvins), and the y-axis Luminosity (watts).] [Circled items in the top left (high temperature and high luminosity):] Supergiants Giants Main sequence White dwarfs Brown dwarfs [Items shown as points and their values:] Betelgeuse: 	3200 K, 	1.6 × 10 31 W Vega: 	10,000 K, 	1.8 × 10 28 W Sun: 	5800 K, 	3.6 × 10 26 W Proxima Centauri: 	2700 K, 	2.0 × 10 23 W HD 189733 b: 	2100 K, 	4.8 × 10 21 W Interior of a hydrogen bomb during detonation: 	~108 K, 	~10 20 W Jupiter: 	285 K, 	1.2 × 10 18 W Venus: 	330 K, 	5.0 × 10 17 W Earth: 	300 K, 	3.0 × 10 17 W Mars: 	255 K, 	2.0 × 10 16 W Moon: 	300 K, 	1.2 × 10 16 W Nuclear Fireball: 	8000 K, 	2.0 × 10 14 W France: 	300 K, 	2.0 × 10 14 W Europa: 	90 K, 	3.5 × 10 14 W Lightning Bolt: 	30,000 K, 	30 GW Ivanpah Solar Plant Salt Tank: 	1200 K, 	1.2 GW Medium-sized Lava Lake: 	800 K, 	32 MW Cruise Ship: 	325 K, 	30 MW Campfire: 	870 K, 	7.0 kW Blue whale: 	280 K, 	78 kW Arc lamp: 	6500 K, 	150 W Lightbulb: 	4800 K, 	75 W LED Bulb: 	5800 K, 	8 W Astronomer: 	310 K, 	100 W
