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Welcome to the explain xkcd wiki!
We have an explanation for all 2 xkcd comics, and only 18 (1%) are incomplete. Help us finish them!

## Latest comic

 Hertzsprung-Russell Diagram Title text: The Hertzsprung-Russell diagram is located in its own lower right corner, unless you're viewing it on an unusually big screen.

## Explanation

 This explanation may be incomplete or incorrect: Created by a RED GIANT - Please change this comment when editing this page. Do NOT delete this tag too soon.

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, in a 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.

Regular Hertzsprung–Russell diagrams start at about 1000K and what is labeled on this diagram as 1021 watts—i.e. the upper-left corner. This diagram has been extended to lower magnitudes on both axes. The joke comes from the absurdity of showing tiny (at least compared to stars) and often mundane objects on a diagram meant for stars.

Though not included in the diagram, the title text notes that the screen displaying the diagram would probably be plotted somewhere in the lower right corner due to its (relatively) low brightness and heat output.

Item Effective Temperature Luminosity Explanation
Betelgeuse 3000 k 1031 W
Vega 10,000 K 1027 W
Sun 6000 K ~1026 W
Proxima Centauri
HD 189733b
Interior of a hydrogen bomb during detonation ~108 K
Jupiter
Venus
Earth
Mars
Moon
Nuclear Fireball
France
Europa
Lightning Bolt
Ivanpah Solar Plant Salt Tank
Medium-sized Lava Lake
Cruise Ship
Campfire
Blue Whale
Arc Lamp
Lightbulb
LED Bulb
Astronomer

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