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


Ambox notice.png 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 cover ranges of about 1,000K to 30,000K, and what is labeled on this diagram as 1021 to 1033 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 screen displaying the diagram would probably be plotted somewhere in the lower right corner due to its (relatively) low brightness and heat output. Bigger screens have a higher power output (in terms of luminosity) and are thus positioned further towards the diagram's top corner. An "unusually big screen" would have to be something like a JumboTron for its luminosity to put it outside of the lower right corner.


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
Venus It appears that this might have been misplaced on the temperature axis, being far too closely placed to France and to Earth. Infact Venus is at 735K where Earth has a mean of 287K.
Nuclear Fireball
Lightning Bolt
Ivanpah Solar Plant Salt Tank
Medium-sized Lava Lake
Cruise Ship
Blue Whale
Arc Lamp
LED Bulb
Astronomer 310K The body temperature of a human (astronomer or otherwise) is about 310K (37°C)


Ambox notice.png This transcript is incomplete. Please help editing it! Thanks.

[A scatter plot is shown, with the x-axis labeled Effective Temperature (in degrees Kelvin, and the y-axis Luminosity (watts).]

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