Editing 2009: Hertzsprung-Russell Diagram

{{comic
| number    = 2009
| date      = June 20, 2018
| title     = Hertzsprung-Russell Diagram
| image     = hertzsprung_russell_diagram.png
| titletext = The Hertzsprung-Russell diagram is located in its own lower right corner, unless you're viewing it on an unusually big screen.
}}

==Explanation==
The {{w|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 {{w|Kelvin}} (degrees {{w|Celsius}} above {{w|absolute zero}}) for {{w|effective temperature}} and, in a unlike many Hertzsprung–Russell diagrams, {{w|Watts}} for {{w|luminosity}}. While most Hertzsprung–Russell diagrams are labelled in units of {{w|solar luminosity}} or {{w|absolute magnitude}}, all three are perfectly valid measures of {{w|luminosity}}, which refers to the total power emitted by the star (or other body). {{w|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<sup>21</sup> to 10<sup>33</sup> watts&mdash;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.

==Table==

{| class="wikitable sortable"
!style="width:10%"|Item
!style="width:10%"|Effective Temperature
!style="width:10%"|Luminosity
!style="width:70%"|Explanation
|-
|{{w|Main sequence}}
|2500 K-45,000 K 
|6.1 × 10<sup>21</sup> W-8.4 × 10<sup>31</sup> W
|Most stars lie along the main sequence, one of several labelled regions in a typical {{w|Hertzsprung–Russell diagram|Hertzsprung-Russell (HR) diagram}}, and are thus classified as main sequence stars. Progressing from the lower-right toward the upper-left end of the main sequence, stars become more massive, hotter, and more luminous. The HR diagram in this comic includes three main sequence stars.
|-
|{{w|Giant star|Giants}}
|2700 K-6000 K
|1.6 × 10<sup>31</sup> W
|A giant star is larger and more luminous than a main sequence star of the same temperature. The HR diagram in this comic does not specifically include any giant stars.
|-
|{{w|Supergiant star|Supergiants}}
|3450-20,000 K
|2.2 × 10<sup>29</sup> W+
|Supergiant stars are among the largest and most luminous stars that exist. The HR diagram in this comic includes the supergiant star Betelgeuse.
|-
|{{w|White dwarf|White dwarfs}}
|10,000K
|5.0 × 10<sup>22</sup> W
|In a white dwarf star, nuclear fusion has ceased. A white dwarf still radiates energy due to stored heat that was generated from fusion earlier in the star's life, but white dwarfs are much less luminous than stars that are still undergoing fusion. The HR diagram in this comic does not specifically include any white dwarf stars.
|-
|{{w|Brown dwarf|Brown dwarfs}}
|2200 K
|5.4 × 10<sup>22</sup> W
|Brown dwarfs are too small to be classified as stars, but are larger than planets. The HR diagram in this comic does not specifically include any brown dwarfs.
|-
|{{w|Betelgeuse}}
|3200 K
|1.6 × 10<sup>31</sup> W
|Betelgeuse is a red supergiant star. At 3200&nbsp;K, it is cooler than the sun but has a higher luminosity owing to its larger size.
|-
|{{w|Vega}}
|10,000 K
|1.8 × 10<sup>28</sup> W
|Vega is a main sequence star that is both hotter and more luminous than the sun.
|-
|{{w|Sun}}
|5800 K
|3.6 × 10<sup>26</sup> W
|The sun is a main sequence star. On a typical {{w|Hertzsprung–Russell diagram|HR diagram}}, the luminosity of the sun is usually the basis of the luminosity scale, i.e. the sun is at "1" or 10<sup>0</sup> on the diagram's vertical scale.
|-
|{{w|Proxima Centauri}}
|2700 K
|2.0 × 10<sup>23</sup> W
|Proxima Centauri, the closest star to the sun, is a main sequence star that is both cooler and less luminous than the sun.
|-
|{{w|HD 189733 b}}
|2100 K
|4.8 × 10<sup>21</sup> W
|This is an exoplanet discovered in 2005. It is comparable in size to Jupiter, but hotter and more luminous owing to its close proximity to its own sun.
|-
|Interior of a {{w|Thermonuclear weapon|hydrogen bomb}} during detonation
|~10<sup>8</sup> K
|~10<sup>20</sup> W
|This is the area where the fusion of hydrogen started and where the bomb is hottest and brightest.
|-
|{{w|Jupiter}}
|285 K
|1.2 × 10<sup>18</sup> W
|Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a giant planet with a mass one-thousandth that of the Sun, but two-and-a-half times that of all the other planets in the Solar System combined.
|-
|{{w|Venus}}
|330 K
|5.0 × 10<sup>17</sup> W
|Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. It has the longest rotation period (243 days) of any planet in the Solar System and rotates in the opposite direction to most other planets (meaning the Sun would rise in the west and set in the east).
|-
|{{w|Earth}}
|300 K
|3.0 × 10<sup>17</sup> W
|Non-luminous objects on Earth are typically the same temperature as Earth, around 300&nbsp;K. As shown in the diagram, Earth-based objects like France, the cruise ship, the blue whale, and the astronomer all have temperatures in the vicinity of 300&nbsp;K. 
|-
|{{w|Mars}}
|255 K
|2.0 × 10<sup>16</sup> W
|Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury.
|-
|{{w|Moon}}
|300 K
|1.2 × 10<sup>16</sup> W
|The Moon is an astronomical body that orbits planet Earth and is Earth's only permanent natural satellite.
|-
|Nuclear Fireball
|8000 K
|2.0 × 10<sup>14</sup> W
|The glowing, rising mass of air that appears just after a nuclear bomb is detonated.
|-
|{{w|France}}
|300 K
|2.0 × 10<sup>14</sup> W
|This is part of Earth (and more precisely a part of Europe), the same temperature as Earth, but less luminous in proportion to its surface area. Including this may be a joke referencing the two possible meanings of ‘Europa’ (see the next entry). [https://goo.gl/images/H8Dmu3 France emits less light at night than neighbouring countries], perhaps due to lower population density.
|-
|{{w|Europa (moon)|Europa}}
|90 K
|3.5 × 10<sup>14</sup> W
|While this term could refer to Europe (a part of Earth, of which France (the previous entry) is a further part), the temperature and luminosity are both too small for that, so it must refer to the moon of Jupiter instead.
|-
|Lightning Bolt
|30,000 K
|30 GW
|The area where the bolt strikes, both with or without connection to [https://en.wikipedia.org/wiki/Back_to_the_Future time travel apparatus].
|-
|{{w|Ivanpah Solar Power Facility|Ivanpah Solar Plant}} Salt Tank
|1200 K
|1.2 GW
|The {{w|Ivanpah Solar Power Facility}} is a large solar power generator in the Californian Mojave desert. It concentrates sunlight from 173,500 reflectors onto three water-boiler towers. Randall appears to have mistakenly confused this power plant with the nearby {{w|Crescent Dunes Solar Energy Project}}, which uses tanks of molten salt to store energy. https://insideclimatenews.org/news/16012018/csp-concentrated-solar-molten-salt-storage-24-hour-renewable-energy-crescent-dunes-nevada
|-
|Medium-sized Lava Lake
|800 K
|32 MW
|Lava lakes are large volumes of molten lava, usually basaltic, contained in a volcanic vent, crater, or broad depression.
|-
|Cruise Ship
|325 K
|30 MW
|A cruise ship is a passenger ship used for pleasure voyages, when the voyage itself, the ship's amenities, and sometimes the different destinations along the way (i.e., ports of call), are part of the experience.
|-
|Campfire
|870 K
|7.0 kW
|A campfire is a fire at a campsite that provides light and warmth, and heat for cooking.
|-
|{{w|Blue whale}}
|280 K
|78 kW
|This must be average surface temperature as whales are warm-blooded at 37&nbsp;°C internally, interestingly this and the cruise ship may be the only entries where a significant amount of power produced is conducted away rather than radiated.  The power seems to be higher than reality. [https://www.researchgate.net/publication/321972840/figure/fig1/AS:574004013604864@1513864629274/Visible-and-infrared-spectrum-images-of-various-humpback-whale-surfacing-features.png These images] suggest a surface temperature around 295K - 300K for a Humpback whale when surfacing.
|-
|{{w|Arc lamp}}
|6500 K
|150 W
|A light source that passes an electrical current through a gas (as in a mercury or sodium vapor lamp) rather than a solid filament (as in a standard incandescent lightbulb) or a semiconductor (as in an LED).
|-
|Lightbulb
|4800 K
|75 W
|The temperature value here refers to color temperature, which for an incandescent bulb is the same as the filament temperature. However tungsten filament lights, commonly referred to as "bulbs", have a color temperature of between 2400 and 3600&nbsp;K, and tungsten melts at 3695&nbsp;K.
|-
|LED Bulb
|5800 K
|8 W
|The temperature value here refers to color temperature, not physical temperature. Color temperature is a better match to effective temperature than physical temperature. As typical semiconductors might be rated for a maximum of 150&nbsp;°C or about 420&nbsp;K, the physical temperature of an LED Bulb is considerably lower than its color temperature. 
|-
|Astronomer
|310 K
|100 W
| The body temperature of a human (astronomer or otherwise) is about 310&nbsp;K (37&nbsp;°C). Skin surface temperature (which would fit the meaning of effective temperature better) is typically 31–35&nbsp;°C. An astronomer standing outside in a thick coat on a cold night would have a much lower surface temperature.

A human being generating 100&nbsp;W for 24 hours needs 2065&nbsp;kcal or 8.64&nbsp;MJ. According to the UN FAO this is e.g. the typical daily energy output of women with weight 55&nbsp;kg between 18 and 59 years having a light activity lifestyle of 1.55 times the BMR (basic metabolic rate).
|-
|{{w|Hertzsprung–Russell diagram}} 
|293 K
|[https://www.thehomehacksdiy.com/how-much-power-watts-does-a-monitor-use/ 20 W]
|Described in the title text, a diagram by itself doesn't have luminance or energy.  To observe it on a computer monitor, there's a certain amount of energy used however it's rare for a modern computer monitor to go above room temperature.  These numbers are indicative of a home user, rather than the setup of an evil genius or massive screens at a music festival.  

|}

==Transcript==
: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<sup>31</sup> W
:Vega: 	10,000 K, 	1.8 × 10<sup>28</sup> W 
:Sun: 	5800 K, 	3.6 × 10<sup>26</sup> W
:Proxima Centauri: 	2700 K, 	2.0 × 10<sup>23</sup> W
:HD 189733 b: 	2100 K, 	4.8 × 10<sup>21</sup> W
:Interior of a hydrogen bomb during detonation: 	~108 K, 	~10<sup>20</sup> W
:Jupiter: 	285 K, 	1.2 × 10<sup>18</sup> W
:Venus: 	330 K, 	5.0 × 10<sup>17</sup> W 
:Earth: 	300 K, 	3.0 × 10<sup>17</sup> W
:Mars: 	255 K, 	2.0 × 10<sup>16</sup> W
:Moon: 	300 K, 	1.2 × 10<sup>16</sup> W
:Nuclear Fireball: 	8000 K, 	2.0 × 10<sup>14</sup> W 
:France: 	300 K, 	2.0 × 10<sup>14</sup> W
:Europa: 	90 K, 	3.5 × 10<sup>14</sup> 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

{{comic discussion}}

[[Category:Scatter plots]]
[[Category:Astronomy]]