explain xkcd - User contributions [en]

2201: Foucault Pendulum

2019-09-11T19:34:38Z

Armasher: /* Explanation */

{{comic
| number = 2201
| date = September 11, 2019
| title = Foucault Pendulum
| image = foucault_pendulum.png
| titletext = Trust me, you don't want to get on the wrong side of the paramilitary enforcement arm of the International Earth Rotation and Reference Systems Service.
}}

==Explanation==
{{incomplete|Created by a BOT. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}
Black hat is attending what appears to be a physics lecture. The professor is talking about the Foucault pendulum, a device which demonstrates the rotation of the Earth. Black Hat, being himself, sees an opportunity to cause chaos and seizes it with both hands, quite literally - that is, he grabs the pendulum. The professor objects strongly to this, seemingly for fear of ruining the delicate demonstration. However, the news anchor in the final panel reveals to us that by arresting the motion of the pendulum, Black Hat has somehow stopped the rotation of the Earth. This is obviously blatantly impossible since the Foucault pendulum's motion is tied to the earth's rotation, not the other way round

A Foucault Pendulum swings from a joint that allows rotation in any direction, like your shoulder joint instead of your elbow. If the Earth were stationary, it would continue to swing in the same plane as when it was released. However, because the earth moves beneath it, over the course of the day the motion gradually changes direction. The low-resistance joint doesn't allow the rotation of the earth to affect the motion of the pendulum, so it stays aligned to its original inertial reference frame rather than the rotating one of the earth.

The fact that the earth's rotation does not influence the motion of the pendulum does NOT mean that other things can't affect it - for example, by running up and manually repositioning the pendulum. Of course, the apparent rotation of the pendulum's plane relative to the earth is an effect of the planet's motion, rather than the cause of it. Thus, stopping a Foucault pendulum manually does not entail pausing the rotation of the earth.

In this case, where the pendulum somehow manages to control earth's rotation, Black hat would probably not want to alter the momentum of the pendulum, unlike most cases of causing chaos(assuming he was told that it was related to earth's rotation and assuming that he would prefer to preserve his own life over making chaos). The reason why is because if the rotation of earth were to be stopped for even very short amounts of time(a few seconds), it would cause everything on earth that wasn't bolted/fasted to the ground would be sent flying eastward(assuming they are near the equator) at a speed of 300-360 meters per second, likely causing the death of most lifeforms on earth within an hour or less, and causing massive windstorms and weather events on a scale not observed on earth, likely causing a mass extinction event and with a ~90% of the extinction of humanity.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

{{comic discussion}}

2009: Hertzsprung-Russell Diagram

2018-10-25T16:19:18Z

Armasher: /* Explanation */

{{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, 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 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 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 × 1021 W-8.4 × 1031 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 × 1031 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 × 1029 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 × 1022 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 × 1022 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 × 1031 W
|Betelgeuse is a red supergiant star. At 3200 K, it is cooler than the sun but has a higher luminosity owing to its larger size.
|-
|{{w|Vega}}
|10,000 K
|1.8 × 1028 W
|Vega is a main sequence star that is both hotter and more luminous than the sun.
|-
|{{w|Sun}}
|5800 K
|3.6 × 1026 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 100 on the diagram's vertical scale.
|-
|{{w|Proxima Centauri}}
|2700 K
|2.0 × 1023 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 × 1021 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
|~108 K
|~1020 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 × 1018 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 × 1017 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 × 1017 W
|Non-luminous objects on Earth are typically the same temperature as Earth, around 300 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 K.
|-
|{{w|Mars}}
|255 K
|2.0 × 1016 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 × 1016 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 × 1014 W
|The glowing, rising mass of air that appears just after a nuclear bomb is detonated.
|-
|{{w|France}}
|300 K
|2.0 × 1014 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 × 1014 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 stikes
|-
|{{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 Crescent Dunes, 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
|Must be average surface temperature as whales are warm-blooded at 37 °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. Also the power seems high compared to what I can find. [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 colour temperature, which for an incandescent bulb is the same as the filament temperature. However tungsten filament lights, commonly referred to as "bulbs", have a colour temperature of between 2400 and 3600 K, and tungsten melts at 3695 K.
|-
|LED Bulb
|5800 K
|8 W
|The temperature value here refers to colour 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 °C or about 420 K, the physical temperature of an LED Bulb is considerably lower than its colour temperature.
|-
|Astronomer
|310 K
|100 W
| The body temperature of a human (astronomer or otherwise) is about 310 K (37 °C). Skin surface temperature (which would fit the meaning of effective temperature better) is typically 31–35 °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 W for 24 hours needs 2065 kcal or 8.64 MJ. According to the UN FAO this is e.g. the typical daily energy output of women with weight 55 kg between 18 and 59 years having a light activity lifestyle of 1.55 times the BMR (basic metabolic rate).

|}

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
: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 × 1031 W
:Vega: 10,000 K, 1.8 × 1028 W
:Sun: 5800 K, 3.6 × 1026 W
:Proxima Centauri: 2700 K, 2.0 × 1023 W
:HD 189733 b: 2100 K, 4.8 × 1021 W
:Interior of a hydrogen bomb during detonation: ~108 K, ~1020 W
:Jupiter: 285 K, 1.2 × 1018 W
:Venus: 330 K, 5.0 × 1017 W
:Earth: 300 K, 3.0 × 1017 W
:Mars: 255 K, 2.0 × 1016 W
:Moon: 300 K, 1.2 × 1016 W
:Nuclear Fireball: 8000 K, 2.0 × 1014 W
:France: 300 K, 2.0 × 1014 W
:Europa: 90 K, 3.5 × 1014 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]]

2009: Hertzsprung-Russell Diagram

2018-10-25T16:18:24Z

Armasher: /* Table */

{{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==
{{incomplete|Fill out the table. Do NOT delete this tag too soon.}}

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, 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 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 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 × 1021 W-8.4 × 1031 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 × 1031 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 × 1029 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 × 1022 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 × 1022 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 × 1031 W
|Betelgeuse is a red supergiant star. At 3200 K, it is cooler than the sun but has a higher luminosity owing to its larger size.
|-
|{{w|Vega}}
|10,000 K
|1.8 × 1028 W
|Vega is a main sequence star that is both hotter and more luminous than the sun.
|-
|{{w|Sun}}
|5800 K
|3.6 × 1026 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 100 on the diagram's vertical scale.
|-
|{{w|Proxima Centauri}}
|2700 K
|2.0 × 1023 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 × 1021 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
|~108 K
|~1020 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 × 1018 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 × 1017 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 × 1017 W
|Non-luminous objects on Earth are typically the same temperature as Earth, around 300 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 K.
|-
|{{w|Mars}}
|255 K
|2.0 × 1016 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 × 1016 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 × 1014 W
|The glowing, rising mass of air that appears just after a nuclear bomb is detonated.
|-
|{{w|France}}
|300 K
|2.0 × 1014 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 × 1014 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 stikes
|-
|{{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 Crescent Dunes, 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
|Must be average surface temperature as whales are warm-blooded at 37 °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. Also the power seems high compared to what I can find. [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 colour temperature, which for an incandescent bulb is the same as the filament temperature. However tungsten filament lights, commonly referred to as "bulbs", have a colour temperature of between 2400 and 3600 K, and tungsten melts at 3695 K.
|-
|LED Bulb
|5800 K
|8 W
|The temperature value here refers to colour 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 °C or about 420 K, the physical temperature of an LED Bulb is considerably lower than its colour temperature.
|-
|Astronomer
|310 K
|100 W
| The body temperature of a human (astronomer or otherwise) is about 310 K (37 °C). Skin surface temperature (which would fit the meaning of effective temperature better) is typically 31–35 °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 W for 24 hours needs 2065 kcal or 8.64 MJ. According to the UN FAO this is e.g. the typical daily energy output of women with weight 55 kg between 18 and 59 years having a light activity lifestyle of 1.55 times the BMR (basic metabolic rate).

|}

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
: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 × 1031 W
:Vega: 10,000 K, 1.8 × 1028 W
:Sun: 5800 K, 3.6 × 1026 W
:Proxima Centauri: 2700 K, 2.0 × 1023 W
:HD 189733 b: 2100 K, 4.8 × 1021 W
:Interior of a hydrogen bomb during detonation: ~108 K, ~1020 W
:Jupiter: 285 K, 1.2 × 1018 W
:Venus: 330 K, 5.0 × 1017 W
:Earth: 300 K, 3.0 × 1017 W
:Mars: 255 K, 2.0 × 1016 W
:Moon: 300 K, 1.2 × 1016 W
:Nuclear Fireball: 8000 K, 2.0 × 1014 W
:France: 300 K, 2.0 × 1014 W
:Europa: 90 K, 3.5 × 1014 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]]

2009: Hertzsprung-Russell Diagram

2018-10-25T16:16:30Z

Armasher:

{{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==
{{incomplete|Fill out the table. Do NOT delete this tag too soon.}}

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, 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 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 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 × 1021 W-8.4 × 1031 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 × 1031 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 × 1029 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 × 1022 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 × 1022 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 × 1031 W
|Betelgeuse is a red supergiant star. At 3200 K, it is cooler than the sun but has a higher luminosity owing to its larger size.
|-
|{{w|Vega}}
|10,000 K
|1.8 × 1028 W
|Vega is a main sequence star that is both hotter and more luminous than the sun.
|-
|{{w|Sun}}
|5800 K
|3.6 × 1026 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 100 on the diagram's vertical scale.
|-
|{{w|Proxima Centauri}}
|2700 K
|2.0 × 1023 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 × 1021 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
|~108 K
|~1020 W
|
|-
|{{w|Jupiter}}
|285 K
|1.2 × 1018 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 × 1017 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 × 1017 W
|Non-luminous objects on Earth are typically the same temperature as Earth, around 300 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 K.
|-
|{{w|Mars}}
|255 K
|2.0 × 1016 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 × 1016 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 × 1014 W
|The glowing, rising mass of air that appears just after a nuclear bomb is detonated.
|-
|{{w|France}}
|300 K
|2.0 × 1014 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 × 1014 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 stikes
|-
|{{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 Crescent Dunes, 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
|Must be average surface temperature as whales are warm-blooded at 37 °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. Also the power seems high compared to what I can find. [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 colour temperature, which for an incandescent bulb is the same as the filament temperature. However tungsten filament lights, commonly referred to as "bulbs", have a colour temperature of between 2400 and 3600 K, and tungsten melts at 3695 K.
|-
|LED Bulb
|5800 K
|8 W
|The temperature value here refers to colour 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 °C or about 420 K, the physical temperature of an LED Bulb is considerably lower than its colour temperature.
|-
|Astronomer
|310 K
|100 W
| The body temperature of a human (astronomer or otherwise) is about 310 K (37 °C). Skin surface temperature (which would fit the meaning of effective temperature better) is typically 31–35 °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 W for 24 hours needs 2065 kcal or 8.64 MJ. According to the UN FAO this is e.g. the typical daily energy output of women with weight 55 kg between 18 and 59 years having a light activity lifestyle of 1.55 times the BMR (basic metabolic rate).

|}

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
: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 × 1031 W
:Vega: 10,000 K, 1.8 × 1028 W
:Sun: 5800 K, 3.6 × 1026 W
:Proxima Centauri: 2700 K, 2.0 × 1023 W
:HD 189733 b: 2100 K, 4.8 × 1021 W
:Interior of a hydrogen bomb during detonation: ~108 K, ~1020 W
:Jupiter: 285 K, 1.2 × 1018 W
:Venus: 330 K, 5.0 × 1017 W
:Earth: 300 K, 3.0 × 1017 W
:Mars: 255 K, 2.0 × 1016 W
:Moon: 300 K, 1.2 × 1016 W
:Nuclear Fireball: 8000 K, 2.0 × 1014 W
:France: 300 K, 2.0 × 1014 W
:Europa: 90 K, 3.5 × 1014 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]]

2062: Barnard's Star

2018-10-25T13:50:22Z

Armasher: /* Explanation */

{{comic
| number = 2062
| date = October 22, 2018
| title = Barnard's Star
| image = barnards_star.png
| titletext = "Ok, team. We have a little under 10,000 years before closest approach to figure out how to destroy Barnard's Star." "Why, does it pose a threat to the Solar System?" "No. It's just an asshole."
}}

==Explanation==
{{incomplete|Too much detail from Wikipedia about Barnard's star, hardly any explanation of the comic itself. Do NOT delete this tag too soon.}}

[[File:Near-stars-past-future-en.svg|thumb|300px|Distances to the nearest stars from 20,000 years ago until 80,000 years in the future]]
{{w|Barnard's Star}} is a very-low-mass red dwarf about 6 light-years away from Earth in the constellation of {{w|Ophiuchus}}. It is the fourth-nearest known individual star to the {{w|Sun}} (after the three components of the Alpha Centauri system) and the closest star in the Northern Celestial Hemisphere. It is a {{w|Red dwarf}} with a mass of 0.144 Solar masses and it is 7–12 billion years old. Because of this low mass the gravitational pressure in the core is much lower and thus the fusion rate is far smaller than in the core of the Sun. In fact this star is so dim, even though it's one of the nearest, it can't be seen by the naked eye. The low fusion rate also means that the lifespan of small stars is much longer. While huge stars might last a few hundred million years, and the Sun about 10 billion years, a small Red dwarf has a lifespan of about a trillion years.

Barnard's Star is the star with the greatest proper motion in the sky. Proper motion is motion in the sky other than that caused by Earth's rotation or orbit. Barnard's star is both very close to the sun (as these things go) and moving at a speed of more than 140 km/s toward the Sun. It will make its closest approach to the Sun in approximately 10,000 years, at a distance of about 3.75 light-years.

In the comic, it shows that Barnard's star is flying by the Sun screaming it's cocky statement(Due to the fact that it will live a lot longer than the sun and most other stars) before flying away. However, the distances shown in the comic are a lot closer than they would actually be(Looking more like Barnard's star is only 500-600 Million kilometers(Between Jupiter and Saturn) rather than 3.75 light years), if they were this close, then it would cause a massive chain reaction that would make the solar system a lot less stable and would most likely cause the death of life on Earth(From Jupiter either flying away from the solar system and causing comets from the Kuiper belt and Oort cloud, or launching Jupiter into the inner solar system and dragging earth and other planets closer to the sun/getting ripped apart from being in the Roche limit of Jupiter).

In regards to "20,000-YEAR-LONG HIGH-SPEED FLYBY", the joke here is suggesting Barnard's Star would need to scream out a trolling statement(That the star has been around for a long time and will be around for a lot longer than the sun would sound cocky to the sun)as quickly as possible due to 20,000 years being such a small segment of time relative to the lifespan of the star (and our Sun, for that matter).

The image on the right shows different stars near the Sun over 100,000 years and it can be seen that none of them are getting closer than 3 light-years. This is a safe distance to our Solar System and the stars will not influence the orbits of the planets or smaller bodies. It's also obvious that much closer approaches never have happened since the Solar System formed 4.5 billion years ago because otherwise the nearly circular orbits of the planets in the same plane wouldn't be possible.

The title text emphasizes that this close approach will not be any hazard to the Solar System, but someone is envious of the long lifetime of Barnard's Star or annoyed by its unpleasant behavior(Yelling at the sun for 20,000 years would be a minuscule amount of time for the stars,but for humans it would be a vast length of time, and would get annoying very quickly).

=Transcript=
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[A black sky is shown with a yellow spot near the bottom, left of the center. Three smaller red spots at the diagonal from top left to bottom right indicate a moving star over time. Above these red spots lines are connected to a text that starts and ends with many ''A''s, first growing, and at the end getting smaller:]
:...AAAAHHi Sun! I was here billions of years before you formed and will shine for trillions of years after you dieEEEEEAAA...

:[Caption below the frame:]
:Sometimes, I wonder what Barnard's Star is saying to the Sun as it performs its 20,000-year-long high-speed flyby.

{{comic discussion}}

[[Category:Comics with color]]
[[Category:Astronomy]]