2009: "Hertzsprung-Russell Diagram"

[NotAllThere]

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

I couldn't find this in the list. It must be there, musn't it? I mean explainxkcd already has an entry... And I don't get the title text at all.

[NotAllThere]

Did the rapture hit? I'm paranoid I know, but am I paranoid enough?!

[cellocgw]

Disappointed that a few things didn't make the chart.

-- nice cold bottle of beer
-- bucket of liquid nitrogen
-- your mama

[madaco]

So, the joke is that these diagrams are usually for stars, but here other things are being included?

[gmalivuk]

I don't get the title text at all.

The image itself has a luminosity and effective temperature if you're viewing it on a computer monitor. That monitor itself (or more precisely the portion of that monitor displaying the image) would be at the lower right corner of this diagram.

Unless you had a particularly large monitor, in which case the luminosity would be higher.

[da Doctah]

Where on this diagram would you place Dr Manhattan?

[cellocgw]

Where on this diagram would you place Dr Manhattan?

Just below Dr. Bronx .

[zjxs]

I don't get the title text at all.

The image itself has a luminosity and effective temperature if you're viewing it on a computer monitor. That monitor itself (or more precisely the portion of that monitor displaying the image) would be at the lower right corner of this diagram.

Unless you had a particularly large monitor, in which case the luminosity would be higher.

I understand everything on here except for whales and astronomers. How do they emit luminosity?

[gmalivuk]

body heat

[Sableagle]

Also bioluminescent plankton and smartphones.

[Cousj001]

I understand everything on here except for whales and astronomers. How do they emit luminosity?

body heat

Also bioluminescent plankton and smartphones.

Drat, I see my idea of making a fortune by selling smartphones to whales has already been though of.

[Soupspoon]

Drat, I though my idea of making a fortune by selling smartphones to whales as already been though of.

^{[cetacean needed]}

[Old Bruce]

Drat, I though my idea of making a fortune by selling smartphones to whales as already been though of.

^{[cetacean needed]}

Okay, a grudgingly given Internets to Soupspoon, grudgingly given because I should have thought of that first. [grudge-face emoticon]

[Reka]

Drat, I though my idea of making a fortune by selling smartphones to whales as already been though of.

^{[cetacean needed]}

THWACK! THWACK THWACK THWACK THWACK THWACK!

Also, +1 internets, but THWACK.

[XbHW_TestEngr]

So what he's really saying is "astronomers aren't very bright".
While they are slightly hotter than a blue whale, they just don't shine.

And the battle between the sciences continues. (Hmmm ... that was in a previous comic ... too lazy to look.)

[qvxb]

Speaking of Body Heat, Kathleen Turner is about 10000 K.

[miturian]

there's an error on there, right? the arrow in the x-axis should be pointing to the left.

[Dave Rogers]

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

This is, of course, known as Hertzsprung-Russell's Paradox.

Dave

[Sableagle]

... and Nanase? She's a lot smaller than the Moon, but shines very brightly indeed ...

... and is hot.

There's an empty space between the cooler Supergiants and the cooler main sequence stars. Why's there an empty space?

[Sandor]

Surely an LED bulb has a lower effective temperature than a normal (incandescent) light bulb. They have about the same surface area, but an LED bulb emits less total EM radiation. LEDs only look "hot" because their spectrum is so different to that of a black body.

[cellocgw]

Surely an LED bulb has a lower effective temperature than a normal (incandescent) light bulb. They have about the same surface area, but an LED bulb emits less total EM radiation. LEDs only look "hot" because their spectrum is so different to that of a black body.

Not clear what you mean by "effective temperature." and don't call me Shirley.

[speising]

Surely an LED bulb has a lower effective temperature than a normal (incandescent) light bulb. They have about the same surface area, but an LED bulb emits less total EM radiation. LEDs only look "hot" because their spectrum is so different to that of a black body.

Not clear what you mean by "effective temperature." and don't call me Shirley.

effective temperature
noun
Physics

noun: effective temperature; plural noun: effective temperatures

the temperature of an object calculated from the radiation it emits, assuming black-body behaviour.

yeah, i wondered about the definition of this, too. effective temp is not actual temp, as i (and Sandor it seems) would have assumed, but the effect measured in blackbody temp it has based on its radiation.

so a 6000K LED has a high effective temp although it probably isn't actually warmer than 300K.

.
.
.
why is a Blue Whale more luminous than an astronomer?

[Soupspoon]

why is a Blue Whale more luminous than an astronomer?

Because blue whales can't turn a light-switch off when it wants to whale, but an astronomer often does when wanting to astron?

[Raidri]

why is a Blue Whale more luminous than an astronomer?

Because blue whales can't turn a light-switch off when it wants to whale, but an astronomer often does when wanting to astron?

A whale has a greater surface area so he emits more radiation.

[Soupspoon]

why is a Blue Whale more luminous than an astronomer?

Because blue whales can't turn a light-switch off when it wants to whale, but an astronomer often does when wanting to astron?

A whale has a greater surface area so he emits more radiation.

And light switches would be far more fiddly. I think that's the most important point. They really couldn't flip a teeny light switch with their flippers. They might be able to swipe it with their tail, but that would still be down to a huge fluke.

[trpmb6]

When looking at this you really have to consider surface areas.

Which is why I was at first a little confused as to the positioning of France. But had to remember the scale of the Luminosity axis. That's why France-Europa-Moon-Earth-Venus-Jupiter seems a little odd at first.

[itaibn]

Drat, I though my idea of making a fortune by selling smartphones to whales as already been though of.

^{[cetacean needed]}

Citation: The entry on Atlantic humpback dolphin in Wikipedia's List of cetacean species.

Also, I'm getting tired of digs on the intelligence of astronomers.

[Soupspoon]

Also, I'm getting tired of digs on the intelligence of astronomers.

The only digs I've seen have been around archaeologists!

[Muswell]

Why is Great A'Tuin not on here?

[Archgeek]

Why is Great A'Tuin not on here?

Heck, where's Eärendil with his silmaril aboard Vingilótë? 'Not sure where an elven spaceship falls thermally, but the silmarils were widely known for their luminosity.

[Sableagle]

Why is Great A'Tuin not on here?

Heck, where's Eärendil with his silmaril aboard Vingilótë? 'Not sure where an elven spaceship falls thermally, but the silmarils were widely known for their luminosity.

He's a little busy helping the Free Peoples reclaim mordor at the moment, making his luminosity extremely hard to measure. We know from examining the stats of the gear people are using there that the luminosity of Eärendil is quantum. We just don't have a way of calculating the total number of those quanta.
If two Champions on two different world servers each use a cuirass with 10 Light of Eärendil, are they between them wearing 20, or are they wearing the same 10 in superposition, with those 10 existing on one world or the other, depending to which server you connect to check?

[SuicideJunkie]

There's an empty space between the cooler Supergiants and the cooler main sequence stars. Why's there an empty space?

Because a cool star on the main sequence is also a very small star and vice versa (red dwarfs). A supergiant, as the name implies, is quite large.
With both being at the same blackbody temperature, that size difference translates to a huge area difference and a huge luminosity difference.

[orthogon]

why is a Blue Whale more luminous than an astronomer?

Because blue whales can't turn a light-switch off when it wants to whale, but an astronomer often does when wanting to astron?

A whale has a greater surface area so he emits more radiation.

And light switches would be far more fiddly. I think that's the most important point. They really couldn't flip a teeny light switch with their flippers. They might be able to swipe it with their tail, but that would still be down to a huge fluke.

Two whale-related puns in one week? You've b[al]een told.

[PM 2Ring]

Surely an LED bulb has a lower effective temperature than a normal (incandescent) light bulb. They have about the same surface area, but an LED bulb emits less total EM radiation. LEDs only look "hot" because their spectrum is so different to that of a black body.

It seems strange to me to see someone calling incandescent bulbs normal. The sale of incandescent bulbs was banned here in Australia almost a decade ago. At least, the traditional incandescent filament bulbs were banned, you can still get some halogen type bulbs. Most domestic light bulbs here are now compact fluorescents, or LEDs. The old incandescent traffic lights were replaced by LEDs shortly before the ban took effect. I guess we'll be getting LED street lights at some stage, currently they're some form of metal halide lamp.

[smprather]

there's an error on there, right? the arrow in the x-axis should be pointing to the left.

Hello fellow 1-poster. Yep. I came here to point out the same thing. I was at first confused about why the hydrogen bomb was on the far left at 100e6K.

[rmsgrey]

there's an error on there, right? the arrow in the x-axis should be pointing to the left.

Hello fellow 1-poster. Yep. I came here to point out the same thing. I was at first confused about why the hydrogen bomb was on the far left at 100e6K.

The short answer is "tradition".

The H-R diagram was originally absolute magnitude against spectral class, with spectral classes going O,B,A,F,G,K,M,L,T with decreasing temperature, so you get a downwards slope. And when the scale got refined to use temperature rather than spectral classes, it stayed the "wrong" way round.