# How cold would it be if there was no sun

tim88
Science 07 Apr '13 11:39
1. 07 Apr '13 11:39
just if there was no sun. do we know?
2. 07 Apr '13 12:325 edits
Originally posted by tim88
just if there was no sun. do we know?
I assume how cold it would be on the surface of the Earth?
It would certainly become cold enough to freeze out most of the Earth's atmosphere apart from possibly a trace amount of hydrogen and helium. Most of the heat energy on the surface of the Earth comes from solar radiation but a tiny proportion, much less than 1%, comes from volcanoes and geothermal activity but I don't know the exact figure on that (does anyone here know the exact figure?). I believe the temperature of deep interstellar space is between 2 and 4 K (can someone confirm that?) so, if it was not for geothermal heat, without the Sun, the temperature on the surface of the Earth would eventually drop down to about ~3K but not much colder than that.

Note that the temperature of the surface of Pluto is about 43 K but I assume that most of that heat comes from what tiny amount of sunlight Pluto gets (can anyone confirm that?)
3. sonhouse
Fast and Curious
07 Apr '13 14:311 edit
Originally posted by humy
I assume how cold it would be on the surface of the Earth?
It would certainly become cold enough to freeze out most of the Earth's atmosphere apart from possibly a trace amount of hydrogen and helium. Most of the heat energy on the surface of the Earth comes from solar radiation but a tiny proportion, much less than 1%, comes from volcanoes and geothermal acti ost of that heat comes from what tiny amount of sunlight Pluto gets (can anyone confirm that?)
Most of that heat is from the sun. If you look at the inverse square law, you just square the difference in distances, lets call Earth 100 million miles from the sun just for grins, and pluto 4 billion miles. So that is 40 times Earth distance or 40 AU. So square 40 and you get 1600. Now we get about 1400 watts per square meter on top of the atmosphere so dividing you get something like 0,9 watts per square meter. Not a lot but enough to keep things about zero Kelvin! Of course those numbers are just total approximations since I am typing and doing this stuff in my head instead of looking up the real numbers but the real numbers won't be too far off my estimation. Around 1 watt per square meter. Looking up the real distance, it is average 39.5 AU. Not bad for a guess. And of course the Earth is about 93E6 miles not 100E6 but that was close enough for a guestimate. So it turns out to be 1.15 watts per square meter. Good enough, eh.
4. sonhouse
Fast and Curious
07 Apr '13 21:02
Originally posted by sonhouse
Most of that heat is from the sun. If you look at the inverse square law, you just square the difference in distances, lets call Earth 100 million miles from the sun just for grins, and pluto 4 billion miles. So that is 40 times Earth distance or 40 AU. So square 40 and you get 1600. Now we get about 1400 watts per square meter on top of the atmosphere so d ...[text shortened]... enough for a guestimate. So it turns out to be 1.15 watts per square meter. Good enough, eh.
So we look at Pluto, maybe it's about the size of the moon, too lazy to look it up.

Say it's 2000 miles in diameter. That would be about 3 million square miles of surface exposed to the sun. At 1 watt per square meter that is about one terawatt spread out over the surface so not inconsequential. !000 gigawatts. That is what is heating up Pluto.
5. wolfgang59
invigorated
07 Apr '13 21:55
Originally posted by tim88
just if there was no sun. do we know?
We had no sun yesterday morning - it was chilly.
6. Soothfast
0,1,1,2,3,5,8,13,21,
07 Apr '13 23:01
Originally posted by tim88
just if there was no sun. do we know?
We here in Pennsylvania know: as cold as it can get.

More seriously, I imagine temperatures would decrease to just a smidge above the cosmic microwave background radiation temperature of about 2.73 Kelvin. A little heat would come in from other stars, as well as from within the Earth itself.
7. sonhouse
Fast and Curious
07 Apr '13 23:07
Originally posted by Soothfast
We here in Pennsylvania know: as cold as it can get.

More seriously, I imagine temperatures would decrease to just a smidge above the cosmic microwave background radiation temperature of about 2.73 Kelvin. A little heat would come in from other stars, as well as from within the Earth itself.
What part of PA? I am near Allentown. I commute every workday to South Plainfield New Jersey, about 80 miles one way:ðŸ™‚
8. RJHinds
The Near Genius
07 Apr '13 23:29
Originally posted by tim88
just if there was no sun. do we know?
We don't know, but I suspect it would get cold enough to freeze the inside of the earth so that it is a ball of ice.
9. Soothfast
0,1,1,2,3,5,8,13,21,
08 Apr '13 00:061 edit
Originally posted by RJHinds
We don't know, but I suspect it would get cold enough to freeze the inside of the earth so that it is a ball of ice.
Do tell, professor. Tell us all how the rays of the sun keep the Earth's core molten.

EDIT: Because, you know, it doesn't.
10. RJHinds
The Near Genius
08 Apr '13 01:24
Originally posted by Soothfast
Do tell, professor. Tell us all how the rays of the sun keep the Earth's core molten.

EDIT: Because, you know, it doesn't.
I have never been to the core of the earth. I was just speculating on how cold the earth is going to get without the Sun heating up the outside. I think it would be very likely to freeze the inside too, given enough time of course. You evilutionists should be familiar with the billions of years speculations.
11. wolfgang59
invigorated
08 Apr '13 02:10
Originally posted by RJHinds
I was just speculating on how cold the earth is going to get without the Sun heating up the outside. I think it would be very likely to freeze the inside too,
So if it would freeze without the sun the sun must currently be having a heating effect .... ? ...... yes?

Tell us all how the rays of the sun keep the Earth's core molten
12. RJHinds
The Near Genius
08 Apr '13 02:33
Originally posted by wolfgang59
So if it would freeze without the sun the sun must currently be having a heating effect .... ? ...... yes?

[b]Tell us all how the rays of the sun keep the Earth's core molten
[/b]
I did not say the rays of the Sun keeps the core of the earth molten. There is only a certain portion of the earth's core that is molten anyway. But if there was no Sun to heat the outside of the earth then it would freeze everything on the outside and eventually there would be no molten core on the insiide. That is my speculation on the matter.
13. Soothfast
0,1,1,2,3,5,8,13,21,
08 Apr '13 03:38
Originally posted by sonhouse
What part of PA? I am near Allentown. I commute every workday to South Plainfield New Jersey, about 80 miles one way:ðŸ™‚
I'm in the general vicinity of Norristown, maybe about 50 miles away from you. I hear you have a Waffle House in your vicinity, you lucky devil.

Wow, I thought my 25-mile (one-way) drive to work was inconvenient. At least you have the interstate most of the way.
14. Soothfast
0,1,1,2,3,5,8,13,21,
08 Apr '13 03:42
Originally posted by RJHinds
I did not say the rays of the Sun keeps the core of the earth molten. There is only a certain portion of the earth's core that is molten anyway. But if there was no Sun to heat the outside of the earth then it would freeze everything on the outside and eventually there would be no molten core on the insiide. That is my speculation on the matter.
What about the Prince of Darkness and his demon hordes? Aren't they supposed to keep the home fires burning for all eternity in your cosmology?
15. sonhouse
Fast and Curious
08 Apr '13 12:54
Originally posted by RJHinds
I did not say the rays of the Sun keeps the core of the earth molten. There is only a certain portion of the earth's core that is molten anyway. But if there was no Sun to heat the outside of the earth then it would freeze everything on the outside and eventually there would be no molten core on the insiide. That is my speculation on the matter.
So tell us how long you think it would take for the core to freeze.