What would happen to Earth's temperatures without an atmosphere?

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Discussion Overview

The discussion centers on the hypothetical scenario of Earth without an atmosphere and its implications for temperature, comparing it to the Moon's temperature variations. Participants explore the reasons behind the expected average temperature of 255K for Earth and question why the oceans would not thaw during the day.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that without an atmosphere, Earth would be completely frozen over with an average temperature of around 255K.
  • Others question the comparison with the Moon, noting that the Moon experiences daytime temperatures of 373K and nighttime temperatures of 100K, suggesting that Earth's rotation and atmospheric conditions would lead to different temperature dynamics.
  • One participant proposes that the size of the oceans would prevent them from thawing during the day, likening it to the difficulty of thawing a large steak.
  • Another participant provides a formula for calculating the temperature based on sunlight absorption and the Stefan-Boltzmann constant, indicating that the average sunlight absorbed is 240 Watts/meter².
  • There is a discussion about the lunar day being 28 times longer than an Earth day, which contributes to the Moon's temperature extremes.
  • Some participants express confusion about why Earth's average temperature would be 255K instead of something closer to the Moon's daytime temperature, given their similar distances from the Sun.

Areas of Agreement / Disagreement

Participants express differing views on the implications of having no atmosphere on Earth's temperatures, with no consensus reached regarding the comparison to the Moon's temperatures or the behavior of oceans in such a scenario.

Contextual Notes

Participants reference specific formulas and assumptions related to temperature calculations, but there are unresolved questions about the applicability of these formulas in the absence of an atmosphere.

Darkmisc
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Hi everyone

I've read that if Earth had no atmosphere it'd be completely frozen over with temperatures around 255K. Why is this the case when the moon has daytime temperatures of 373K (and night time temperatures of 100K)? Why wouldn't the oceans thaw during the day? Are they just too big to do that?

Thanks
 
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Darkmisc said:
Hi everyone

I've read that if Earth had no atmosphere it'd be completely frozen over with temperatures around 255K. Why is this the case when the moon has daytime temperatures of 373K (and night time temperatures of 100K)? Why wouldn't the oceans thaw during the day? Are they just too big to do that?

Thanks

It’s hard to comment without seeing the context of what you were reading. I think your observation regarding the moon is spot on. The side of the Earth facing the sun would get hot and the side away would get cold. The Earth rotates once per day rather than every 28 days so the excursions from the mean would be less. However the daily swings would be huge. You will freeze to death at night. You would roast in the day time.

There would be no oceans. The would evaporate.
 
Darkmisc said:
I've read that

On PF we always try to give the links. Where did you read that?
 
Darkmisc said:
I've read that if Earth had no atmosphere it'd be completely frozen over with temperatures around 255K. Why is this the case when the moon has daytime temperatures of 373K (and night time temperatures of 100K)?
What's the average of 373 and 100?

Note that the lunar day is 28x as long as the Earth day, which helps enable the temperature extremes.
Why wouldn't the oceans thaw during the day? Are they just too big to do that?
Way, way, way too big. It takes all day just to thaw a big steak on my counter!
 
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https://www.lpl.arizona.edu/~showman/greenhouse.html

255K was obtained by using the following formula:

T = (F/&sigma)^1/4.

Plugging in F=240 Watts/meter^2 and &sigma=5.67 x 10^-8 Watts/meter^2 Kelvin^4, we find that T=255 K, which corresponds to a temperature of -18oC or 0oF. (Sorry, the indices and superscript didn't copy and paste properly). 240 Watts/meter^2 is the amount of sunlight absorbed. 5.67 x 10^-8 Watts/meter^2 Kelvin^4 is the Stephan-Boltzmann constant.

Thanks. I didn't know a lunar day was 28 days.

The average of 373 and 100 is close to 255K, but it looks like the formula only applies when the Earth is receiving sunlight. If that's true, why do we get 255K rather than something like 373K, given the moon and Earth are roughly the same distance from the sun?
 
Darkmisc said:
The average of 373 and 100 is close to 255K, but it looks like the formula only applies when the Earth is receiving sunlight. If that's true, why do we get 255K rather than something like 373K, given the moon and Earth are roughly the same distance from the sun?
240 w/m^2 is the average over the entire globe, including the part that isn't receiving sunlight.
 
Cheers. Thanks
 

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