Calculating stellar temperature at a distance?

On 01/12/2013 9:03 AM, Yousuf Khan wrote:
How does one calculate the temperature of the space surrounding a
stellar body at a certain distance from it? I was just using an inverse
square relationship between temperature and distance, but that comes up
with non-sense results.

Let's take the Earth and Sun as an example. If the Sun's surface
temperature is 9000K, and its radius is 700,000 km, and the Earth is 1
AU (1.5E+8 km) away from the Sun. At that distance using an inverse
square relationship, I get 0.2K as the answer. Obviously the Earth is
much warmer than that. What's the real way to obtain temperature here?

Yousuf Khan

BTW, I was able to find a website that does online calculations of the
habitable zone.

VPL - Habitable Zone Calculator
http://depts.washington.edu/naivpl/s...s/HZ_Calc.html

And here's an explanation of the formula used:

Calculating the Habitable Zone
http://webcache.googleusercontent.co...t=clnk &gl=us

Yousuf Khan

In article ,
Yousuf Khan writes:
BTW, I was able to find a website that does online calculations of the
habitable zone.
VPL - Habitable Zone Calculator
http://depts.washington.edu/naivpl/s...s/HZ_Calc.html

That looks very nice. Details are given in the paper by Kopparapu et
al. (2013 ApJ 765, 131) with a preprint at
http://xxx.lanl.gov/abs/1301.6674 .

From a quick glance, the planet's temperature appears to be based on
a climate model with a specific atmospheric composition or perhaps a
range of compositions. That's fine, but I wonder whether a different
atmosphere would give different results. No doubt it's all described
in the paper. In any case, this is a far more sophisticated
treatment than the simple calculations we discussed earlier.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

On 16/01/2014 23:54, Steve Willner wrote:
In article ,
Yousuf Khan writes:
BTW, I was able to find a website that does online calculations of the
habitable zone.
VPL - Habitable Zone Calculator
http://depts.washington.edu/naivpl/s...s/HZ_Calc.html

That looks very nice. Details are given in the paper by Kopparapu et
al. (2013 ApJ 765, 131) with a preprint at
http://xxx.lanl.gov/abs/1301.6674 .

From a quick glance, the planet's temperature appears to be based on
a climate model with a specific atmospheric composition or perhaps a
range of compositions. That's fine, but I wonder whether a different
atmosphere would give different results. No doubt it's all described
in the paper. In any case, this is a far more sophisticated
treatment than the simple calculations we discussed earlier.

The inner HZ limit is a bit surprising to me. I hadn't realised we on
Earth were quite so close to the water loss runaway greenhouse limit.

Also the outer limit for Mars being wet and warm isn't yet realised so
the model must still be incomplete (or Mars initial atmosphere denser).

--
Regards,
Martin Brown

On 17/01/2014 4:52 AM, Martin Brown wrote:
The inner HZ limit is a bit surprising to me. I hadn't realised we on
Earth were quite so close to the water loss runaway greenhouse limit.

Also the outer limit for Mars being wet and warm isn't yet realised so
the model must still be incomplete (or Mars initial atmosphere denser).

It's likely that the rest of credit for keeping a planet habitable is
the planet itself. I think if either Mars or Venus had a powerful
magnetic field like the Earth, they would've remained habitable too.
Venus lost most of its water due to solar winds stripping it of its
hydrogen. The solar winds wouldn't have had so much of an effect had it
had a magnetic field. Similarly, Mars wouldn't have had so much of its
entire atmosphere stripped away, had it not been for the solar wind.

The Earth without a magnetic field is as dead a planet as these other two.

Yousuf Khan

On Friday, January 17, 2014 3:41:51 AM UTC-8, Yousuf Khan wrote:
On 17/01/2014 4:52 AM, Martin Brown wrote:

The inner HZ limit is a bit surprising to me. I hadn't realised we on

Earth were quite so close to the water loss runaway greenhouse limit.



Also the outer limit for Mars being wet and warm isn't yet realised so

the model must still be incomplete (or Mars initial atmosphere denser).



It's likely that the rest of credit for keeping a planet habitable is
the planet itself. I think if either Mars or Venus had a powerful
magnetic field like the Earth, they would've remained habitable too.
Venus lost most of its water due to solar winds stripping it of its
hydrogen. The solar winds wouldn't have had so much of an effect had it
had a magnetic field. Similarly, Mars wouldn't have had so much of its
entire atmosphere stripped away, had it not been for the solar wind.

The Earth without a magnetic field is as dead a planet as these other two.

Yousuf Khan

The core of Venus is simply too newish or fission active to offer a magnetic component. The bulk of such fission elements probably didn't come from our sun.

Lots of magnetic doom and gloom offered within the following link.

http://www.youtube.com/watch?v=ILdFD-VShJM