93

Firstly, Mars has a mean distance from the Sun of 1.524 AU, so by the inverse square law the energy it gets from the Sun is about 40% of what the Earth gets. But the main reason that Mars is so cold is that its atmosphere is very thin compared to Earth's (as well as very dry, see below). From Wikipedia Atmosphere of Mars: The atmosphere of Mars is much ...


27

I'm just going to expand and deepen on what the other answers already said. In the following I contrast the atmospheric transmission ($T$) and absorption ($A$, which is $A=1-T$) of Mars and Earth. The Mars plot (top) is from Prof. J. Irwin via this review by P. Read et al. 2015 and the terrestrial data (bottom) is from wikipedia. The plots of $A$ and $1-T$...


16

Mars does have a greenhouse effect, only somewhat weaker than Earth's. Mars' atmosphere is very dilute, with a with a surface pressure only 0.6% of Earth's. So even if 95% of it is CO2, that's not a lot. However, it is actually a higher absolute abundance of CO2 molecules than on Earth, which only has a CO2 abundance of 0.04% (by volume; e.g. NOAA, ...


8

An answer to your question is contained within What is the largest hydrogen-burning star? The hottest observed main sequence stars are of type O3V, with photospheric temperatures of about 50,000 K. However, it is indeed possible that hotter main sequence stars may exist in the present-day universe, but have simply evolved into Wolf-Rayet stars (and lost a ...


5

UY Scuti is a red supergiant star. When stars start to run out of hydrogen fuel, their cores start to collapse, causing the core of the star to heat up, and heavier elements start to be used as fuel. This means that the core of the star is hotter and producing more energy. The effect on the outer layers of the star is to cause them to expand, and as ...


3

They are mostly empirical. Found by measuring the $B-V$ for stars of known $T_{\rm eff}$ (which are in turn measured by knowing the luminosity and radius of a star, and this is only known for a small number of stars). The relationships also depend on stellar surface gravity and composition. An alternative approach is to derive "synthetic" relationships by ...


2

Do we know the fluctuations and constant temperature depth of the moon? Yes, at some Apollo landing sites, it's been carefully measured! The astronauts make deep holes in the Moon's regolith and put in thermal probes that precisely measured temperature. These signals were radioed back to Earth by a solar-power transmitter, in some cases for years. These ...


2

There are two parts to the answer and neither has anything to do (directly) with how far away the Sun is. The first part is to consider the temperature of the Sun vs the temperature of your furnace. The amount of radiation power emitted per unit area is proportional to $T^4$ (the fourth power of temperature) and it really doesn't depend on anything else. ...


2

Thermonuclear fusion has nothing to do with the central temperature of the Sun. You can get a rough estimate of the temperature (with some necessary simplification) following this line of reasoning: The material of the Sun is an ideal, completely ionized, gas (all electrons are separated from nuclei); This means that pressure of the gas is proportional to ...


2

If the pressure were the same as the current pressure on Titan, the planet would be slightly warmer for a while, but not for long. The CO2 would soon be frozen out. It is probable that 4 billion years ago the atmospheres of Venus,Earth,Masrs and Titan were much more similar. A hotter Saturn may have warmed Titan in those days. It probably,like the others, ...


2

Another key point to bear in mind is that if one is asking for the "hottest" star, then presumably it is "effective temperature" that is referenced. Effective temperature is related to the luminosity L and the radius R from which the light emerges (not the static surface of the star, R can be well out in a dense stellar wind) by the Stefan-Boltzmann law, ...


1

Hint: There is an approximate relation between luminosity, radius and temperature for stars: $$ L = 4\pi R^2\sigma_B T_S^4 $$ Can you solve it from here?


1

One thing to keep in mind is that planet temperature doesn't follow a neat equation when an atmosphere is involved. Without an atmosphere, it's pretty straight forward and there's even an equation for it. See here, or here. Note, the first link above has an error in it. It says Venus' clouds block 10% of the sun. I think it's closer to 80% of the sun, ...


1

The hottest stars that are still fusing in their cores are Wolf-Rayet stars that are on the extreme end of the WC sequence, appropriately classified as WO stars, which display prominent Oxygen emission lines. The hottest known star is WR 102, which has a spectral type of WO2 and a surface temperature of 210,000 Kelvin. WR 102 is thought to have a mass of ~...


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