Temperature of a planet with an atmosphere: the greenhouse effect
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- čas přidán 27. 08. 2024
- Finding the equilibrium temperature of a planet heated by a star, including the effects of reflection and re-emission of radiation by its atmosphere (i.e. the greenhouse effect). The result depends on the albedo and emissivity of the atmosphere in appropriate wavelength ranges.
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About me: I studied Physics at the University of Cambridge, then stayed on to get a PhD in Astronomy. During my PhD, I also spent four years teaching Physics undergraduates at the university. Now, I'm working as a private tutor, teaching Physics & Maths up to A Level standard.
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using R = 6.957x10^8 m, D = 1.482x10^11 m, T0 = 5772K, and using the values i found online for albedo and emissivity, 0.434 and 0.95 respectively, you get a temperature of 285K, which is 12°C or 53°F. according to NASA the avg temp of Earth is 15°C or 59°F. pretty good!!
That's pretty good indeed!
Great question 😊
Hello Dr ben,
Very intresting vid.
Could you create a video on the expansion dynamics of a helium-filled spherical balloon in a vacuum? Specifically, I'm interested in understanding how the velocity of the expanding bubble and its pressure change over time. Your expertise in this area would be invaluable!
Interesting idea! I'll try working through the details and will see what I can come up with.
Do climate scientists put their models in one equation? Where can one see an example? How does it compare in terms of variables?
Not my area of expertise but I'd imagine the models that are used in practice have many, many more variables. Presumably many atmospheric layers are used, each with its own temperature, and a realistic model should also take into account the chemical composition of the atmosphere (since different molecules interact differently with EM radiation) as well as the wavelength dependence of properties like the emissivity. You'd end up with a system of many equations that needs to be solved numerically!
Here is a question. Doesnt the star heat up the atmosphere? Like the planet does to atmo
Yes, to some extent, but the heating effect from the planet itself dominates. That's because the radiation from the star has a much shorter wavelength than the radiation from the planet. The molecules that make up the atmosphere absorb the longer wavelength radiation much more efficiently, at least for an Earth-like atmosphere. So the method in the video is approximate, but it should be a very good approximation!
Doesn't the star would also heat up the atmosphere through radiation?
Yes, to some extent, but the heating effect from the planet itself dominates. That's because the radiation from the star has a much shorter wavelength than the radiation from the planet. The molecules that make up the atmosphere absorb the longer wavelength radiation much more efficiently, at least for an Earth-like atmosphere. So the method in the video is approximate, but it should be a very good approximation!