Aaron Hurwitz asked:
Why is it that the sun warms us up on Earth while it remains cold above us despite the fact that above us is really closer to the sun and at some point closer to the sun itís probably really hot so at what point does it become freezing cold?
Chris - If you have a gas, which is, say, in an aerosol, says the contain youíre going to spray into your armpit with your deodorant, thereís a gas under pressure in there. When you spray it in your armpit, it feels very, very cold. Whatís happened? Well the gas has expanded. I thought about simply if you imagine thereís some kind of piston, inside the aerosol can, when the gas expanded it effectively pushed on the piston, itís done some work, letís say. If something has does some work, it must have less energy, after itís done the work than before it did the work. Since temperature is proportional to the energy in the particles, if somebodyís got less energy, is therefore going to lower the temperature so the temperature must fall and thatís why we think that when a gas expands, the temperature goes down.
Dave - OK. And now this is actually very related to why mountains are cold. Okay. The temperature of things on Earth is sort of balance between the amount of heat which is getting either from the sun or from heat moving around the world and the amount of heat it can lose by radiating into space or radiating anything at room temperature, radiating heat and infrared really quite well. And so, basically the only things which can absorb sunlight very well tend to be at the ground. The atmosphere is transparent so the heat is going into the ground and heating it up and then that heats up the air above it. And now, the tops of mountains are very, very small. So basically, whatís the temperature of the atmosphere at 30,000 feet? 10,000 meters, or 9,000 meters? And the reason why thatís very cold is because if you have pockets of air which is being warmed up on the surface of the Earth and then it lifts up by convection, itís moved upwards, the pressure drops about half the pressure it was before, which means that gas expands and as gases expand, they get cold so the air gets very, very cold. So, the air around the mountain is very, very cold and also anything which is pointy like a mountain has got lots Ė can emit infrared light in lots more directions and the flat thing has got more surface area compared to mountain sunlight which hits it. So it cools down better during the night and emits light into the space very much better so it tends to be very cold.
Aaron Hurwitz asked the Naked Scientists: Hi Dr. Chris and crew, Love your show. Why is it that the sun warms us on Earth while it remains cold above us, despite 'above us' being closer to the sun? †I assume that right around the sun it is indeed hot. †At what point does it become freezing cold? Also, was Mt. Everest always the world's tallest mountain? †Is it still growing? †If yes, by how much every year? †Is it's growth rate been steady over thousands of years? Thanks, Aaron Hurwitz Jerusalem, Israel What do you think? Aaron Hurwitz , Fri, 30th Oct 2009
By 'above us' I assume you mean in the space between Earth and the Sun, ie outside our atmosphere, in which case, the reason is because there is nothing to heat outside our atmosphere.
The earths atmosphere traps the heat. latebind, Fri, 30th Oct 2009
We are a cloud of mass, in a void of space just within a remarkably unique distance from an irradiating body. Radiation is by definition, massless, as so are the least of the particles predicted by the standard model. Energy, according to the translation of quantum mechanics, is when particles reach high velocity in quite a large collection. The result is simply that the material they compilate begins to get hotter.
All due respect, but if it is not allowed a quantum physical description (which isn't hard to involve when talking about subjects like radiation, then it shouldn't be in the quantum physics and cosmology section. It should be in general sciences, if anyone protests. Mr. Scientist, Sat, 31st Oct 2009
quote author=Mr. Scientist link=topic=26446.msg281315#msg281315 date=1256988543]
It's really nice answer to the question but very tricky or confusing though. Mr.american scientist, Sat, 26th Dec 2009