Brotoro

The little tufts of frozen oxygen at the bottom of the second stage were interesting. The view of the satellites separating and being visible in a big spiral pattern in the distance was beautiful. Nice job.

Liftoff and landing in the dark were different...but quite interesting.

They have an obvious error in that article where it says "The peak thickness for this lunar atmosphere, the researchers claim, would have occurred about 3.5 million years ago, and it managed to persist around the Moon for about 70 million years before it all trickled out into space." ...but that should read '3.5 BILLION years ago' (judging from the original paper).

Look at the time scales. Even you say that it would take 16 years to lift all of the air out of there with 100% maximum efficiency. At that rate, escaping molecules simply can't carry away energy very quickly over short timescales. At the rate sunlight is pouring energy into the system, the temperature will rise very rapidly in a much shorter period of time (the Moon currently goes from -150°C to over 100°C in a matter of days, even when radiating IR unimpeded to space). The temperature in the proposed atmosphere would rise rapidly to the point where IR emission dominates -- there is no other way for the energy to escape in the short term.

The velocity of the gas molecules scales as the square root of the temperature (T1/2). The rate of radiation loss from an opaque gas or solid scales asT4. That's a T8 difference. So, as the temperature of the atmosphere (and Moon) rises, the rate of IR radiation out to space, be it from either the lunar surface or from the opaque layers of the atmosphere (depending on which scenario above you want to discuss), would vastly outstrip the energy loss by escaping molecules. The energy will take the easy way out (IR radiation), so you are only going to have a small fraction of the incoming energy to cook off the air molecules.

Ah...You are correct in that I misquoted 500 seconds. But my disagreement comes from his calculation where he uses all of the incoming energy to remove the atmosphere...when most of the incoming energy is going to get re-radiated back to space as infrared radiation. Only a small fraction will be usable for removing the atmosphere. (earlier misquotes now fixed)

Yes, energy is put into the atmosphere and heats it up (by radiation coming in and by the surface radiating outward, and by convection). THEN that warmed air re-radiates the energy as infrared...some making it out to space, and some warming the surface more than it would be without the atmosphere. The temperature of the atmosphere and surface will increase until the outgoing infrared (from surface and atmosphere...mostly from atmosphere) balances the incoming solar radiation. After the equilibrium is reached, not a lot more energy is going to be captured to heat up the atmosphere (it's already warmed up to the equilibrium state). The Earth absorbs about 235 Watts per square meter of energy from the Sun: 168 W/m^2 by the surface, 67 W/m^2 by the atmosphere. Some light energy is reflected directly back into space by the clouds, air, and surface). The warked-up surface radiates The surface re-radiates only 40 W/m^2 directly from the surface into space...most of the re-radiated IR from the surface gets trapped by the atmosphere. The warmed up atmosphere radiates about 195 W/m^2 into space, and the surface radiates 40 W/m^2 directly to space. So you get almost the same amount going out as coming in (some small amount of energy comes out of the interior of the Earth, and some energy is lost from the atmosphere by escaping gas molecules, but these are small amounts compared to the equilibrium radiative input and output. On the hypothetical Moon with a thick atmosphere, the same thing would be going on. Most of the energy input by solar radiation is going to be re-radiated by the atmosphere and surface as infrared (with less coming from internal heat and more being lost as kinetic energy of escaping molecules compared to Earth). But you are not going to have anywhere close to all of the incoming solar energy to use in removing the atmosphere (in 500 million seconds)...most of the energy will get re-radiated by the warmed-up atmosphere as infrared. (The numbers in paragraph 2 come from a diagram in the Wikipedia article on the greenhouse effect.)

No. It will only keep putting lots of energy into the atmosphere until you reach approximate equilibrium temperature. Then the surface and atmosphere will be radiating the infrared energy to space about as fast as the planet is receiving it from the Sun. If you add greenhouse gasses (in addition to the oxygen/nitrogen specified in the original question), that will only mean the equilibrium temperature will end up being higher before the outgoing IR balances the incoming solar radiation.

Yes, but the details of the situation (how much of the incoming solar radiation is reflected directly, how much is absorbed by the surface and atmosphere) does not change the fact that most of the incoming radiation is re-emitted as infrared (be it by the surface of by the atmosphere), so that outgoing energy is not available to lift the atmosphere out of the gravity well. Only the difference between what goes in and what goes out as radiation (the vast majority) is available to remove the atmosphere. So your calculation assuming all the energy goes into removing the atmosphere (in 500 million seconds) is wildly off.

The Moon is in thermal equilibrium, more or less. Most of the solar energy input goes to heating up the surface to the point where it can radiate energy away (in the infrared) about as fast as it comes in. Only the difference between radiative input and radiative output would be available to remove the atmosphere.

I doubt it. The solar wind may be going fast (hundreds of km/sec), but the density is extremely low (a few to a few hundred atoms per cubic cm). That's not a lot of kinetic energy compared to all the mass that would need to be lifted out of the Moon's gravity well. Because the lunar surface gravity is 1/6 that of the Earth, you are going to need about six times as much gas sitting over every square meter of the Moon as we do on Earth to get the same surface pressure. The Earth has 13.4 times the surface area of the Moon...so that means the total mass of this hypothetical lunar atmosphere would be around 45% of the mass of the Earth's atmosphere (which Wikipedia, the fount of all knowkedge, tells me is 5.15x10^18 kg)... so we have to lift about 2.3x10^18 kg of mass out of Moon's gravitational well. That's a tall order. Plus, you better lift it all of the way out of the Earth's gravity as well, otherwise you're going to get a lot of it in a torus straddling the Moon's orbit...and the Moon will be able to sweep some of it back up.

I suspect that the Moon would hold an atmosphere for several thousands of years.

With an exhaust velocity of many times the solar system escape velocity, I wouldn't think you need to be too concerned about the exhaust (as long as you are careful to point it away from anything you don't want to spray with radioactivity).

Looks like fun. Let's go!

Drat. I thought it might finally be the BulgariaSat video.

I continue to be unsatisfied. But thank you for taking the time to discuss it. I enjoyed that interaction. Have a Like.

If the fermions are not interacting... how does the second fermion know the first one is already in that primo parking location?

I don't see how you can say there us no interaction going on between fermions. If just two fermions try to inhabit the same location with all of their other quantum states being the same, it will not happen because the rules of quantum mechanics prohibit it. One electron could sit there just fine. The other electron could sit there just fine. But try to put both there at the same time and it will not happen. How does this not involve an interaction between these two electrons?

You see, it's the "That effect which is counterbalancing the force of gravity is not a 'force'..." song and dance that seems to be sidestepping the issue. Particles are trying to move inward under the force of gravity. Interactions with other particles are preventing that from happening. Just saying "It's not a force" doesn't change the fact that particles are interacting with measurable effects without it being caused by any of the four fundemental force interactions that can occur between particles. Unsatisfying.

Of course, atoms repel each other because of the electromagnetic force between their electrons. But I think the reason mikegarrison says that it involves the Pauli Exclusion Principle is because you then have to answer the question "but what is keeping the electrons in place?". Or, skip atoms completely and go to the question of degenerate electron pressure in a white dwarf or degenerate neutron pressure in a neutron star. The force of gravity is acting inward to try to collapse these objects, but they are not collapsing...so some outward force must be acting to counterbalance gravity. This force cannot be the result of the electromagnetic force because it operates for any fermions, even uncharged fermions. That quite real outward force is NOT the result of any of the four fundemental 'forces', but instead results from the PEP.

Now THAT is an interesting question, for which I’ve never received a satisfying answer (although I asked about it in the context of degenerate pressure in white dwarfs and neutron stars).

Nicely done. I don't mind at all not watching the second stage when I have a first stage landing to watch.

I watched the total solar eclipse from near Mount Juliet, Tennessee, where the totality was 2 minutes 28 seconds. There were some cumulus clouds threatening an hour before totality, but these dissipated as the temperature dropped while the partial phases progressed. Totality was beautiful. I shot pictures for the first half of totality, and you can see a thin band of wispy clouds moving in as my photo sequence ends. But that band was too thin to spoil the view while I was looking at the second half of totality (mainly with binoculars). Regulus was just to the left of the Sun during totality (with Venus blazing further off to the right...Venus popped into view during the later part of the partial phases). There were some high cumulus clouds off to the west and east, and we could see those darken and lighten as the shadow approached and receded before and after totality. The birds were confused and all roosted in a big bunch on some power lines as totality approached. I saw very faint shadow bands on the ground about a minute before totality, and strong shadow bands about a minute after the end of totality. They look like an effect you'd see by shining light through heat shimmers. I can't post pictures now (I will be spending the next 11 hours sitting at airports or driving home).

I think that the Apollo 15 crew suffered from heart arythmia from lack of potassium, but I don't know if that was exacerbated by drinking distilled water. This was corrected on later Apollo missions with potassium supplements added to their Tang (or whatever).

Didn't the astronauts drink water made by the fuel cells on Apollo flights (in the Command Module, anyway)? Wouldn't that have been pure water?