Exposing PseudoAstronomy

September 7, 2008

Apollo Moon Hoax: Huge, Deadly Temperature Variation Claims

All posts in this series:

This second installment on bashing the Apollo Moon Hoax deals with the various claims that the moon gets to about -200 °F in the shade and up to +200 °F in full sunlight. According to conspiracy theorists, this range is way too much and would have (a) rendered the film unusable (because it would have shattered in the cold or melted in the heat), and (b) been very dangerous to the astronauts, if not deadly.

In order to properly understand why this claim really doesn’t present insurmountable odds, you must first understand how heat is transferred. There are three ways that heat moves from one object to another:

  1. Radiation: Radiation is the least efficient process of transferring heat.  It involves exactly what it sounds like – radiation, or light-based energy (photons).  The photon is emitted from the heat source and is absorbed by the target.  The act of absorbing the photon – a packet of energy – adds to the energy of the target material, thus heating it up.

    The Sun heats all objects in the solar system mainly through radiative heat transfer.  This is also the same mechanism behind “heat lamps” – those hot red lights that are oh-so-common in cafeterias, keeping the french fries or the pizza warm.

    There’s another aspect to this that does not play a role in the other two heat transfer processes:  Some surfaces will absorb heat faster than others.  This is because objects that are whiter will absorb less radiation because they reflect more.  Objects that are blacker will absorb more radiation because they reflect less.  Astronomers call this “albedo.”  You may have noticed this effect if you’re outside in the summer and wear a white shirt vs. a black shirt – you’ll heat up much more quickly in black.

  2. Conduction:  Conduction is the process where heat is transferred by one object physically touching another object.  For example, when you place a pot of water on the stove to boil, the heating element of the stove physically touches the pot, heating it up, and the pot physically touches the water, heating that up.
  3. Convection:  Convection is the most efficient process of heat transfer.  It involves the physical mixing of material of two different temperatures, which distributes the heat.  An everyday example of this is adding ice to a glass of water and then stirring it around.  This stirring physically moves the ice and water to better distribute the heat than if the ice just sat there (conduction).

    Another good example is a pot of thick stew or chili on the stove.  I learned this lesson the hard way – while soup convects quite easily, chili only conducts.  In other words, in most soups, you generally get a good boil going and the liquid circulates throughout the pot, carrying and distributing the heat very well.  Thicker foods like chili, however, do not convect; the heat conducts up through the pot to the food on the bottom, and then it just stays there.  The bottom will continue to absorb heat, but because the food is so thick, these warmer parts of the food don’t move anywhere, they just sit there, slowly conducting heat away at a slower pace than the pot is conducting heat to it.  This results in burnt chili on the bottom and barely warm chili on top.

There’s one more piece of information that you need to remember when trying to understand this claim:  The moon lacks an atmosphere – there’s no air!  This may seem like a basic, obvious statement, but it really makes all the difference.

On Earth, the Sun heats the ground (because the air really absorbs very little radiation) through Radiation.  The ground, in contact with the air, then heats the air near the surface by Conduction.  Because air is like soup and not like chili, it easily Convects, warming the whole planet.  This is part of why there is comparatively very little difference between the day and night air temperatures on the planet, as opposed to, say, Mars.

The the moon, the first step is the same – the Sun heats the ground through Radiation.  And then it stops.  There is no atmosphere to speak of, and so there is absolutely no way for the heat to distribute throughout the moon other than through the slow process of conduction (which doesn’t heat more than a few meters deep, called the “skin depth”).  The region of space directly above the moon’s surface does not change temperature any real amount even though the surface below it goes through 400 °F temperature swings.

With this in mind, let’s place an Apollo astronaut on the surface, with a camera attached to his chest (I’m using male pronouns not out of any sexism, but because they were all men).  The solar radiation is heating the surface fairly well, since the lunar albedo is about 0.08 (it reflects only 8% of the radiation it receives, absorbing the other 92%).  The astronaut and the camera, however, has an albedo fairly close to 0.90 (new-fallen snow, reflecting 90% of the light it receives, absorbing 10%).

So right away, you can tell that the astronaut’s suit – in the absence of any cooling or insulation – will heat up more than 10x more slowly than the ground just through the solar radiation.  However, to be fair, there is a very small contribution from the lunar surface because it has a certain temperature and so radiates, as well.  But, this contribution is very small compared with the Sun.

Now, with an astronaut standing on the lunar surface, there’s an additional heat transfer process:  Conduction.  The ground physically touches the astronaut’s boots, allowing them to conduct heat, and so contributing to heating up the astronaut.  This is a smaller effect, though, than conspiracy theorists may have you believe.  After all, the saying goes, if you walk down a beach on the dry sand with the sun out, your feet quickly roast.  But, the lunar surface material – regolith (we don’t call it “soil” because soil implies an organic origin) – is very loosely consolidated.  In other words, it’s more like trying to conduct heat through flour as opposed to sand or asphalt.  And the heat that was transferred was generally shielded by the insulation in the astronauts’ boots, preventing this fairly slow process from transferring too much heat.

So at this point in the discussion, we have pretty well shielded from any excessive temperatures.

This brings up my third (I think third) point:  The astronauts AND the cameras had insulation around them.  This insulation – like a nice warm winter jacket – prevented a lot of heat from being transferred both into and out of the suits and camera housing.

But this brings up a fourth argument:  Even if the astronauts were not properly insulated from the cold temperatures, where would their heat go?  The process of getting too cold happens when heat is transferred from you to the environment.  But there was no environment on the moon to which the astronauts or their cameras could transfer the heat.  The only way they could do it was conduction back through the insulation in the astronauts’ boots to the lunar regolith, or through radiative heat transfer to empty space.  And with their insulation, neither of these played any significant role.

My fifth and final point deals with the timing of the missions.  NASA knew that the moon’s surface went through these temperature swings.  But, that doesn’t mean that as soon as a square meter of lunar surface rotates into the Sun’s light that it suddenly, immediately goes from -200 °F to +200 °F.  It takes time to absorb the radiation and heat up!  And that is why all of the lunar missions were planned for “dawn” on the moon, before the surface had heated up to the +200 °F temperatures, but after it had warmed a little from the -200 °F temperatures.  So even while the lunar surface does experience wide temperature swings throughout it’s nearly 700-hr day, the astronauts did not experience those extremes!


Finally, to summarize why this claim does not hold up under scrutiny:

  1. The astronauts and the cameras were covered in reflective material, limiting radiative heat transfer.
  2. The lunar regolith is loosely compacted, resulting in very slow conduction of heat from it to the astronauts’ boots.
  3. The astronauts and the cameras were covered in insulation, limiting heat transfer.
  4. There’s no atmosphere on the moon to conduct heat to or away from the astronauts and cameras.
  5. The EVAs (Extra-Vehicular Activities, or moonwalks) were all during lunar dawn, so the astronauts did not even experience the massive temperature swings that conspiracy theorists report.

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