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My brother has recently been converted to a Flat Earther and is convinced that something that proves his theory is the moon landings being faked by NASA. I have managed to counter argue the majority of his points, however yesterday he sent me a video which showed the various layers of the Earth’s atmosphere. The thermosphere in particular has temperatures that reach upto around 1500 Celsius. My research shows the majority of the Apollo 11 Spacecraft was made from an aluminium alloy, which has a melting point of 660.03 Celsius so I wondered how did it not melt whilst going through the atmosphere?

I am sorry if this is an obvious question/answer but I haven’t been able to find a good answer and I need something to stop him from going on about it! Thanks to anyone for any help.

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    $\begingroup$ The important thing to note is that 'melting point' is the temperature that the material itself needs to be in order to melt. $\endgroup$
    – Jack
    Commented Aug 17, 2018 at 9:23
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    $\begingroup$ I am probably going to be very sorry for even asking this question, but … Why exactly does the Moon Landing being faked prove the Earth is Flat? Why would the Earth care whether Neil Armstrong stepped on the Moon or a studio in North Hollywood? $\endgroup$
    – Jörg W Mittag
    Commented Aug 17, 2018 at 11:27
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    $\begingroup$ @JörgWMittag - It's not that the Moon landing being faked proves the Earth is flat, but rather that a flat Earth means that the Moon landings had to have been faked. Flat Earth is possibly the most dangerous religion there is. $\endgroup$
    – David Hammen
    Commented Aug 17, 2018 at 12:10
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    $\begingroup$ A simple analogy, how do ice cubes removed from the freezer survive without instantly melting until good several minutes later? The Apollo capsule was well scorched on the outside, and the heatshield had most of its ablative cover burned off. So, in fact, yes, it did "melt" but only on the very outer surface. $\endgroup$
    – SF.
    Commented Aug 17, 2018 at 12:27
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    $\begingroup$ Why can you reach into a hot oven to remove whatever you happen to be baking? But if you accidentally touch the pan, you get burned. It's a matter of heat content and conduction rates. You can hold red-hot shuttle insulation tiles in your bare hands: gizmodo.com/… $\endgroup$
    – jamesqf
    Commented Aug 18, 2018 at 17:13

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Although the temperature at altitude can be several thousands of degrees, the atmosphere is so thin it does not transfer heat efficiently. Wikipedia explains it very well -

The highly diluted gas in this layer can reach 2,500 °C (4,530 °F) during the day. Even though the temperature is so high, one would not feel warm in the thermosphere, because it is so near vacuum that there is not enough contact with the few atoms of gas to transfer much heat. A normal thermometer might indicate significantly below 0 °C (32 °F), at least at night, because the energy lost by thermal radiation would exceed the energy acquired from the atmospheric gas by direct contact.

https://en.wikipedia.org/wiki/Thermosphere

The high temperatures experienced by those travelling out of and back into the atmosphere are those of greatest concern, particularly the latter. On ascent, temperatures are high but comfortably within the parameters of modern materials because the craft are travelling relatively slowly in the thicker atmosphere and faster when the atmosphere thins/becomes vacuum. On descent, i.e. re-entry, the shock wave caused by spacecraft colliding with atoms in the air causes the air to compress, which in turn creates heat. It is not due to friction. If you want to see the same effect on a smaller scale, take a deflated football and pump it up as fast as you can, then quickly feel the nozzle of your pump. It will be hot, because the compression of air causing heat has transferred to the nozzle.

Flat earth is an unfortunate belief at odds with mountains of evidence. Sorry to hear your brother has fallen for it.

I suspect that even providing evidence will not be sufficient to dissuade him, based on my own experience of flat-earthers.

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    $\begingroup$ Why does air compression cause heat? $\endgroup$
    – Krupip
    Commented Aug 17, 2018 at 20:05
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    $\begingroup$ @opa - not specifically "air", but compression of any gas. Compressing the gas makes the molecules come closer together and bump into each other more frequently. Like an air conditioner, compress the gas (Freon) to basically a liquid and it heats up. Remove the heat with a coil and a fan (outdoors). Then send the now cooled/warm liquid back (indoors) to another coil/fan where the Freon is now expanded, which makes everything very cold. ---> $\endgroup$
    – Kevin Fegan
    Commented Aug 17, 2018 at 20:18
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    $\begingroup$ @opa - (continued) - Gay-Lussac's Law: The Pressure Temperature Law. This law states that the pressure of a given amount of gas held at constant volume is directly proportional to the Kelvin temperature. As the pressure goes up, the temperature also goes up, and vice-versa. $\endgroup$
    – Kevin Fegan
    Commented Aug 17, 2018 at 20:21
  • $\begingroup$ @opa You compress the gas by moving a piston under force (and the force is way larger than just to overcome friction of the piston), hence you perform work on the gas, which means you add energy to it. Heat is essentially the only way a gas has to store internal energy (there is of course also pressure, which according to its units is literally energy density) $\endgroup$
    – Hagen von Eitzen
    Commented Aug 18, 2018 at 15:01
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    $\begingroup$ Perhaps an analogy is helpful to "proof" intuitively that the near-vacuum of the thermosphere means the heat isn't that relevant: Consider a bath of water at room temperature vs the air at room temperature. The bath feels quite a lot colder because it is much better at conducting heat then the air. Likewise, 2500C normal air is uhm, bad for you because it transfers a lot of heat to you. But if there's barely any air like there is in the thermosphere nothing much happens because there's so little heat transfer. $\endgroup$
    – Elva
    Commented Aug 20, 2018 at 9:36
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It's not the temperature that matters, it's the heat transfer.

The density of the atmosphere up in the thermosphere is very very thin. There simply isn't nearly enough mass to transfer any significant amount of heat from the thermosphere to a spacecraft travelling through it.

Spacecraft do need heat protection to survive re-entry, but that is because they're travelling so fast relative to the surrounding medium, not because of the temperature of the tenuous atmosphere that the medium consists of.

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    $\begingroup$ A somewhat related recent question $\endgroup$
    – Jack
    Commented Aug 17, 2018 at 9:13
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    $\begingroup$ To illustrate the importance of material density in transferring heat, touching water at 70C will produce third-degree burns almost immediately. But you can heat your oven to 250C and stick your hand in for a remarkably long time without injury. $\endgroup$
    – Mark
    Commented Aug 17, 2018 at 20:11
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    $\begingroup$ You probably meant to say, don't try this at home! If you touch any part of the metal frame of the oven with your hand, you'll get burned instantly. It's only the air in a heated oven that is not immediately dangerous: the metal parts are EXTREMELY dangerous at that temperature. $\endgroup$
    – Ed999
    Commented Aug 17, 2018 at 22:20
  • $\begingroup$ @Ed999 That's why oven handles are usually insulated, so you can open them without burning your hands. $\endgroup$
    – Mast
    Commented Aug 19, 2018 at 18:31

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