# What was the temperature of the Apollo 11 moon landing zone?

It's soon 50 years from the Apollo 11 moon landing, so in honor of that event, I decided to post a question here.

I understand that moon has due to its long day and long night and also due to the lack of water very large temperature variations. For example, googling for "moon temperature" finds:

Daytime on one side of the moon lasts about 13 and a half days, followed by 13 and a half nights of darkness. When sunlight hits the moon's surface, the temperature can reach 260 degrees Fahrenheit (127 degrees Celsius). When the sun goes down, temperatures can dip to minus 280 F (minus 173 C)

What was the temperature of the moon landing zone in Apollo 11?

If the temperature differed from what we consider normal, how did the astronauts manage to survive in the prevailing temperature during walking on the moon surface?

• We consider it normal to have ambient air and a comfortable air temperature. But there is no air on the moon, only vaccuum without a temperature. So the moon boots should have a heat and cold resistant sole with good temperature isolation properties.
– Uwe
Jul 16 '19 at 21:56
• @Uwe Right, but there is also thermal radiation. If you're walking on 127°C hot surface, it might feel as if there was a hot atmosphere surrounding you. Jul 17 '19 at 6:34
• @EverydayAstronaut But the thermal radiation of the hot surface was blocked by the many layers of the EVA space suit worn. The astronauts did feel only the temperature of the liquid cooling undergarment worn under the suit.
– Uwe
Jul 17 '19 at 8:32

Apollo 11 deployed the Early Apollo Lunar Surface Experiments Package (EASEP), a set of scientific instruments that measured various parameters on the moon and transmitted them back to the earth, this included temperature.

Here is a picture of Edwin Aldrin deploying the EASEP:

There is a Technical Memorandum from Bellcomm Titled: Lunar Surface Temperatures From Apollo 11 Data, that has this great chart detailing the temperature data from the instrument (as well as all the information you could ever want about the temperature instruments):

you can see that the temperature when they were landed (July 20-21st 1969, or 201-202 GMT) was between $$250 K$$ and $$280 K$$ or $$-23^\circ C$$ to $$7^\circ C$$.

The astronauts survived because of their Space Suits, which had environmental control equipment, as well as the Apollo Lunar Module (LM) which also had environmental control equipment as part of the life support system.

• That's a pretty tolerable temperature range to me, from a country where -23 degrees C is common... Jul 16 '19 at 20:45
• @juhist I'm also surprised by the comfortable range. Moreover, keep in mind the matchless intensity of solar radiation on the Moon, as there is no atmosphere. I guess it heats up the spacesuits quite a bit. Jul 17 '19 at 6:30
• Note that the lunar day (and temp cycle) is 28 Earth days. You can see the min and max over the entire cycle is -53 to +67C. The fact that the astronauts spent ~2/28th of a lunar day on the surface is like flying to Florida in July but only staying for two hours in the morning when it’s 74F out and claiming “oh that wasn’t so bad”. :-)
– cms
Jul 17 '19 at 19:44

The landing time was selected to avoid the extreme temperatures. That's why there are huge shadows, the Sun's declination is low (I don't remember if it was early morning or late afternoon). During the 22 hours they were on the surface (Apollo 11, some others up to 4 Earth days IIRC) the lunar day didn't progress too much.

Any time there is a question about temperature in space I think it's worth saying a little about what that measurement even means. The temperature always has to be the temperature of something. Here on earth, when a weather report gives "the temperature", it's the temperature of the air. The temperature of the ground nearby can be higher or lower depending on how much light it absorbs and whether it is in the shade.

On the moon, there is no air, so in some sense there is no temperature above ground. The space suit loses heat via radiation to the dark sky, and gains it by radiation from the sun and the surface of the moon, depending how warm the rock is. But there is no dense mass of atoms bouncing around outside most of the suit that you could take the temperature of.

So instead they measure the temperature of the surface. This matters because it's good scientific information, and it also matters to the astronauts because their boots do touch the surface (I left that out above), but also because the heat radiating off the surface (properly, infrared light) does affect the heating/cooling balance of the suits.

The surface temperature can vary a lot based on being in the light or shade, so it will be an average, but the landing site was pretty uniformly illuminated. If you look at the document referenced in Mark Omo's answer, you will see that the thermometer was above ground and gave the "brightness temperature". I think that is the temperature that you would calculate for an object to produce the amount of heating detected in the thermometer by radiant heating, and I imagine it is similar to what you would get if you stuck a thermometer shallowly into the ground.

• Space suits used on the Moon were cooled by evaporation of water, cooling by radiation only did not suffice.
– Uwe
Sep 6 '21 at 17:10
• Good point, Uwe. I meant to be talking about the "natural" heat balance that any active cooling or heating would have to correct for. Sep 7 '21 at 14:44