• Question: How much does the sky weigh?

    Asked by anon-267532 on 17 Nov 2020.
    • Photo: Sam Geen

      Sam Geen answered on 17 Nov 2020:

      The mass of the atmosphere is 5 million trillion kg (5 followed by 18 zeros). The “weight” (how much gravity it feels) is maybe a bit less because some of it is a bit further away from Earth, which is why we use “mass” instead.

      For reference, the Earth’s mass is a million times bigger than that.

    • Photo: Jesse Dykes

      Jesse Dykes answered on 17 Nov 2020: last edited 17 Nov 2020 1:28 pm

      This is a tricky question. Taking the composition of the air (mostly nitrogen, with some oxygen, carbon dioxide, and other elements, which all have different weights) you would have to calculate how much air there is at each altitude across the earth, and then measure the gravitational field strength across the earth (gravity is different in different places depending on how much matter is beneath you) and then calculate how that field strength changes with altitude as well. It’s a big question! I’ll leave you to work it out yourself.

    • Photo: Katherine Manfred

      Katherine Manfred answered on 17 Nov 2020:

      When we talk about air pressure – like in weather forecasts or on airplane maps – that number basically describes the weight of the air on top of you!

      Today, the weather where I am (York) is about 1029 mbar, which is 102900 Pa in SI units. This is a force per area. If we take an example of, say, someone’s head, that’s around 200 cm^2 in area if you’re looking down on them from above. That means the pressure of air pushing down on your head is the same as wearing a 235 kg hat!

      Luckily, we don’t usually feel this because our bodies have their own internal pressure pushing outwards. But one of the ways you might notice the huge air pressure is if you put your hand close enough to feel the pull of a household vacuum cleaner (but please don’t get your hand stuck!). Now, your hand has high pressure (air pressure) on one side and low pressure (vacuum) on the other side, so your hand is going to feel pushed by the air towards the vacuum.

    • Photo: Roan Haggar

      Roan Haggar answered on 17 Nov 2020:

      Hi Ayisha, this is quite a deep question, I like it! There’s some nice answers above, but it’s important to also remember that the sky isn’t really an object that hovers above us, like your bedroom ceiling or an umbrella.
      —
      The sky is just what we see when we look upwards, away from the Earth, towards the rest of the Universe. In the day it looks blue because of sunlight reflecting off of the atmosphere, it’s not a solid object that you could go up and touch. Many of the things we can see in the sky (such as the Sun, stars and galaxies) are also much larger than Earth, and so weigh a lot more than Earth does.
      —
      The sky is more like an open window that we can look through, to try to see all of the interesting things in our Universe. Hope this helps!

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