Measuring the temperature at home

We’ve done it. You’ve had a chance to have a look at how wind speed and wind direction vary with place and how you can measure that very simply using bubbles. But there are lots of other aspects of the weather that you might like to have a go at measuring. And one of the simpler ones of those is temperature. It’s probably the element of the weather that affects us most directly. You can measure temperature with a whole range of different sorts of thermometers. I’ve got a very simple one here. It’s a digital thermometer, and it’s telling me that it’s measuring a temperature of about 12 degrees at the moment.

Another sort of thermometer which I really like using are these infrared thermometers which are very easy to get a hold of these days. They’re not speed guns, but if you hold them at a moving vehicle, I guarantee that it will slow down. But actually, how these work, is that they pick up the heat from any object and to convert that into a temperature. And the nice thing about that is that you don’t actually have to touch the thing that you’re trying to measure the temperature of. So, for example, I can measure the temperature of my hand. And it’s about 14 degrees, because it’s quite cold out here. Or I can measure the temperature of the grass.

And it’s giving me a temperature of about three degrees. If you want to measure the air temperature, obviously, that’s a little bit trickier to do with one of these thermometers. Because it’s going to pick up the heat that’s being emitted by the thing behind the air. So the thing to do is to take out a piece of white paper, leave it in the air long enough for it to adjust to the air temperature. And then you can just measure the temperature of the piece of paper. And basically, the further something is away from you, the bigger it has to be before this can measure its temperature. So if it’s 12 metres away, it has to be one metre big.

If it’s 12 kilometres away, it has to be one kilometre big. Which means that I can measure the temperature of the clouds. If I point it at that cloud there, I get a temperature of minus 16 degrees. And if we know that the temperature of the atmosphere falls by about six degrees per kilometre up that you go, so if my clouds are minus 16, and the ground is about six, so that’s a temperature difference of 22 degrees. So that’s roughly somewhere between a three- to four-kilometre height for those clouds that we’re seeing at the moment. Another great thing that you can do with these thermometers is if you’ve got some blue sky, you can point them at the blue sky.

And now I’m getting a reading of minus 42 degrees for that blue sky. Well, what is it in the blue sky that’s emitting heat. Well, it’s the greenhouse gas molecules. So if you’ve got greenhouse gas molecules in the atmosphere emitting heat, sending it back down to the Earth’s surface, that’s what these thermometers are picking up. So it’s a great demonstration of the greenhouse effect, particularly if you’ve got a day not like today. But if you’ve got a day when there’s blue sky everywhere, you can point this thermometer at different angles through the atmosphere.

And you should find that if you point it towards the horizon, that the temperature is much warmer than if you point it straight up through the atmosphere. And that’s because the atmosphere is fairly thin. So if you point the thermometer straight up through the atmosphere, there’s not very much– well, there’s only a certain amount of greenhouse gas in the way. So you’re picking up a certain amount of heat. If you point it at an angle, the thermometer is taking a much larger path through the atmosphere. So there’s much more greenhouse gas in the way, so it’s picking up much more heat. So it’s registering a much warmer temperature.

So these things are great fun, and there’s lots of things you can do with them. But whatever sort of thermometer you have access to, I’d really recommend that you go outside and have a go and see whether the temperature in different places is actually influencing the way you think of them. Whether your favourite places are actually warmer or colder than maybe some of the other places around. So get out, have a go, try doing some field work.