Claire Bretherton answers your questions about the Moon

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Claire Bretherton answers your questions about the Moon

Claire Bretherton answers questions you’ve left on our new Big questions answered phone line. This month, discover why we can see the Moon in the daytime, why Moon-landing conspiracy theories don’t convince astronomers, and what we can see further out into space.

Claire:
Hello, I’m Dr. Claire Bretherton, from the Royal Observatory, Greenwich, and welcome to our Big questions answered podcast. Thank you very much for all the fantastic questions you’ve rung in with this month. Let’s get started and answer some of our favourites.

Jason:
Hi, Dr. Claire. This is Jason. I’d like to know if man really did land on the Moon. Thanks a lot.

Claire:
Thank you Jason for that question. Yes, man really did land on the Moon. Neil Armstrong was the first man to walk on the Moon on 20 July 1969. And 12 people walked on the Moon in total, finishing with Eugene Cernan in 1972.
And there have been lots of claims that it all could have been a hoax, people suggesting that the flag couldn’t possibly be flying because there’s no air on the Moon, or asking why the scene was so carefully lit up. But I think we can fairly certain that it really did happen.

First of all, we can actually bounce signals off arrays that have been left on the Moon by the men who walked there. But, perhaps more importantly, when the Americans did touch down on the Moon, they were in a massive space race with what was then the Soviet Union. And the Soviets were, therefore, monitoring their programme very, very carefully. If even they believe that Americans walked on the Moon, then I don’t think we can really disagree.

But it has been 36 years since man last walked on the Moon, which is an awful long time. And many countries are thinking of trying to send people back there in the near future. It’s not actually that difficult, because the Moon really is relatively close. It’s just very, very expensive.

The Moon is so close that if you were driving at the national speed limit, it would actually only take you around 150 days to get there, whereas to get to the Sun, it would take around 150 years, and to get to the next nearest star would take around 10 million years.

Claudia:
Hello. My name is Claudia and I would like to know why you can sometimes see the Moon in the day.

Claire:
Thank you, Claudia. You’re right. We can sometimes see the Moon in the daytime. The Moon of course goes round the Earth, and to go from one full moon to the next full moon takes around 29.5 days.
Now, when we see a full moon, that’s because the Moon is on the opposite side of the earth to the Sun, so we see the whole of the lit-up half of the Moon. As we go through the month, the Moon moves around the Earth, so we see less and less of the lit-up side of the Moon. But, of course, the Moon then appears closer in the sky to the Sun, and because it’s daytime when the Sun in is the sky, then if the Moon is closer to the Sun in the sky, then we can sometimes see the Moon in the daytime too.

Derek:
Hello, Claire. My name’s Derek, and I’d like to know what’s the most distant object that we can see in the night sky. Thank you.

Claire:
Thank you, Derek. The most distant object you can easily see with the naked eye is the Andromeda Galaxy, M31. This is the nearest big spiral galaxy to our own, very much like your own Milky Way. It contains several hundred thousand million stars.
This galaxy is 2.5 million light years away, which means that the light that we see from it today left Andromeda 2.5 million years ago. You can actually see it in the sky this evening at this time of year. You’ll see it roughly towards the south east, fairly high in the sky towards the beginning of the night.

But, if you went somewhere really, really dark and you had particularly good eyesight, you may also be able to see the nearby Triangulum Galaxy, M33. This is around three million light years away. But you’d have to be in very, very good conditions.

There have also been a handful of observers who’ve claimed to have been able to see Bode’s Galaxy, M81, which is 12 million light years away from the Earth.

Graham:
If we could build a powerful enough telescope, could we look right back to the Big Bang? That’s a question from Graham.

Claire:
Thank you, Graham. Unfortunately, even if we could build a very, very powerful telescope, we can’t look all the way back to the Big Bang. But, we can get pretty close. We can see back to around 400,000 years after the Big Bang, to something called the Cosmic Microwave Background. So, that’s looking 13.3 billion years back in time.
The Cosmic Microwave Background is a faint glow left over from the Big Bang and the expansion of the universe. It’s at a temperature of 2.73 Kelvin, so that’s colder than -270 degrees Celsius.

We can detect the Cosmic Microwave Background from all directions in the sky, and we can find slight differences in temperature, which we think then led to all the structure we see in the universe today.

Well, that’s all of our questions for this episode, but if you do have your own big question about astronomy, then do ring our phone line at 0208 123 9911. Once again, we’ll pick a selection of our favourites to answer in the next edition. Thank you very much. Bye-Bye.

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