Claire Bretherton answers your questions about the stars, planets and the Moon

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Claire Bretherton answers your questions about the stars, planets and the Moon

Claire Bretherton answers a fresh batch of your astronomy questions, this time about the stars, planets and the Moon.

Claire:
Hello, I’m Dr Claire Bretherton, and welcome to Big questions answered. Once again we’ve had some fantastic questions this month, and today we’re going to cover a variety of subjects including stars, planets, and the Moon.
So let’s get started with our first question.

Pat:
Hello, I’m Pat. You’re talking to a complete ignoramus. I’m just wanting to ask, is it true that at different times of year certain stars or constellations are more visible? So is January associated with one constellation or star, and February another? Thank you very much. Bye.

Claire:
Thank you, Pat, that’s an excellent question. You’re absolutely right, different stars and constellations are visible at different times of the year. This is because our Earth goes around the Sun once every year. But because the Sun is so bright in the sky, we can’t see the stars which are in the same direction as the Sun, we can only see the stars in the opposite direction, which we see during our night time.
So as the Earth moves around the Sun as we go through the year the Sun appears in a different part of the sky, and so the stars we can see also change.

Now this is not going to change significantly on a month-by-month basis, but there are groups of stars that we associate with different times of the year. For example, at the moment, the constellation of Orion the Hunter dominates the winter skies. It can be easily spotted by three bright stars in a line across his belt.

Jonathan:
My name is Jonathan, and I’ve been doing my homework. I’ve had to look at some pictures but I’m still not sure what color Neptune is. So please can you tell us? Bye!

Claire:
Thank you, Jonathon. That’s another great question. Neptune is the eighth and the last planet from the Sun. It’s big enough to fit the Earth inside it 60 times over. It’s made mainly of gas like Jupiter, Saturn, and Uranus. Neptune was discovered in 1846, but it had already been predicted because astronomers had seen small changes in the orbit of Uranus, the seventh planet from the Sun. It takes 165 years to go around the Sun once. It also has the strongest winds in the solar system, reaching 2000 km an hour.
The name Neptune comes from the Roman god of the sea, because of the planet’s deep blue color. We think this color comes from methane in the outer atmosphere of Neptune, which absorbs a lot of the red light from the sun, but reflects a lot of the blue light.

Butt:
Good morning, Claire. My wife and I went to Jodrell Bank, and one of the things they were indicating was that the Moon is moving away in its path around the Earth at something like 3 cm a year. I asked them what they had looked at in terms of a) will it ever stabilize or will it escape completely from the Earth’s influence, and b) have they ever thought what the world would be like without the effect of the Moon on tides and seasons? That’s it, my duck. My name is Butt. B-U-T-T. Thank you, Claire. Bye now.

Claire:
Thank you, Butt. The Earth’s moon is the fifth largest in the solar system and it’s the largest relative to its planet’s size. It has a diameter of around a quarter of the Earth’s. We think the Moon was made when something the size of Mars crashed into the early Earth, throwing huge amounts of material up into the sky. Now most of this material fell back down onto the planet again, but some of it clumped together under gravity to form the Moon.
And the Moon has been gradually been moving further and further away from the Earth since it was first created. It continues to do so today. It’s moving away by around 3.8 cm each year. What this means is that the rotation of the Earth is also gradually slowing down.

This can’t go on forever, because eventually the Earth and Moon are moving toward what we call synchronisation, where the length of the Moon’s orbit is going to match the length of the Earth’s day, which of course will be much longer by then. When this happens, just like the Moon always shows the same face to the Earth now, the Earth will also show the same face to the Moon. So the Moon will always appear at the same part of the sky.

Now the time scales for this are very, very long. So it’s unlikely that this will ever actually happen before the Sun reaches the end of its life. So the Moon will never fully escape from the Earth. But if we had never had the Moon in the first place, then the Earth would be a very different place. The Moon is responsible for two-thirds of the Earth’s tides.

Many of the Earth’s creatures rely on the Moon cycles, including human beings, who use them for the basis for our calendars. But the Moon also acts to stabilise the Earth’s tilt at 23.5 degrees, and this gives us the seasons that we know, which are different, but not too severe. These differences are probably very important in the evolution of complicated life on Earth as they forced simple life to adapt, but were not so severe that life was killed off completely.

If we didn’t have such a large Moon, then Earth’s tilt could vary dramatically over the period of just a few tens of millions of years. This is probably not long enough for complicated life to have developed.

Well, that’s it for this month. Please do keep your big questions coming in on 020 8123 9911. Until next month, goodbye.

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