Stargazing: a beginner's guide

Can you separate your stars from your planets and satellites? Robert Massey teaches the basics...
21 April 2020

Interview with 

Robert Massey, Royal Astronomical Society


Someone shining a light up from a mountain at the stars and Milky Way.


This week we’re gazing up at vault of the heavens and revealing its mysteries. We’ve gone through the sky during the day, and now it’s time for the sky at night. Robert Massey from the Royal Astronomical Society taught Chris Smith the basics of stargazing...

Robert - Actually going to the Australian outback and looking up at the stars is the stuff of dreams in many, many ways for many people looking at it. But I think the best thing to do is to start to learn the constellations, the names of some of the stars above our head, and be able to spot the brightest planets in the sky. And also if you have access to something like a small pair of binoculars, that's a really nice addition too. It's important to realise you don't need to spend a great deal of money on expensive kit. I mean obviously that's very, very easy to do, but I think there's simply no point in doing that. The best thing to do is actually get a feel for the sky to begin with.

Chris - I'm glad you brought that up because that was sort of foremost in my mind. How do I know what I'm actually looking at? Because when I look at maps of the sky, and then I look up at the sky, it's quite hard to make that mental translation between what I see in a book and then what these bright pinpoints of light are. How do you do that?

Robert - You're quite right because you look at a map in a book, and it may be that that's a map showing you many more stars than you can see. If you're exceptionally lucky, you might be in a place where you see more stars than the book shows and that could confuse the shapes as well, but the best thing to do is to start to recognise the patterns and now there are some really nice signposts. For example, in the spring sky as we are now, pretty much after sunset you see the Plough, or the Big Dipper in North America, swinging overhead: those seven stars with that kind of saucepan shape. You can use the curve of the handle of the saucepan, track it down, and you come to a really bright star called Arcturus. And these kind of things are the way that you find your way around the sky.

Chris - It's interesting that you mentioned a star there, because of course when we look heavenward, we're going to see stars, we're going to see planets, and then we might even see small satellites that we've made and put up in space. So how do we tell them all apart?

Robert - That's a really, really good question. Something like Arcturus is a bright star and sometimes people think, “oh, maybe that's a plane or something.” And the answer is generally that stars tend to twinkle. And the reason they do that is that they're very far away, so they're effectively point sources of light; the light gets to us, it travels pretty much unfettered all the way through the cosmos, arrives at the Earth's atmosphere, and then the shifting air currents move that light around and we see a twinkling effect. Now with a planet, although planets are generally much smaller than stars, they're much, much closer. The ones we can see, they tend to look quite bright as well, which is another giveaway, but they have a steady light too. If you see something like Venus in the evening sky, as you can right now actually, you'll see it's not only bright but it's steady too. That's a great big giveaway. And something like a satellite, which kind of varies in brightness and so on... but actually again, they don't tend to twinkle or they move very, very obviously as well. It only takes a couple of minutes typically for a satellite to go from one side of the sky to the other.

Chris - Venus is incredibly bright, isn't it? Even I know where Venus is, and it stands out for being so bright. Mars: very, very red. Is that some other reason, that they look bright because they’re close to the Sun and red because they're made of red stuff, or is that a myth?

Robert - No, I mean the colour of Mars for example... if you want to see Mars actually, it's visible in the dawn sky just before the sunrise at the moment. And in the case of Mars, it is genuinely red; as if you ever look at the pictures from the rovers that have driven around its surface, that's really, really obvious. It's covered with this rusty stuff. Something like Venus generally has a whitish colour, because it's a thick carbon dioxide atmosphere and it reflects a lot of light, so it's genuinely bright. But planets, unlike stars, are shining due to reflected sunlight; and something like Venus is close to the Earth, it's closer to the Earth than the Sun is at the moment, and because it's close and it's about the size of the Earth, then we're seeing it well because it reflects a lot of light. And that light doesn't have that far to travel compared with a star, so it appears really, really bright in the sky. In fact, it's actually so bright that if you're in the right set of circumstances - and you can try this, but I would only suggest that you make sure the sun is hidden behind a building - you can actually see Venus during the day. I've done that quite a few times if the sky's very, very clear.

Chris - And just to finish, Robert, can we just bring up one thing which really does deserve recognition; because this week, a very important birthday is going to be celebrated: 30 years since the Hubble Space Telescope was launched. And it's really been something that's been present throughout my growing up and has revolutionised arguably our understanding of the heavens and our view of the skies. I just wondered if you had any thoughts on that too.

Robert - Absolutely extraordinary success. The remarkable thing is when it was launched back in 1990, it didn't work that well because the mirror was slightly the wrong shape, so they had to fly a correction mission up a couple of years later; and then all of that was forgotten because ever since that time, it's been a phenomenal success. It's sent back images of planets in our own solar system, of distant galaxies. Actually, it's helped find planets around other stars and forming solar systems around other stars, and it also helped us understand the age of the universe. So it's been an extraordinary success.


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