What's in the night sky of the week of 5 to 11 December 2022 in our weekly stargazing guide.

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Chris Bramley Hello and welcome to Star Diary, the podcast from the makers of BBC Sky at Night Magazine. You can subscribe to the print edition of the magazine by visiting www.skyatnightmagazine.com. Or digital edition by visiting on iTunes or Google Play.

Ezzy Pearson Greetings, listeners, and welcome to Star Diary, a weekly guide to the best things to see in the Northern Hemisphere as night sky. As we're based here in the UK, all times are in GMT. In This episode we'll be covering the coming week from 5 to 11 December. I'm Ezzy Pearson, the magazine's features editor. And I'm joined on the podcast today by reviews editor Paul Money. Now, Paul, last week you did tease that this week might be quite a good week for stargazing. So what have we got coming up?

Paul Money Well, I mean, you know what they say? They usually say these things come in threes. Well, this time it's twos. The Moon occults two planets this week. All in one week!

Ezzy Hmm, yes.

Paul So but it will get even more amazing as we get towards the end of the week. But we start off with an interesting one, which I'm determined to see. I mean, you know, we'll battle the clouds, won't we. That's the enemy of an astronomer. The clouds. It's the planet Uranus. Now, on December 5th. So we start off the kicking off the week on December 5th, we have an occultation of Uranus by the Moon and you get to see the whole thing. Now it does occur in evening twilight. But Uranus is a bright planet. We're not worried about the moons in this particular case because they are quite faint. But Uranus is bright enough to be seen in binoculars, but I would recommend using a telescope. And because it's a disc, it does take quite a few seconds to actually disappear. So it's not like a star. A star will vanish instantly, whereas something like Uranus or any other planet will always take... it'll be a gradual change, usually a few seconds.

Ezzy We should we should first say an occultation is when a planet or a star appears to disappear behind another celestial object. So in this case, it's going to be the planet Uranus is going to be passing behind the bright Moon, which is always an exciting thing to see.

Paul And especially as the actual disappearance is on the dark limb. So you have to really pay attention because what will happen is you can't see the actual limb on that side because it's dark isn't it? It's experiencing night-time. So you need to keep your eye... If you got a telescope, the tracks, you need to keep your eye on Uranus and suddenly you'll start to see there's a bit taken out and then a little bit more, and it will literally disappear behind this dark limb. So we're looking at about, I would suggest from 4:30 p.m. onwards. Occultation is about 4:49, 4:50 in the evening and it will disappear inside the dark limb. The reappearance on the bright limb is around 5:17 onwards. Now you've got to bear in mind times will vary depending on where you are in the UK. So that does change the timings. We always say start at least 10 to 15 minutes before and keep an eye on the area where you expect the disappearance to take place and the reappearance as well. Because, you know, this is... These... You don't want to miss the reappearance. although I say it'll be gradual, but I always like to try to get the very beginning of it when it's a planet, because I say several seconds. So you, you know, you just... But it's very difficult on the bright limb because the bright limb will be matching and brighter than the actual planet itself. So you'll only suddenly notice it, I think, when it's about halfway out.

Ezzy Hmm. One of the things I've never been sure of is if it's something like this, where there's an occultation. Is it better to sort of pre-look at the place on the Moon where you think it's going to disappear or is it better to to try and follow the planet or just get into the general area?

Paul Well, it depends on whether you've got go to if you've got go to lock it on the planet and then just allow the Moon to pass over the view. And so you know hopefully the centre of the view will be where Uranus is. So it will give you an idea and it'll add to the anticipation and the excitement, hoping that the actual telescope is tracking properly. And in theory, if you're homed in on Uranus, then as the moon glides by Uranus should reappear. You know exactly where Uranus is. But you're right. If you're using a manual system, I always think it's better. And I think it should make good practise to observe the name of the Moon, say, around about half an hour before all these events take place. Both limbs, the dark limb and the bright limb. And get familiar with where they expect to come out and identify the craters so you have a good idea of where on the limb it will actually reappear and where on the dark limb it should actually disappear. So I think that makes good practise myself. But I say if you've got a go to system, so you're almost the lazy astronomer. I remember when Go-Tos came out and it was like, "Oh, that's lazy astronomy, you should do it properly and find the stars yourself." But you know, I'm a complete convert now to Go-To Mounts, so I have to say I'll probably be cheating and putting on Go-To and just watching the centre of the View.

Ezzy Yeah, there's definitely some times when it's the kind of tracking it down and trying to find it yourself, that's half the fun. And there's definitely times when having a system that does everything for you is much better.

Paul And you can do a lot more with one of those systems sort of thing. You know, you can get through a lot more objects, but I agree, I do like trying to find these objects myself sometimes just for the sheer fun of it and to remind me of the good old days. I'll gosh begin. And how old now? Now the thing about the occultation of Uranus is that it's really a practice run for the big event later in the week, but we'll come to that in a few moments. Now, December 6 and 7, we just take our eyes off these occultations for a moment because you can watch the Moon pass through the constellation of Taurus. It's heading towards full, which will occur on 8th, and we'll come to that in a moment. But on the six it lies below the Pleiades. Then on the 7th to the upper right of Mars. This is in the evening. So we're looking around about 7:00 in the actual evening itself. So it gives you a guide sort of thing. But the only problem is with as you got to such a full bright Moon, it will drown out the vast majority of the Pleiades. Now, the Pleiades is one of those things that I always say to people, see how many you can count, don't do it full Moon. You really want a dark sky to see the individual faint stars of the Pleiades.

Ezzy I suppose that could actually be quite an interesting exercise, you know, to just see what effect the full Moon has, you know, try and count it when there's no Moon next to it and then try and count on the full moon and see see the difference. And then you can really sort of learn to appreciate how much the full Moon does or doesn't affect what you're seeing.

Paul Which in a way sort of thing also illustrates the effect of light pollution because basically the full Moon, I mean, all of deep sky observers sort of thing, you know, we "oh no! The Moon's up, it's light pollution." but we can't do anything about that. But we can do something about all artificial light pollution. That's the key. But yeah, we can't do anything about the Moon. I mean, you know, we're not... oh gosh, what was that film sort of thing then? The one before the Minions and all that.

Ezzy Oh, Despicable Me.

Paul Despicable Me! When he stole the Moon.

Ezzy He steals the Moon.

Paul You know, I mean, it was a good... I love the film sort of thing. But the science, you know, if we got rid of the Moon like that, oh it would be terrible sort of thing. The tides will all be changed and oh gosh all sorts of disasters that happen on the Earth.

Ezzy I know, I know. You deep-sky astronomers might not particularly like the Moon, but it does a lot for us. So can we keep it around, please? Thank you.

Paul But that is a good idea for a project. Compare the two. Deep Sky and especially if you've got a site without any light pollution. Count the Pleiades and then count how many when the Moon's nearby, especially if it's close to full, and just see how much it diminishes and you lose the fainter stars. So there we are.

Ezzy If anybody does do that, please do let us know. You can find our details over on www.skyatnightmagazine.com. So let us know what the difference is if you do manage to see that.

Paul Now the excitement. Wow. I mentioned the Moon is to the right of Mars on the evening of 7th but this is where it gets exciting because full moon occurs on the 8th, in the early hours, in actual fact. The key is, though Mars reaches opposition, it is opposite the Sun in the sky. That's actually the same definition really as the Moon at Full. The full Moon is opposite the Sun in the sky. It's just that we have a different term for it. We call it full Moon. But technically the Moon is our opposition so every month. The Moon has got to have at least one opposition as such, so its opposite the Sun in the sky. So that's when it's full and the fact that Mars is at opposition, you know, within an hour of the Moon being opposition, that leads to one really important effect. The fact is, Mars gets occulted by the Moon. I mean, this is so rare, I can't even think of the time that it might happen in the future. We may be looking at hundreds, we may even be looking at thousands of years in the future before something like this happens at the point of opposition for both the Moon and Mars. That's why I think this one is so exciting and that, you know, it's one of those that, you know, you have we have a lot of landmark events to look forward to. And betraying my age, I can always remember looking forward to the 1999 solar eclipse. Oh, my gosh. It's 22 years ago. 23 in fact.

Ezzy Oh, my goodness. It is.

Paul 23 years! You know. But yeah, I can remember as a boy looking forward to that and wondering where I'll be. Ended up in Devon and it was cloudy. Classic isn't it? So, you know, but this is one of those other events. We have various events and we look forward to a Mars opposition on December 8th 2022. At the same time as it gets occulted by the Moon is one of those rare events you you've got to try and see it. You know. There's no excuses, right as we tell everybody no excuse. Every single listener you are ordered to listen... To watch this event. Not that we can order you to do these things, but you know, this is one of those that you... It really is an unmissable event. You know, it's so rare that it's worth having to go at. So as the moon occults Mars, it takes about an hour. So it's nice and conv... I mean, how easy is this? Except one thing. It's in the morning sky. I know. Oh, come on. You've got to set an alarm, haven't you Ezzy. You've got to set an alarm.

Ezzy I think this is one where it is worth getting up at silly o'clock in the morning and and trying to observe this one.

Paul I'll definitely be up at around about 3:30 no later than 4:00. I mean the occultation is about 4:57. Remember, the timings do vary slightly and it takes around about 34, 35, 36 seconds depending on your location for Mars to disappear. So it gives you an idea of how big Mars is. I mean, with Uranus it's just a few seconds, but Mars, we're talking about, you know, half a minute effectively. Really. Aren't we so, you know, it will take a while. Now, it'll be fascinating if you can see any albedo features at the time to watch them being occulted as well. I've never seen this. I've seen Occultations with Saturn and Jupiter, but I've not seen an occultation of Mars. So I'm fascinated by this. I can't wait for it. So you do need to have an early night, get plenty of time to get ready. So, you know, don't leave it until of like 10 minutes before and then think, oh, look, the sky is clear. I'll go out, get out, get ready. Whether you're visually observing it or whether you're photographing it sort of thing. And as you know, Ezzy, we always encourage people to to write in if you see this, because this is such an unusual event.

Ezzy Absolutely.

Paul So this appearance occurs or that begins around 4:57 a.m. and Mars is now 17.2 arcseconds across. So it takes about 34 to 35 seconds to disappear. Reappearance is about an hour later. I mean, that's pretty convenient, I have to say. I mean, that makes the timing a lot easier. And again, much like we said for Uranus, if you using a Go-To telescope, so get it locked on Mars and then just allow the Moon to drift through the view. I mean, that's fascinating enough of knowing that in theory, you're looking at position for Mars and you can see then the real motion of the Moon as the Moon drifts through your field of view and then Mars will start to become uncovered. So about an hour after the occultation takes place. Now the reappearance is actually at the bright limb. But because we're full Moon, both events take place at the bright limb. There is no dark limb with it being a full Moon. So that'll be an interesting contrast. But Mars is a bright planet. We're not talking about a star that can be overwhelmed by the actual light of the moon. Normally we wouldn't recommend occultations when it's full Moon in actual fact. Because it makes it harder to see that disappearance. But we're dealing with a planet, aren't we? So there we are, sort of thing. Keep an eye out of these. It shows you the regularity, the clockwork of the Solar System, doesn't it?

Ezzy Absolutely. And you did mention there that Mars is quite a bright planet, is in fact, a naked eye planet. Is this something that you would be able to to see with the naked eye as well, though obviously not in as much detail.

Paul You appeared to notice the Moon getting closer and closer. And the question will be if you watch it with the naked eye, if you've got nothing else and fair enough, watch it with the naked eye and you'll see the Moon creeping closer and closer to Mars and then judging the point when it disappears. It will be interesting because Mars should fade sort of thing rather than disappear as a star would do. So that will be the interesting thing. And then if you keep an eye on around about the right time, just wait for the star to emerge from the other side. So you should be able to see something. Obviously, we'd always recommend binoculars or a telescope for an event like this, but if you've got nothing like that, still look. Have a look. It'll be amazing to watch. This star, this red star, which we know is a planet, actually disappear behind the moon and reappear.

Ezzy Yeah, but that is always the possibility. You can you can always watch it with with your eyes. We also have live... I'm sure we'll have a live stream that will be having a nice detailed view as well. They'll be on a website www.skyatnightmagazine.com, so do be sure to check there. We also have a lot of guides in the December issue because funnily enough, this kind of once in a lifetime event was something that we thought you guys might like to know about. So we have lots of detailed guides about, you know, capturing it on camera, where to look and how to to make sure that you make the most out of this event and don't miss a thing.

Paul And finally. Let's get back to something boring. Oh, they're back to normal now. Finally, for the week, the ends with the waning gibbous moon forming a triangle, Castor and Pollux in Gemini on the late evening of 10th. So we're back to normal after this. This is the week for really observing. But, you know, we're back to normal now and it's back to normal events with the Moon and the stars themselves. But I still find them fascinating and hopefully if it's clear, you'll be able to see them as well.

Ezzy Thank you very much, Paul. That sounds like it's going to be an absolutely incredible week in terms of stargazing. On 5 December, you've got the occultation of Uranus as the planet appears to disappear behind the Moon. Then we have two days where the Pleiades will have the Moon coming by on 6th and Mars on 7th. And then, of course, the show stopping event on the 8 December is the Mars Occultation. That's the one that you really want to set in your diaries and get up in time for to go and see. Then finally on 10th, we have Castor and Pollux forming a triangle with the Moon. If you do manage to capture any of those incredible events that we talked about, please do let us know. You can always reach us at contactus@skyatnightmagazine.com. We always like to hear from our listeners.

If you want to find out even more spectacular sites that will be gracing the night sky throughout the month, be sure to pick up a copy of BBC Sky at Night Magazine. Well, we have a 16 page Pull out Sky guide with a full overview of everything worth looking up for. Whether you like to look at the moon, the planets, or the deep sky, whether you use binoculars, telescopes or neither. Our sky guide has got you covered with the detailed star charts to help you track your way across the night sky. From all of us here at BBC Sky at Night Magazine. Goodbye.

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Chris Bramley Thank you for listening to this episode of the Star Diary podcast from the makers of BBC Sky at Night Magazine. For more of our podcasts, visit our website at www.skyatnightmagazine.com or head to ACast, iTunes or Spotify.

Authors

Elizabeth Pearson
Ezzy PearsonScience journalist

Ezzy Pearson is the Features Editor of BBC Sky at Night Magazine. Her first book about the history of robotic planetary landers is out now from The History Press.