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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 digital edition of the magazine by visiting iTunes, Google Play, or Apple News, or to the print edition by visiting skyatnightmagazine.com.
Ezzy Pearson: Greetings listeners. And welcome to Star Diary, a weekly guide to the best things to see in the northern hemisphere's night sky. As we are based here in the UK, all times are in BST. In this episode we'll be covering the coming week from 2 to 8 September. I'm Ezzy Pearson, the magazine's Features Editor, and I'm joined today by astronomy writer Mary McIntyre.
Hello, Mary.
Mary McIntyre: Hi, Ezzy.
Ezzy: So what do we have to look forward to in this week's night sky?
Mary: Well, this week Mercury returns, which is great. It's going to be at its best morning show of the year. We've got some lunar pairings, a starry waterfall, and a moving star cluster. We'll get onto that later.
So I'll start off with the planets.
Venus is still very much lost in the evening twilight. It's setting about 40 minutes after the Sun, so it's kind of even closer to the Sun than it was last week. So you will need binoculars if you are going to see it, and as is so important, wait until after it is set before you try to look for it with binoculars.
It's going to set at around about 7:45PM, so then just wait probably until about 8:00PM and then try to find Venus, just to keep your eyes safe.
Saturn is a much easier target. That is mag +0.2. It actually reaches opposition on 8 September, so it's the end of this week.
So it's well placed all month, visible all night long. Lies in Aquarius is rising about 7:50PM in the twilight and then will remain visible all night long. So that's a great one to look for.
Neptune also reaches opposition later this month on 20 September, so that also is visible all night and is well placed all month, in fact.
So this is an important note with planets when they come to opposition, you can observe them usually all that month and the month before, usually. It's not just a kind of one night thing, so you've got great opportunities all month to see Neptune or Saturn.
Uranus is mag +5.7 and that lies in Taurus and is rising about 9:50PM, so obviously Neptune and Uranus at those magnitudes you will need optical aids to see them.
Mars this week is mag +0.6 and that is also in Taurus and is rising about 11:45. We've got a couple of conjunctions with Mars as well this week. On 5 September, Mars is going to be just 8 arc minutes away from NGC 2129. And then the night after that, on 6 September, Mars is going to be 10 arc minutes from 1 Gemini. So a couple of close conjunctions there.
Mercury is back. It reaches great to western elongation on 5 September. It's going to be mag -0.2, so it's pretty bright. Obviously, Mercury never gets particularly high, but it can be very bright. So if you have got a clear horizon, it's always worth having a look.
This is going to be its best morning show of the year. It's located in Leo and is rising about 4:45AM in the morning, which is nearly two hours before sunrise. So there's plenty of opportunity to see it before the Sun actually rises.
And on 8 September, it's going to be just 1.6º northeast of Regulus. So it'd be good to see Mercury near the bright star Regulus. So yeah, it's great to have Mercury back. I've not seen it for a while, so that's awesome.
Ezzy: It completes the set.
Mary: Yes.
Ezzy: That's all. Well, I was about to say eight planets, and then I realised there's only seven that we can see unless you count Earth, which I suppose you can see if you're not on Earth, then you've got some problems.
At least unless you're an astronaut on the ISS, I suppose. But great opportunity to see all of them in one night.
Mary: Yeah, there are lots of opportunities for some more Jupiter fun and games with the moon shadows. On 2 September, Io is in transit as Jupiter rises, and that will leave the disk again at 12:20AM.
On 3rd, the Great Red Spot is really well placed as Jupiter rises, so if you've never seen the Great Red Spot, that's a great time to have a look for that. Even just with a good pair of binoculars, you should be able to see that.
6 September, 12:05AM. Again, the Great Red Spot is well placed.
And then on 7 September, from 1:20AM till 3:10AM, we've got a Ganymede transit.
8 September, we've got Io shadow transit followed by Io itself transiting again.
So there's just so many of these things that happen every week. Not always necessarily visible from your location, but it's always worth just having a look online and seeing what other shadow transits are taking place from your location.
There are also some moon transits on Saturn this week as well. On 2 of September at 2:50AM, Titan, which is Saturn's largest Moon, that is actually going to be located immediately south of Saturn's south pole, so that'll be really good fun.
And then 2:25AM on 3 September, Tethys and the shadow of Tethys will begin to transit on Saturn.
And then 3:15AM in the morning, the Dione moon and shadow will also join them. So, if you look at 4:22AM, all of these are going to be central to the disk of Saturn, so they'll be really easy to see. You'll see the shadows of both of them kind of central on the disk of the planet. So, really good fun to look for shadow transits on Saturn as well as Jupiter.
More of a challenge is Pluto, which still lies between Capricornus and Ophiuchus. It reaches its highest point at 14º above the southern horizon at about 10:20PM in the evening, and it sets at about 2:15AM. So, it's mag +14.0, so it is a challenging object. You will need a telescope to see that.
Ezzy: Yeah, probably want to be photographing it to really make sure you get it.
Mary: Yeah, photography technology means that it's easier to capture these things than it is to see them. Especially if your eyesight's like mine, as I get older it gets worse, so I kind of rely on my camera more and more as I get older.
Ezzy: You can't change the exposure time on your eyes, unfortunately. At least not yet.
Mary: Not yet.
Moving on to the Moon, this week the Moon is moving from new Moon up to first quarter, so it's a great opportunity to look at all of those southern hemisphere craters that you can see so beautifully on a crescent Moon and first quarter Moon.
On 5 September, the 6.4% waxing Moon is left of Venus in the evening twilight. That's going to be a challenge as we already discussed, Venus is a challenging object at the moment, but that will be a really good pairing through binoculars if you can seek those out. And on 6 September at 8:00PM in the evening after sunset, the 11% Moon is going to be just 29 arc minutes below Spica and 15º left of Venus.
So Venus will be nearby again that night, but we've got Spica in with the mix as well. So definitely good for looking for those, but yeah, definitely just point your binoculars at the Moon this week, any night, and you'll be treated to a great display of southern hemisphere craters.
Ezzy: I do have to say I have a soft spot for anytime you can see a crescent Moon with a bright planet next to it.
There's just something about that sight that just looks very beautiful to me.
Mary: Comet 13P Olbers is still very slowly moving through Comet Berenices and this week slowly moves into Böotes. At 21:15 it's going to be 15º above the western horizon but it is only mag +9.6 so again probably more of a photographic object really. You'll definitely need optical aids to be able to see that.
There's a couple of deep sky things to talk about. The first one, I know I mentioned this probably a couple of months or so ago, but it's Kemble's Cascade. And it's worth mentioning again because this month it's orientated so it's vertical, so the whole chain of stars is actually vertical.
And it's called the cascade because it looks like a waterfall and the star cluster at the bottom of it actually look like a splash pool. So it's the perfect time to actually see it looking like the cascading waterfall that it was named after.
It's actually located in Camelopardarlis which is a very faint constellation between Polaris and Capella. It's actually a triangle shape.
So once you've found, found the shape of Camelopardalis, which is a giraffe, by the way, if you didn't know. It was one of the more modern named constellations, so there's no mythology about the giraffe, which is very disappointing. I feel like I should make some up, because that'd be a fun time.
Ezzy: I just love the fact that the Latin name for a giraffe literally means camel leopard, because ... How do you describe it? It looks like a camel but it's got spots like a leopard. It's just a very 'say what you see' way of calling things.
Mary: Yeah, I love the name Camelopardalis anyway, it's fun to say.
But if you look at the bottom of that triangle, about two thirds along the bottom edge there is a fainter star and that star is like really in the middle of that entire chain of stars. So with binoculars, even with like small 8x42s you can easily see this cascade. It is absolutely gorgeous. One of my favourite binocular objects and it's just a really good time to look at that.
I also wanted to talk about the Alpha Persei moving cluster. So it is literally called the moving cluster. So this is a pretty extensive cluster. It covers four degrees of sky and it's within Perseus and it extends out from Merphak, which is Alpha Persei, the brightest star within Perseus. And this cluster contains lots of very young stars, so they're very blue and white, so they really just look so beautiful against the background sky.
And when we say young stars, we mean they're about 50 million years old rather than several billion, so they're still old by human standards, but they're still relatively new. The reason that it's called called the moving cluster is that these stars actually demonstrate proper motion.
For the most part, when we look at stars, they do not change at all within our lifetime. They feel very fixed, and that's usually just because they're so far away. But the stars themselves are moving relative to each other a tiny amount within a human lifetime.
And this cluster does display proper motion, but it is a minuscule amount of movement. And I'm impressed that people were able to even spot this movement, and they've linked that all the stars within this cluster are moving the same amount. They're obviously gravitationally linked, but they're moving such a tiny amount that I'm just like, mind blown that they were even able to discover this movement in any way.
So, they move about 0.035 arcseconds per year. That is a tiny amount. So, within a human lifetime, that is only 2.45 arcseconds, which is a really, really small amount of movement.
But because they are moving, it's got the name The Moving Cluster. Just for comparison with the proper motion, Barnard's star is one of the more well known stars for displaying proper motion. And within a human lifetime, that basically moves about a quarter of a degree, which is half the diameter of a full Moon.
So compared to how minuscule the amount of movement is in the Alpha Perci cluster... again, I'm just always really impressed that people were able to plot that and realise that they're all moving the same amount relative to each other. But if you study over a really long period of time with a big telescope, you will see that the stars have moved their positions.
So, it's a beautiful cluster to observe. You are never going to see that kind of movement yourself with binoculars. You would need a big telescope and a very full lifetime of taking pictures to plot it. But I just love the fact that it's named the Moving Cluster, even though it kinda isn't really.
Ezzy: It's one of those things that when you start looking at how precise these measurements are, because I remember back when I was doing my degree, there was a joke about when you're measuring the distance to a star, the error bars were so big, it could be half a light year on the other side of Earth, and that would still be an accurate measurement.
Now, there's these incredibly precise measurements that they can take of these things. And that's the other thing, because we're now getting to the stage of not only do we have the technology that can make these measurements, we've had it for long enough that we can have been making these measurements for 20 years.
And that's what you need. As time goes on and more of these like huge surveys start happening, we're going to start finding even more of these sorts of amazing measurements and finding out all kinds of weird things that we wouldn't be able to without lots of people working together over a long period of time.
Mary: Very exciting time, isn't it, for stuff like that? But I know quite a few amateur photographers that have kind of over the last decade taken pictures of stars like Barnard's star that actually do move and they can show that movement, align the pictures and make an animation and it's mind blown that we are able to do that from our back gardens now.
We're not going to see it actually moving tonight, so it was a bit click baity in my introduction. It is such a beautiful cluster to kind of look at, so you can tell all your friends that you've looked at a moving star cluster and then explain.
Finally, there are some really nice pre dawn International Space Station passes all week this week. There are multiple per night, so if you've got a clear night and you're up really early, just make sure that you are looking out for the times that the space station will transit.
Ezzy: That sounds like there are some absolutely fascinating things to get to grips with in this week's night sky. Thank you very much, Mary, for taking us through all of them.
And if our listeners at home would like to get even more stargazing highlights, do subscribe to the podcast and we'll be back here next week.
But to summarise this week again, Venus is going to be up in the early evening sky. It's not the best planet to see at the moment. However, much better is going to be the planet Saturn, which will actually be reaching opposition 8 September.
Meanwhile, Neptune, Uranus, Mars and Jupiter will all be rising throughout the evening sky and Mercury also will finally be visible in the morning sky as well. It'll put on its best show of the year on 5 September when it reaches greatest western elongation.
Whilst you're out looking at the planets, you might want to take a closer look at Jupiter, which will have several moon transits and the Great Red Spot will also be making an appearance throughout the week.
Also Saturn will have several moon transits as well, particularly on the second and third of September, so keep an eye out for those.
The Moon is moving from new to first quarter throughout the week. The crescent Moon is going to be near to Venus just after sunset, so keep an eye out for that one.
Comet 13P Olbers will be moving through Coma Berenice into Böotes throughout the week.
It's also a great opportunity to see Kembel's Cascade in Camelopardalis, so take an opportunity to look at those cascading stars and star clusters throughout that region.
You can also take a look at star cluster Alpha Perseae, which is very, very slowly moving across the sky. You won't be able to perceive it this week, but you can get a glimpse of it, perhaps take a photo of it and come back in a couple of years time and see if you can notice any differences.
And finally, the ISS is continuing to make several great pre dawn passes throughout the week, so keep an eye out for those, look up if there's any happening in your local area as well.
So lots of things to be seeing in the night sky, some near, some far, but hopefully you'll find something that will float your boat.
And we'll see you back here next week. From all of us here at Sky at Night Magazine, goodbye.
If you want to find out even more spectacular sights that will be gracing the night sky this month, be sure to pick up a copy of BBC Sky at Night Magazine, where we have a 16 page pullout sky guide with a full overview of everything worth looking up for throughout the whole month.
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 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.
Chris: Thank you for listening to this episode of the Star Diary podcast from the makers of BBC Sky at Night Magazine, which was edited by Lewis Dobbs.
For more . Of our podcasts, visit our website at skyatnightmagazine.com/podcasts, or head to Spotify, iTunes, or your favourite podcast player.
