Jupiter appears to gain another moon this week as ithe planet passes by a background star. Find out how to see it and other astronomy highlights in this week’s stargazing podcast guide.
Chris: Hello and welcome to Star Diary, the podcast from the makers of BBC Sky at Night Magazine. You can subscribe to the print edition by visiting skyatnightmagazine.com or to our digital edition by visiting iTunes or Google Play.
Ezzy: 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 being Here in the UK all times are in GMT. In this episode, we'll be covering the coming week from 15 to 21 January. I'm Ezzy Pearson and I'm joined this week by Paul Money.
Hello Paul.
Paul: Hello Ezzy. Oh, I've got surprise for you this week.
Ezzy: Oh really? Do we have something really interesting coming up. Please do enlighten us.
Paul: Well, we always have something interesting to come up. But we start with the evening sky. I mean, there's a shock.
Ezzy: Oh my goodness, that will, people get a lie in this week.
Paul: I know, sort of thing. But we begin this week in the evening sky. Look for the crescent Moon below right of Neptune. Now, admittedly, Neptune, in actual fact, needs binoculars, but you've got the Moon as a guide. So look above the Moon. And if you've got a good star chart from Sky at Night Magazine, then you'll be able to find Neptune as well.
So the crescent moon acts as a brilliant guide to the position of Neptune, but you will need binoculars or a small telescope for the planet itself. But while you're on the Moon, we have an interesting libration. Libration is this gentle rocking of the Moon, whereby, you know, I mean, moon doesn't technically rock, but basically what happens is that we get slightly out of sync sort of thing as we orbit, as the Moon orbits the Earth sort of thing.
So the speed of its orbit... because everybody thinks the orbit is perfectly circular, it isn't. And so the effect of this slight mis-synchronization is we start to see a little bit, a bit further around the side.
And this is called liberation. It happens in the northern hemisphere, the southern hemisphere, eastern and western horizons as well.
So, but it happens throughout the year. You can't, you know, you get to see over a complete year, you can get to see 58 percent of the moon's surface. I mean, theoretically, we should only see 50%. But this libration gives us the extra bit. But it's not all at the same time. You can't physically, it's always only 50 percent at the time.
But, this libration is particularly good. Because we've got a grand view of Mare Crisium. Now Mare Crisium, it's the first mare. That you can actually see in the crescent moon. It's quite prominent. It's really circular. I always think it's quite a pretty sight, sort of thing, when you get to this sort of phase of the Moon.
But the reason for the actual libration effect is that Mare Humboldtionium- if I've got that right, I can never pronounce that one right, Humboldtianum. Now I'm gonna, I'm gonna give up on that one. But it's right on the edge and, and quite often it's obscured, it's hidden. Because the tilt means it's right on the edge or on slightly other side. So we can't see it.
So this is a really good time to see this little tiny mare up further in the northern part of the Moon. So have a look at that, because it's just an effect of this libration. Because next month you'll look and you won't really see it properly. Now you see it, now you don't.
Ezzy: It does always kind of, again, blow my mind a little bit, that you can almost peek around the corner.
It sort of almost feels a little bit like cheating, um, despite the fact that it is. It's a part of, you know, how nature works that the fact that there's sort of this gravitational wobble going on. And people always talk about the far side of the Moon and how we've never seen 50 percent of the moon. It's actually, it's only 40 percent.
Or we hadn't seen it until the advent of the space race. We have now seen the far side of the Moon and in fact landed on it. So with, with robots and so on.
Paul: But as you say, visually, you know, from our, our point of view, we can only say this idea of 58 percent is weird, isn't it?
You don't, don't feel right.
Ezzy: There's very few people who have seen the far side of the moon with their naked eyes. Put it that way.
Paul: Apart from the Apollo astronauts. In fact, they're the only ones, aren't they?
Ezzy: Apart from the Apollo astronauts.
Paul: Yeah, they're the only ones physically to have seen it.
We're gonna stick with the Moon now. We're talking about January 17 to 20. We're still in the evening sky because at the moment the Moon's in the evening sky, progressing through the constellations. And we start off really on 17th as twilight ends, and the first quarter Moon forms a line with two planets.
Now one's really bright, one's faint. The two planets are Jupiter and Uranus. So, but they form a line, so you could actually take a line from the Moon, go through Jupiter, and carry on, and in theory about almost the same distance, you come to the planet Uranus as well. Having said that, the next evening we find the Moon is directly above Jupiter.
So you can't miss that. There will be lots, I bet on social media, there'll be lots of people say, hey, what's that star below the Moon? Because we always get that sort of thing. We get these queries to the magazine as well. So what's that star below the Moon? And we can say quite confidently, that's no star.
That's the planet Jupiter. Sometimes, of course, it's another planet, Saturn, as we had last week, or they actually could be Venus in the morning sky. But in this particular case, it is, in actual fact, Jupiter. A good cha... I mean, you can't mistake Jupiter, I think, really, and the evening sky. It's the brightest of the planets at the moment.
But it is nice to have something even brighter as a guide, just saying, "Here, if you're not sure, this is it." So there we go. On 18th, I think, we've got the actual moon directly above Jupiter.
Now, the Moon doesn't sit still. The phase is heading towards Gibbous phase now, so it's going from this first quarter onwards.
And so, we'll actually see on 19th, it lies above Uranus. So there you are, another guide to fainter planets. I mean, technically, you might get them in binoculars, so I think you'll be able to use it. Uranus is definitely visible in binoculars, magnitude +5.8, as a rule. So, you know, that is, it's technically a naked eye, but you've got a bright Moon nearby.
But binoculars should actually show it. And then, to finish off this sequence the next morning sort of thing we're talking about on 20th. Sorry, the evening of 20th, it's actually to the lower left. This is the Moon to the lower left of the Pleiades, Messier 45. Now, the moonlight will wash out a lot of the cluster members, but even so, it'll still be, I think, a pretty sight.
And again, if you use binoculars, you'll see the bright moon, but if you look carefully to the right, you'll start to realize there's a faint smattering of stars, and that is the Seven Sisters of the Pleiades.
Ezzy: It's also, if you're not entirely sure where the Pleiades are, you can always use the Moon to point you the way tonight, and then come back again tomorrow, the next night, when the Moon's out of the way, to find it, and then you'll know where the Pleiades are.
So, it's a great way to help begin navigating your way around the night sky.
Paul: And we like advantage things like this sort of bright planets giving us a guide. And bright Moons are very handy for these deep sky objects and other objects to see.
Okay, so while we're generally in this direction, let's go back to 17th and Jupiter. We've often mentioned about the shadow transits and the transits of the moons across the disc of the planet. This is a little bit more unusual.
We like unusual, don't we Ezzy. We like to get the unusual events. So look at Jupiter through a telescope on 17th and have a wide enough fill so that you can actually see that the moons.
But there's a bit of an oddity. Hang on, it's got another moon. It's fainter, but we'll have another moon. It isn't. There's a star.
Now, we forget that Jupiter, we usually image it so we only see Jupiter and the moons. If you did a deep exposure, a) you'd burn out Jupiter, but you'd see the stars in the background.
And most of the time, they are quite faint. But this particular night, there's actually going to be a star below the southern hemisphere of Jupiter. If you watch slowly during the evening you will see Jupiter is slowly moving past the star.
It'll look as if the star's moving. It's one of those weird things you tend to think, oh the planet's fixed but the star's moving.
It isn't. The star is the one that's fixed. It's Jupiter slowly moving past the actual star itself. So, you know, well worth having a look at this because you've effectively got an extra moon. You know, so hang on there's a fifth moon of Jupiter. Yes there are there's a lot Jupiter's got lots but it's only the four Galileans that are relatively easy, you know.
I mean, I think Jupiter's being greedy. I don't know about you, I think Jupiter's being greedy with the amount of moons it's got. It's naughty.
Ezzy: I can never remember because they keep finding new ones. I think Jupiter and Saturn are around about 80 or 90 moons each at the moment.
And some of them are quite small, they're just a couple of kilometres across.
I can't remember who's in the lead at the moment. I think at the moment Saturn might be in the lead for most number of moons.
Paul: It almost changes day by day, don't it?
Ezzy: That will change within a year or two as they find a whole bunch more.
Paul: Those two planets are in a bit of a ding-dong as to which one's going to be the king of the moons.
Ezzy: Yes, but if you if you want to try and find moons, those are definitely the two planets to be looking towards.
Paul: Without a shadow of a doubt. Talking of shadows This is the unusual thing for this particular evening, because we haven't just got this moon masquerading as an extra, this star, I should say, masquerading as another moon of Jupiter.
Watch Ganymede, because as the evening, from about 7pm, keep an eye on it, because ironically, Jupiter's shadow is stretching off. Now, I'm using the northern hemispheres at the top. And the Southern Hemisphere is at the bottom. So in this particular case, Jupiter, has Ganymede and Io to its left. But Ganymede will go into Jupiter's shadow, because Jupiter's shadow is stretching off to the left now.
And so, as it does so, it will slope. Because it's, as you mentioned, it's actually the largest moon in the Solar System. It's bigger than the planet Mercury. And so he's got quite a disc, and amateurs are now imaging features on the disc of these moons. I just think that's extraordinary! That the, the quality of imaging is just to the point where they can actually see features on these moons.
But it will do a disappearing act, and it'll do it, fade it gradually, because it's got a disc. So it'll move into the shadow, and you'll see it fade until it's gone out completely. So, Jupiter will lose a moon! Ha ha ha!
Ezzy: Things that you couldn't even do with professional telescopes 20, 30 years ago, and now people in their back garden are able to do it.
Though, to be fair, quite often, amateurs can do a lot of observations that professional observatories can't because back garden astronomers have something that a lot of professional observatories don't and much more abundance, which is time. That they can dedicate entire months and hours and hours just observing one object over and over again.
Whereas if you're in a professional observatory, you have to justify the time a lot more, so you quite often don't get as much time to be able to observe these things. So that's a very precious resource and one that way that a lot of amateur or back garden astronomers can help out with quite a lot.
Paul: And I suppose the other advantage is the fact that the professionals often have to apply for time with the large telescopes.
So if these events don't happen during the time when they've got, been allocated, it's tough. Whereas we can do it when we like, as long as the sky is clear.
Having said that, that is our only thing that stops us, you know, is the weather and if the weather is clear, then we can be out there actually doing these observations.
So they're fascinated.
Ezzy: Even if it's cloudy over here in the UK, there might be, you know, somebody in France or Germany or somebody else, it's slightly clearer and they'll be able to capture it. So working together as a community, there's a lot of work that amateur astronomers can do. That's incredibly important scientifically.
Paul: Exactly. I mean, a lot of international collaboration goes on in the amateur community, which is great to see.
Now, 19th, look at the Moon, now, if you're a deep sky observer, well, you probably won't want to do this, that's up to you, but if you're a Selenophile, I think that must be the right term, because Selene is the moon, you're a Selenophile, so, ...
Ezzy: it sounds right, doesn't it?
Paul: So, the thing is, if you like the Moon, on 19th, the terminator, this is the day night boundary, crosses over the Crater Clavius. Now the thing about Clavius is that it's got a set of craters there's actually three and in fact there's more than that because they go from large, medium to small so there's a nice progression.
But the lighting is such whereby the light illuminating one edge of two of the craters make it look like it's got eyes. And this is one of these other Clair Obscur effects, the eyes of Clavius.
So do have a look at that sort of thing. Tycho will be further up from that where we get lots of rays coming out, and a lot of terracing on the walls of Tycho as well, so that's well worth having a look at as well. But it's the eyes of Clavius, this Clair Obscur effect, so it looks as if the craters looking at you. Watching it, watching you, watching it, watching you, yes,
Ezzy: It's one of those, it just kind of looks like a little sort of cartoon head just poking up to say hello around the edge of the Terminator.
That's the light between the light and dark side of the Moon. I think it always looks very cute.
Paul: And it's one of the easiest ones, to be fair, as well. Someone quite, you know, you really have to look for a minute, and you've got to get the timing right as well. Lunar X and V, you've got to get the timing right, otherwise you just don't see them.
Ezzy: Some of them It is like you've got an hour.
Paul: Yeah. Yes, it is that narrow.
Ezzy: You've got an hour whilst the sun is in the right place.
Paul: But that's the fun of astronomy sort of thing. And again you can see something change literally right before your eyes. And in this case, the eyes of Clavius. I think I'll stick with the day job.
Finally, all week we've been keeping an eye on Venus and Mercury, but now we're getting towards the end of the week, 21st, but all week watch as Mercury begins to drop down towards the horizon. So you're gonna lose Mercury. So it's a case of, although Venus had been trying to catch up, look at seven o'clock in the morning, very low down to the lower left of Venus will be Mercury, but we are literally in the last few days before we lose it, and it's gone for another few months. So definitely finish off the week by catching your last glimpses of Mercury before it's actually gone in the morning sky. So there we are, plenty to look out for, isn't there?
Ezzy: And definitely always with Mercury, especially when it's dropping just out of the horizon, be careful of the Sun.
You'll be watching very close to when the sunrise is happening, so make sure that you know exactly when the sunrise is going to happen in your location so you don't accidentally catch it in your optics and hurt your eyes.
But yes, lots of things to look forward to in this week's night sky. Thank you very much for taking us through them, Paul.
Paul: My pleasure.
Ezzy: And if you want to keep up to date with all of the latest tips of stargazing hints to see in the night sky, do subscribe to the Star Diary podcast.
But to summarise that week again, we start on 15 January as the crescent moon points the way to Neptune. You'll also be able to see the libration feature Mare Humboldtianum.
Moving forward onto 17th through to 20th. You can watch the moon as it passes by Jupiter, Uranus, and the Pleiades, and it'll be lining up quite nicely with all three of those throughout that time.
And then again on 17th, take a closer look at Jupiter as it'll appear to have got another moon as it's actually passing by a background star but it will appear to have another moon for that time.
But it would also appear to lose a moon as Ganymede disappears from view as it passes into Jupiter's shadow. That's all on the 17th. Then on the 19th, you can take a look at the moon where a clair obscur effect called the eyes of Clavius will appear to look at you from just by the terminator on the Moon on 19th.
And throughout the week make sure that you capture Mercury as it's dropping very rapidly back towards the horizon and it's the last few days before it will be gone for another couple of months. So make sure that you catch that planet as well. And we'll hope to see you all 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 pull out 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.
For more of our podcasts, visit our website at skyatnightmagazine.com or head to aCast, iTunes or Spotify.
Listen to next week's episode of Star Diary 22 to 28 January 2024
