Saturn's moons - including Titan, Iapetus and Dione – will be putting on a great show this week. Find out how to catch them and other astronomy highlights in this week's episode of the Star Diary 6 to 12 November 2023.
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 based here in the UK, all times are in GMT. In this episode, we'll be covering the coming week from 6 to 12 November. I'm features editor Ezzy Pearson, and I'm joined by reviews editor Paul Money.
Hello, Paul.
Paul: Hello, Ezzy hey, we've got a good week this week.
Ezzy: Oh really? Please do tell what we've got to look forward to this week.
Paul: Well, let's start off with a bit of an unusual observation. It's not something you can see directly apart from the planets. But I happen to notice that all the giant planets are viewable in the evening sky but are also just slightly below the ecliptic.
Now that's the path the sun makes across the sky, which is really the Earth's orbital plane, isn't it? Projected against the sky. But as it happens, they're all just below it. And it got me thinking. So I thought, when do they cross that ecliptic?
Jupiter's the first, it'll cross in 2025, late 2025. So we've only got a couple of years left before it crosses into the northern half of the sky.
Uranus 2029, so a bit slower. Saturn in 2034. And wait for it... slow moving Neptune in the last days, literally the last three days.
Ezzy: Oh my goodness.
Paul: So it's just the fact that they're, I just noticed that they're all below the ecliptic and it just got me intrigued. I still thought, oh, I wonder how long that takes before they're above it?
And then I started investigating. It's amazing what we can do nowadays with software, isn't it? Where we can project the planets into the future and see where they're going to be. So Jupiter being the fastest mover, of course, of those four was the one that would actually be crossing the ecliptic sooner.
But it just it intrigued me, intrigued me as I was looking at it, but you can't visually see the ecliptic, but you know, your software will tell you where it actually is in the sky, sort of thing, because it's this... it's an important line, it is our path in the sky itself, and to us it makes it look like the Sun's going along it.
Ezzy: I think also it's one of those reminders that, especially when you're in school and you're learning about the planets, you learn that they all go around the orbit in the same plane together. And it is quite easy to forget that it's not everything's all perfectly lined up.
There's quite a lot of variation between the different planets orbits, and they do dip up and below the line of the ecliptic, the line of the Sun, quite often.
So being able to sort of see that. In the sky, even though you will have to imagine or know where the line of the ecliptic is to be able to see it. I think that is a really fascinating thing to bear in mind.
Paul: And of course, I didn't mention the inner planets because they're so close to us. They're bobbing up and down quite a lot.
So, so they're not quite as exciting as sort of thing waiting until 2025 for Jupiter and 2029 for Uranus, et cetera, sort of thing. Uh, I won't be around in 2084 with the best will in the world. I'm afraid I won't see that one sort of thing. So, uh, you know, that's poor slow moving Neptune for you.
Now, all week from the 6th, it's worth, we mentioned Jupiter last week because it was our opposition, and it's easy to forget that we tend to concentrate and mention the planets when they're at opposition and look at them in detail, but we do tend to forget that, you know, we've got the other planets actually still visible and well worth having a look at as well.
So on 6th, I thought I'd home in on Saturn, because over the next few years, the rings are slowly closing up. So this is the time really to observe them reasonably wide open and get things like the Cassini division. Now you will need a telescope actually to magnify it up so you can see the actual rings well, but the Moons are there as well.
Titan is the easiest one and generally can be seen if you're careful and we've got good... I would put binoculars on a tripod for this sort of thing. But you can just see it in binoculars as a tiny dot. You've got to have it when it's at its furthest away. It's eastern or western elongation from the planet as such.
But you can see it's got such... when the tilt, the rings are tilted open like this, Titan does move north and south of the planet and misses the planet quite a lot. Which is why in the next few years when it does go ring plane crossing, all the planets then do transits across the actual disk of the planet as well sort of thing, so it makes it rather unusual.
But there's Rhea, there's the Iapetus, there's Dione, and Tethys as well to have a look for, and those who have big telescopes might want to go in for Mimas and Enceladus as well, but they're very close to the rings. The ring glare tends to cause a bit of a problem when you're trying to observe them. So let's not forget Saturn.
Saturn has got belts. Well, one main northern hemisphere belt and one southern, but the moment the southern is getting harder to see because the tilt of the rings, they're closing up. The whole planet is gradually tilting.
So, you know, it's one of those things. But the tilt of Saturn tells us that, well, Saturn has seasons just like the Earth.
So they just take a very long time. Orbital period of 29 years, so you're having seasons that last years. Oh, can you imagine winter lasting years? Oh, that'd be awful, wouldn't it? So it's an idea just not to forget Saturn and point a telescope at it while we've got it. Because over the coming months, it's gradually getting lower towards the southwest, and so it won't be too long before we, lose it in actual fact and it goes back into the morning sky.
Ezzy: I think it's also people sometimes need to remember that Saturn has moons too. People talk a lot about Jupiter's moons, and quite rightly, they're big and really easy to see even through a relatively modest telescope. But Saturn has these moons and they are very, very interesting to follow as they transit around the planet.
So, yes, definitely make sure that Saturn gets its due in the night sky.
Paul: Now we mentioned Jupiter last week because it was at opposition, so it's really well placed. It's around about opposition that we get particularly good transits of the moons going across and their shadows as well. So, I thought I'd throw in a few for this particular time.
So, this is still 6 November, and we're talking about just before half past 10 in the evening. Starting about 10:21, Io begins to cross the disk of the planet. Now, at this particular stage, so close to opposition, the shadow quickly moves on as well.
Now, as we gradually move away from opposition, then what happens is you get a longer gap between the actual moon crossing the actual disk of the planet and then the shadow coming onto the disk of the planet as well, because the angle is changing with the Sun from Jupiter's point of view.
And we've got Io and its shadow creeping onto the Jovian disk. Keep watching till just after midnight for the full transit, but these events happen reasonably regularly during the month of such, especially for Io because it has a shorter orbital period as we mentioned last week in actual fact, so just a few days going around Jupiter.
We do mention these in the actual magazine. You know, we always mention it in the monthly notes sort of thing. So do have a look at the magazine, for such events, because they're fascinating to watch. Because we mentioned, we often talk about, don't we, the clockwork motion of the Solar System, and we're often talking in terms of occultations and things like that.
But in actual fact, Jovian moons are a way of showing the motion of the Solar System, and in this case, as Galileo first noted, the moons going around Jupiter, which of course reinforces the idea that, you know, the Sun probably was at the centre of the Solar System rather than the Earth, because there was Jupiter with moons going around it.
And surely that shouldn't be allowed. So it's quite amazing. Now, there's another event on 8th involving Io as well, but it's in the early evening, not long after Jupiter's risen. So on 8th, start watching Jupiter after it's risen, and keep an eye out for another transit of Io and its shadow.
I just think they're fascinating, and I say, to actually watch them going across. And it's surprising how quick they move. across the disk.
But you've also got another strange effect. You've got the planet rotating as well. So sometimes you find they seem to be hovering over a particular spot or a feature in Jupiter, and they're almost moving in tandem. There becomes a very slight difference between the two, becomes apparent towards the end of the transit.
I find that fascinating. So you've got the rotation of Jupiter, and you've got the motion of the Moon as well. Talking of the Moon, and in this case, our Moon, 9 November, very interesting day. In fact, very interesting morning, because Venus is in the morning sky, and so is the crescent Moon at the moment.
And on 9th, around about 5am, you can see the crescent moon directly above Venus. I mean, it'll be a wonderful sight anyway for astrophotographers. So they'll be about, they'll have risen for about an hour or so earlier. So if you're really keen and want to watch them from the horizon, fair enough.
But I like to let them get a bit higher up. Mainly because I've got a very big shrub filled bank that blocks my view of the eastern sky. So I have to wait until it clears that. However, if you're able to observe it over even a matter of sort of half an hour to an hour, you'll notice the Moon is creeping closer to Venus.
Now, this is the morning sky, and that has an important implication, because what it means is Venus is in the morning sky, so therefore it'll be visible, uh, ahead of the sun in the daytime sky.
And so, what we get is an occultation during daylight. And it feels sort of like the, a reasonable time, I have to say. Obviously, it doesn't help if you're at work. It's just one of those things. Take a day off. Hopefully, hopefully there are clear skies.
Ezzy: It depends where you work. You might be able to persuade your colleagues to nip outside on their coffee break. Say, hey, do you want to see this cool thing?
Paul: Exactly! Set up a small telescope, what not, convince your boss that this is science, which it is really, you're watching the motion. It's amazing how people, I remember showing my colleagues when I used to work at a certain retailer many, many, many moons ago.
But I showed them Mercury just as they were finishing we had this long line of, we had a corridor with big windows and I'd spotted Mercury and I thought, I wonder how many of my colleagues had ever seen Mercury?
None of them. I was pointing out Mercury as they were literally heading home sort of thing, but enough of them stopped and were amazed because they'd never seen the planet Mercury, but it was so obvious that they couldn't mistake it. They are often fascinated, so you never know. So we want to be looking about 9:43 to about 10:41.
Times will vary depending where you are in the UK, but it'll be a subtle difference between them. You can use binoculars. I mean, Venus is bright, even in daylight. I mean, if you know where to look for it, you can actually see it in binoculars. But of course, you'll have the advantage of a crescent moon creeping ever closer to it as well.
And when it reappears, it'll be on the dark side of the Moon. So it's one of those things you'll be watching. Then suddenly you'll start to notice something appear. And it'd be like a blip and then it'd get bright and then it's fully out of such.
So, well worth having a look at. And this is one of those things whereby we're not dealing with a faint planet where it's a real challenge to see it against a blue backdrop. Venus is bright, so it can be well seen as such. There we are. And of course, if you get any pictures, we're always, we're always after the pictures, aren't we, Ezzy.
Ezzy: Always want you to see your pictures. We have details on how you can submit them to the magazine over on skyatnightmagazine.com. I'll put a link down in the notes below as well, and we print the best ones in the magazine.
So if you'd like to get your images out there, please do send them in. We always love to see them.
Paul: Finally, we've got on 10 and 11th, we've actually got, again, before sunrise, we've got the crescent moon. It actually is moved away. Venus will be above it now, but the crescent Moon will actually be just to the lower right of Porrima.
Then on 11th, it'll be just to the upper left of the star Spica, or 'Speaka' depending on how you want to pronounce it. Both in Virgo. And I always love it when you get these crescents because you've got the chance of Earthshine, as well.
So you've got the light bouncing off the earth's bright atmosphere acting almost like filling flash. Photographers will be familiar with that sort of idea and it illuminates the night side gently so you get this ghostly view of the dark side of the Moon as well. I wonder if that's what inspired Pink Floyd?
Ezzy: Yes, that's the thing.
People often call the dark..., the far side of the moon, the dark side of the moon. But actually, the dark side of the Moon changes every night.
Paul: Yeah, it's one of those things, isn't it. People always assume that, and never realise that the Moon does actually turn on its own axis as well. It just happens to be facing the Earth, or like synchronised with the Earth.
But of course, it does mean when we see the phases that it's daylight. The night is the dark bit, so it naturally follows. It just takes longer, like 29 days, there we go. Lots to see this week then Ezzy.
Ezzy: Yes, it certainly sounds like we've got a lot to look forward to. And if you want to hear about more stargazing highlights, be sure to subscribe to the Star Diary podcast so that you can listen to them next week.
And so to summarise those again, throughout the week you'll be able to see all of the giant planets in the evening sky. They're also all below the ecliptic at the moment. That will last until 2025 when Jupiter moves above that line. But it's still a great opportunity to be able to look at that now.
You'll also be able to see Saturn, which, even though Jupiter is at opposition, so it's a great time to look at Jupiter, Saturn is also well worth having a look at, so do be sure to catch that, and also take a look out for its moons.
On 6 November, you want to look out for the transit of Io across the disk of Jupiter. Io and its shadow will both be visible moving right the way across the disk.
And if you want to find out more about what's going on with the moons of Jupiter throughout the month, we have a monthly guide in the magazine in our sky guide section, where every month we list out what's going on with the four Galilean moons around Jupiter.
So if you want to make sure that you've always know what's going on with the Moon, be sure to subscribe to the magazine.
Then on 9 November, there will be a daytime occultation of Venus. It'll be happening in the morning, and you'll need telescopes or a pair of binoculars to be able to see it.
The Moon should be visible even in the morning sky. So it should be relatively easy to find where you need to be looking.
Then on 10 to 11th, we finish off the week with the crescent Moon near Porima and Spica in Virgo.
So lots of things to be getting on with this week, and hopefully we'll see you here next week to find out even more stargazing highlights that we have coming up.
So from all of us here at Star Diary Podcast, 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 skynightmagazine.com or head to Acast, iTunes or Spotify.
