Caoimhín's Content

Today we are going to be looking at the moons of Jupiter from a couple of specific locations. Importantly, we are now past the solar eclipse. I hope many of you got to see the solar eclipse on August 12th. If you didn’t get to see the solar eclipse, I hope you at least saw the Perseid meteor shower which continued into the early hours of the morning after the night of the eclipse. If you didn’t see the solar eclipse or the Perseid meteor shower, there is at least a lunar eclipse coming up on the 28th of August, so we have that coming up at the end of the month. On the 15th, in the morning, there is a close conjunction of Mercury and Jupiter. You can take a look at a couple of my previous posts if you would like to see more details of the recent solar eclipse. The last post talked about the next lunar eclipse, there’s a recent post on the Perseid meteor shower as well. Today however, we’re going to be trying to catch an occultation of some of Jupiter’s moons,

To do so, we’ll have to change location and the date. Although the moons do look very close together, from here in Ireland on the 15th, they’re practically obscured by the glow of sunrise and they’re only visible very early in the morning, when they’re close to the ground and extincted by the atmosphere. We can get rid of the atmosphere and the ground in Stellarium. this lets us follow the jovian system for longer and check if we can get these moons to move in front of each other. It looks like Europa is moving in front of Io, but taking a closer look, it’s not quite. These moons are so small that until we’re zoomed in quite close, they do just look like quite colored blobs. On closer inspection, Europa and Io are moving near each other, past each other, but they’re not occulting each other from this location. It would be very difficult, given that these moons are so small and so far from us, to try and find the exact location on Earth where this looks good. Especially just by hopping around using the map provided by Stellarium. However, a helpful commenter has already found found several locations, mostly in the Pacific, where some partial occultation of this kind will be visible, and they have provided the dates and the locations.

I needed to check if the city names provided were in Stellarium. As we earned from the solar eclipse article, for example, when we were looking at Greenland and Iceland, there weren’t that many towns available in Stellarium’s map. However, when we were looking at Southern Europe, there was many cities and towns available. Not every town is available, but luckily these are capital cities. Starting with Avarua in Polynesia, in the Cook Islands specifically. We’ll bring back the atmosphere and the ground, and we’re going to move forward to the 19th, which is the date I was told to look at. We’ll come back to sunrise because we are still looking for Jupiter and Jupiter’s moons. We were seeing them at sunrise here in Ireland, that means they are going to be visible at sunrise from Avarua as well. So let’s take a closer look here at Jupiter and the moons. We’ll move through a little bit of time, but the ground gets in the way, so we must be moving in the wrong direction. Moving forward, the sky gets very bright, so we will get rid of the ground and the atmosphere. Io gets occulted by Jupiter at least, and pops out the other side.

Moving through time under these artificial conditions, all four Galilean moons move around and pass close to each other. Eventually, taking a look at Europa and Io, they do get very close but they don’t completely occult each other. At least this is still a close conjunction. However, at 1:30, the sky will be too bright for them to be visible and of course, there they are high in the sky with the Sun practically over in the west because it is after midday. Moving back to sunrise, we’ll check how they behave when they’re actually visible. We will come back to the earliest time where we can see them, which is just as they come above the horizon. This is a time when they will be partially extincted by the atmosphere. Taking a close look Io and Europa are both visible, but moving forward they don’t overlap and the Sun comes up. We wouldn’t be able to see this with most telescopes, simply because the light of the Sun is too bright, you would damage your eyes and you would damage the telescope, but Io disappears behind Jupiter and without the atmosphere or the ground, if we move a little further forward, we can see Europa and Io coming very close together. A little further forward again, Europa passes just in front of Jupiter as well, which is a nice thing to catch. However, Io and Europa here, although they are moving close together, it’s not a true occultation and when they are at their closest together, they are impossible to see with human eyes.

Luckily, there are a few other locations that have been suggested, so we will take a look at one of the alternatives. Thankfully, the names of the cities are all in Stellarium, otherwise I would have to type in the various different latitudes and longitudes. We are not in the Pacific this time but on the Atlantic, on the coast of Mauritania in the capital Nouakchott, right at the coast of West Africa. This is another location where we have been told to take a look for a different date. We’ll get back on the atmosphere and the ground and we will travel forward to the 22nd, we’re still going to be looking towards sunrise. Jupiter is still above the Sun towards the east in the morning, and we’re very close to the equator, so this is a fantastic place in which to view Jupiter. We will come back to the very moment when it rises above the horizon, even as it gets fainter due to atmospheric extinction. If we take a closer look, Europa and Io are already looking like they’re on top of each other. Taking an even closer look, and they are right next to each other in the sky. Moving forward, they do partially occult each other from this angle at this time. What’s more is that this is a time where they are still visible through a telescope, where the sky isn’t too bright. We’ve only checked two locations so far, but this is the one getting my vote as the best, so far at least. Io and Europa slide past each other before the sky becomes too bright to observe them with a telescope and while they are actually above the horizon.

Luckily, we have a couple of other locations to check and the view may be even better from there. The view has gotten better so far. We are now going back into the Pacific, to Melanesia, to Honiara, the capital of the Solomon Islands off the coast of Papua New Guinea. Again, all of this information was given to me by a helpful commenter. We will go back to the east at morning time to see Jupiter above the horizon and we will move forward again to the 26th. Jupiter still nice and high above the horizon to the east, we’re still fairly close to the equator here, certainly much closer than we are in Ireland. We’ll move down until Jupiter is just getting extincted by the atmosphere, but not obscured by the ground. Taking a closer look, Io and Europa are definitely close together again. Moving forwards in time, Io and Europa do seemingly overlap, at least through a low power telescope. Taking a closer look, and there’s another occultation of Europa by Io. Partial, but still, Io is blocking out part of Europa. This is visible at just 6 o’clock in the morning from Honiara, but it is a little bright. You would need protective equipment on your telescope to see this. I think that describing what’s coming up in the sky so that people can prepare themselves to go and see these things is good, but I also think that showing people things that they would otherwise not be able to see is important. This is mostly going to be the latter.

Coming back to Polynesia, specifically to French Polynesia’s capital Papeete. We’ve changed our location and we will still see Jupiter above the Sun in the morning. The later we move in August, the easier this will be to see, even for us here in Ireland. We still need to change the date, moving forward to the 30th, which only brings Jupiter higher in the sky and easier to see. We’ll move back so that Jupiter is just coming above the horizon and we’ll zoom in to see how those moons are behaving. Europa and Io are already practically on top of other each each other. Taking a closer look, they’re not quite there yet. We’ll move forward, and it’s Europa occulting Io this time. Again, it’s only partial, but now we’ve gotten to see it both ways around, with Io blocking Europa and with Europa blocking Io. This one occurs coming up to 5 o’clock in the morning, so the sky is actually dark enough to use a telescope. Everything is so low in the sky that you will need a clear horizon, but if you have one, we can see these things moving past each other comfortably for a while, up until about 5:30. After that, the sky definitely gets too bright. Zooming back out, the glow of morning twilight is obvious, it’s definitely too bright to use a telescope anymore. Thankfully, you don’t have to worry about using a telescope to see these occultations because you have already gotten a description here.

If you are actually in the right location and you have a protected solar telescope perhaps, then maybe you will get a chance to see one or two of these partial occultations. In all of those locations at least you will get to see Jupiter in the morning at sunrise at the end of August. Indeed, we will in Ireland as well, though it will be a little bit more difficult. Even though those occultations are going to be impossible to see with the naked eye, you know when and where they are occurring. Thank you to the commenter who let me know the dates and locations. I hope that you enjoyed this piece, if you did then please do like it. If you like this kind of content, then please subscribe to this website and my YouTube channel. Thank you very much for reading and hopefully I’ll see you back here next time.