Caoimhín's Content

Today we will continue looking at the month of September. We’re starting just a couple of days into the month on the 3rd of September and we’re going to be looking at Jupiter and its moons around sunrise. We are going to be taking a look at some of Jupiter’s moons occulting each other and I have been given various locations and various dates to take a look at. The first was Dublin in Ireland, but of course here in Cork we’re not too far away so we’ll take a look from here first. Jupiter is up just before sunrise in the morning, it’s quite low in the sky to start with, but it rises high enough while the sky is dark to be less affected by atmospheric extinction. It’s not being reduced too much and it is still dark enough for us to take a closer look at Jupiter without risking damage to things like telescopes and our eyes, at around 5 o’clock. We are mainly looking at moons blocking each other out though I’m sure some moons will be disappearing behind Jupiter as well. Looking just at Io and Europa, there is a partial occultation and it is visible from Cork, which I am happy to know, though we will take a look at it from Dublin as well.

With a big enough telescope, Europa is visible in front of Io, it’s a very clear occultation. Io certainly looks much larger than Europa, and because Europa must be closer to us, the fact that Europa still looks smaller than Io indicates something about their relative size. Stellarium provides the necessary information, Io is 3600 and a bit kilometers in diameter, and Europa is only 3100 and a bit kilometers across. Europa is a smaller moon, so a little bit of Io would be visible even if the occultation was perfect. This is quite early in the morning so we will zoom back out to check how low in the sky they are. They are pretty low in the sky, but really that is a good thing. The fact that the occultation is happening while the sky is still quite dark means that it should be finished by the time the sky is brightening. When the moons are actually overlapped, it’s at just 5:09 in the morning. I would suggest starting to look at about 5:05, that should give you enough time to see this happening. By the time it finishes, the sky is still fairly dark and it’s still safe enough to use a telescope.

Cork is pretty close to Dublin, there are a few different Dublins in the world and we want the one in northern Europe here. There won’t be too much of a difference because the places are so close together. The other locations we will be looking at much further afield. Starting again at about 5:05, Europa comes up, contacts Io, and reaches its peak at around 5:09. It’s finished by just 5:11, so this is quick. These moons do orbit Jupiter very quickly, so their relative positions are changing very quickly, but again, that’s all visible while the sky is reasonably dark. Dublin is quite a large city, the light pollution will be a bigger issue than in Cork, but Jupiter will be visible despite the light pollution. Jupiter is a very bright planet, so you will at least be able to locate Jupiter in the sky. Of course none of these occultations are going to be visible without the use of a telescope.

We are going to move to Majuro, the capital of the Marshall Islands, in Micronesia. That puts us way out, very close to the equator out in the Pacific. We’re moving forward to the 7th, and again we’re going to have to move back to morning time. We’re still looking at Jupiter and its moons, so no matter where we are on Earth during the month of September, Jupiter is going to be visible in the morning. We are much closer to the equator, so that is going to improve our view of Jupiter and there’s a fantastic view of Mars having a close conjunction with the Moon as well. The commenter who supplied me with these dates and locations did mention a couple of other things like the conjunction between the Moon and Mars, which I very much appreciate. Most importantly, Jupiter is visible quite high in a great level of darkness.

Zooming in to take closer a look, we are still looking for Io and Europa. I wonder which one will be in front because of course these moons are orbiting Jupiter, so either one of them could be closer to us. In this case it is Europa passing in front of Io again. This is happening much later and still in a good level of darkness. We are at 5:19, so maybe 5:16 or 5:17 will be a good time to get started. Europa will contact Io around 5:19, with it peaking just before 5:20 in the morning, and then finishing at just 5:23- 5:22. Again, these occultations and conjunctions are going to be brief, but Jupiter is certainly in complete darkness from the equator. It’s still visible to the naked eye quite clearly coming up to 6 o’clock and even later at 6:15. This is because we’re at the equator and we’re the ecliptic is at a very different angle than it would be from Ireland. In Micronesia, on the Marshall Islands, the level of light pollution would be far reduced compared to what we’re seeing in Cork as well. However, we have more locations to check out.

We are moving back into Eurasia, to Ashgabat in Turkmenistan, right in the middle of Eurasia pretty much. We are moving forward again to the 9th, still just before sunrise. As we come up to sunrise, here comes Jupiter, very close to the Moon, so the Moon will have a fairly close conjunction with Jupiter as well. Of course this is very close to the date of the Jupiter Moon occultation/conjunction that I covered in a recent piece, which is also coming up in September around the 8th or the 9th for the Kamchatka peninsula. Zooming in on the Jovian moons, Io is in front of Europa. It is nice that we’re getting both options. Of course, you’d only really get both options if you’re willing to travel from Dublin to Turkmenistan or from the Marshall Islands to Turkmenistan. We’re very early, starting at just about 4:45 in the morning. It’s reaching its peak with Europa almost entirely occluded by Io and at just about 4:48. We might as well be precise because this is so quick, by 4:50 the best of it is over, and by just before 4:51, the deep partial occultation has finished. Io is covering a lot of Europa, and the commenter who provided me with these locations provided me with large cities as viewing locations, which does make the locations a lot easier to find than simply changing the latitude and longitude.

Given that Io is covering so much of Europa, I decided to check if some subtle changes in location would reveal a total occultation. I thought I could exploit parallax to find a position where these would fully occult over each other. With Jupiter being so far away, moving here on the planet doesn’t cause much of a difference in the view. Changing location will also change when the Sun is rising, so that’s going to make things potentially more difficult to see. I may have been too cautious with my adjustments, but I didn’t want to mess with it too much because I’d lose it entirely. I won’t be greedy this time, the partial occultation alone is certainly a nice one to catch.

Yet again we’re changing location fairly drastically, to Juneau in Alaska, very far from the equator. We’re also moving forward to the 12th. While on the 8th, still zoomed in on the moons, the partial occultation is still occurring. Of course that was happening during the day, during the afternoon, so it wouldn’t actually be visible even though it was occurring. We’re going to move back to sunrise and already the angle of the ecliptic is clearly very different, it’s much steeper than what we were seeing when we were looking at these things from the equator. It’s closer to what we would see from here in Ireland and of course Juneau in Alaska is even a little further north. Zooming in on the correct date, we’re here at 4:30 in the morning, so very early. Io and Europa are already fairly close together, but we will need to change time for them to occult. It looks like we’ve got Io in front again, and this time it’s a perfect occultation. There is a total occultation of Europa by Io, it’s completely blocked out. We don’t need to mess around with the locations or latitude or longitude, it is already perfect from Juneau, Alaska, which is a fairly big city, so hopefully there were plenty of people there who’ll see it.

We’ll come back to the beginning, we’re looking at just before 5 o’clock in the morning, I would say 4:55 would probably be a good time to start preparing for this. It justs begins at about 4:57, and it is absolutely perfect at just 4:59. 4:59 is when the occultation is reaching its maximum, and Io blocks out Europa for a little bit, because Io is larger than Europa and closer to us. Just at about 5 o’clock is when Europa peaks out from behind Io again. It is brief, the maximum lasts for less than a minute and by the time it finishes off, we’re at almost 5:02, we’ll say 5:02, by the time it’s complete. The absolute perfect view is at just about 4:59, for anyone who is in Juneau, Alaska. This is the best option of the whole lot so far, even better than what we are going to see here in Ireland.

There are a few of several similar conjunctions that are later in the September. I hope that you enjoyed this piece and I hope that you get to see some of these occultations, although most of them are partial. If nowhere near you is mentioned in this piece, do not worry about, we will have another piece in the near future covering even more locations where other moons will be involved, like Callisto and Ganymede. Make sure to like this piece if you did enjoy it and subscribe to this website so that it is more likely you will catch the future piece where we will look at more of these occultations and conjunctions. Most importantly, I hope that you enjoyed this piece, thanks for reading and I’ll see you back here next time.