Caoimhín's Content

Today, we are going to look ahead to an event that is coming up in the future. This time we are only looking a few decades ahead, to 2092. For those of you who are regular readers of these posts, you know that we take a look into the future for future events occasionally, although it has been a while since we looked into the future. In previous posts we’ve looked hundreds of years both ahead and into the past. We are going to be looking at decades ahead into the future, but we are also looking at a date that has passed, the 27th of March.

We’re beginning in Ireland as usual, looking forward to the correct date and we are looking almost at the correct time, which is 7:45. As with many of our looks forward, this one depends on the suggestions of a viewer over on YouTube. We will be looking at the planet Jupiter and the position of a couple of its moons. It looks like Jupiter is not above the horizon for us here in Ireland at this time, which is why, presumably, I was unable to see this event the last time that we took a look. I may have looked at Jupiter for the date of the 27th, but it would have been in the morning, when Jupiter is visible above the sunrise. At he right time of 7:45 or so, it simply isn’t visible from Ireland. Removing the ground and atmosphere, we can take a closer look anyway. Jupiter’s Galilean moons are visible, and they are the core of the event that we should be able to see. We have Ganymede occulting part of Callisto, and Ganymede also slides a little bit over Io. If we keep moving through time, there’s an occultation of Callisto by Io as well. Of course it’s not a full occultation, even if they were lined up perfectly, Io is so much smaller than Callisto and Ganymede it wouldn’t be able to block them completely. However, the Ganymede- Callisto we’ll see at 7:53, from a slightly different position that would be a true occultation. Ganymede is bigger than Callisto and from this position it is in front of Callisto, making it appear even bigger.

If we drift back to 7:45, around here is the time that we were told to take a look at, and the three moons are certainly all next to each other. However, we are looking at these moons and Jupiter from the Earth, and Jupiter is not an inconsiderable distance from the Earth. If we take a look at the distances, Jupiter is 5.6 AU from the Earth. It is further from us than it is from the Sun and it is five times further from the Sun than we are. These values do change a little thanks to the orbits involved. Either way, Jupiter is significantly far away from us, and this makes a difference when it comes to time. When using Stellarium to look at things in the sky, the software assumes that light is traveling, that light is taking its time to reach these planets from the Sun and then reflect back to us. Even at the speed of light, there is a significant delay, in this position about five times the eight minute or so delay that we get from the Sun. Light from the Sun takes about eight minutes to reach us, it’ll take about five times longer to get all the way out to Jupiter and from this position, about five and a half longer to get all the way back to the Earth. In Stellarium, that’s something that we can change. By using the view panel and the solar system objects tab, there is a simulate light speed checkbox that we can uncheck.

Stellarium essentially builds in a delay, it accounts for the eight minutes that it takes for light to travel to us from the Sun, it accounts for the even longer time that it takes light to reach us from Jupiter. With the light speed simulation taken away, if we move back to 7:45 without lightspeed, things will be in a very different positions. Io is invisible in the shadow of Jupiter, so we can’t see it, though it emerges from the shadow of Jupiter if we move backward. I think this is something nice to see as well, a half Io, because it is blocked by the shadow of Jupiter. Io’s illuminated side is facing us and facing the Sun, it has to be, we’re closer to the Sun than it is. This also shows that the shadow of Jupiter is not directly in line with Jupiter. Io reappears some distance from the planets edge. Looking at the details of Jupiter, it’s 99.4% illuminated, not 100%. It is certainly not anywhere near its opposition, which is when we would see it directly behind the Earth and fully illuminated. It is closer to being behind the Sun than the Earth, and this angle means it’s casting its shadow a little to the side. Now that we’ve taken away our light speed, we should still see these occultations happening in a similar way, but at a different time. Ganymede blocks off just the top of Callisto and just barely the top of Io, but these things are happening at a significantly different time, there’s a difference of almost an hour and that is down to light speed. That is just how long it takes for the light to reach us.

When we’re seeing these moons, going through these conjunctions/occultations, we are really looking into the past. It is 7:05 when this is really happening. If we turn back on lightspeed we can double check what time we see it. The very same occultation, and we’re finally seeing it at 7:53, almost 50 minutes later, and that’s our indication of how long light must be taking. It must take that long for light to reach us so we can see this conjunction happening. Even though we’re only looking within our own solar system, we need to account for light speed, especially if we are looking as far away as Jupiter. Otherwise, we’re going to be trying to look for these events the wrong time. Now, we are high on the planet, so we are looking down on Ganymede and Callisto, roughly, assuming Jupiter isn’t too far from the ecliptic, which I generally assume it is not. That means that our position on the Earth might influence our view a little, so we will change our location and see if we can leverage the effect of parallax to maybe make this occultation/conjunction a little bit better.

It does seem to be a little bit better from higher on the planet, but the difference is slight if at all. If we move down on the planet, our perspective does change, but the amount of occultation that we’re catching is more or less the same. If we change our longitude rather than our latitude, we’re still not getting enough of a difference to be able to leverage parallax to give us a significantly different view. We are, of course, looking at something that’s quite far away, and the moons are relatively close together. We would need to travel quite a significant distance to be able to use parallax here, and normally when we are using parallax, we’re not just traveling a few hundred kilometers across the Earth. Instead we travel 2 AU, from one side of the Sun to the other. From our position on one side of the Sun, 1 AU away from the center, all the way around to our position on the other side of the Sun, a whole other AU onto the other side, it’s two AU overall. By looking at a given object, usually stars, from one side of the year to the other side of the year, we’re traveling a lot further, so parallax makes a much bigger difference. Traveling across the surface of the Earth, not so much.

We’re going to move forward here again to 7:53 UTC, we’ve got our alignment, we’ve got Io, Callisto and Ganymede. There’s other moons out there as well, such as Metis and Thebe, and there is Jupiter’s Great Red Spot. We’re just able to see Jupiter’s Great Red Spot at this time, if we’re simulating for light speed. If we remove that simulation, the Great Red Spot comes even more into view. Turning the lightspeed simulation on and off, Jupiter appears to rotate back and forth by what would be a little bit less than 50 minutes, and that’s just down to light speed. This isn’t going to be visible from Ireland, so let’s find out where it is going to be visible from. We want to see Jupiter in the morning, because it is just to the west of the Sun. We want to be somewhere where the Sun is just rising while it’s 7:45 here in Ireland, which is the same as UTC for the date in question. The Sun has just set for us, so the sunset terminator would be passing through west Africa. All of the Americas would still be in daytime, and all Asia would still be in night time. We want to move back to somewhere that’s almost coming up to sunrise at this time.

We’ll take a look from East Asia. We’ve gone quite far across the map, and it does look like Jupiter is just about above the horizon, but we need to turn the ground and atmosphere back on. It’s not blocked by trees or buildings, and it’s not blocked by the glow of the Sun. The exact first location that I thought it would be visible from, it is, so that’s nice. Often these things are a little bit tricky to line up properly. From around Japan and the Korean Peninsula, the whole sequence of alignments seems visible. The occultation of Callisto by Io is maybe even cooler than the Ganymede conjunctions. This is visible at about 4:30 in the morning local time, from the otherside of the planet, from the Far East. Since we looked at this view from different latitudes, I am confident in saying that this would be visible from everywhere along this latitude, from East Asia and Australia, but that is worth testing. Jumping to Central Australia, Jupiter is much higher off the horizon because we are a little closer to the equator, just 26 degrees south. That means Jupiter and its moons are going to be above the horizon for this entire process, for all of these conjunctions and alignments, these occultations of the moons by the other moons. They are visible from Australia as well.

That is an event that we have to look forward to coming up in 2092. We’ll see it on the 27th of March at 7:45/7:53 UTC. To actually see it, it looks to be on the morning of the 28th at about 4:30 from Australia or the Far East. Those seem to be the best locations to see it because from Ireland Jupiter is still unfortunately under the ground at 7:45. I hope that some of you get a chance to see this conjunction of the moons, of course it’s going to be decades in the future, so I hope at least this you enjoyed this description of what that conjunction is going to look like. If you have future events that you would like to see or hypothetical events that you would like to know if they are possible, please do leave a comment here, on YouTube or on Instagram, wherever you would prefer. Most importantly, I hope that you enjoyed this piece, if you did then please do like it. If you enjoy 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.