Caoimhín's Content

Today we are going to take a quick look yet again at the Moon and talk a little bit more about the Artemis II mission to the Moon, the first crewed mission to the Moon in decades.

To take a look at the Moon, we’re going to have to wait for it to come up. Of course, we had our Full Moon on the 1st of April, so it’s going to take a little bit longer for the Moon to come up. Starting with sunset on the 7th, we have to wait until we are through to the 8th of April. Of course, the Artemis mission must be near the Moon and for us here in Ireland, the Moon isn’t going to come up until pretty close to 5 o’clock. We’re going to look at just 5:30 on the 8th of April. That’s when the Moon is going to be up and visible for us. The Moon won’t quite be at last quarter. Last quarter is the Half Moon that we get after the Full Moon and on the 8th the Moon is not quite there yet, we need to go a little bit further to get to a half. By then, around the 10th or the 11th, the Artemis II mission will be back home, at least if everything goes according to plan. The morning of the 8th is when we’re next going to see the Moon from here in Ireland. Just before the time of posting, the Artemis mission had just gone behind the Moon, by the time we’re through to about 5:30, I would expect the Artemis craft to have come out from behind the Moon.

The far side of the Moon is often called the dark side of the Moon, and we’re going to go quickly to the Sun in order to take a look at that side of the Moon. We call it the dark side, but the far side of the Moon and the near side of the Moon both receive just as much sunlight. If we simplify things and say that the Moon takes a month to go around the Earth, then for two weeks of that time one side of the Moon is in darkness, and for two weeks of that time the same side of the Moon is in the light. From the Sun, we need to find the Earth, and the Moon can’t be far away. The Moon and the Earth are far too close together to appear particularly distant from each other from the Sun. We are still looking at the 8th, but we are now looking at 4:30 in the morning because we’re no longer paying attention to summertime, which adds an hour to the time that we use here in Ireland. Our local time for summer is UTC+1, and really we want just UTC. From the Sun, we’re seeing a little bit of what we would call the dark side of the Moon and a little bit of what we would call the light side of the Moon, simply because the Moon isn’t completely new from the Sun. If the Moon was completely new from the Sun, then we would only be seeing the dark side of the Moon, and we can move ahead a few days to see that.

We can tell the dark side of the Moon, because it has these two very small mare or dark regions, close to opposite sides of the Moon. There are also a few small dark regions that are associated with craters, but the vast majority of the dark side of the Moon is incredibly pale. It doesn’t have those big seas or mare that we see on the light side of the Moon. Moving back in time to turn the Moon around reveals the light side of the Moon covered in dark seas and plains with only a small region that’s completely white. The dark side of the Moon is brighter, it at least reflects a little bit more light so it looks brighter. The dark side of the Moon looks brighter to the eye and it will to those very few astronauts who’ve gotten to go and see it. Of course, it is only a small number of astronauts who have gone around the back, the far side of the Moon. When a spacecraft is in that position, there is a comms blackout or communication blackout. The dark side of the Moon is dark in terms of our knowledge, we don’t know as much about it and it causes a comms blackout, it blocks your view of the Earth. If you are a spacecraft orbiting the Moon and you’re on the far side of it, you can’t talk to the Earth, and that is what happened with the Artemis II mission just a couple of hours ago.

We’re going to return to the Earth and we’re going to see if we can see where the Artemis probe is or where it would be, where it should be at this time. So we’re back to 5:30 local time, 4:30 really according to UTC. NASA knows, and various people know, where the Artemis spacecraft is. Unfortunately, spacecraft are not something that Stellarium is usually aware of. Stellarium tracks satellites in orbit, but the Artemis mission, or more specifically the Orion capsule, isn’t something it tracks. There are loads of things to do with Orion in Stellarium’s database, but none of them are the Orion capsule, which is the spacecraft carrying the astronauts on this Artemis II mission. Artemis is really the name of the mission and Orion is the name of the capsule.

Luckily, even though Stellarium doesn’t know, people do know, it is tracked, we do know where the Artemis II mission is and you can find out for yourself where it is and in the sky. One way to do this is to use the Jet Propulsion Laboratory’s Horizons System. If you go to the JPL website, it’s under the Horizon system, and it’s the app tab. Here is a link: https://ssd.jpl.nasa.gov/horizons/app.html#/ . This is a system that allows you to figure out where something is going to be in the sky and it does track various spacecraft.

Firstly, the Ephemeris Type needs to be set to observer table, and this is the default so it should be like that anyway. You can look up the Artemis II, with 2 in Roman numerals. The default observer location assumes the center of the Earth which is for mathematical reasons, for calculating various orbits, it’s a good default location to go with, but you can put in your own location, you can add in where you are on Earth. We’ll go with 8 degrees west and 52 degrees north, which is at least near Cork City. The full grid square of that latitude and longitude does encompass a reasonably large space, but the exact coordinate ( 8 degrees, zero seconds and minutes, the same for longitude) might be a little bit off. Then a time range must be selected. The Orion capsule, the Artemis space mission, is only tracked for certain times. we need to make sure that the start time and the stop time line up with the minimum and maximum. The given min and max are a little over precise to me, I don’t need to know within millisecond accuracy where everything is, we can simply select April 2nd at 02:00 until April 10th at 23:30, 11:30pm. Simplifying them like this makes things easier for our increments as well. An increment will decide how long between data points, and because this whole mission is occurring over the course of only a few days, we need a short increment. If we were to calculate where it is in the sky once a day, we’d get 9 very spread out positions. An increment of 30 minutes is perfect, as we’re looking at 04:30.

Lastly, you select what details you need, and there are a lot of these things that we don’t need. For example how bright things are going to be, where the Sun is. A lot of this kind of information would be more to do with if you were looking for an asteroid or a comet. Really all we need is the astrometric RA and DEC. The apparent RA and DEC are corrected for the atmosphere because the atmosphere will bend things, so when things are lower in the atmosphere they will get refracted and appear slightly differently. It’s just like the sunrise appearing to occur a little bit before it technically does because of the light being bent. We can ignore this because Stellarium will.

All of that will generate a big list for us. There’s loads of details, loads of, loads of hints on how to read the list, but really what we’re looking for is just the position at a given time. It gives you the time and the RA and the DEC. It will cover almost the entire length of the mission, we need to go to the time and the date that we’re looking at. I went with the whole span of the mission just to show that you can get this information, and you can find whatever time, in UTC, suits you. We’re really looking at 4:30 UTC, so here is a small section of the ephemeris for that time:

Date        Time      RA          DEC
2026-Apr-08 03:30  m  16 39 25.57 -29 14 14.8
2026-Apr-08 04:00 Am  16 39 15.17 -29 16 11.0
2026-Apr-08 04:30 At  16 39 04.67 -29 17 48.8
2026-Apr-08 05:00 Nm  16 38 54.47 -29 19 08.3
2026-Apr-08 05:30 Cm  16 38 44.95 -29 20 09.6
2026-Apr-08 06:00 *m  16 38 36.50 -29 20 53.3
2026-Apr-08 06:30 *m  16 38 29.50 -29 21 20.3

o4:30 is the coordinate that we need. You can copy and paste the RA and DEC into the position search window of Stellarium, but do each separately. We’re looking for a specific position rather than a specific object or a known thing. We know what we’re looking for, we’re looking for the Artemis II mission, the Orion capsule. Stellarium doesn’t need to know that, Stellarium only needs to know where we’re looking. With the right coordinates, a small target or reticle appears pointing at the right location. For us, this a location just next to the Moon, slightly south and west of the Moon, which is what we would expect for the return journey. We can now put a little marker there. Multiple markers can be used to track the position over time, if you go through a few data points.

For this to work est, we need to pause time, otherwise things will drift away from us. We want to be looking at exactly 5:30 (local time) because this process is very sensitive to the time of your observation as well as the location of your observation. Even with all the care, we’re going to be almost a minute off, but this should be just about the location of the Artemis II mission from the Earth at this time when it first becomes visible to us, and you can do this for anywhere. These are based on the coordinates for Cork City, but you can shift these coordinates to be wherever you are.

In the above data set, we have our date and our time over on the left hand column and over on the two rightmost columns we’ve got RA and then DEC. In between, the column of letters, we’ve got whether or not the Moon is up and whether or not we’re in astronomical, nautical or civil twilight. The little letter codes are to do with the Moon rising, the Moon being up and the Moon setting. This is a little bit of extra information to help make sure that you’re looking at the right time. It’s showing 04:30 as “At” which means the Moon being up and it’s astronomical twilight. Indeed, if zoom back out from the Moon, we might notice that the sky isn’t completely dark. There is a little bit of glow coming into the sky from the Sun and that’s our astronomical twilight.

So that’s where the Artemis II mission is going to be when we next get a chance to see it from here in Ireland, using the JPL Horizon System to get the ephemeris. It’s only a little bit of ephemeris that we need, only the RA and DEC, it’ll tell you when you need to look in the sky, you just have to correct for UTC, you have to correct for your local time, whatever it may be. So I hope, even if you don’t get to see the Orion capsule in space, you would need a pretty good telescope to see it, we now know where it’s going to be just starting its return mission to the Earth after coming back out from behind the Moon. That’s where it’s going to be at this time when we next get to see it here in Ireland. I hope you get a chance to see it or at least find out where it would be no matter where you are. I hope that you enjoyed this piece. If you did, 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.