Caoimhín's Content

Today we are going to take a look at a variety of deep sky objects, starting with a group of galaxies. Stellarium, as I mentioned in the previous piece, it did recently have an update and that update included new listings for things and hopefully it may contain some new images as well. We’re looking first for Stephan’s Quintet, which is a group of galaxies. We’re seeing it in Pegasus, pretty much in the hooves of Pegasus. Just a bit after sunset the square of Pegasus is just down towards the east, kind of cut off at the bottom by the horizon.

This is a group of galaxies out beyond Pegasus in this direction, they’re just magnitude 13. Technically this is the kind of thing that would be visible through binoculars, but better through a telescope. Stephan’s Quintet is a group of five galaxies. They’re interacting galaxies, or at least two of the galaxies are definitely interacting, another two galaxies are in the same realm or region, all of those galaxies are going to merge together in the near future. The fifth galaxy is nearby but not as close as the others, and there is another galaxy kind of in the background. The fifth galaxy of the quintet is an elliptical galaxy, while the others are spiral. Stephan’s Quintet is labeled by Stellarium, different parts are labeled in different ways. There is an “E” for the fifth part of Stephan’s Quintet, and that does indicate that it is an elliptical galaxy. Unfortunately, that elliptical is the one getting highlighted when we click on interacting galaxy, normal galaxy and active galaxy. It seems like these other members of Stephan’s Quintet are not being included by Stellarium’s search function. Really, the four spiral galaxies are the main part of Stephan’s Quintet, they are the ones that are blending and merging together, the elliptical is simply another galaxy that’s quite nearby.

The image that we’re seeing in Stellarium is presumably an image from the Hubble Space Telescope, but this group of galaxies was imaged more recently, back in 2022, by the James Webb Space Telescope. The James Webb Space Telescope, of course, is a space telescope, it’s a telescope that’s floating out in space and it’s particularly sensitive in the infrared spectrum.

Our next target is the Great Nebula in Carina, which means it’s going to be under the horizon, the constellation Carina isn’t visible from the Northern Hemisphere. That’s not something that’s going to bother the James Webb Space Telescope. This is a nebula that we haven’t looked at particularly much in these pieces before because it is in the Southern Hemisphere, and I do tend to usually look at things in the Northern Hemisphere. Regardless, it is a HII region, so that means there’s ionized hydrogen in the nebula. There are plenty of dark clouds, and those are regions of star formation. We can also see red emission regions. The stars in the cloud are hot enough and close enough to the gas that they’re heating it up until it is glowing with a kind of soft pinkish color. As we know from a few articles ago when we spoke about the colors of stars, we know that this color is somewhere in the 3000-ish Kelvin range, a kind of a deep red color.

The Carina Nebula is another thing that the James Webb Space Telescope targeted, and the James Webb Space Telescope is particularly good for looking at these dark regions of gas. The dark regions where we don’t see any stars, they’re not holes in space where there are no stars, those are clouds of dark gas that are blocking the light of the stars behind them. They are mostly blocking visible light, a lot more infrared comes through these dark clouds, and that infrared is generated by young stars. This is one of the regions where the James Webb Space Telescope has been able to peer through these gas clouds in the infrared in a way that the Hubble Telescope, using the visual spectrum, couldn’t. This is a particularly interesting target, as I mentioned, it is an emission nebula. It’s not the only one. We’ve got plenty of emission nebulae up here in the Northern Hemisphere, the Carina Nebula just so happens to be one that the James Webb Space Telescope particularly targeted.

Looking back to the northern sky, we’re after moving a little close to morning time we’re going to come back until Orion is just above the horizon. Looking this far ahead into April, of course, we’re no longer seeing much of Orion. Thankfully, while we’re using software like Stellarium that allows us to zoom in on things, even if they’re occulted by the atmosphere we can see it clearly. Looking at Orion’s Sword, there’s another emission nebula, another HII region where a lot of stars get formed. Similarly up in Orion’s Belt, we have the Horsehead Nebula, the Flame Nebula, these are other HII regions where young stars are forming. We can’t see them, their light is blocked out by the clouds of gas, but their heat is still heating up the gas around them. Heat is infrared emission, emitted heat is infrared energy, it’s an infrared wavelength. Really, heat is light, when heat radiates,it is light that’s radiating, it’s just not light that we can see. There are other ways that heat can be transmitted, but not really through space, the only way that heat is coming through space is as infrared electromagnetic wavelengths and we can’t see that.

The Hubble Space Telescope couldn’t see that, but the James Webb Space Telescope of course could, can, and still is. The James Webb Space Telescope was only launched quite recently, just about four years ago and in that time it has made numerous discoveries, it’s imaged numerous interesting things, but those images haven’t made their way into Stellarium yet by the looks of it. I do think that image of Stephan’s Quintet and the Carina Nebula are older images that we got, possibly from Hubble, possibly from ground based telescopes as well. I know that the Carina Nebula in particular has been imaged by ground based telescopes in the Southern hemisphere. One of the reasons that I am bringing up the James Webb Space Telescope is because of the Moon. Recently the Artemis mission, the Artemis II crewed mission went around the back of the Moon, but beyond the Moon is where the James Webb Space Telescope always is.

The James Webb Space Telescope is in a special kind of orbit, it is in an Earth Lagrange Point, Lagrange 2. We’re going to head out to the solar system observer and we’re going to look down on the Earth-Sun system. From that vantage point we can see the Earth and the Sun at the same time. I’m also going to bring up the orbit of the Earth because the orbit of the Earth is related to what we’re interested in. Normally if something orbits closer to the Sun than the Earth, it’s going to orbit faster. For example, Venus, significantly closer to the Sun than the Earth, it’s going to orbit the Sun faster. Its year is shorter than ours, and then shorter again for Mercury. However, if you place something in just the right spot, a little bit closer to the Sun than the Earth, the Earth’s gravity will essentially stabilize it. Any object that is just inside the Earth’s orbit will orbit the Sun with the Earth.

That’s the first Lagrange point. The second Lagrange point is just out on the other side. Normally, things that are further from the Sun than the Earth, like Mars, orbit for slower. Mars is further from the Sun than the Earth, it orbits more slowly, its year is longer. For objects that are in just the right place, the Earth’s gravity pulls on them and essentially helps to pull them around the Sun at the same speed as the Earth. That’s where the James Webb Space Telescope is, it’s hanging out at a point, L2 or the second Lagrange point. That is a point that orbits the Sun with the Earth, even though it is further from the Sun than the Earth, and generally we would expect that to cause things to orbit slower.

There’s a couple of other Lagrange points. The third one is on the opposite side of the Sun. An object that is directly opposite the Earth from the Sun will be in a stable point where it orbits the Sun at the same speed as the Earth. That one isn’t very useful for us because it’s very difficult for us to communicate with objects that are on the opposite side of the Sun. It’s also difficult for us to communicate with objects that are on the far side of the Moon, but of course, the Moon is orbiting around us. The James Webb Space Telescope is fixed in that location opposite the Earth from the Sun. That does mean on a Full Moon, the James Webb Space Telescope is pretty much behind the Moon from the Earth, but as the Moon orbits the Earth, the James Webb Space Telescope stays exactly where it is.

There’s two other Lagrangian points, 4 and 5. You could say they are left or right, top or bottom, it doesn’t really matter in space. Either side of the Earth, there are two sort of kidney bean shaped regions where objects can orbit being influenced by the Earth’s gravity and the Sun’s gravity in such a way as that they orbit with the Earth, following the Earth or ahead of the Earth, orbiting with it. The three first Lagrangian points, 1, 2 and 3, they’re kind of small points, whereas L4 and L5 are more regions of space in which things can be stable. Jupiter in particular has a lot of asteroids at its Lagrange points, the Trojan asteroids at L4 and L5, I think it’s the Trojan and the Greek asteroids, one at L4, one at L5. Those are objects that are naturally trapped in the Lagrange point. The James Webb Space Telescope is of course, an artificial satellite that we have put out there in space.

That’s a couple of deep sky objects and a little bit about the James Webb Space Telescope, because it is quite far from the Earth in that stable location. It’s even further than the Artemis II astronauts just traveled, but of course, the James Webb Space Telescope isn’t crewed, there is nobody on the James Webb Space Telescope. Hopefully we’ll talk more about that and maybe about the Jupiter Lagrangian asteroids, the Trojan and Greek asteroids, in a future piece. Until then, 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.