Caoimhín's Content

Today we are going to take a look at some of the larger asteroids that are in the asteroid belt. We’re starting with the sky during the day for the 1st of May. With the atmosphere turned off, we can see planets around the Sun, particularly Mercury, Mars and Saturn on the western side of the Sun. Saturn is coming back into view in the morning for us as we come through May, but if we turn to the east for sunrise, it’s not quite visible for us just yet. If we bring back the atmosphere, those planets are blocked from view. Thanks to the conjunctions that recently happened with these planets next to the Sun, I’ve been looking in that direction. While taking a look that way, there are a couple of comets mentioned in a previous post, and Neptune is out there as well.

Also out there are Vesta and Pallas, two of the larger asteroids in the asteroid belt. Not the largest, but definitely quite close. In fact, one could argue that Vesta is the largest asteroid in the asteroid belt if Ceres is classified as a dwarf planet, but Ceres is normally double classified as both a dwarf planet and an asteroid. Those minor planets or asteroids are further from the Sun at sunrise than Saturn or Neptune, which means they’re going to be a little bit easier to see. They’re going to get easier and easier as we push further and further into the year. Pallas is above the horizon before sunrise, Vesta just below. Taking a quick closer look at Pallas, it is the one that is up currently, technically above the horizon, and we will see a sort of round shape. Pallas isn’t considered a dwarf planet and one of the reasons it’s not considered a dwarf planet is because it isn’t really under hydrostatic equilibrium, it hasn’t really made itself round, it is lumpier and bumpier than than a real sphere. It’s quite faint at just 10th magnitude and that’s without the atmosphere. With the atmosphere turned on, with it being so low in the sky, it’s reduced to just 12th magnitude, which makes Pallas a tough target at the moment, definitely in the glow of sunrise,

Pallas won’t be up above the horizon when the sky is truly dark just yet, not for another little while. Pallas is orbiting the Sun, its period is just about four Earth years and it is about three times further from the Sun than we are. So it is orbiting the Sun pretty slowly, and that means that its position in the sky is mostly going to change because of our orbit around the Sun, very similar to Saturn and Jupiter and those more distant planets. Vesta is currently lower in the sky, lower than Neptune. The Sun needs to be very nearly above the horizon for Vesta to be up. Vesta is further from the Sun then Pallas, but Pallas is higher above the ecliptic. It looks like Vesta is pretty close to the ecliptic currently, lining up with Saturn and the other planets. That’s putting it even lower to the horizon. The asteroids in the asteroid belt, many of them vary pretty far from the ecliptic. Compared to the planets, some of the asteroids can be much more highly inclined.

Vesta is officially (4)Vesta, because it was the fourth asteroid to be discovered and it’s at magnitude 7.8. It’s so low in the sky and so close to sunrise, it’s getting reduced to 10th magnitude by the atmosphere, but 7.8 is significantly brighter than Pallas and it is within the realm of what you can see with a binoculars. Of course, Vesta is quite small, so it will only appear as a small dot through most binoculars. Vesta looks pretty round in Stellarium, but it’s also only considered an asteroid and not a dwarf planet. That’s two and four, Pallas is (2)Pallas. These are two of the largest asteroids, but the largest asteroid is the dwarf planet Ceres. Ceres, isn’t in a great position for us to see at the moment, it’s up at sunset, but not very high. It’s just setting with the Sun, a little bit further from the horizon than the Sun, but not far enough to be above the horizon in darkness. A better view is possible with no trees or buildings in the way. If you are at the coast, you will be able to watch things get closer to the horizon then we’re able to see them with trees in the way.

As the Sun sets, Ceres is still above the horizon, but not really in a position where we’re going to be able to see it. It is listed here as a dwarf planet, but it is still considered the first asteroid, (1)Ceres. It’s currently at magnitude 8.84, which is faint for Ceres. Ceres is practically on the far side of the Sun from us, it’s about as far from us as it can get. It’s just under three times as far from the Sun as we are, but it’s an extra AU away from us due being almost on the far side of the Sun. Taking a closer look at Ceres, which is certainly round, it looks very similar to a small planet or the moons of many planets. Ceres is under hydrostatic equilibrium, big enough and round enough to be a dwarf planet. It isn’t in control of its orbit, Ceres shares its space with various other asteroids, but Ceres is the bulk of the asteroid belt. Ceres is so much larger than the other asteroids, even the other large asteroids like Vesta and Pallas. Ceres is so much larger that it makes up the bulk of the asteroid belt on its own, almost half of the total mass. There are other asteroids out in the direction of Ceres, such as (6)Hebe, which is not a particularly big one. Itsjust 10th magnitude and smaller than Pallas and Vesta. It’s not the sixth largest asteroid, but it was the sixth to be discovered. There are lists in Stellarium, that can be used to find different things in the sky, including a list of asteroids. They are ordered by their first number, but of course this means that 3 is followed by 311999, followed by 3200, rather than 4. As such, they’re not in order of discovery or anything like that.

Juno is the third asteroid, (3)Juno. We’ve already looked now at 1, 2 and 4, so this is 3. Juno is also about 10th magnitude, and it is up much closer to the middle of the night. It also looks like a little ball, but the ball shape of these asteroids isn’t quite the same as the spherical shape that forms when a body is under hydrostatic equilibrium. There’s a good chance that the material inside these asteroids haven’t been squeezed into one solid mass. That makes these asteroids a little bit more like balls of aggregate rather than solid balls of rock, and that is part of what shows that they are not under hydrostatic equilibrium. The fact that they are spherical or close to spherical or appear spherical doesn’t necessarily mean that they are under hydrostatic equilibrium. Normally people describe hydrostatic equilibrium as being big enough and heavy enough to become round, to become a ball under its own gravity. However, even a looser association of material will come together in a sort of a spherical way, but they can be lumpier and bumpier. Asteroids aren’t very well understood because it’s very difficult for us to get to them, there have been probes that have visited asteroids and flown past asteroids, but there is still a lot that we don’t know about them, even quite big and famous ones like Juno, like Vesta, like Ceres and Pallas.

Those are a few of the larger asteroids in our solar system, including the asteroid that’s big enough to be considered a dwarf planet, Ceres. Pallas and Vesta happen to be, quite close to the sunrise at the moment, quite near to the planets Saturn, Mercury, Mars and Neptune that are just on the west side of the Sun. They’ll be coming back into view over the near future the same way that Saturn’s coming into view as we get into next month. I hope you enjoyed this quick look at those objects. They’re not the most famous objects, they’re not quite as famous as the planets, but they are out there in our solar system as well. 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.