Today we are going to take a look at a couple of the other things that are visible in the October sky, starting with a particular cluster of stars that is visible in the morning.
We looking at the morning of the 14th, with Mars in Cancer the Crab. Even though the constellation Cancer isn’t very visible, we can see the Sickle of Leo low to the east with Jupiter and the Twins of Gemini are just a bit higher to the southeast. In between is the region of the sky which must be Cancer, even if it’s difficult to see. If we zoom in a little bit closer, near the center of Cancer and just next to Mars, is a little parallelogram of stars with the Beehive Cluster in the center. That is a cluster that we took a look at in a recent piece. Just a couple of days ago, Mars was passing through this cluster, but it is out the other side of it now. Of course, Mars wasn’t really passing through the cluster, but in front of the cluster. These clusters of stars, even open clusters, they are certainly outside of our solar system. Moving down a little bit lower in the constellation of Cancer, there is another cluster of stars, but it is a little bit fainter, a little bit harder to see than the Beehive Cluster. It is commonly called the Golden-Eye Cluster.
Another name for this cluster is the Cobra Cluster or the King Cobra Cluster. We’ll need to zoom in a little bit more to start seeing the cluster, especially from the city. With a close enough look it is visible as a dense collection of stars. Zooming in a little bit more reveals some distinctly colorful stars in this cluster. This is another cluster of stars that is observable through binoculars, even coming down to a smaller binoculars there is a visible collection of stars in that region. A small telescope will give another potential view, for example a Meade ETX90 is a fairly small telescope, and it still resolves the prominent foreground stars and the fainter scattering of stars in the background. This is the King Cobra Cluster, and in 2031, the conjunction of the Moon and Venus is going to occur very close to that cluster, Down in the southern region of cancer is where the King Cobra Cluster is, and further up, more in the center of Cancer, that’s where we’re going to get the Beehive Cluster.
One of the interesting things about the King Cobra Cluster is that it is an open cluster of stars. This is a group of stars that all formed together, very similar to the Pleiades and, of course, the Beehive Cluster. These open clusters of stars are stars that all formed from the same nebula. The Pleiades is one of the most famous examples and certainly one of the easiest to see, we can see the distinct stars in that cluster even with our naked eye. Even in the city, we can usually see one or two, at least. The Pleiades are blue stars, and many of them are double stars, so Stellarium doesn’t give us the same kind of information about the individual stars involved. Many of them are double stars because they formed in a dense cluster, close enough together to begin orbiting each other. Even though they look like individual stars, it is actually multiple stars together. These stars, many of them are O, B and A class stars, they’re bright blue stars with very short lifespans. The Pleiades are only going to last for another few hundred thousand years, maybe another million years or so, which is very short for the lifespan of a star.
If we zoom back in on the Cobra Cluster, the stars are older. Some of them are orange and red stars. We’re still not getting the exact information, as again many are double stars. These stars are older, changing to G, K and M as they cool from blue to red. They did all form in the same cluster together, but they’ve been drifting through space for longer and have had time to go through that stellar evolution, and they are stars that are old enough and have been around for long enough to develop exoplanets. Stellarium can label them if we zoom in close enough. They appear to be around the edges, but based on the identifiers provided by Stellarium, starting with YBP, these are planetary systems that have been discovered in this open cluster. This is a young group of stars that have recently enough formed together, but we can tell by their colors that they’ve gone through a fair bit of stellar evolution, so they’re not as young as other open clusters that we’ve seen, and they are old enough to have developed planets around them.
Stars don’t have to be particularly old to develop planets around them. If we look towards Orion and zoom in on Orion’s Sword, which we know is a star forming region, Stellarium labels many objects as planetary systems, and some of them are, but these stars are truly young. This is the condition that stars are in, surrounded by a cloud of gas, before they become an open cluster, before the cloud of gas is blown away and they are revealed. In this nebula in particular, and I believe some of the other clusters and star forming regions that are in Orion, there have been protoplanetary systems discovered. That is a star with a disk of gas around it which will eventually become planets, a disk of gas and dust that eventually wraps up into planets. Objects far too small to be considered a planet, objects as small as our Moon or smaller, have been found going around these stars. Those planetesimals, those little planets, they’re very likely to collide together and form true planets, planets as large as the Earth or Jupiter or even bigger.
If we start zooming in towards the end of the Plough, we’re getting a couple of exoplanets being indicated in that direction, but if we zoom in more we’ll find the Whirlpool Galaxy. It doesn’t look like we’re being indicated any planets by Stellarium, which makes sense because the the putative planets, the tentatively proclaimed planets, are just that, still speculative and not widely confirmed. Technically we are outside of the constellation with the Plough, the Ursa Major constellation, into the constellation of the Hunting Dogs, Canes Venatici. Canes Venatici is one of the newer constellations that was added by a Jan Hevelius. Jan Hevelius added it in 1687, so that is fairly new compared to many of the other constellations in the sky. Focusing on the Whirlpool Galaxy, just west of the core at the star of an arm, there are a couple of bright spots. At least one of those spots is believed to be the accretion disk of a black hole, which may have a planet around it. Or not. There seems to be a ball of rock going around this black hole, but planets are objects that go around stars, that’s part of the definition, a body orbiting a star.
Technically, rogue planets flying through space don’t match the definition of planet, unless we change it to say “formed around a star”. In this case, the planet may have actually formed around the black hole, in the accretion disk. The same way that a star forming in a cloud of gas picks up dust and material around it, which can form planets, a black hole picks up a disk while material is falling in towards the center, much of it gets caught orbiting around the black hole’s singularity. That’s another region where planets can form, or blanets. Blanets with a B for black hole, if you want to be distinct, if you want to show the difference between a true planet, something orbiting a star directly, and a blanet, something orbiting a black hole instead. Of course, extrasolar, or even extragalactic rogue planets , that are flying through space not around any star, they certainly formed around something. Or did they?
Really there is only a fuzzy line between star and planet. Some brown dwarfs are right in between a gas planet like Jupiter and an actual star. They are just shy of being a star, but still much larger than what we would typically call a planet. Those can form on their own in the same kinds of star forming regions as normal stars. It’s not just real productive stars that form in nebulae, but almost stars, objects that don’t quite wrap up enough material to start fusion. They sometimes form as well and can end up flying through space on their own. They are really something different that doesn’t quite fit the definitions that we have. The definitions that we have, they’re based on what we know and we’re always learning more. That’s why the definition of dwarf planet was brought in, because we’d learned about so many dwarf planets. I’m sure that our current definition of planet, or blanet, or rogue planet, these things are going to change over time as well. The more we learn, the better we will be able to pin down what these things actually are.
You can take a look at many of these things, the Beehive Cluster and the King Cobra Cluster, or Golden-Eye Cluster in Cancer, the Sword of Orion and that star forming region, the Pleiades up in Taurus, they’re all visible down in the south and southeast over the next few mornings. The Whirlpool Galaxy is just off the handle of the Plough to the north. I hope you get a chance to see some of those things in the sky, and even if you can’t see the planets that are there, you now know that they’re there, even if they’re not visible to the eye. 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.
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