Caoimhín's Content

Today we are going to take a closer look at the planets Neptune and Uranus. We have taken a look at both planets before, each in their own separate post on this website, so if you want to take a look back at the pieces dedicated to Neptune and Uranus individually, they are still up although they are a few years back in the archive now. Unfortunately, it’s unlikely that much information has gone out of date.

We are going to look at both of these planets for July, as they both happen to be up. We need to push through towards morning time, and we will come a little bit further back in the month to get the Moon out of the way and to keep things dark. We want to have Saturn above the horizon, because Neptune is just next to Saturn, so if Saturn is above the horizon, Neptune is as well. This occurs reasonably early in the evening, but I also want to get the Pleiades above the horizon. The Pleiades or the Seven Sister can be difficult to spot from the city, but I know that they’re out near Venus somewhere. Venus is still close to the Hyades and Aldebaran, the Head of the Bull Taurus, and the Pleiades are just at the back of that constellation. Once we know where to look, the Pleiades are just about visible, they seem to be one faint star rather than the collection we’d expect, especially seeing them so close to sunrise and low in the sky. Uranus is just a little south of the Pleiades, a little lower in the sky. Looking at the sky for 3:30 in the morning on the 10th, looking a little into the past, both are above the horizon. We can spot Uranus once we start zooming in a little bit closer near the Pleiades, and they do form a nice sort of tableau with Venus just below them to the east. If we move through a couple of days, we can see Venus and Uranus and the Pleiades getting even closer together, as they were even earlier in the month, they’re now moving further and further apart as we push into the future.

If we zoom in and take a closer look specifically at Uranus, Uranus is listed at magnitude 5.8, reduced to 6.62. Around magnitude 6 or 7 is the limit of human vision. In a perfectly dark sky, technically, you should be able to spot Uranus with the naked eye, but recognizing it as a planet, seeing it as something different to the background stars, that’s very difficult. Even over time it is tough due to Uranus’s very long orbital period. Its year is very long, 84 Earth years is how long it takes Uranus to get around the Sun once. As such, it does take a long time for Uranus to move relative to the background stars, which makes it harder to recognize as a planet. Taking a closer look at the current time, we’re looking pretty much at one of the poles of Uranus. I’m not sure if it’s the north pole or the south pole, because of course it’s not pointing really north or south, it’s almost pointing directly at the Earth. Uranus isn’t exactly on its side, it’s tilted either about 82 or 98 degrees depending on which pole you consider north. Assuming the closest pole to pointing north is the north pole, then Uranus is close to northern summer, with that pole almost pointing at the Earth. This lets us see the rings of Uranus there from above, which is a great way to see them. They are very thin rings and very difficult to see. You wouldn’t expect to see the rings through any normal telescope that you could easily set up. Much larger telescopes can see Uranus’s rings and of course, such as the Hubble space telescope.

Uranus was visited briefly back in the mid 1980s by the Voyager 2 probe. Voyager 2 was sent to swing past the giant planets and then head out of the solar system. It swung past Uranus in 1986, and then around Neptune in 1989. This was only a flyby of Uranus, but it discovered some of the moons and discovered more of the rings. Now that we have space telescopes, we can look at Uranus from the Earth in some amount of detail, but it’s still not quite the same as actually going there and taking a closer look. Uranus and Neptune have had far fewer visitors than Saturn and Jupiter. Jupiter has had 8 probes visit it, while Saturn has had 4, both including voyager two. Saturn has even had one lander, the Huygens probe, which landed on Saturn’s largest moon Titan. We don’t have the same amount of information when it comes to Uranus and Neptune. While recording the attached video, I noticed that albedo was listed as a feature of Neptune. I wasn’t seeing albedo for the moons in the last video, but I did see the albedo this time. This is, more or less, the reflectiveness of a surface, how much light is getting bounced back by the surface. I’m not seeing albedo for Uranus however, so it’s interesting what gets listed for what different things.

Turning to Neptune, much further out again, it is around magnitude 8, past the possibility of being visible to the naked eye. Its year is 165 Earth years, it takes an incredible long time for Neptune to get around the Sun. This means of course that its motion against the background stars is even harder to detect. Triton, Neptune’s largest moon, has an atmosphere, albeit a very thin, hazy atmosphere. It’s not as thick and as obscuring as the atmosphere that we see on Titan, but it is atmosphere, and moons with an atmosphere are rare. We’ve only found two of them in our solar system, out of the hundreds and hundreds of moons that our solar system has, Saturn alone has about 200 moons. There are only two that are big enough to retain an atmosphere, Triton and Titan, so if there was any other moon in the solar system we might want to land, it should be Triton. Unfortunately, with Neptune being so far from the Sun, it is that little bit harder to get there and study it. Any probe sent to Neptune would take much longer to arrive. We can see Neptune’s very faint rings in close up, but again these are only visible through very large telescopes, and Neptune’s moons are also only visible through large telescopes.

Triton is just about visible with the upper end of commercial telescopes, as it is quite bright and reflective. We will take a look at Neptune through a simulated telescope and we’ll go right up to a massive telescope, there’s no point in using anything small here. Even quite large telescope can struggle to resolve Triton. Using the biggest telescope that Stellarium simulates, a Meade LX 200 with 16 inches of aperture, we still need some good eyepieces and Barlow lenses to see it. The eyepieces reduce our field of view, but increase the amount of magnification we’re getting on what’s left. With all that, we can just about see Neptune and Triton as separate things, only with this is a massive telescope. With anything a bit closer to a normal, more affordable telescope without these extra lenses to help, it’s almost impossible. Even with an 8 inch aperture telescope, you might spot Triton, it is a different color, but almost certainly only when it appears at its greatest extension from Neptune. If we move through a couple of days, you might just about see it moving around Neptune, but that’s incredibly difficult to pull off. Even though we can now study Neptune and Uranus through things like the Hubble Space Telescope, the best information that we have about both of those planets is still from a flyby in the 1980s.

Looking at the sky with no light pollution, Stellarium should label Uranus. Neptune is still not labeled because Stellarium knows that it’s definitely not visible to the naked eye, Stellarium does register Uranus as being visible to the naked eye, even though I don’t think I can see it. The Voyager 2 probe, in the 1980s, took a closer look at both Uranus and Neptune, taking the images where we get our recognition of their colours. Looking at these planets through a telescope, they might look a little bluish, but details will be obscured. The richer blue colour and the details of the clouds, white bands and the dark blue spot on Neptune, most of that comes from Voyager and later the Hubble Space Telescope. Stellarium shows Neptune as a quite blue, greeny-blue color. When we take a look at Uranus, it should look a little bit paler. In reality, they’re almost equally pale, and that’s something that we did figure out recently using the data taken from the Voyager 2 probe in the 1980s. Taking a closer look at Uranus, it has more of an almost sickly color, not quite as blue, certainly not quite as cerulean as the way people imagine Neptune to be. However, it turns out that that imagination, that presentation, it was just because of how the images were analyzed. The images that were taken by Voyager 2 had to be turned into something we could actually see. It had to compress its images down into a data stream and then send it back to the Earth, where it was turned back into an image. We now know, by taking a closer analysis of those images, that Neptune and Uranus are, in fact, almost the same color. We mostly know that still from looking at information from that probe in the 1980s, even though the Hubble Space Telescope can look at Uranus and can look at Neptune, that’s not really what the Hubble Space Telescope was built for, and it’s not what gets given priority from the Hubble Space Telescope. The Hubble Space Telescope is very often used to try and discover new things, and looking at these planets from the Earth, it’s hard to discover new things simply because they’re so far away and it’s so hard to see detail.

Hopefully we will get a new mission to Uranus and Neptune in the near future, there has been some discussion recently about a mission specifically to look at the ice giants. We don’t know as much about the ice giants as we do about the gas giants, about Saturn and Jupiter. As we discover more planets in other solar systems, understanding how these different kinds of planets work is useful, as it gives us a better idea of how they form, and what they can tell us about the conditions of the solar system they are it. Not just our own solar system, but other solar systems as well. Looking at these things forming in younger solar systems may help us to get a better idea of the real composition of Uranus and Neptune. A better idea of the moons around these planets and their compositions will give us a fuller picture of how things in our solar system are composed, which in turn gives us a better picture as to how our solar system was composed when it was still forming.

This is of course just a little bit about Uranus and Neptune, because we don’t know as much about them. They’re these kind of distant, edge of the solar system objects, that we’re aware of but don’t really see, and that we don’t really see in research as often. Saturn and Jupiter, those nearby gas giants, they get the bulk of the missions, and it is easier and cheaper to send those missions. I feel that, maybe, we’re getting to a point of diminishing returns. Obviously, we want to learn more about Saturn and Jupiter, but we will get more new information, more novel information, quicker, by sending probes to Uranus and Neptune. Currently, there is so much less that we know about them, that we’ll find out new things without having to try as hard, if we can just get there and take a slightly closer look.

I hope you did enjoy this piece, this exploration of Uranus and Neptune. If you did enjoy this piece then please do like it. If you enjoy this kind of content, then you can subscribe to this website or my YouTube channel in order to see more. Hopefully, I’ll see you back here next time.