Caoimhín's Content

This video is similar to the recent video on Mercury, we will be taking a closer look at some planets and the view from them. Unlike that video, this one won’t focus on just one planet or its motion through the sky. Over two videos we’re going to look at the gas giants, Jupiter and Saturn. As well as taking a closer look at both of them, we’re going to take a look at the sky from Saturn, with the next video taking the view from Jupiter and a look at the system of moons orbiting the planets.

We are going to begin by looking at Saturn as it is in our sky at the moment. Saturn is appearing quite low in the sky as the Sun sets. By the time it has gotten truly dark, Saturn has dropped very close to the horizon. If you are using a telescope, the closer you are to the horizon, the more atmosphere you’re looking through, so your view of Saturn with a telescope will be blurrier and shakier. This is besides the fact that trees and buildings can block out objects that are low to the horizon making them completely invisible, especially if you are observing from a city or built up area.

Given that Saturn is about to disappear behind the Sun, and it won’t pop up again for a while when we’ll see it in the morning, I want to take a closer look at Saturn before that point. even with quite little magnification, the brightest moon of Saturn, Titan, becomes visible very quickly. It appears as an orange dot quite easily, and it’s orange colour helps it to stand out. The orange colour is caused by the same thing that makes Titan so bright and visible, its atmosphere. The atmosphere of Titan is composed of gasses like methane, ethane and other organic molecules. Here, when I say organic I don’t mean “coming from things that are alive”, and certainly not “produced without pesticides and chemical fertilizers”. In chemistry, organic really just means based on carbon, and these carbon based molecules give the atmosphere of Titan its distinctive orange colour. This thick atmosphere also reflects plenty of light, causing Titan to appear bright for much the same reason as Venus. Titan is cold, about -100 degrees Celsius, which keeps these compounds liquid most of the time, Titan even has the rivers and lakes of liquid methane and ethane, some could even be called seas.

Taking a closer look at Saturn, especially with the moons labelled with their names, we can see that although Titan is the biggest, it isn’t the furthest from Saturn and is far from the only moon. In close up we can see the rings of Saturn, there is more than one, with gaps between them. You’ll also see bands of colour on the planet, much fainter than the bands of colour on Jupiter, but still visible in detailed images. We can also see a good number small moons here close to Saturn, but this is only a small fraction of them. Saturn has many more small moons that orbit far from the planet, with over a hundred recorded in total. However, a lot of these moons, especially the ones that are both small and orbit the planet distantly, aren’t going to be visible from here on Earth. We can see the larger ones reasonably easily, and if you zoom in close to Saturn, you may see some of the smaller ones that orbit near to the planet, which led to those moons being discovered, and named, first. Saturn’s moons were generally named after the Titans from Ancient Greek and Roman mythology, but there are only so many of them. As new moons were discovered, the names were opened up to other mythologies, like Celtic and Norse. However, these names still had to come from huge beings, giants in these other stories. This includes the moon Fionn, from Fionn MacCumhail, one of the giants form Irish mythology. Celtic mythology covers more than just Ireland, and some of Saturn’s moons are named for other Celtic mythologies, such as Welsh and Breton.

Moving on to Jupiter, this planet is much further East than Saturn and will stay in the sky for longer each night, as well as staying visible in the evening for many more nights to come. Even with quite a small telescope, there’s a good chance you’ll see all four of the largest moons of Jupiter, Io, Europa, Calisto and Ganymede. In the first close up in the above video, Io and Europa are practically in line with one another which makes it look more like three moons, and of course if a moon is behind, or directly in front of, Jupiter then it will also be hidden from view. These moons orbit reasonably quickly, so even within a couple of days the moons will move and you can see them stretched out on either side. These moons are known as the Galilean Moons after Galileo Galilei as he was the first person to observe them and see that they were moons orbiting Jupiter. Galileo was working with one of the first telescope ever made, the first telescope used to look into space, rather than check for incoming or distant ships, a real telescope and not just a spyglass. Galileo didn’t invent the telescope, it was a patented if not invented by a Dutch man named Hans Lipperhey. Telescopes have gotten much better, allowing us to look even closer at Jupiter.

Often, you can see Jupiter’s Great Red Spot when you take a closer look, but this isn’t guaranteed. Jupiter rotates and as it does we see different sides of the planet. Luckily, Jupiter rotates very quickly, every 10 hours compared to our 24. This means, that if you don’t see the Great Red Spot one night, there is a very good chance that you’ll see it if you go back out at the same time the next night. Furthermore, if Jupiter is in the sky for at least 5 hours, then you can watch it turn from one side to the other, bringing the Great Red spot into view if it wasn’t already. In fact, at a time of year where the night is at least 10 hours in your location, if Jupiter is up for the whole night than you can watch it turn the whole way around, its entire day in one of our nights.

The “meat” of this video so to speak, is the view of the sky from Saturn. Stellarium offers the handy feature of looking at the sky from other locations in the solar system, including locations called “Observers”, such as “Earth Observer” and “Jupiter Observer”. These are positions where you are looking down at the planet towards its poles, giving great views of the moons. That’s a bit of foreshadowing for the next video, you get some extra information if you read these posts as well as watch the videos, but of course either can be enjoyed alone.

Right now, we’re going directly to Saturn, into its upper atmosphere. There may be no surface for us to stand on at all, and if there is it’s under hundreds of kilometers of gas, we wouldn’t be able to see the stars at all. So we’re going to float in the upper atmosphere, or even a little above it, starting close to the equator of Saturn. The view from the equator presents the ring as a thin arc across the sky. Saturn’s ring extends hundreds of kilometers out from Saturn, it is very wide, but not very thick. It is a couple of kilometers thick or deep, which is a fair distance, but it’s nothing compared to how wide they look, which makes it appear quite thin if you are directly underneath it.

We’re still seeing the same constellations from Saturn as we see form the Earth. In the video we can see Orion and Canis Major with the bright star Sirius, quite close to the arc of the ring. We’ll look at Saturn’s stars in more detail in a future video dedicated to Saturn.

Looking at Saturn’s sky in the middle of the night makes part of the ring seem to disappear. This is due to Saturn’s shadow falling on the ring, which also causes a lot of eclipses of Saturn’s moons. Many of these moons are closer to Saturn than our Moon is to us, which also causes them to orbit much quicker. Even from night to night the arrangement of moons changes drastically. Some of Saturn’s smaller moons, like Pan, are so close to the planet that they become as easy to see as much larger moons, like Enceladus, which is a little bit further from the atmosphere of the planet.

If we change location, up to the middle of Saturn’s northern latitudes, the ring will appear much thicker, as we are looking down on its width from the north. In the middle of the night you might be able to see a little bit of fuzziness in the sky where the ring is hidden by Saturn’s shadow, but still catching a little light from the moons and illuminated parts of the planet. Saturn’s ring is only visible thanks to light that it reflects, just like our Moon and the other planets. Speaking of other planets, Jupiter is visible in Saturn’s sky, but we aren’t seeing any of the other planets. Stellarium gives every planet a blue daytime sky, but if you are just above Saturn’s atmosphere there would be no gas around you to scatter the Sun’s light, leaving you with a view of the sky similar to what you would see from the surface of our Moon or an asteroid. This would let you see the Planets next to the Sun during the day, which would probably require protective eye coverings.

With this view we can absolutely see Mercury, Venus, Earth and Mars, though Mars is a little faint, as is Mercury. From the perspective of Saturn all of these planets would have to say quite close to the Sun in the sky, only visible at sunset and sunrise, eve Jupiter will behave a in a similar way, as it is inside the orbit of Saturn, though it is much further from the Sun and closer to Saturn than the rocky inner planets, and so it would be visible for much longer. Just as Mercury and Venus appear to move retrograde in our sky, as their orbit brings them around behind or in front of the Sun, even the Earth will appear to move this way from Saturn. This is generally true, if we were on Neptune then all the other planets would shift from one side of the Sun to the other over the course of the year, never appearing in the middle of the night sky at midnight, as distant planets do for the Earth.

We will come back to Saturn, in it’s own video in the future, but also at the end of the next video as we look at its collection of moons along with Jupiter’s. We are of course going to look at the sky from Jupiter next time, but without the ring we’ll be able to deal with some other things in that video as well. As always, there will be a post here about the video, so I hope you’ll come back to read it.