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In this video, we finally take a closer look at Jupiter. Jupiter has been incredibly prominent in our sky for months now, especially standing out as the brightest object in the sky at sunset the past couple of months, appearing as the very first object when the sky begins to darken. Jupiter is much further from the Sun and so has a much longer orbit, taking about 12 Earth years to finish one Jovian year. Due to this, it takes a while for Jupiter to noticeably move in front of the stars, but just like everything in our sky it will appear to move due to our orbit around the Sun, changing position just like the stars over shorter timescales. Just like any star, Jupiter first begins to appear in the morning sky, rising earlier and earlier until it is with us all night long. Then it begins to set earlier and earlier, as the Earths orbit continues, eventually putting us on the far side of the Sun from the earth. We are fast approaching that moment, and soon Jupiter will disappear from our evening sky. Luckily it won’t be long before it reappears in the morning, just about a month, but we’re going to take a closer look at it here before it does.

On the night of the April 8th solar eclipse visible in the United states, Jupiter is still appearing a good bit above the western horizon, but it is already quite low by the time that the sky becomes dark. On the 10th, the Waxing Crescent Moon will be right next to Jupiter as they set together in the evening. I don’t mention it in this video, but the comet 12P/Pons-Brooks is still pretty close to Jupiter in the sky on those dates, but the glow of sunset will obscure it.

Taking a closer look at Jupiter with even a small telescope will almost always show you a couple of moons. Depending on the night you might see anywhere form 1 to 4 moons, usually 2 or 3. It isn’t uncommon to see all four of Jupiter’s largest moons arranged in a line either side of the massive planet. Jupiter’s moons orbit it quite quickly, faster than our Moon orbits us, so they will be in a different position every night you look at them. On nights when Jupiter is up for a long stretch of time, you can watch the moons change position over the course of just a few hours. At this time of the year, Jupiter won’t be in our sky for that long, but you can still see differences from night to night, and it is still up long enough to take a quick closer look.

On the evening of the 8th, just as Jupiter began to be visible, the Great Red Spot was visible, almost facing towards the Earth. By the time the sky darkened enough to take a clear closer look, the Great Red Spot was moving off towards the far side of the planet. On the 9th at the same time, it on the far side of the planet at the same time, and once we get to the 10th the Great Red Spot is back to pointing right at the Earth. Jupiter’s quick rotation means that the Great Red Spot is visible almost every second night, and may be visible at certain times of the night, but out of view at another time the very same night.

Jupiter is one of the gas giants and a large portion of Jupiter is gas, including all of the portions we can see. Jupiter has a thick blanket of hydrogen, helium and other gases, full of storms and clouds. The entire planet is mostly made of these elements, which we normally consider as gases. However, even here on Earth we can create liquid forms of these gases, by cooling them down to incredibly low temperatures. High pressure will also cause these gases to become liquid or even something like a solid, but it takes a lot of pressure if temperatures aren’t low. Jupiter’s atmosphere is able to provide such pressure, even though it isn’t particularly cold. Being a massive planet, it retains a lot of heat from when it formed, the same way that Earth is big enough to have a hot liquid mantle and outer core, while Mars is small enough that it has cooled more and mostly solidified. Jupiter also receives some heat from decaying radioactive elements and possibly some other unknown processes as well. The pressure from hundreds and hundreds of kilometers of atmosphere is able to convert hydrogen and helium from their gaseous form into a liquid ocean of elements that we normally consider gases. Under the liquid ocean, the pressure may be high enough to create metallic hydrogen, which would take up a large portion of the planets interior. Metallic hydrogen is hard to study, and seems to act like a liquid metal, but it may also exist closer to a solid under enough pressure, and Jupiter certainly generates a lot.

Observing Jupiter, even for reasonably short lengths of time, lets you see that Jupiter is rotating, even in just half an hour or so if there are storms visible on the surface to make the motion easier to see. Here on Earth it takes 24-hours to turn around, it only takes Jupiter about 10 hours. A little less than 10 hours, about 9 hours 55 minutes, giving a very quick day night cycle. One side effect of this is that different parts of Jupiter’s atmosphere are going to end up getting deflected. The faster a planet is rotating, the more quickly air is going to be deflected from its path from the pole to the equator. Air generally wants to move from the colder areas to the warmer ones, carrying heat along the gradient, but the rotation of the planet diverts some air to the side forming the stripes of gas that we can see when looking at Jupiter through a more powerful telescope. Here on Earth we rotate a lot slower, meaning that there are fewer of these deflections and fewer bands or cells. These bands aren’t really visible on the Earth, but you can pretty much divide the Earth up into just a couple of cells. We have our equator with a jet of air travelling pretty much around the planet, followed by the Hadley Cells covering the tropics into the sub tropics, another jet and then Ferrell Cells covering most of the temperate zone. Lastly, a jet divides the Ferrell Cells from the the Polar Front and Polar Cells. We can see on Jupiter that there’s a lot more stripes like that, we can see these bands towards the poles are pretty thin compared to the ones near the equator. The massive planet has got room for all the stripes, as well as room for very big storms and that is of course what the Great Red Spot is.

The Great Red Spot is a storm like a hurricane or tornado, a vortex of air spinning around that moves with the planet. It mostly moves as the planet rotates, but it does also drift a little bit along the band it occupies. You can see a lot of disturbed, turbulent air behind it, spins it sheds these vortexes of air that travel out behind it, these smaller spirals and swirls are generated by air moving around the Great Red Spot. Further South of the Great Red Spot, there are a series of white spots which are also storms, vortexes of air that work a little differently to the Great Red Spot, they are often called Small White Ovals. These storms are not quite as long lived. The Great Red Spot seems to have been around as long as we’ve been able to get a good view of Jupiter, since telescopes were invented, though there is a potential gap where it wasn’t reported as being seen. If it has been around the entire time that we’ve been able to see it, then there is a good chance that it has been around for hundreds of years if not thousands of years longer. The Small White Ovals tend to decay and pop up, but there is almost always going to be a few of them on Jupiter’s atmosphere. If one vanishes another will pop up, so you will usually have a few of them in the upper atmosphere of Jupiter where we can see them.

Jupiter is a huge planet, giving it a big gravity well which can hold a lot of moons, some of which are as big as planets. However, it is still pretty far away from becoming a star, our Sun is still much much larger than Jupiter. Our Sun takes up about 99.6% of the mass in our solar system, with Jupiter then taking up a large portion of the what’s left, so Jupiter is very very big compared to the other planet, but it’s still pretty small compared to a star like our Sun. Granted our Sun isn’t the biggest kind of star by any means, our Sun as a yellow dwarf, it’s pretty small, but it is also not the smallest kind of star. If Jupiter was much more massive then it could become a red dwarf, a very small star, Really the only thing that makes a star a star and a planet a planet is that stars are big enough to generate nuclear fusion. They’re big enough and heavy enough that the pressure on the nuclei of hydrogen buzzing around in their core is enough to force them close together, so that while they’re buzzing around they are more likely to collide and produce heat and fuse into heavier nuclei. That’s not going to happen with Jupiter, just because there’s not enough hydrogen to create the high levels of pressure necessary. If we kept adding hydrogen, eventually Jupiter would get big enough to ignite. We do often find stars orbiting around other stars, binary star systems are surprisingly common, so there is a chance that our solar system could’ve been a binary star solar system, if there was more available hydrogen in the cloud of gas where the Sun formed. Had Jupiter gotten big enough it could have become a red dwarf orbiting the yellow main sequence star of our Sun. Jupiter would need to be almost twice as massive, but that extra mass would generate more gravity, squeezing it down to a pretty similar volume, just much denser. That didn’t happen of course, but it could happen in other solar systems, and we do find binary star systems in other solar systems. Some of them are probably composed of stars that began co-orbiting after they formed near each other as well.

As I mentioned, Jupiter is going to disappear behind the Sun as our orbit changes our relative positions. As we come to the end of April it’s already really really close to the Sun at sunset. Jupiter will stop being visible once it gets too close to setting with the Sun, it won’t be visible due to the glow of sunset before it actually moves directly behind the Sun. It will be on the far side of the Sun for a few weeks, and once the Earth has moved a little further along in its orbit Jupiter will pop up again in the morning. Jupiter will really only be invisible for about a month, about the month of June this year. We can still catch Jupiter at sunset time in April and we will begin to catch the sunrise time in July, so it will only be invisible for a small portion of the year. When exactly it will vanish and reappear will depend on your location, Jupiter will be invisible for longer form higher latitudes like Ireland, it will stay visible for longer and reappear earlier in locations closer to the equator. I find it a little bit easier to stay awake until 9 or 9:30 than to get up at 3 or 4 o’clock in the morning when the Sun is still rising, but it may be different for you. If it is then you’ll be able to see Jupiter easily in the near future when it pops up again in the morning. For those of us who prefer to stargaze in the evening ,we are going to have to wait for months and months before Jupiter pushes its way round again to be visible in the evening sky.

That is just a little about Jupiter, Jupiter has almost a 100 moons orbiting around it, and even just the four largest moons could have videos dedicated to them alone. I will almost certainly commit more videos exclusively to talking about Jupiter in the future but I will probably leave it another month or two before I do so. I hope that you get to see Jupiter as the Sun is setting over the next couple of weeks , it is going to be your last chance to see it before it disappears for about a month. I will no doubt mention when Jupiter becomes visible again when I make a video looking forward into July, and the best way to make sure that you don’t miss that video is to subscribe to this website or my YouTube channel. Between now and then I’ll continue keeping you up to date on what you can see in the sky and looking at various astronomical objects and topics. Hopefully, you’ll stick around for those.