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Jupiter

In this lesson you’ll learn where to find Jupiter over the coming months and what features to look for when you’ve got it in your telescope.

Jupiter

Jupiter is a massive planet.

Measure the width of Jupiter’s disc and you’ll get somewhere between 30 and 50 arcseconds across, depending on how close it is to us. Mars, which is significantly closer to us, is just 3.5 to 25 arcseconds across. So, even at its furthest from us, Jupiter appears larger than Mars at its closest.

We astronomers benefit from that massive size because it reflects such a lot of sunlight back in our direction, making it the brightest planet in the night sky after Venus. Depending on its distance from us, the apparent magnitude of Jupiter ranges from -1.6 to -2.9. It’s large disc and interesting surface patterns also mean there is always something to look at.

Where to Find Jupiter in the Night Sky

The following calendar shows you where Jupiter can be found for each month to the end of 2022. The best time of year to observe the massive planet is around opposition in late September. The worst conditions are from February to April as Jupiter travels around the back of the sun.

2022

January: As the year begins, Jupiter is a few weeks from it superior conjunction, which is when it will be directly behind the sun from our perspective. As it heads behind the sun, the largest planet in the solar system begins to disappear from our night sky. As it is, we’ll see it after sunset for a couple of hours before Jupiter itself sets.

Jupiter is best viewed as soon as the sky gets dark because this is when it’ll be at its highest. In the middle of January, Jupiter is 25° over the southwest horizon 40 minutes after sunset. When you spy it in Aquarius, you’ll see its 34 arcsecond disc shining at magnitude -2.1. By the end of the month, Jupiter is only 14° over the southwest after the sky gets dark.

February: The shrinking of Jupiter towards the sun continues at pace in February. The middle of the month is the practical cut-off for being able to see this giant planet. If you look for it after sunset, you’ll see Jupiter is only just over the horizon. A few days after that, the gas giant is too close to the sun to be seen.

March: Jupiter’s superior conjunction happens on the seventh of this month. After that point, Jupiter is a morning object, rising before the sun. However, the ecliptic is very shallow in the morning this month so, even as Jupiter puts distance between it and the sun, it barely rises above the horizon before the dawn breaks. Practically, Jupiter is unobservable this month.

April: Forty minutes before sunrise in the middle of April, Jupiter is just 5° over the eastern horizon. That improves to 11° by the end of the month. If you point your telescope its way, you’ll see the planet has crossed into Pisces, has a disc 34 arcseconds wide, and shines at magnitude -2.1.

May: Viewing improves steadily again in May. At the middle of the month, Jupiter is 18° high as dawn breaks, and 25° high at the same time on the last day of the month. May 30 is a great day to look for Jupiter because it is with half a degree of planet Mars – we’ll be able to see both planets in the same eyepiece view.

June: Jupiter’s opposition this year happens on 26 September. This is the point when we are closest to Jupiter, when the giant planet is opposite the sun with us in the middle. It is the time when our planet is closest to the largest planet in our solar system. Right now, Jupiter is getting closer to us with every day that passes and we see the pace of that increase throughout June.

What we see over the course of this month is that the size of Jupiter’s disc grows 10% from 36 arcseconds to 40 arcseconds, revealing more detail to our telescopes. To find the planet, look one third of the way above the southeastern horizon before dawn – it is the brightest object in the night sky except for the moon and Venus.

If you’re looking for more detail than this, take a look at the Virtual Astronomy Club. Each month we issue detailed guides for observing Jupiter, including exactly where to look each day.

July: Jupiter spends July in the constellation of Cetus and, for the first time this year, it rises before midnight and reaches its highest point in the sky before sunrise. If we look for Jupiter at 5am on the last day of the month, we’ll see it over halfway between the horizon and overhead point. The Jovian disc grows to 44 arcseconds wide and shines at magnitude -2.7.

August: Jupiter spends the whole month in Cetus and grows to 47 arcseconds wide. It’s rising in the evening and, by the end of the month, we can observe it before we go to bed. If you look for the giant planet at 11pm on the last day of the month, you’ll see it 23° over the eastern horizon.

The best time to observe Jupiter is as it transits the southern horizon. In the middle of August, this happens at 4am when Jupiter will be midway between the horizon and the overhead point.

September: The opposition takes place on 26 September, which is also when the Jupiter is closest to us. At that time, the Jovian disc is in Pisces (where it remains for the rest of 2022), is almost 49 arcseconds wide, and shines at magnitude -2.9.

The planet is visible all night long this month, reaching its highest point around midnight. Those of us who prefer early evening astronomy can also enjoy this spectacle – Jupiter is 25° above the southeast horizon at 9pm.

October: The Jovian disc stays large and wonderful for telescopes throughout October; it doesn’t shrink below 48 arcseconds until the 17th of the month. The planet is now an evening object and, in the middle of October, Jupiter transits the southern horizon 50° high just before midnight.

November: During November, Jupiter’s disc shrinks to (a still huge) 44 arcseconds across and remains shining brightly at magnitude -2.6. The big change this month is when it is best to view the planet. In the middle of November, Jupiter is highest in the sky at 8:30 pm when it will be midway between the horizon and zenith.

December: We finish the year with Jupiter’s transit now happening before 7pm in the middle of December. It is still bright, shining at magnitude -2.5, but the disc is 20% smaller than it was at its peak in September, being 40 arcseconds wide.

What to Look for When Viewing Jupiter

I suspect Jupiter is most famous for its Great Red Spot (GRS), and we’ll get to that below. What’s easier to see are the different cloud bands on its surface, which even the smallest scope for this course will show you in good conditions.

As well as the planet itself, there are its four Galilean moons that are easy to get familiar with. The harder moon challenge is to see a shadow transit crossing. Find out how to tackle that towards the end of this section.

Jupiter’s Cloud Bands

The planet jupiter is famed for being split into many different colored bands.

Other than the GRS, they are its most striking feature and their vibrancy is unique in the solar system. We are all used to seeing the stunning pictures of Jupiter from NASA, like the ones below…

Jupiter

Of course, as you’ve discovered for yourself by now, the bands won’t be anywhere near as detailed as this in your own telescope, but you can clearly see some of them! When you see them for yourself, I guarantee you’ll be mighty impressed with the view.

To see the bands for yourself, get Jupiter centred in your telescope and take some time to just look at it. You’ll know you have the right thing when you see an unmistakable disc and not just a point of light. The other big clue that you’ve found Jupiter is seeing up to 4 points of light – looking light tiny stars – in a line either side of the planet. These are the Galilean moons of Jupiter and we’ll look at them next.

At first look, the planet’s surface might appear to be a uniform white / gray colour. But stare at it for a while, letting your eyes adjust to the view and using averted vision (see tip 10 on this page), and you will soon see bands of different shading. They won’t be in color because your scope doesn’t collect enough light for that, instead they will be in shades of gray, something like this picture, but perhaps not as clear – this is through a 10″ telescope.

After the initial excitement of being able to see the bands, what I found most rewarding was being able to put a name to them, so let’s do that next.

To be technically accurate, ‘bands’ refers to the dark regions on the surface of Jupiter. The light bands are actually called ‘zones’. I know this sounds pedantic, but it’s a point worth knowing when we come to look at their names.

The image below (source) gives the initials for each named band and zones, the names themselves are below the picture.

The abbreviations on the picture above stand for:

  • NPR = North Polar Region
  • NNTB/Z = North North Temperate Belt / Zone
  • NTB/Z = North Temperate Belt / Zone
  • NTropZ = North Tropical Zone
  • NEB = North Equatorial Belt
  • EZ = Equatorial Zone
  • SEB = South Equatorial Belt
  • STropz = South Tropical Zone
  • STB/Z = South Temperate Belt / Zone
  • SSTB/Z = South South Temperate Belt / Zone
  • SPR = South Polar Region

Whilst it’s unlikely you’ll be able to see these all individually, there are certainly ones (and groups) that stand out more than others and you should be able to pick out. That’s helpful because, personally, I start with the center and work north and south to try and identify the other belts.

The lighter equatorial zone crossing the middle of the planet is easy to see because it is flanked above and below with the south and north equatorial belts, which are also easy to distinguish, even in a smaller scope. Some of the thinner belts are harder to pick out, especially in a smaller scope, or if your seeing is not great, but you will probably be able see the darker north and south polar regions at the top and bottom of the planet.

Using a higher magnification works well with Jupiter. In fact, on nights of great seeing, and if your scope is large enough, don’t be afraid to try 200x or more magnification to tease out more detail in the banding.

I don’t do this myself, but many astronomers find the detail they detect is improved by sketching what they can see. Sketching helps concentrate your brain on details and may help you tease out the narrower zones and bands on the planet.

The Galilean Moons of Jupiter

I mentioned it earlier, but one of the ways to know for certain you have Jupiter in your sights is the presence of up to four pinpricks of light in a straight line on one or both sides of the planet. This brief YouTube video shows what they look like through a small telescope (about 6 minutes in).

These are the four largest moons of Jupiter and collectively they are called the Galilean moons, because it was Galileo Galilei who first discovered them and realised what they were back in 1610.

From nearest Jupiter outwards they are called

  • Io
  • Europa
  • Ganymede
  • Callisto

Because they are so distinct in a telescope, it should come as no surprise to you that these are massive bodies. Indeed, every one of these four moons is bigger than Pluto.

Their continual orbit of Jupiter makes them a good study to make over the period of a few nights. I use Sky & Telescope Magazine as a ready-reckoner for where each moon will be on any night, but any astronomy software will give you a view of them.

Io fair whizzes around the planet, it completes a full orbit every 42 hours or so. This means you can actually see movement within a single viewing session. Note where the closest moon is in relation to the planet, then return an hour or two later and you will be able to see it has moved.

The effect is easiest to appreciate at times when the moons are close together, As you return every hour to look at them you will see they have moved closer together or further apart.

The further from Jupiter they are, the longer the other moons take to complete an orbit. The orbital periods for the remaining three are: Europa 3.5 days; Ganymede 7.2 days, and; Callisto 16.7 days.

One final note with regards to watching the Galilean moons – don’t assume the one you can see closest to the planet is Io. It could be you are seeing Ganymede reappear from behind the planet so it appears close – there is no 3D perception at this distance. always refer back to a chart to see which one you are looking at.

Later on in this section I’ll be talking about the moons’ ‘shadow transits’ but, for now, it’s time to turn to the one feature you’ve been waiting for…

The Great Red Spot

Everyone who gets a new telescope has an ambition to see the Great Red Spot (GRS).

The GRS is a storm on Jupiter’s surface which has been raging for centuries, and – for all we know – it may rage for centuries to come.

Like everything to do with Jupiter, it is large. Almost unbelievably, it is twice the size of our whole planet!

The winds inside this hurricane swirl at 400mph. The whole storm orbits the planet within the South Equatorial Belt and takes just 10 hours to orbit the planet, which is amazing if you think about the size of Jupiter.

Despite its size, color and reputation, seeing it in a smaller scope is a real challenge.

You need great seeing, a dark night to coincide with Jupiter being nearby to have a decent chance of seeing it. Ideally, you will be well over 100x magnification and over 150x is better. And, finally, the GRS needs to be facing us. With the best setup and conditions in the world, there is no seeing the GRS if it’s on the far side of the planet.

To find transit times for the GRS use either your favorite software (Sky Safari has it, for example) or use this free website. If you use this resource, remember that the times it gives are in UT (universal time), so you need to add or subtract hours from that to get local time. This link will tell you how many hours difference your timezone is from UT.

Finding GRS Transit Times on Sky Safari 5 (orange box)

Image Courtesy of SkySafari Pro – www.SkySafariAstronomy.com.

When you have good viewing and (ideally) when Jupiter is near opposition and so closer to us (as in June 2019) take a look for yourself. Go armed with the GRS transit times for the date you are observing. It might even help to have a colored filter to give the spot contrast. Use #38A Dark Blue, or #80A Blue, the cheapest ones cost only around $20 from Amazon.

Look towards the south of the planet, the GRS straddles the South Equatorial Belt and South Tropical Zone. These are the bands immediately below the lighter equatorial zone which circles the middle of the planet. Be prepared for it to take a long time to find, but have patience because, after you find it for the first time, it will be so much easier the second!

Next, we move to the final Jupiter observing challenge: A shadow transit…

Shadow Transits of the Galilean Moons

A transit is what astronomers call one body moving over the face of another. Mercury and Venus sometimes transit the sun, for example.

The moons of Jupiter frequently transit the face of the planet. Unfortunately for us, they are almost the same (gray) color as Jupiter in our eyepieces, making them impossible to detect in front of the planet with a small to medium sized scope.

However, when a moon transits Jupiter, it casts a shadow on the planet’s surface. That shadow is, of course, black, and we can pick that up in a smaller telescope. This is called a shadow transit.

Shadow transits happen every day. The trick is to spot the ones happening at night, when Jupiter is high in the sky and you have good seeing. To find the next ones happening that you can see, you can use your astronomy software (see the screengrab from Sky Safari 5 above – underneath the orange box you can see it says ‘Io Shadow Transit Begins…’), or use this free website.

There is nothing left for you to do now than take the Jupiter quiz and get your telescope out to have a look.

Summary

Jupiter is the biggest planet in the solar system and appears as the largest one in the night sky too. You can see cloud band/zone details on its surface quite easily, but the Great Red Spot and shadow transits are more of a challenge.

Seeing the Galilean moons do their dance either side of the massive planet is also a simple observation exercise.

Next we’ll visit the last and most visually stunning planet of this course: Saturn.

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