Jupiter and Saturn unite in a once in a lifetime show in the December sky: science

Skywatchers have a rare surprise as Jupiter and Saturn get so close they almost seem like a single glowing planet in the sky.

Saturn has been following Jupiter in the night sky for the past few months.

The two planets will get closer and closer over the next three weeks, until they appear together above the western horizon around one hour after sunset on December 21st.

This event, known as the great conjunction, occurs approximately once every 20 years.

But the proximity of the two planets makes this conjunction very rare.

With only a tenth of a degree separating the two planets – which is a fifth of the Moon’s width – this is the closest period they will have appeared in the sky to each other in nearly 400 years. The last time it occurred was in 1623.

They will be so close together that you can see them in an eyepiece of a telescope, says Andrew Jacob, curator of the Sydney Observatory.

The two planets will no longer appear so close to each other until 2080.

While the planets appear close to each other from Earth, they are actually separated by great distances as they orbit the Sun.

From Earth we see the planets moving east to west across the sky along the same narrow band as the Moon and the Sun.

While Saturn takes nearly 30 years to complete one orbit, Jupiter takes nearly 12 years, so we see Jupiter lapping Saturn every 20 years.

The distance between them each time depends on how the inclination of the orbits of the two planets aligns.

But you don’t have to wait until December 21 to enjoy the two planets.

What is the best time to see the planets?

From now on, Jupiter and Saturn will be remarkably close night after night above the western horizon in the evening twilight.

“This is a good opportunity to see the movements [of the sky] in action, ”says Dr. Jacob.

Astrophotographer Anthony Wesley observed the two planets from his property in Rubyvale, central Queensland.

“I think they will only really look their best from the naked eye perspective in first week of December“, Says Mr. Wesley.

“They are a little higher in the sky and if people are in town with street lights you just have a little more chance of seeing them before they go too low.”

As the weeks pass, Saturn gets closer to Jupiter, but both planets get closer to the western horizon and sunset comes later.

Above December 17, the planets, now just a finger away from each other, will put on a beautiful crescent moon show, says amateur astronomer Ian Musgrave.

“It will be particularly spectacular with the naked eye as well as with binoculars and telescopes,” says Dr. Musgrave.

Interesting Fact: If you hold your left fist at arm’s length and cover the Moon with the knuckle of your index finger, you will not only hide Jupiter and Saturn, but block nearly 80% of all known moons in our solar system, (thus like Pluto, which will be under your little finger but too small to see).

Of December 21, Jupiter and Saturn will appear in the evening twilight about half an hour after sunset, but will only be visible for an hour before disappearing below the western horizon.

“The further north you are the longer I am in the sky,” says Dr. Musgrave.

While the planets will appear very close wherever you are on December 21st, the actual conjunction occurs at exactly 13.33 UTC, by which time it has set over much of Australia and is just disappearing from sight from Perth.

What to look for

Assuming the weather is clear, you will be able to see planets even in light-polluted areas without any equipment.

With the naked eye, look for two points – the smaller Saturn which appears to be chasing the larger and brighter Jupiter – towards the western horizon.

On December 21, the two planets get so close that you may not be able to see the gap between them, says Dr. Musgrave.

Whether you see one or two spots will depend on the degree of twilight, how close they are to the horizon, and how good your eyes are.

Mr. Wesley expects to have a good view of the event.

“Out here [central Queensland], there is nothing but dirt and kangaroos, so I have no problem seeing them as far as the western horizon, “he says.

Mr. Wesley captured extraordinary images of the planets using a high-speed video camera connected to a 400mm telescope, such as these spectacular images of Jupiter’s great red spot.

However, with a binocular or a small to medium telescope you will be able to grasp details such as The four largest moons of Jupiter, he says.

“The innermost moon Io takes only three days to make a full orbit. So even in the space of an hour or two, it moves quite noticeably compared to other moons,” Wesley says.

With a small telescope you may grasp details such as the two dark bands on either side of Jupiter’s equatorand, if you’re lucky, you might even be able to make out the file big red spot.

“Jupiter only takes about 9 hours and 40 minutes to make a full rotation, so at some point in each of these rotations it faces the Earth,” says Mr. Wesley.

There are apps and online calculators that you can use to see when the red spot is facing the Earth when the planets are above the horizon in the evening sky you live in.

One of them, Stellarium predicts that the red spot will be visible from Australia on the evening of December 21st.

“There’s nothing else like the red spot in the solar system, so it’s a real treat to be able to see it,” says Mr. Wesley.

You will also be able to see the file rings of Saturn and a couple of its moons like Titan through a small telescope.

“Saturn’s rings are the same size as Jupiter, so even with a moderately small telescope you will see Saturn and you will see the rings,” he says.

Geminid meteor shower in mid-December

December is also the month to see the annual Geminid meteor shower.

And this year, with no moon to wash away the sight, it will be a cracker.

The meteor shower, which is caused by the passage of the Earth through a trail of debris created by the asteroid 3200 Phaethon, will be at its best early in the morning of December 14.

“We should be seeing rates from one every minute to two every minute in most of Australia, which is pretty damn good,” says Dr. Musgrave.

You’ll also get decent early morning rates December 15.

The meteors come from a point in the constellation of Gemini, which rises in the late evening and is at his highest – and will give the best view – around 2am.

“If you look north it is very easy to see Castor and Pollux [the two bright stars of Gemini].

“The radiant of the Geminids is just below Castor, and on one side are Orion and Taurus.”

There will be fewer meteors December 13 but if you stay on your feet, you will be rewarded with the crescent Moon and Venus close to each other on the eastern horizon about half an hour before sunrise.