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A place where you can see the western horizon
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IT ISN’T common to see two planets in the same part of the sky, but on 24 November, Jupiter and Venus will be in what is known as conjunction. This happens when their position in space relative to that of Earth means they appear to line up.
Most of the time, Venus and Jupiter are far away from each other in the sky, but roughly once a year they line up. The last conjunction of Venus and Jupiter happened on 22 January 2019, and the next will be 11 February 2021.
The two planets will still be on the opposite side of the sun to Earth, so they won’t be at their brightest. But despite Venus being much smaller – Jupiter’s diameter is a whopping 140,000 kilometres, more than 10 times that of Venus, at about 12,000 kilometres across – it will appear bigger and brighter than Jupiter. That’s partly because it is much closer to us, and partly down to reflectivity.
The light we see from planets is all reflected from stars, in this case the sun. Venus reflects 75 per cent of the light that hits it thanks to a thick, permanent cloud layer containing sulphuric acid. It makes Venus the second most reflective object in our solar system after Saturn’s moon Enceladus. Jupiter’s atmosphere of water, ammonia and other gases reflects only 34 per cent of the sun’s light.
At conjunction, Venus passes just 1.4 degrees from Jupiter in the sky. As a general idea for the separation you should expect to see, this is about three times the width of the moon. The planets will stay in conjunction for a few days, so if it is cloudy on 24 November, you can still see them together on another day, albeit slightly further apart.
To see the planets, go somewhere with a clear view of the horizon in the direction the sun is setting. As we learned a few weeks ago, planets follow the same line as the sun, known as the ecliptic. They will start to appear low in the sky about 45 minutes after sunset. If you’re having trouble finding them, an app can help.
It’s easy to tell the two planets apart as Venus will always be brighter. In the days after the conjunction, Jupiter will start to move closer to the sun while Venus will appear higher up, away from the sun.
The planets will set at a time that depends on your latitude. For example, at 35 degrees north, Venus and Jupiter set about 1 hour and 40 minutes after sunset on 24 November, so you will only have about an hour to look at them. At the equator, you will get an extra 10 minutes, while at 35 degrees south they set 2 hours after sunset.
Use this as an opportunity to consider how small we are. Venus and Jupiter are close together in astronomical terms, but they are still nearly 700 million kilometres apart.
Abigail Beall is the author of The Art Of Urban Astronomy (Buy from *)
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For next week
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Next in the series:
2 How to watch the Leonid meteor shower
3 Venus and Jupiter in conjunction
4 Mercury at its greatest elongation
The best time to see the planet directly
5 How to see the Northern Lights
6 Find the Andromeda galaxy
7 How to see Santa (the ISS) on Christmas Eve
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