ON 14 September, stargazers will be treated to a lunar occultation of Uranus. In this rare event, the planet will pass behind the moon in the sky, with the moon temporarily blocking Uranus from view. Around an hour later, it will re-emerge on the moon鈥檚 other side.
Because the moon is so close to Earth compared with everything else we see in the night sky, it appears at different points, relative to the stars and planets, depending on where you look from. This means that lunar occultations, where the moon appears to move in front of a planet, are only visible from certain parts of the world. This occultation will be visible in Europe, north Africa and north-west Asia.
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To find out exactly when you need to look, it is best to use software such as to check what the night sky will look like where you are on the evening of 14 September. From the UK, the occultation will be visible at around 10.30pm, but you should start looking at around 10.15pm. Uranus will reappear on the other side of the moon just before 11.30pm.
To see this event, you will need a dark sky away from light pollution and a pair of binoculars. Look for a small, fuzzy dot of light to the left of the moon as you are looking at it, next to the moon鈥檚 sunlit part, which will be 80 per cent visible.
Through binoculars, the little dot might appear greeny-blue and look more like a disc than a point of light. Then just sit back for the next hour and watch as Uranus passes behind the moon, then pops out again on the moon鈥檚 unlit side.
Uranus is the seventh planet from the sun, and it is sometimes visible with the naked eye from places that are dark enough. But to guarantee you will see it passing behind the moon, use a pair of binoculars.
Uranus and Neptune both appear blue because of methane in their atmospheres, but Uranus has a hazy layer that looks white-ish, dulling its colour compared with the brighter Neptune. Both are ice giants, but Neptune, being much further away, is never visible with the naked eye.
If you don鈥檛 get clear skies this time around, don鈥檛 worry. There will be another chance for those in western Europe to catch a lunar occultation of Uranus on 5 December. If you aren鈥檛 in that part of the world, you might get your chance when, on 12 October, another lunar occultation of Uranus will be visible from much of the US, Canada and Greenland, or again on 8 November, when it will be seen from much of east Asia and Alaska.
If you are based in Australia or New Zealand, unfortunately you won鈥檛 see an occultation this year. But in 2023, parts of Australia will be treated to a total solar eclipse, so it isn鈥檛 all bad.
What you need
Binoculars or a telescope
Dark skies
Software like Stellarium (optional)
Abigail Beall is a feature editor at New Scientist and author of The Art of Urban Astronomy @abbybeall
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