What’s that bright ‘star’ in the evening sky?

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A brilliant star in the sky after dusk is beginning to attract some attention. In fact, it is not a star at all but the bright planet Venus.

The Moon and Venus pictured close in the sky on March 28, 2020, from Walmer Kent. Image credit: Paul Sutherland

It moved into the evening sky in late March, 2021, after dazzling onlookers with a brilliant appearance in the morning sky over previous months, when it resembled a bright beacon before dawn.

On 26 March, Venus passed through a point on the far side of Sun known as Superior Conjunction. Because the orbits of Venus and Earth are slightly tilted to one another, it did not pass directly behind the Sun.

Venus is our closest planetary neighbour, and can come between us and the Sun. It is the second planet from the Sun, after Mercury.

In the months before Superior Conjunction, Venus’s phase through a telescope changed from a narrow crescent to a small, gibbous disk, like the Moon. Only the inner, or inferior, planets can show us crescent phases.

In early April, 2020, during its last spell in the evening sky, astronomers watched Venus travel across the Pleiades, or Seven Sisters, which is one of the best-known star clusters in the night sky. Its movement from one night to the next was very evident.

A montage of photos taken over four nights from April 2-5, 2020, shows Venus’s passage across the Pleiades star cluster. Image credit: Paul Sutherland

Now it is setting after the Sun again as a brilliant “evening star”, and its gibbous phase will gradually change to a larger crescent phase again as it heads back to the part of its orbit on this side of the Sun. Even binoculars or a small telescope will show you these phases, though be careful not to use them if the Sun is still up and nearby.

This evening apparition of Venus is a very much better one for southern hemisphere observers than for those of us at northern latitudes. That is because the ecliptic, or the plane of the Earth’s orbit in the sky, will be at a shallow angle to the horizon for the rest of the year in the hours after sunset.

The other planets also lie approximately in this same plane, so Venus will never get more than a few degrees above the horizon for observers in the north, even as it moves further out from the Sun in the sky.

By contrast, the situation is a lot happier for skywatchers in southern countries such as Australia, New Zealand, South Africa, Argentina, Brazil and Chile. From such locations, the ecliptic will stand at a steep angle to the ecliptic during the rest of 2021, and Venus will be high in the sky after sunset.

Venus moves gradually out from the Sun to its farthest point, which is known as its Greatest Elongation East, on 29 October. It will then lie 47° from the Sun, and its phase will be more like a half-moon.

After that, it swiftly heads back in towards the Sun as viewed from Earth, but it does not reach Inferior Conjunction, the point when it lies between Earth and the Sun, until 8 January, 2022. (Venus will not pass directly in front of the Sun, so there will be no transit).

Venus becomes so bright that it attracts the attention of people who don’t usually notice the sky, and it has often been mistaken for a UFO! This year its brightness will increase from -3.9 to -4.3 in October.

Venus, on the right, shows a crescent phase just like the neighbouring Moon in this shot taken in 2015 when it was in the morning sky. Image credit: Paul Sutherland

Venus can shine as brightly as  -4.3, using the astronomer’s scale of magnitude, making it the brightest natural object in the sky after the Sun and the Moon.

That means it will come into view before any of the stars when in the evening sky, and stays visible after stars have disappeared in the morning twilight. Indeed, under perfectly clear skies, Venus is bright enough to be seen in daylight. But do NOT try to view it with binoculars while the Sun is above the horizon as an accidental view of the Sun through them could damage your eyesight.

Related: How to observe Venus

Related: Venus – our neighbour from hell

Venus photographed during a previous apparition, using a Meade ETX-90 telescope as the camera’s lens. It shows a half-moon shape. Image credit: Paul Sutherland

You can never see Venus in a midnight sky because it never gets more than about 47° from the Sun. This means it can’t set more than about about 4 hours after the Sun or rise more than 4 hours before it when it is in the morning sky.

Twilight is a good time to look at Venus through a telescope. That is because it will appear less dazzling against the brighter sky than against a darker background.

You can photograph Venus easily thanks to its brightness. Choose a nice foreground, such as some trees silhouetted against the twilight sky, and even a snapshot camera or smartphone should be able to record it. Hold the camera, or phone, steady to avoid camera-shake. If you have one, a photographic tripod will be useful.

Related: What else is in this month’s night sky?


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