Stargazing in April: The incredible shadow-casting planet

As the reduction of light pollution in the night sky continues, brilliantly bright Venus comes out to play

Nigel Henbest
Wednesday 01 April 2020 15:12
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The Evening Star is at its most luminous this month
The Evening Star is at its most luminous this month

With the glorious weather we were enjoying in March, you can’t have failed to spot a brilliant light high in the evening sky after sunset. Is it a plane, is it a flying saucer? No, our Evening Star is the planet Venus.

The second planet from the Sun is the brightest object in the night sky, after the Moon. And in April Venus is at its most brilliant this year – so bright that it can cast shadows! Around mid-month, when the Moon is not about, check if you can spot Venus shadows of yourself, at a really dark spot away from all light pollution.

Point a telescope at Venus, and you’ll see it’s currently shaped like the crescent Moon. During the month, the planet appears ever larger and the crescent narrower, as Venus swings towards the Earth.

But even the most powerful telescope won’t show you much more. Venus conceals her secrets behind brilliant white veils: continuous layers of high cloud, made of droplets of sulphuric acid, with enigmatic dark patches coming and going.

Further down, the atmosphere is composed of unbreathable carbon dioxide gas, so dense that the pressure at the planet’s surface is 92 times higher than Earth’s atmospheric pressure. Carbon dioxide is famously a “greenhouse gas,” and it traps so much of the Sun’s heat that Venus’s temperature has soared to 462C – almost twice as hot as the highest setting on your kitchen oven.

Beautiful though the planet may look, then, I’d advise against a visit in person. You’d be simultaneously corroded, suffocated, crushed and roasted!

Spacecraft have visited the planet though, and Russian landers have even survived a short time on its baking surface. Orbiting spacecraft have used radar to peer through the clouds, and have revealed a landscape from Hell: contorted plains of congealed lava, dotted with hundreds of volcanoes. The radar sets can’t see if they are active, but there’s a lot of indirect evidence: hot spots that are probably lava lakes, the sudden appearance of volcanic gases in the atmosphere, and fresh rocks that haven’t yet tarnished in the planet’s toxic atmosphere. It’s led scientists to conclude that the volcanoes of Venus are erupting right now.

You might think that scientists looking for life elsewhere in the Solar System would give this toxic world a wide berth. But no...

First, Venus hasn’t always been such a hostile planet. It’s very much the Earth’s twin in size, and for its first billion years or so Venus too probably had oceans teeming with microscopic life. But its belching volcanoes contaminated the air with so much carbon dioxide that the greenhouse effect went wild, heating the planet until the oceans boiled away.

There had been plenty of time, though, for winds to whisk some of the microbes up into the clouds. It’s happened here: there are plenty of simple life forms floating around high in the Earth’s atmosphere. And Venus’s clouds are not such a bad place to be: around 50km high, the temperature is about 60C. And even the acidity of cloud decks may be a bonus. In iron mines on the Earth, researchers have found bugs that thrive in conditions as acid as a car battery.

Which brings us back to the dark patches in the planet’s clouds. Scientists don’t know what they are made of, but the way they absorb light suggests the particles here are about the size of bacteria. In our images of Venus’s shining face, then, perhaps we are seeing the silhouette of alien life.

What’s Up

Venus starts April with a most unusual performance. Glance at the Evening Star on 3 April, and you’ll see it looks fuzzy. A pair of binoculars or a small telescope will reveal why. Venus is passing right in front of the Seven Sisters (Pleiades) star cluster, which seem to swarm around it. On 26 April, the Evening Star has another rendezvous, forming a gorgeous tableau with the crescent Moon.

The Moon has its own starring role on 8 April. The full Moon that day is the closest this year, so it’s around 30 per cent brighter than the faintest full Moon. Other than that, the ‘supermoon’ won’t have any noticeable effect on the Earth: I’m not predicting earthquakes or volcanic eruptions!

On the night of 21 April, watch out for shooting stars seeming to whizz across the sky from the constellation Lyra. The Lyrid meteors are fragments shed by a celestial vagabond, Comet Thatcher, burning up high over our heads. The display is best after midnight, if you don’t mind staying up into the wee small hours.

The spring constellations are now well on view: the cat-shaped outline of Leo (the Lion) and the distinct Y of stars forming Virgo (the Virgin). Their brightest stars, blue-white Regulus and Spica, form a large triangle with orange Arcturus, in the constellation Bootes (the Herdsman).

The night sky at around 11pm this month 

In the morning sky, we have a trio of planets. Brightest is Jupiter, with Saturn and Mars to its left. The Moon lies near them around the middle of April.

And last, but far from least, there’s a comet about! In December, astronomers using a telescope of Nasa’s Asteroid Terrestrial-impact Last Alert System (Atlas) in Hawaii, found a faint smudge, heading towards the Sun. Comet Atlas suddenly brightened in February and March, and it’s now visible in binoculars almost overhead. I’ve marked its position on the chart with a comet-shaped symbol, though at the moment it’s just a dim blur, without a tail.

According to the most optimistic forecasts, Comet Atlas will be brilliant in May. I’ll update you in next month’s Independent Stargazing column: watch this space!

Diary

3 April: Venus in front of the Pleiades

4 April: Moon near Regulus

7 April: Moon near Spica

8 April, 3.35am: Full Moon (supermoon) near Spica

14 April, 11.56pm: Last quarter Moon

15 April (am): Moon near Jupiter and Saturn

16 April (am): Moon near Mars

21/22 April: Maximum of Lyrid meteor shower

23 April, 3.26am: New Moon

25 April: Moon between the Pleiades and Aldebaran

26 April: Moon near Venus

28 April: Venus at maximum brilliance

30 April, 9.38pm: First quarter Moon

Philip’s 2020 Stargazing (Philip’s £6.99) by Heather Couper and Nigel Henbest reveals everything that’s going on in the sky this year.

Fully illustrated, Heather and Nigel’s The Universe Explained (Firefly, £16.99) is packed with 185 of the questions that people ask about the Cosmos

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