Venus, Earth’s hellish twin, at its highest for eight years

Alan Pickup

Author: Alan Pickup
The maps show the sky at 23.00 GMT on the 1st, 22.00 GMT on the 16th and 21.00 GMT (22.00 BST) on the 31st. Venus is plotted at mid-month and its path shown by an arrow. Summer time begins at 01.00 GMT on the 29th when clocks go forward one hour to 02.00 BST.

The current evening apparition of Venus reaches its climax during March when it stands higher at sunset than it has for eight years. While Orion remains an imposing sight in the south at nightfall, it is falling lower towards the west by our star map times.

Attention, though, is still fixed on the red supergiant star Betelgeuse at Orion’s shoulder, see map, which has been suffering from the deepest plunge in its brightness ever see. For much of February, the star has been close to the magnitude 1.6 of Bellatrix, the star at Orion’s other shoulder, and more than a magnitude fainter than usual. Meantime, images of the star’s surface using the Europe’s VLT (Very Large Telescope) in Chile show an apparent change of shape, perhaps due to a giant star-spot or to obscuration by a cloud of dust ejected from the surface.

Studies of periodicities in Betelgeuse’s lesser pulsations over the years had led some analysts to suggest that 21 February might bring a turning point in its fortunes. In fact, measurements show that its brightness decline may have reversed a few days earlier than this, though it has far to go to regain its former prominence.

March sees the Sun climb 12° northwards to cross the sky’s equator at 03:50 GMT on the 20th, marking our vernal or spring equinox. Edinburgh’s sunrise/sunset times change from 07:03/17:48 GMT on the 1st to 06:45/19:50 BST (05:45/18:50 GMT) on the 31st, after we set our clocks forward on the 29th. The Moon reaches first quarter on the 2nd, is full on the 9th, at last quarter on the 16th and new on the 24th.

Our charts show the Sickle of Leo high on the meridian as the Plough is approaching the zenith from the east and the Pleiades star cluster is sinking in the west where it lies 7° above-right of the Moon on the 1st. Between Gemini and Leo lies the dim constellation of Cancer and its Praesepe or Beehive star cluster at a distance of 577 light years. Praesepe’s individual stars may be spotted through binoculars but will be swamped by the Moon when it lies just above-left of the cluster on the evening of the 6th.

Venus, brilliant and unmistakable at magnitude -4.2, stands 36° high in Edinburgh’s south-west at sunset on the 1st and sets in the west-north-west at 22:22 GMT. Tracking east-north-eastwards against the stars, it brightens to magnitude -4.4, slides to the left of Hamal in Aries, and approaches to within 3° or 6 Moon-breadths of the Pleiades by the evening of the 31st. Its distance drops from 133 million to 98 million km, while, viewed telescopically, it swells from 19 to 25 arcseconds in diameter and evolves from gibbous to crescent in phase as the dazzlingly-lit portion of its disk changes from 63% to 47%.

The slim young Moon is below Venus on the 27th and near Venus and the Pleiades (again) on the 28th. Venus is furthest from the Sun (46°) on the 24th – its so-called greatest elongation – but is actually highest at sunset two days later at 38.6°.

There is a curious correlation between the orbital periods of Venus and the Earth in that eight orbits of the Earth take 2922 days while 13 orbits of Venus total 2921 days. This means that this apparition of Venus is an almost exact day-for-day (or night-for-night) replay of the one it enjoyed eight years ago, in 2012, and we will not see Venus so high again in the evening until 2028.

In some respects, Venus is almost the twin of the Earth since it is 95% as wide and has 81% of its mass. However, if the ancient Romans had been aware of its true nature, they might not have chosen to name it for their goddess of love and beauty. The planet has a dense atmosphere of carbon dioxide and a surface as close to hellish as we can imagine. Any astronaut brave enough to descend through its opaque clouds, mainly of sulphuric acid, would find themselves roasted at 460°C and compressed under an atmospheric pressure 92 times that at the Earth’s surface, comparable with that at an ocean depth of 900m.

Venus spins backwards on its axis in 243 earth-days and much of its surface, only really “visible” to orbiting probes via radar, appears to be blanketed by plains of lava with no sign of the plate tectonics that drive so much of our planet’s geology. There are more volcanoes than on the Earth and suggestions that a handful may have been erupting as we “watch”. There are impact craters, too, but few small ones because of the shielding effect of the atmosphere. The Roman heritage lives on in that most of its surface features are names for real or mythological women – one notable exception is that its highest mountain, Maxwell Montes, is named for Edinburgh’s James Clerk Maxwell.

Mercury stands furthest west (28°) of the Sun on the 24th but stays hidden from our view in the dawn twilight. The other bright planets are inconveniently low in our south-south-eastern sky before dawn. The brightest, magnitude -2.0 Jupiter, stands 8° high one hour before sunrise and is about 7° to the right of the fainter Saturn, magnitude 0.7. Fainter still is Mars (magnitude 1.0 to 0.8) which lies 10° to the right of Jupiter on the 1st but moves to pass 0.7° south of Jupiter on the 20th and 0.9° south of Saturn as the month ends. Catch the waning Moon below-right of Mars and Jupiter on the 18th.

Diary for 2020 March

1st 17h Moon 7° S of Pleiades

2nd 16h Moon 3° N of Aldebaran

2nd 20h First quarter

6th 22h Moon1.4° N of Praesepe

8th 09h Moon 4° N of Regulus

8th 12h Neptune in conjunction with Sun

9th 15h Venus 2.4° N of Uranus

9th 18h Full moon (supermoon)

11th 20h Moon 7° N of Spica

15th 03h Moon 7° N of Antares

16th 10h Last quarter

18th 08h Moon 0.7° S of Mars

18th 10h Moon 1.5° S of Jupiter

19th 00h Moon 2.1° S of Saturn

20th 03:50 Vernal equinox

20th 06h Mars 0.7° S of Jupiter

24th 02h Mercury furthest W of Sun (28°)

24th 09h New moon

24th 22h Venus furthest E of Sun (46°)

28th 11h Moon 7° S of Venus

28th 23h Moon 7° S of Pleiades

29th 01h GMT = 02h BST Start of British Summer Time

29th 23h BST Moon 4° N of Aldebaran

31st 12h BST Mars 0.9° S of Saturn

This is an extended version, with added diary, of Alan’s article published in The Scotsman on 29 February 2020, with thanks to the newspaper for permission to republish here.