Mercury joins brilliant Venus in the best evening sky of 2020
Ourfebruaryevening sky is often lauded as our best of the year, not least because the majestic constellation of Orion is climbing through the southeast at nightfall and stands proudly in the south one hour before our star map times.
Orion brings a supporting cast of other noteworthy constellations but is of particular interest at present because one of its major stars, Betelgeuse, is misbehaving and might, just might, be about to explode.
If Betelgeuse were to become a supernova it would far surpass the planet Venus which is climbing higher and blazing ever more brilliantly in our south-west as the night begins. Its popular title of evening star dates from ancient Greece and Egypt and survived long after its true nature was recognised, to the occasional confusion of the public but the delight of writers and poets.
Venus’s altitude at sunset improves from 27° to 35° during February and it brightens from magnitude -4.1 to -4.3 as it speeds through the dim constellation of Pisces.
Viewed telescopically, it shows a dazzling gibbous disk that swells in diameter from 15 to 19 arcseconds as its distance drops from 162 million to 133 million km. Venus sets at Edinburgh’s western horizon at 20:45 on the 1st and as late as 22:12 on the 27th when it makes an impressive sight 6° above-right of the young earthlit Moon.
February also sees the little innermost planet Mercury, sometimes also called an evening star, making its best appearance in our evening sky of 2020.
In some years, Venus and Mercury stand as near neighbours in the sky and we can find the fainter Mercury by reference to the unrivalled Venus. This time, though, there is plenty of space between them and they come no closer than 24° on the evening of the 8th.
A better plan might be to find a clear and unobstructed horizon between the south-west and west and to note where the Sun sets.
One hour after sunset, Mercury stands almost directly above the sunset position, its altitude improving from almost 3° on the 1st to more than 6° by the 10th when it is furthest (18°) from the Sun. Between these dates, it dims a little from magnitude -1.0 to -0.5 but should be a naked eye object in the fading twilight provided the sky is clear.
Thereafter, Mercury falls away and dims more quickly. By the 17th it is a couple of degrees lower but a quarter as bright at magnitude 1.1 so that it has become difficult to spy in the twilight, even through binoculars. It reaches inferior conjunction on the Sun’s near side on the 26th.
The Sun climbs almost 10° northwards in the sky during February while Edinburgh’s sunrise/sunset times change from 08:08/16:45 on the 1st to 07:06/17:46 on the 29th, leap year day. The Moon is at first quarter on the 2nd, full on the 9th, at last quarter on the 15th and new on the 23rd.
As Orion crosses the meridian, look overhead for the yellowish star Capella in Auriga, the sixth brightest star in Earth’s night sky and the fourth brightest ever seen from Scotland.
Even so, it is only a quarter as bright as Sirius in Canis Major, which twinkles furiously below and to the left of Orion.
Seventh in the stellar premier league is the blue supergiant star Rigel at the lower-right of Orion where it represents the hunter’s left knee or foot.
Opposing Rigel, on the other side of Orion’s Belt, is the contrasting red supergiant Betelgeuse which pulsates in size and brightness and can occasionally surpass Rigel. Usually, though, Betelgeuse is a mid-league player, hovering around 10th place and keeping a few places brighter than the magnitude 0.9 red giant star Aldebaran, 21° away in Taurus (see chart).
Betelgeuse began to fade in October and was close to magnitude 1.5 a few days ago, putting it a full magnitude below its average brightness and at its faintest on record.
Indeed, it is now around the 22nd brightest star meaning that it has relegated itself from our premier league. We can compare its brightness for ourselves by reference to Bellatrix, at Orion’s other shoulder, which shines at magnitude 1.6. Will Betelgeuse dim below Bellatrix during February, or…?
Betelgeuseislikelytoexhaust its nuclear fuel and “go supernova” within the next 100,000 years but, despite its current performance, astronomers are far from convinced that its disintegration is imminent.
If it were to happen, Betelgeuse might flare as brightly as the full moon and be visible in broad daylight before gradually fading and disappearing from our night sky, changing forever the appearance of Orion.
Fortunately, it is far enough away at 700 light years for there to be no danger to the Earth.
Mars rises at about 05:00 and continues as a morning object very low down in the south-east to south-south-east before dawn.
This month it brightens from magnitude 1.4 to 1.1 as it tracks eastwards from southern Ophiuchus. Don’t confuse it with the slightly brighter red supergiant star Antares in Scorpius which flashes red a few degrees to Mars’ right. The planet is passing above the so-called Teapot of Sagittarius when it stands close to its most southerly point in the sky and alongside the Moon on the 18th.
The following morning sees the Moon 7° to the right of Jupiter as the latter starts to emerge as a conspicuous magnitude -1.9 object that hugs our south-eastern horizon before dawn. Saturn, fainter at magnitude 0.7, is more difficult to spot 9° to the left of Jupiter as the month ends.
STELLAR FACT
“Orion brings a supporting cast of other noteworthy constellations but is of particular interest at present because one of its major stars, Betelgeuse, is misbehaving and might, just might, be about to explode