Winter stars sparkle as the days start to lengthen

Alan Pickup

Author: Alan Pickup
The maps show the sky at 21:00 GMT on the 1st, 20:00 on the 16th and 19:00 on the 31st. An arrow depicts the motion of Mars.

Their widely publicised meeting behind them, Jupiter and Saturn are now sinking into our twilight at dusk to leave Mars as the only prominent planet in a sparkling winter’s sky dominated by the unrivalled constellation of Orion the Hunter. We have only a short time to wait for one of the new year’s top three meteor showers, the Quadrantids.

The shower is expected to yield more than 80 meteors per hour for someone under an ideal dark sky. For us, sadly, the peak is rather narrow and expected during daylight on the 3rd. However, respectable numbers should still be seen during the nights of the 2nd and 3rd and, despite the moonlight, particularly during the morning hours as the radiant point from which the meteors appear to diverge climbs high in our eastern sky. This point is plotted on our north star map and lies in what is now northern Bootes, below and left of the Plough’s handle.

Mars stands high in the south-east at nightfall, moving into the south-west by our map times and onwards to the west-north-western horizon six hour later.

Like a bright non-twinkling orange-hued star, Mars halves again in brightness from magnitude -0.2 to 0.5 in January as it tracks 15° eastwards from Pisces into Aries. En route it is passed by the Moon which is at first quarter when it stands 9° below-right of the planet on the 20th. On that evening, Mars stands 162 million km away, exactly 100 million km further than it was at its closest in October, and appears less than 9 arcseconds across telescopically. The three spacecraft on their way to Mars are due to arrive between the 11th and 18th of February.

Betelgeuse, the red supergiant star at the top-left shoulder of Orion, is usually outshone (as at present) by the contrasting blue supergiant Rigel at Orion’s lower-right. Between them are the three stars of Orion’s Belt named, from left to right, Alnitak, Alnilam and Mintaka. Hanging below these, as I mentioned last month, is Orion’s Sword with the glowing star-forming region of gas and dust we know as the Orion Nebula – best spotted through binoculars.

The line of the Belt slants down to Sirius, the brightest star in Earth’s night sky, and upwards towards the orange giant Aldebaran in Taurus. The latter lies 65 light years away and is a foreground star between us and the V-formation Hyades star cluster, perhaps the most important cluster in the whole sky. At 153 light years, it is the closest and best studied star cluster, having played a vital role in calibrating the relationship between the colours and luminosities of stars while they are generating their energy by fusing hydrogen into helium in their cores. For all its scientific significance, the Hyades usually plays second-fiddle in popular culture to the brighter Pleiades cluster, 12° away to the north-west – catch the Moon between the two on the 23rd.

Following the winter solstice on 21 December, the Sun climbs 6° northwards during January causing Edinburgh’s days to lengthen by almost 90 minutes and sunrise/sunset times to change from 08:44/15:50 on the 1st to 08:09/16:44 on the 31st. The Moon is at last quarter on the 6th, new on the 13th, first quarter on the 20th and full on the 28th.

It is just a coincidence that our winter solstice came on the same day as that rare close conjunction between the two largest planets, their closest visible convergence in almost 800 years. However, stories that Jupiter and Saturn formed a “Christmas Star” akin to the Star of Bethlehem are, frankly, overblown and misleading. Anyone expecting a wondrously bright spectacle was to be sorely disappointed since the combined brightness of the two was a barely perceptible 10% greater than that of Jupiter alone, and Jupiter, in any case, is only half as bright as it was in our midnight sky just a few months ago.

We need a clear unobstructed south-western horizon to see Jupiter as it stands 8° high for Edinburgh 30 minutes after sunset on the 1st, and probably binoculars to glimpse Saturn, 1.2° below and to its right. Jupiter shines at magnitude -2.0, brighter than Sirius, while Saturn is a tenth as bright at magnitude 0.6.

They separate as they slide lower into the twilight, so that the equivalent altitude of Jupiter on the 9th is down to 5° and they are a further degree apart. The smallest and innermost planet, Mercury, joins them to shine at magnitude -0.9 when it lies 1.8° below Saturn on the 9th and 1.4° below-left of Jupiter on the 11th. By the 14th, with Jupiter down to 3°, Mercury is 4° above-left of Jupiter and the same distance to the right of the thin sliver of the young Moon, only 3% sunlit. Saturn reaches conjunction beyond the Sun on the 24th followed by Jupiter five days later.

Mercury remains an evening object as it moves to lie furthest east of the Sun (19°) on the 24th. Between the 19th and 31st, it stands more than 7° high in the south-west 30 minutes after sunset and, horizon permitting, should be easy to spot through binoculars as it dims from magnitude -0.8 and 1.0.

Just as two bright planets slide into our evening twilight, so the most brilliant of all, magnitude -3.9 Venus, is disappearing before dawn. On the 1st, it rises in the south-east 90 minutes before the Sun and stands 7° high at sunrise. By the 25th, though, these numbers diminish to 32 minutes and 3° although it will be late in March before it reaches its so-called superior conjunction on the Sun’s far side.

Diary for 2021 January

  • 1st 08h Moon 2.7° N of Praesepe
  • 2nd 14h Earth closest to Sun (147,093,163 km)
  • 2nd 22h Moon 5° N of Regulus
  • 3rd 14h Peak of Quadrantids meteor shower
  • 6th 10h Last quarter
  • 6th 19h Moon 7° N of Spica
  • 10th 03h Moon 6° N of Antares
  • 11th 20h Moon 1.5° S of Venus
  • 13th 05h New moon
  • 14th 08h Moon 2.3° S of Mercury
  • 20th 21h First quarter
  • 21st 06h Moon 5° S of Mars
  • 22nd 00h Mars 1.7° N of Uranus
  • 23rd 05h Moon 6° S of Pleiades
  • 24th 02h Mercury furthest E of Sun (19°)
  • 24th 03h Saturn in conjunction with Sun
  • 24th 05h Moon 5° N of Aldebaran
  • 27th 16h Moon 4° S of Pollux
  • 28th 15h Moon 2.6° N of Praesepe
  • 28th 19h Full moon
  • 29th 02h Jupiter in conjunction with Sun
  • 30th 05h Moon 5° N of Regulus

This is an extended version, with added diary, of Alan’s article published in The Scotsman on December 31 2020, with thanks to the newspaper for permission to republish here.