Mars at its best alongside the Harvest Moon

Alan Pickup

Author: Alan Pickup
The maps show the sky at 23:00 BST on the 1st, 22:00 BST (21:00 GMT) on the 16th and at 20:00 GMT on the 31st. An arrow depicts the motion of Mars. Summer time ends at 02:00 BST on the 25th when clocks are set back one hour to 01:00 GMT.

Mars is about to reach opposition and is the undoubted star of our October nights. Now at its brightest and best for observation from Scotland, it stands in the east as darkness falls and climbs to blaze like an orange beacon the heart of our southern sky a few hours later. Jupiter continues as a prominent object low in the south at nightfall, while Saturn lies to Jupiter’s left and Venus is glaringly obvious in the east before dawn.

The full moon on the 1st, being the one closest to our autumnal equinox on 22 September, is this year’s Harvest Moon. This traditional name comes from the fact that its nightly motion makes only a shallow angle with our eastern horizon over several evenings, meaning it can to illuminate our harvesting toils well into the night. Look for it well to the right of Mars on the 1st and 4° to the right of the planet on the next evening. The two make an impressive sight that night, drawing to within 1.2° as they sink in our western sky before dawn on the 3rd. They meet again on the 29th when the Moon is 3.5° below Mars as they climb in the east.

Mars’ opposition comes on the 14th when it shines at magnitude -2.6 and lies opposite the Sun in the sky so that it rises at sunset and stands almost 40° high in the south at 01:00 BST. Appearing to track 9° west-south-westwards against the dim stars of Pisces, it is also edging outwards from the Sun in its orbit, so it is actually closest to us at 62 million km on the 6th when it appears 22.6 arcseconds wide if viewed through a telescope. By the 31st, Mars has dimmed to magnitude -2.1 and contracted to 20 arcseconds is diameter.

This opposition brings Mars closer than it will be again until 2035, but not as near as the 58 million km it reached in the summer of 2018. It is much better from our viewpoint, though – back then it was in the grip of a dust storm which hid much of its surface detail, and its location some 30° further south in the sky made it poorly placed for study.

The southern hemisphere of Mars is tipped at about 20° to our view and its southern polar cap appears as a small white button, much smaller than a few months ago because expanses of its frozen carbon dioxide ice have disappeared, subliming away under the warmth of that hemisphere’s summer. Elsewhere on the rusty iron-rich Martian surface, dark and light markings once thought to be seas and continents are now recognised as regions of rocky highlands and dusty low-lying plains.

The Sun sinks 11° southwards during October, causing our sunrise/sunset times for Edinburgh to change from 07:16/18:47 BST (equivalent to 06:16/17:47 GMT) on the 1st to 07:18/16:34 GMT on the 31st. We revert from BST to GMT at 02:00 BST on the 25th when our clocks are set back one hour to 01:00 GMT.

Tomorrow’s full/Harvest Moon is followed by last quarter on the 10th, new moon on the 16th, first quarter on the 23rd and full moon again on the 31st, which tradition calls the Hunter’s Moon.

Although the Summer Triangle formed by Vega, Deneb and Altair is still well placed high in our southern sky at nightfall it has moved into the west by our map times. Meanwhile, the Plough, part of the large constellation of Ursa Major, is rotating to the right below Polaris, the Pole Star, in the north and the “W”-pattern of Cassiopeia is nearing the zenith.

Below the Square of Pegasus, approaching the meridian in the south, is the so-called Circlet of middling stars that represent one of the two fish of Pisces while 10° below the Circlet and near the eastern edge of Aquarius is the binocular brightness (magnitude 7.8) farthest planet Neptune. The next most remote planet, Uranus, lies in Aries to the other side of Pisces and Mars and reaches its own opposition at a distance of 2,811 million km on the 31st. At magnitude 5.7, it near the limit of naked-eye visibility but relatively easy to spot in binoculars given a better chart.

Jupiter, conspicuous at magnitude -2.4, stands less than 12° high in the south as darkness falls, but is setting in the south-west by our map times. Saturn, fainter at magnitude 0.5, lies 7° to the left of Jupiter at present but the gap between them shrinks to 5° by the month’s end as both worlds creep eastwards in the constellation Sagittarius. Catch the Moon below Jupiter on the 22nd.

As Mars meets the Moon on the morning of the 3rd, there is a very close conjunction on the opposite side of the sky involving the dazzling morning planet Venus and Leo’s leading star, Regulus. Venus shines at magnitude -4.1 and rises in the east-north-east some four hours before sunrise. Speeding eastwards through Leo, it is caught by the waning earthlit Moon in another spectacular conjunction on the morning of the 14th.

The Orionids meteor shower is active for much of October but may be best around the 22nd when perhaps 20 meteors per hour, and occasionally many more, may be glimpsed in our Moon-free morning sky. Like May’s Eta Aquarids shower, its meteoroids come from Comet Halley. These disintegrate as they enter the atmosphere at 66 km per second and, although they appear in all parts of the sky, perspective means they diverge from a radiant point in north-eastern Orion, above-left of Betelgeuse.

Diary for 2020 October. Times are BST

  • Times are BST until the 25th, then GMT
  • 1st 17h Mercury furthest E of Sun (26°)
  • 1st 22h Full moon (Harvest Moon)
  • 3rd 01h Venus 0.1° S of Regulus
  • 3rd 04h Moon 0.7° S of Mars
  • 6th 03h Moon 6° S of Pleiades
  • 6th 15h Mars closest to Earth (62m km)
  • 7th 03h Moon 4° N of Aldebaran
  • 8th 13h Peak of Draconids meteor shower
  • 10th 02h Last quarter
  • 11th 14h Moon 2.4° N of Praesepe
  • 13th 03h Moon 4° N of Regulus
  • 14th 00h Mars at opposition at distance of 63m km
  • 14th 01h Moon 4° N of Venus
  • 16th 21h New moon
  • 19th 21h Moon 6° N of Antares
  • 21st-22nd Peak of Orionids meteor shower
  • 22nd 18h Moon 2.0° S of Jupiter
  • 23rd 05h Moon 2.6° S of Saturn
  • 23rd 14h First quarter
  • 25th 02h BST = 01h GMT end of British Summer Time
  • 25th 18h Mercury in inferior conjunction
  • 29th 16h Moon 3° S of Mars
  • 31st 15h Full moon (Hunter’s Moon)
  • 31st 16h Uranus at opposition at distance of 2,811m km

This is an extended version, with added diary, of Alan’s article published in The Scotsman on September 30 2020, with thanks to the newspaper for permission to republish here.