Giant planet Jupiter at its closest and brightest in 166 years

Alan Pickup

Author: Alan Pickup

The maps show the sky at 23:00 BST on the 1st, 22:00 on the 16th and 21:00 on the 30th. An arrow shows the motion of Mars.

We have a wealth of planets and stars to hold our interest throughout September’s lengthening nights, but little to compare with Jupiter which it at its best in years. Saturn is in the south at our star map times and Mars is becoming more prominent from the late evening as it glides eastwards in Taurus. We may even spot the brightest planet of all, Venus, just before sunrise.

The first stars we see high in the south as darkness falls tonight are the corner stars of the Summer Triangle, Vega, Deneb and Altair. The Triangle topples into the west by the early hours, giving way in the south to the Square of Pegasus and Andromeda, with the oval glow of the Andromeda Galaxy. By then, too, the glorious constellation of Orion, destined to become the centerpiece of our winter nights, is rising in the east.

Jupiter, though, outshines every star as it climbs through our eastern evening sky to pass 35° above Edinburgh’s southern horizon at 03:00 BST on the 1st and more than two hours earlier by the month’s end.

The giant planet, almost 11 times wider than Earth and 320 times more massive, reaches opposition on the 26th, meaning that it lies directly opposite the Sun and at its closest to us. Indeed, it is marginally nearer on the 26th than at any time in the 166 years between 1963 and 2129. At a distance of 591 million km, and at its brightest at magnitude -2.9, its disk appears 50 arcseconds wide through a telescope.

This is 1/36th as wide as the Moon and easily large enough for telescopes to reveal its parallel bands of cloud – the dark and bright ones called belts and zones respectively. They carry streaks and spots that drift across the disk as Jupiter rotates in a little under ten hours. The most obvious feature is the Great Red Spot in the southern hemisphere, though this anticyclonic storm is less than a third as wide as it was a century ago.

Also obvious through any telescope, and even visible through stable binoculars, are the four main moons of Jupiter which swing from side to side of the planet every few days. At present, the three inner ones may be seen occasionally crossing in front of the disk, throwing their inky black shadows onto the cloud-tops. Very few of the other 76 recognised Jovian moons are large enough to see without large telescopes or from passing space probes.

Jupiter creeps west-south-westwards against the stars of Pisces this month and crosses southwards over the sky’s equator, coincidentally on the day of opposition. It lies some 13° to the east (left) of the loop of stars known as the Circlet of Pisces, while 5° below the bottom of the Circlet is Neptune. A dim binocular object of magnitude 7.8, the farthest planet is 4,325 million km away at opposition on the 16th.

Following its own opposition in mid-August, Saturn climbs from the lower south-east at nightfall to pass 18° high across Edinburgh’s meridian. Fading slightly from magnitude 0.3 to 0.5 as it edges westwards in Capricornus, its rings span 42 arcseconds around its 18 arcseconds globe and have their north face tipped 15° to our view.

Mars rises shortly before our map times but climbs through our eastern sky to stand more than 45° high in the south-east when we lose it in the dawn twilight. It approaches from 143 million to 117 million km this month, with its distinctive orange glow brightening from magnitude -0.1 to -0.6. As the month begins, Mars lies almost in line between the Pleiades and Taurus’ leading star Aldebaran, but its motion carries it 14° eastwards to end the period between the Bull’s horns. Its ochre disk swells from 10 to 12 arcseconds and is large enough for telescopes to show some surface details.

Mercury reaches inferior conjunction on the Sun’s near side on the 23rd and remains unseen in the twilight. Venus, though, is drawing closer to the Sun’s far side and may be glimpsed at its brilliant magnitude of -3.9 in the bright dawn twilight. For Edinburgh, it rises 87 minutes in advance of the Sun on the 1st and only 40 minutes before on the 30th.

As the Sun tracks southwards, it crosses the celestial equator at 02:04 BST on the 23rd. This marks our autumnal or fall equinox when days and nights are roughly equal in all parts of the world. Edinburgh’s sunrise/sunset times change from 06:17/20:07 BST on the 1st to 07:14/18:51 on the 30th.

The Moon is at first quarter on the 3rd when it lies 3° above-left of the red supergiant star Antares in Scorpius very low in south-west at the start of the night. It stands below-left of Saturn on the 8th and is full on the 10th – as the full Moon closest to the equinox, this is the Harvest Moon. Look for it below-left of Jupiter on the night of the 11th, below the Pleiades on the 15th, above Mars on the 16th and at last quarter a day later. I think it unlikely that we could spot the Moon as the slenderest of crescents to the left of Venus a few hours before new on the 25th.

Uranus is occulted by the Moon while low in the east in the constellation Aries on the 14th. At magnitude 5.7, and normally visible through binoculars, we will need a telescope to watch the distant world slip behind the bright upper-left edge of the Moon at 22:37 as seen from Edinburgh. It reappears at the shadowed upper-right edge 50 minutes later.

The only other planet to be hidden by the Moon this year is the much brighter Mars – coincidentally, at the very same hour on 8 December that Mars reaches opposition. By then Mars will be back near its current location in Taurus but a stunning five times brighter than it is at present.

Another event to note is the planned collision of NASA’s DART (Double Asteroid Redirection Test) probe with the asteroid Dimorphos at 00:14 BST on the 27th. Dimorphos is around 160 metres across and takes 136 minutes to orbit its larger companion asteroid, Didymos, some 800 metres wide. Measuring how the impact changes Dimorphos’ orbit could give valuable information about how we might eventually deflect an asteroid should one be found on a hazardous collision course with the Earth.

Diary for 2022 September

Times are BST

  • 3rd 16h Moon 2.5° N of Antares
  • 3rd 19h First Quarter
  • 5th 02h Venus 0.7° N of Regulus
  • 8th 12h Moon 4° S of Saturn
  • 9th 02h Mars 4° N of Aldebaran
  • 10th 11h Full Moon
  • 11th 16h Moon 1.8° S of Jupiter
  • 15th 20h Moon 2.8° S of Pleiades
  • 16th 23h Neptune at opposition at distance of 4,325m km
  • 17th 03h Moon 4° N of Mars
  • 17th 23h Last Quarter
  • 20th 09h Moon1.9° S of Pollux
  • 21st 11h Moon 4° N of Praesepe
  • 23rd 02:04 Autumnal equinox
  • 23rd 06h Moon 5° N of Regulus
  • 23rd 08h Mercury in inferior conjunction on near side of Sun
  • 25th 06h Moon 2.8° N of Venus
  • 25th 23h New Moon
  • 26th 21h Jupiter at opposition at distance of 591m km
  • 27th 00:14 DART probe impacts asteroid Dimorphos
  • 30th 22h Moon 2.3° N of Antares

This is an extended version, with added diary, of Alan’s article published in The Scotsman on 31 August 2022, with thanks to the newspaper for permission to republish here.