Watch for noctilucent clouds as planets buzz the Beehive

Alan Pickup

Author: Alan Pickup

The maps show the sky at 01:00 BST on the 1st, midnight on the 16th and 23:00 on the 30th.

There is no hiding the fact that June is often a poor month for astronomy in Scotland. The persistent twilight swamps the fainter stars while observers further north may struggle to locate even the brighter ones.

One of the brightest visible at our chart times is Capella in Auriga, near its low-point 12° above Edinburgh’s northern horizon. If we can find it, then we should be alert for the occasional appearance of tenuous noctilucent (“night-shining”) clouds in its vicinity.

Noctilucent Clouds from Edinburgh by Ramsay McIver

Noctilucent Clouds from Edinburgh by Ramsay McIver

These, the highest clouds of all, consist of banks of tiny ice crystals hanging at a height of some 82 km where they are able to catch the Sun’s light after our more usual and lower terrestrial clouds are in darkness. They are glimpsed from Scotland between late-May and August each year, and when the Sun is more than 6° below the horizon, from about one hour after sunset until one hour before sunrise. Often taking on a silvery hue and similar to cirrus, they may appear rippled or striated and, although they can reach much higher, they are usually confined to below 15° in altitude between the north-west and the north-east.

Conditions are only ripe for their formation during the summer months when, surprisingly, temperatures at that height, in the atmosphere’s mesosphere, reach their lowest of the year. This allows what little water vapour exists at that altitude to freeze onto particles of dust, perhaps the debris from meteors, volcanoes or man-made pollution.

The Sun is furthest north at 15:58 BST on the 21st, the moment of our summer solstice when it is directly above the Tropic of Cancer near the northern latitude of 23.4°. Edinburgh’s sunrise/sunset times vary this month from 04:35/21:47 BST on the 1st, to 04:26/22:03 on the 21st and 04:30/22:02 on the 30th.

Venus by Mike McGovern

Venus 27 May 2023 by Mike McGovern

Venus continues as our most outstanding planet though it stands noticeably lower in our evening sky each day, its altitude in the west-north-west 30 minutes after Edinburgh’s sunset falling from 21° on the 1st to only 10° by the 30th. While the planet reaches its furthest east of the Sun in the sky, 45°, on the 4th, the fact that it has also turned southwards relative to the Sun explains its decline in height.

Venus brightens from magnitude -4.3 to -4.5 as it approaches from 110 million to 75 million km this month, with telescopes showing its diameter swelling from 23 to 33 arcseconds. Venus appears almost D-shaped as the month begins, with the official moment of dichotomy, when it is exactly 50% sunlit, on the 4th. Curiously, observers often report Venus to look 50% sunlit a few evenings earlier than predicted, a phenomenon due to sunlight scattering in the deep Venusian atmosphere and named Schröter’s Effect after the German amateur astronomer who first noted it 230 years ago. By June’s end, Venus is a 32% crescent.

Venus tracks eastwards this month from below-left of the star Pollux in Gemini and through Cancer. En route it passes 0.9° north of the Praesepe or Beehive star cluster in the 13th, though we need binoculars or a telescope to glimpse the cluster’s stars in the twilight.

Mars, preceding Venus through Cancer, lies 11° to its left on the 1st and less than 4° above-left of Venus by the 30th. Mars is much less obvious, though, at magnitude 1.6 to 1.7 and appears very small through a telescope, less than 5 arcseconds wide. It also buzzes the Beehive, appearing against its stars and only 0.2° above the cluster’s heart on the 2nd. By the month’s end, both Mars and Venus have crossed into Leo, with Mars just 6° to the right of Leo’s main star, Regulus, and about to set at our map times.

Crescent Moon and Venus, 23 May 2023, Mark Phillips

Crescent Moon and Venus, 23 May 2023, Mark Phillips

After new moon on the 18th, the very slender young Moon may be glimpsed to the left of Pollux low in the north-west on the 20th. It makes an impressive sight on the next evening, still brightly earthlit, almost 4° above and right of Venus while on the 22nd it is 5° above-left of Mars. Last quarter comes on the 26th.

The Moon stands very close to the red supergiant Antares in Scorpius on the 3rd, a day before it is full. Last quarter follows on the 10th, a few hours after it stands below the planet Saturn, low down in our predawn sky in the south-east. Saturn is magnitude 0.9 while telescope shows it to be 17 arcseconds broad with rings 39 arcseconds wide and tipped at 7°.

Almost two decades of imaging and analyses led to the confirmation in the last month that Saturn has a further 63 moons, boosting its total to 146, no less than 51 more than Jupiter’s current tally. All the additions are incredibly faint and no more than 3 to 5 km wide, with most more than 20 million km from Saturn itself and probably captured asteroids or the fragments from collisions between them

Jupiter is conspicuous at magnitude -2.1 and just emerging from our morning twilight where it lies 1.4° left of the waning crescent Moon on the 14th. Watch it rise in the east-north-east at 03:26 on the 1st and by 01:42 on the 30th. Mercury is hidden in the Sun’s glare before dawn.

M101 SN 2023ivx Mark Phillips

M101 SN 2023ivx 24 May 2023 by Mark Phillips

The brightest supernova since 2014 was discovered by a Japanese amateur astronomer on 19 May and is ideally placed in our sky, the twilight notwithstanding. The cataclysmic explosion of a supergiant star at the end of its life, it is visible in a spiral arm of the glorious spiral galaxy M101, 21 million light years away. Also called the Pinwheel Galaxy, this lies in Ursa Major where it forms an almost equilateral triangle with the end stars of the Plough’s handle, Alkaid and Mizar (see map). Its light may have peaked near magnitude 11.0 around 25 May but it should remain visible in small telescopes for several more weeks.

Diary for 2023 June

Times are BST

  • 2nd 18h Mars 0.2° N of Praesepe
  • 3rd 23h Moon 1.5° N of Antares
  • 4th 04h Venus dichotomy (50% illuminated)
  • 4th 05h Full Moon
  • 4th 12h Venus furthest E of Sun (45°)
  • 9th 21h Moon 3° S of Saturn
  • 10th 21h Last quarter
  • 13th 15h Venus 0.9° N of Praesepe
  • 14th 08h Moon 1.5°N of Jupiter
  • 16th 02h Moon 1.9° S of Pleiades
  • 18th 06h New Moon
  • 18th 16h Saturn stationary (motion reverses from E to W)
  • 20th 11h Moon 1.7° S of Pollux
  • 21st 12h Moon 4°N of Praesepe
  • 21st 15:58 Summer solstice
  • 22nd 02h Moon 4° N of Venus
  • 22nd 11h Moon 4° N of Mars
  • 23rd 09h Moon 4° N of Regulus
  • 26th 09h First quarter
  • 27th 21h Moon 3° N of Spica

This is an extended version, with added diary, of Alan’s article published in The Scotsman on 31 May 2023, with thanks to the newspaper for permission to republish here.