Growing sunspot activity triggers strongest aurora in decades

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.

Image by Ramsay McIver

The aurora seen across Scotland on the night of 10/11 May was the strongest in more than 20 years and ranks among the greatest seen since records began. We usually count ourselves lucky to glimpse the northern lights low in the north, but this time the lightshow extended overhead and well into our southern sky. In fact, aurorae were spotted all across Europe and, in the USA, as far south as Florida and Hawaii.

Countless photographs show rays of green, pink and blue which were continually shifting and changing in intensity. The colours were more impressive in photographs and many of us used our smartphone cameras for a better view – naked eyes are just too poor at distinguishing colour at such low light levels.

The event occurred after a giant sunspot group that was crossing the Sun’s southern hemisphere unleashed several solar flares, explosions of radiation that blasted material away from the Sun and, on this occasion, towards the Earth.

AR 3663 by Robert Arnold

That material, mainly electrons and protons, was steered by the Earth’s magnetic field towards higher latitudes where it slammed into the atoms and molecules high in the atmosphere. These were excited to glow like the gas in a neon tube, producing the colours we saw. Variations in the atmospheric density and composition, and the energies involved, all played roles in generating different colours, with oxygen molecules above 100 km producing the more typical green hues and both oxygen and nitrogen responsible for the reds and pinks.

Having rotated around the Sun’s far side, the sunspot group responsible for our aurora survived to reappear at the Sun’s edge on 28 May and was again approaching its prime position where it faces the Earth. It might be too much to expect a repeat performance, but there are other spots aplenty as we near solar maximum, the peak of the Sun’s 11-years cycle of activity. In fact, sunspot numbers appear to be some 50% above the levels that were being predicted five years ago and there are suggestions that sunspot maximum could occur at any time between now and the end of this year.

You would not expect me to ignore the real dangers involved in looking at the Sun. To avoid serious eye damage, never look at the Sun directly. Rather, a web search for “safe solar observing” details what we might do instead.

The Sun is at its furthest north in the sky at the summer solstice at 21:51 BST on the 20th. Edinburgh’s sunrise/sunset times change from 04:35/21:48 BST on the 1st to 04:26/22:03 on the 20th and 04:31/22:02 on the 30th.

Now that the Sun is passing at its shallowest below our northern horizon during the night, our sky remains bathed in a night-long twilight that is enough to hinder aurora-spotting and swamp all but the brighter stars.

The brightest one visible is Arcturus in Bootes which stands high in the south at nightfall and moves into the south-west by the map times. Those maps show Leo setting in the west and the supergiant star Antares in Scorpius less than 8° above Edinburgh’s southern horizon, its red colour only accentuated by its low altitude. High in the south-east is Vega in Lyra, the leading star in the Summer Triangle it forms with Altair in Aquila and Deneb in Cygnus.

The Moon is new on the 6th and is a slender crescent, less than 3% sunlit, low in the north-west at about 23:00 BST on the 7th. By the 9th, it is brightly earthlit in the west-north-west and 8° to the left of Pollux in Gemini. It lies to the right of Regulus in Leo on the 11th, reaches first quarter on the 14th and stands just left of Spica in Virgo on the 16th. It passes Antares on the 20th and is full in Sagittarius early on the 22nd.

Later in June, the Moon lies right of Saturn before dawn on the 27th and to Saturn’s left on the 28th a few hours before its last quarter.

You may see claims that Saturn and almost all the other planets make an impressive line in the eastern sky before dawn in early June, but this is misleading and false for observers in the UK. Saturn is there, shining at magnitude 1.1 and rising in the east for Edinburgh at 02:27 on the 1st and as early as 00:35 by the 30th. However, as civil twilight floods the sky at 03:37 on the 1st, Saturn is only 9° high, and 11° right of the Moon, too low for any decent telescopic views.

We might also catch Mars which stands 3° right of the slim waning Moon on the 3rd, but it is only 3° high in the brightening twilight at 03:30 and may be a difficult spot at magnitude 1.0. Both it and Saturn are slowly climbing higher each day, so that, by the same time on the 30th, Mars is 13° high and Saturn is at 21°.

The distant and dim planets Uranus and Neptune also lie near that line from Saturn to the Sun at dawn, but are unlikely to be visible in the twilight. Jupiter, Mercury and Venus are certainly too close to the Sun for us to see at present, with Venus reaching superior conjunction on the Sun’s far side on the 4th, followed by Mercury on the 24th. Jupiter, bright at magnitude -2.0, might be glimpsed low in our north-eastern morning twilight after mid-June, though even by the 30th it is only 5° high at 03:30.

Noctilucent Clouds from Edinburgh by Mark Phillips

Noctilucent Clouds from Edinburgh by Mark Phillips

The shallow midnight Sun does mean that we may have views of noctilucent clouds, literally night-shining clouds, that form at a height of around 80km where they remain in sunlight even when our all-too-familiar lower-level clouds are in darkness. Often cirrus-like and electric-blue in colour, their favoured position migrates from the lower north-western sky from about one hour after sunset to the north-east an hour before sunrise.

Diary for 2024 June

Times are BST

  • 1st 04h Moon 0.02° S of Neptune
  • 3rd 01h Moon 2.4° N of Mars
  • 4th 17h Venus in superior conjunction of far side of Sun
  • 6th 14h New Moon
  • 9th 09h Moon 1.7° S of Pollux
  • 10th 09h Moon 4° N of Praesepe star cluster
  • 12th 05h Moon 3° N of Regulus
  • 14th 06h First quarter
  • 16th 19h Moon 1.2° N of Spica
  • 20th 12h Moon 0.3° N of Antares
  • 20th 21:51 Summer solstice
  • 22nd 02h Full Moon
  • 24th 18h Mercury in superior conjunction on far side of Sun
  • 27th 16h Moon 0.1° N of Saturn
  • 28th 23h Last quarter
  • 30th 22h Saturn stationary (motion reverses from E to W)

This is an extended version, with added diary, of Alan’s article published in The Scotsman on 31 May 2024, with thanks to the newspaper for permission to republish here.