Scotland to enjoy a partial eclipse of the Sun on the 10th
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.
An eclipse of the Sun on the morning of Thursday, the 10th, is Scotland’s celestial highlight for June, but the brighter planets are keeping a low profile and our twilit summer nights are far from ideal for stargazing.
Indeed, the night of May 30/31st was the last one until 12 July during which the Sun dipped more than 12° below Edinburgh’s northern horizon in the middle of the night and we enjoyed any official nautical darkness. For the next few weeks, then, the twilight is relentless, becoming brighter and more obtrusive the further north we travel.
The Sun itself reaches its most northerly point at 04:32 BST on the 21st, the moment of our summer solstice when the Sun is overhead at the Tropic of Cancer, 23.4° north of the equator. Sunrise/sunset times for Edinburgh, meanwhile, change from 04:35/21:47 BST on the 1st, to 04:26/22:04 on the 21st and 04:31/22:02 on the 30th.
The Moon is at last quarter on the 2nd, new as the eclipse occurs on the 10th, at first quarter on the 18th and full on the 24th. During the eclipse, the centre of the Moon’s shadow in space paints a path more than 525 km wide which crosses parts of northern Canada and Greenland and grazes the North Pole on its way to north-eastern Russia. The Moon, though, is too far away in its orbit and appears too small to hide the Sun completely at mid-eclipse. The result is that observers along the path witness an annular eclipse in which a dazzling ring of sunlight, a so-called Ring of Fire, encloses the inky black lunar disk for up to four minutes.
In a zone that stretches as far south as the Mediterranean, observers see a partial eclipse of the Sun as the Moon takes a bite out of the northern part of the Sun’s disk. Viewed from Edinburgh, the eclipse begins at 10:08 BST as the Moon touches the upper-right edge of the Sun’s disk. Mid-eclipse occurs at 11:18 when the Moon extends across the northern 43% of the Sun’s diameter. The event is over when the Moon exits the top-left edge of the Sun at 12:32.
The eclipse is deeper the further north we travel, so from Lerwick in Shetland it lasts from 10:15 until 12:43, with fully 50% of the Sun’s diameter hidden at 11:27. From London, though, only 32% is obscured at 11:13.
Remember that observing the Sun directly through any telescope or binoculars, or even with the naked eye, can lead to permanent eye damage. I could fill this note with recommended alternatives, but please check out “safe solar observing” online for yourself.
Of course, solar observing brings us into the realm of observing sunspots. These magnetic solar storms have been rare in recent years as the Sun experienced a lull in its approximately 11-years cycle of activity. Now, though, there are signs that sunspots are increasing in numbers as they build towards the next solar maximum in, perhaps, 2025.
The brightest star visible at our star map times is Arcturus in Bootes in the middle of our south-western sky though it is only marginally brighter than Vega in Lyra, high in the south-east, and Capella in Auriga low in the north.
Looking in the lower northern sky we should also be alert for noctilucent (or “night-shining”) clouds which can appear anywhere between the north-west and north-east and between, say, one hour after sunset and one hour before sunrise. Caused by ice crystals at altitudes around 82 km, these reflect sunlight to shine with a bluish light long after our all-too-frequent lower-level clouds are in darkness. Noctilucent clouds often occur with a straited or rippled appearance, not dissimilar to cirrus clouds.
In the opposite direction, low in the south, is the pronounced reddish hue of the supergiant star Antares in Scorpius. Ophiuchus the Serpent Bearer and Hercules, the Roman equivalent of the Greek hero Heracles, sprawl above Antares and include several notable star clusters though our twilit June nights are not the best for seeking them out in binoculars. Foremost is the Great Globular Cluster M13 in Hercules. Discovered by Edmond Halley of comet fame, this ball of hundreds of thousands of stars, each more than twice as old as our Sun, lies some 25,000 light years away, a gulf similar to that between us and the centre of our Milky Way galaxy.
Of the planets this month, Venus is brilliant at magnitude -3.9 and stands 10° high in the west-north-west at sunset, setting itself some 90 minutes later. Mars, also low in our western evening twilight but much fainter at magnitude 1.7, tracks from 5° below and left of Pollux in Gemini to stand near the heart of the Praesepe or Beehive star cluster in Cancer on the night of the 23rd.
Look for the slender earthlit Moon almost 7° above-left of Venus at nightfall on the 12th and just 2° above Mars a day later. The Moon lies above-right of Regulus in Leo on the 15th, above Spica in Virgo on the 19th and above Antares on the 22nd.
Saturn and Jupiter rise less than one hour after our map times and stand more than 10° high in the south-east before dawn. Jupiter, in Aquarius and conspicuous at magnitude -2.4, is 7° above-left of the Moon tomorrow morning while Saturn, fainter at magnitude 0.6 in Capricornus, lies 18° to Jupiter’s right and is slightly higher. They have another conjunction with the Moon later in the period, with Saturn above-left of the Moon on the morning of the 27th and Jupiter above the Moon on the 29th.
Diary for 2021 June
Times are BST
- 1st 10h Moon 5° S of Jupiter
- 2nd 08h Last quarter
- 10th 12h New moon and annular solar eclipse
- 11th 02h Mercury in inferior conjunction on near side of Sun
- 12th 08h Moon 1.5° N of Venus
- 13th 08h Moon 3° S of Pollux
- 13th 21h Moon 2.8° N of Mars
- 14th 08h Moon 3° N of Praesepe
- 16th 01h Moon 5° N of Regulus
- 18th 05h First quarter
- 19th 23h Moon 6° N of Spica
- 21st 04:32 Summer solstice
- 21st 06h Jupiter stationary (motion reverses from E to W)
- 23rd 05h Moon 5° N of Antares
- 23rd 20h Mars 0.02° S of Praesepe
- 24th 20h Full moon
- 27th 10h Moon 4° S of Saturn
- 28th 20h Moon 4° S of Jupiter
This is an extended version, with added diary, of Alan’s article published in The Scotsman on May 31 2021, with thanks to the newspaper for permission to republish here.