A partial eclipse of the Moon next to Saturn on the 16th
July brings a slow return to darker and longer nights as the Sun’s trek southwards continues in the wake of our summer solstice. Until the 12th, the Sun dips no more than 12° below Edinburgh’s northern horizon so that twilight persists through every night. By the month’s end, though, we enjoy almost four hours of effective darkness and, with the Moon out of the way, the fainter stars are once again on show.
The 50th anniversary of Apollo 11’s pioneering lunar landing occurs on the 20th while, for stargazers and the weather permitting, the highlight may be the partial eclipse of the Moon which comes four days earlier on the evening of the 16th, though the Moon rises, and the Sun sets, while the eclipse is already underway.
The event begins at 19:44 BST when the Moon begins to encroach of the edge of the outer shadow of the Earth, the penumbra. Between 21:02 and midnight, part of the Moon lies within the central dark umbra where, in the absence of any direct sunlight, it is illuminated in only a dim reddish glow by sunlight refracting around the edge of the Earth. The Moon rises above Edinburgh’s south-eastern horizon at 21:44 and greatest eclipse occurs at 22:31 when the Moon stands only 8° high in the twilight with its northern 65% covered by the umbra. The eclipse ends when disk exits the penumbra at 01:18.
Sunrise/sunset times for Edinburgh change from 04:31/22:01 on the 1st to 05:14/21:23 on the 31st. New moon on the 2nd brings a total eclipse of the Sun visible along a track that crosses the south-eastern Pacific to Chile and Argentina. Surrounding areas, but not Europe, enjoy a partial eclipse. The Moon reaches first quarter on the 9th, is full at the lunar eclipse on the 16th and at last quarter on the 25th.
Saturn, the fainter of the two bright planets low down in our southern night sky, lies 8° to the right of the Moon and a little higher on the evening of the lunar eclipse. One week earlier, on the 9th, it reaches opposition in the constellation Sagittarius when it lies directly opposite the Sun so that it rises at sunset and is highest in the south in the middle of the night, albeit at an elevation of only 12°. It is also closest to us, 1,351 million km, and at its brightest at magnitude 0.1.
A telescope shows Saturn’s disk to be 18 arcseconds wide while its rings extend across 42 arcseconds and have their northern face tipped Earthwards at 24 degrees. Saturn’s globe is blanketed with clouds of ammonia crystals whose shade varies in bands running parallel to its equator. They appear much less prominent than the equivalent bands on Jupiter and there are few noticeable spots.
Jupiter, itself, lies in southern Ophiuchus some 31° to the right of Saturn and far outshines its neighbour even though it dims slightly in July from magnitude -2.6 to -2.4 as its distance grows from 649 million to 691 million km. It lies just below the bright Moon on evening of the 13th when a telescope shows its disk to be 44 arcseconds wide.
The previous evening, the 12th, would be an opportune time to check out Jupiter’s Red Spot which, as I mentioned last time, appears to have been spooling some of its reddish material into its adjacent cloud belt. It is certainly measurably smaller than it was just a few weeks ago but there are also signs that the disturbance may have subsided.
The other naked eye planets are poorly placed. The brightest, magnitude -3.9 Venus, rises 50 minutes before the Sun and stands less than 5° high in the north-east at sunrise. Mercury stands 4° to the left of Mars in the west-north-west during the hour after sunset on the 1st but both are too dim, at magnitudes of 1.2 and 1.8 respectively, to be glimpsed in our bright twilight.
Mars is edging towards the Sun’s far side and reappears before dawn in October. Mercury reaches inferior conjunction between the Sun and the Earth on the 21st when it passes 5° south of the Sun on its way to our morning sky in August. When Mercury next reaches inferior conjunction, on 11 November, it passes almost centrally across the Sun’s disk in a transit that we hope to witness from Scotland.
Our charts show Jupiter and Saturn low down in our southern sky while the star Vega, only slightly brighter than Saturn, crosses the meridian high above them. Vega, of course, forms the Summer Triangle with Deneb in Cygnus, high in the east, and Altair, lower in Aquila. Our map projection squashes the Triangle somewhat – in fact, Deneb and Vega are closer together in the sky than is either star to Altair. An even larger triangle, this one almost equilateral, fills our south-western sky and has its corners at Vega, Jupiter and Arcturus, which lies due west as the leading star of Bootes.
Capella in Auriga stands at its lowest below Polaris in the north and often features in images of noctilucent clouds or NLCs. Little did I realise when I mentioned these silvery-blue “night-shining” clouds last time that 2019 was to unleash some of our best NLC displays in decades. Formed by ice condensing on high-altitude dust particles, some perhaps debris from meteors, they catch the sunlight when our usual lower-level clouds are in darkness during the middle hours of our nights. Researchers are investigating why this should be such a special year for NLCs but expect the bonanza to continue into August.
Diary for 2019 July
Times are BST
2nd 20h New moon and total solar eclipse
4th 23h Earth farthest from Sun (152,100,000 km)
6th 04h Moon 3° N of Regulus
7th 15h Mercury 4° S of Mars
9th 12h First quarter
9th 18h Saturn at opposition at distance of 1,351 million km
13th 21h Moon 2.3° N of Jupiter
16th 08h Moon 0.2° S of Saturn
16th 23h Full moon and partial lunar eclipse
20th 21h 50th anniversary of first manned lunar landing
21st 14h Mercury in inferior conjunction
24th 00h Mercury furthest E of Sun (25°)
25th 02h Last quarter
28th 02h Moon 2.3° N of Aldebaran
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on June 29th 2019, with thanks to the newspaper for permission to republish here.
Is Jupiter’s Great Red Spot unfurling before our eyes?
The Sun reaches its most northerly point at 16:54 BST on the 21st, marking the summer solstice in our northern hemisphere. Between its setting in the north-west and its rising in the north-east, it follows only a shallow arc below Edinburgh’s horizon and stands, at most, 10.6° below Edinburgh’s due-north horizon at 01:14 BST. As a result, twilight persists throughout our June nights and we must stay up late to glimpse even the brighter stars and planets.
The sunrise/sunset times for Edinburgh change from 04:36/21:46 BST on the 1st, to 04:26/22:03 on the 21st and 04:30/22:02 on the 30th. The Moon is new on the 3rd, at first quarter on the 10th, full on the 17th and at last quarter on the 25th.
At times like these, some stargazers forsake their hobby for a couple of months while others switch to observing the Sun, or, perhaps, noctilucent clouds. This June, though, the giant planet Jupiter is well worth a look as it comes to opposition on the 10th. It is then closest to us (641 million km) and stands directly opposite the Sun, so that it rises in the south-east at sunset and passes (for Edinburgh) less than 12° high in the south in the middle of the night.
Conspicuous at magnitude -2.6 as it creeps westwards against the stars of southern Ophiuchus, Jupiter outshines every other object in our night sky except for the Moon which lies close to it on the night of the 16th-17th. A small telescope or good steadily-held binoculars reveal its four main moons, the Galilean moons, as they orbit from east to west of the planet in periods that range from 1.8 days for Io to 16.7 days for Callisto. Jupiter has more moons, 79 at the latest count, than any other planet, with Saturn’s tally of 62 coming second. Jupiter’s 75 lesser moons, though, are too small and dim to be spotted using any but the largest telescopes.
Jupiter’s globe is shrouded in clouds, mainly of ammonia crystals but tinted red and brown by other compounds which may include hydrocarbons. Telescopes show bands of darker cloud and a plethora of streaks and spots that transit smartly across the disk as the planet rotates in its sub-ten-hour day.
The most famous feature, the Great Red Spot, is an anticyclonic storm that may be more than 300 years old and was once larger than three Earths. It has shrunk significantly over the last century but observations over the past two weeks suggest something startling may be afoot and even that the spot may be disintegrating. It appears that 10,000-km-long streamers of reddish gas, perhaps methane-rich, are peeling away from the spot into the adjacent cloud band, the South Equatorial Belt, that circles the planet. Likened by some to the spot unfurling, nothing on this scale has been seen before so it is just as well that NASA’s Juno probe has a ring-side view as it orbits Jupiter.
Some 30° to the east of Jupiter, below the so-called Teaspoon of Sagittarius, is our Sun’s other gas giant planet, Saturn. Rising in the south-east about one hour before our map times, it brightens slightly from magnitude 0.3 to 0.1 to rival the two brightest stars on our south map – Vega in Lyra which stands very high in the east-south-east and Arcturus in Bootes in the middle of our south-western sky. When Saturn lies just left of the Moon on the night of the 18th, it lies 1,361 million km away and a telescope shows its disk and rings to span 18 and 41 arcseconds respectively.
The constellations of Ophiuchus and Hercules sprawl across the meridian at the map times, though our twilight means that this is not the best month for spotting M13, the Great Globular Cluster in Hercules (see map). Discovered by Edmond Halley of comet fame in 1714, this ball of hundreds of thousands of stars is some 160 light years across, 22,200 light years away and is thought to have formed 11.65 billion years ago. Under the best conditions, binoculars show it as a fuzzy circular patch around two-thirds as wide as the Moon.
Although Venus is brilliant at magnitude -3.9, it rises in the north-east around 40 minutes before the Sun and is unlikely to be noticed in Scotland’s dawn twilight. Mars is now as dim as magnitude 1.8 and becoming much harder to spot low down in our north-western evening twilight. Tracking eastwards in Gemini to pass below Castor and Pollux, it sets for Edinburgh at 00:05 BST on the 5th when it is 4° to the right of the slender young earthlit Moon. Mercury, much easier at magnitude -0.7, lies 11° below-right of Mars at that time and is 4° above the horizon one hour after sunset between the 5th and 19th. Mercury passes 0.2° above Mars on the 18th and stands furthest east of the Sun (25°) on the 24th.
Scotland’s noctilucent cloud season is just beginning and we can look forward to occasional displays of these “night-shining” clouds until August. Often with a bluish-white sheen, they may appear as wisps, streaks and whirls and merge into banks with cirrus-like herring-bone patterns. The clouds are formed when ice crystallises on dust particles in a narrow range of altitudes near 82 km. Here they are high enough to catch the sun’s light when our more typical lower-level terrestrial clouds are in darkness, from, say, one hour after sunset until one hour before sunrise. They rarely reach more than 20° above the horizon and favour directions towards the north-west at nightfall shifting to the north-east before dawn.
Diary for 2019 June
Times are BST
3rd 11h New moon
4th 17h Moon 4° S of Mercury
5th 16h Moon 1.6° S of Mars
7th 09h Moon 0.5° N of Praesepe
8th 21h Moon 3° N of Regulus
10th 07h First quarter
10th 16h Jupiter at opposition at distance of 641 million km
16th 20h Moon 2.0° N of Jupiter
17th 10h Full moon
18th 16h Mercury 0.2° N of Mars
19th 05h Moon 0.4° S of Saturn
21st 16:54 Summer solstice
24th 00h Mercury furthest E of Sun (25°)
25th 11h Last quarter
30th 17h Moon 2.3° N of Aldebaran
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on May 31st 2019, with thanks to the newspaper for permission to republish here.
Dust storm rages on Mars as it stands closest since 2003
Mars comes closer to the Earth in July than at any time since its once-in-60,000-years record approach in 2003. It is just our luck that a dust storm that began a month ago now engulfs the entire planet so that the surface markings may now be glimpsed only through a patchy reddish haze.
Both current Mars rovers, Opportunity and Curiosity, are also affected. This is the most intense storm to impact Opportunity since it landed in 2004 and the vehicle has shut down because it lost power as the dust hid the Sun and coated its solar panels. It is hoped that, after the storm subsides, friendly gusts of wind will waft the dust from the panels and Opportunity will revive. If not, this would mark the end of a remarkable mission which had been planned, initially, to last for only 90 days. Its sister rover, Spirit, succumbed in 2010 after becoming stuck in soft soil.
Meanwhile, the more advanced Curiosity rover has been operating since 2012. Being nuclear powered, it is less vulnerable to the dust but its cameras are recording a dull reddened landscape beneath dusty orange skies.
For watchers in Edinburgh, Mars rises in the south-east just before midnight at the beginning of July and is conspicuous at magnitude -2.2 but only 11° high in the south during morning twilight. Look for it 4° below the Moon on the 1st as Mars moves westwards in the constellation of Capricornus.
Mars reaches opposition on the 27th when it stands opposite the Sun, rises during our evening twilight and is highest in the south in the middle of the night. By then it blazes at magnitude -2.8, making it second only to Venus in brilliance, and stands 58 million km away. A telescope shows it to be 24 arcseconds wide, with its southern polar cap tilted 11° towards us. Because Mars is edging inwards in its relatively elongated orbit, it is actually around 100,000 km closer to us on the 31st.
As Mars rises at its opposition on the 27th it once again lies below Moon, but this time the Moon is deep in eclipse as it passes almost centrally through the Earth’s shadow. The total phase of the eclipse, the longest this century, lasts from 20:30 to 22:13 BST and it is in the middle of this period, at 21:22, that the Moon rises for Edinburgh. By 22:13, and weather permitting, it may be possible to see the Moon’s dull ochre disk 5° high in the south-east. From then until 23:19, the Moon emerges eastwards from the Earth’s dark umbral shadow, and at 00:29 it is free of the penumbra, the surrounding lighter shadow.
The Earth stands at its furthest from the Sun for 2018 (152,100,000 km) on the 6th. Edinburgh’s sunrise/sunset times change from 04:31/22:01 on the 1st to 05:15/21:22 on the 31st. The Moon is at last quarter on the 6th and new on the 13th when a partial solar eclipse is visible to the south of Australia. First quarter on the 19th is followed by full moon and the total lunar eclipse on the 27th.
Our chart shows the corner stars of the Summer Triangle, Vega in Lyra, Altair in Aquila and Deneb in Cygnus, high in the south to south-east as the fainter corner stars of the Square of Pegasus are climbing in the east. The Plough stands in the middle of our north-western sky and the “W” of Cassiopeia is similarly placed in the north-east.
Venus sets before our chart times but is brilliant in the west at nightfall. It brightens from magnitude -4.0 to -4.2 but is sinking lower from night to night as it tracks southwards relative to the Sun. It passes 1.1° north of the star Regulus in Leo on the 9th as the much fainter planet Mercury (magnitude 0.4) stands 16° below-right of Venus. The little innermost planet stands furthest east of the Sun (26°) on the 12th but is a challenge to glimpse in the twilight this time around.
Venus lies to the left of the young earthlit Moon on the 15th, below-right of the Moon on the 16th and, by month’s end, stands less than 10° high at sunset before setting itself some 70 minutes later.
Jupiter lingers as a conspicuous evening object in the south-south-west at nightfall, sinking to set in the west-south-west one hour after our map times. Moving very little against the stars of Libra, it dims slightly from magnitude -2.3 to -2.1 and shows a 39 arcseconds disk when it lies below-left of the Moon on the 20th.
Saturn reached opposition on June 27 and is at its best at our star map times, albeit low in the south at a maximum altitude of less than 12° for Edinburgh. At magnitude 0.0 to 0.2, it is creeping westwards above the Teapot of Sagittarius where it lies near the Moon on the 24th and 25th. Its disk and wide-open rings appear 18 and 41 arcseconds wide respectively.
Our noctilucent, or “night-shining”, cloud season is now in full swing with sightings of several displays of these high-altitude blue-white clouds since late-May and further ones expected until August.
Often with a wispy cirrus-like appearance, noctilucent clouds are composed of ice-crystals at heights near 82 km and glimmer above our northern horizon where they catch the sunlight long after our more usual lower-level clouds are in darkness. Their nature is still something of a mystery but it may not be coincidental that the first definite record of them dates only as far back as 1885, just two years after the cataclysmic eruption of the Krakatoa volcano in Indonesia.
Diary for 2018 July
Times are BST
1st 03h Moon 5° N of Mars
6th 09h Last quarter
6th 18h Earth farthest from Sun (152,100,000 km)
9th 21h Venus 1.1° N of Regulus
11th 05h Jupiter stationary (motion reverses from W to E)
12th 06h Mercury furthest E of Sun (26°)
13th 04h New moon and partial solar eclipse S of Australia
14th 23h Moon 2.2° N of Mercury
16th 04h Moon 1.6° N of Venus
19th 21h First quarter
21st 01h Moon 4° N of Jupiter
25th 07h Moon 2.0° N of Saturn
27th 06h Mars at opposition at distance of 58 million km
27th 21h Full moon and total lunar eclipse
27th 22h Moon 7° N of Mars
29th Main peak of Delta Aquarids meteor shower
31st 09h Mars closest to Earth (57,590,000 km)
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on June 30th 2018, with thanks to the newspaper for permission to republish here.
Saturn at its best as noctilucent clouds gleam
The first day of June marks the start of our meteorological summer, though some would argue that summer begins on 21 June when (at 05:25 BST) the Sun reaches its most northerly point at the summer solstice.
Sunrise/sunset times for Edinburgh vary surprisingly little from 04:35/21:47 BST on the 1st, to 04:26/22:03 at the solstice and 04:31/22:02 on the 30th. The Moon is at first quarter on the 1st, full on the 9th, at last quarter on the 17th and new on the 24th.
The Sun is already so far north that our nights remain bathed in twilight and it will be mid-July before Edinburgh sees its next (officially) dark and moonless sky. This is a pity, for the twilight swamps the fainter stars and, from northern Scotland, only the brightest stars and planets are in view.
If we travel south, though, the nights grow longer and darker, and the spectacular Milky Way star fields in Sagittarius and Scorpius climb higher in the south. From London at the solstice, for example, official darkness, with the Sun more than 12° below the horizon, lasts for three hours, while both Barcelona and Rome rejoice in more than six hours.
It is in this same area of sky, low in the south in the middle of the night, that we find the glorious ringed planet Saturn. This stands just below the full moon on the 9th and is at opposition, directly opposite the Sun, on the 15th when it is 1,353 million km away and shines at magnitude 0.0, comparable with the stars Arcturus in Bootes and Vega in Lyra. The latter shines high in the east-north-east at our map times and, together with Altair in Aquila and Deneb in Cygnus, forms the Summer Triangle which is a familiar feature of our nights until late-autumn.
Viewed telescopically, Saturn’s globe appears 18 arcseconds wide at opposition while its rings have their north face tipped 27° towards us and span 41 arcseconds. Sadly, Saturn’s low altitude, no more than 12° for Edinburgh, means that we miss the sharpest views although it should still be possible to spy the inky arc of the Cassini division which separates the outermost of the obvious rings, the A ring, from its neighbouring and brighter B ring.
Other gaps in the rings may be hard to spot from our latitudes – we can only envy the view for observers in the southern hemisphere who have Saturn near the zenith in the middle of their winter’s night. For us, Saturn is less than a Moon’s breadth further south over our next two summers, while the ring-tilt begins to decrease again.
On the other hand, we can sympathize with those southern observers for most of them never see noctilucent clouds, a phenomenon for which we in Scotland are ideally placed. Formed by ice condensing on dust motes, their intricate cirrus-like patterns float at about 82 km, high enough to shine with an electric-blue or pearly hue as they reflect the sunlight after any run-of-the-mill clouds are in darkness. Because of the geometry involving the Sun’s position below our horizon, they are often best seen low in the north-north-west an hour to two after sunset, shifting towards the north-north-east before dawn – along roughly the path taken by the bright star Capella in Auriga during the night.
Jupiter dims slightly from magnitude -2.2 to -2.0 but (after the Moon) remains the most conspicuous object in the sky for most of the night. Indeed, the Moon lies close to the planet on the 3rd – 4th and again on the 30th. As the sky darkens at present, it stands some 30° high and just to the west of the meridian, though by the month’s end it is only half as high and well over in the SW. Our star maps plot it in the west-south-west as it sinks closer to the western horizon where it sets two hours later.
The giant planet is slow-moving in Virgo, about 11° above-right of the star Spica and 3° below-left of the double star Porrima. As its distance grows from 724 million to 789 million km, its disk shrinks from 41 to 37 arcseconds in diameter but remains a favourite target for observers.
The early science results from NASA’s Juno mission to Jupiter were released on 25 May. They reveal the atmosphere to be even more turbulent than was thought, with the polar regions peppered by 1,000 km-wide cyclones that are apparently jostling together chaotically. This is in stark contrast to the meteorology at lower latitudes, where organized parallel bands of cloud dominate in our telescopic views. In addition, the planet’s magnetic field is stronger and more lumpy than was expected. Juno last skimmed 3,500 km above the Jovian clouds on 19 May and is continuing to make close passes every 53 days.
Both Mars and Mercury are hidden in the Sun’s glare this month, the latter reaching superior conjunction on the Sun’s far side on the 21st.
Venus, brilliant at magnitude -4.3 to -4.1, is low above our eastern horizon before dawn. It stands at its furthest west of the Sun in the sky, 46°, on 3 June but it rises only 78 minutes before the Sun and stands 10° high at sunrise as seen from Edinburgh. By the 30th, it climbs to 16° high at sunrise, having risen more than two hours earlier. Between these days, it shrinks in diameter from 24 to 18 arcseconds and changes in phase from 49% to 62% illuminated. It lies left of the waning crescent Moon on the 20th and above the Moon on the following morning.
This is a slightly-revised version of Alan’s article published in The Scotsman on May 31st 2017, with thanks to the newspaper for permission to republish here.
Juno to begin hazardous mission at Jupiter
The Sun is edging southwards again but our night-long summer twilight subsides only slowly and, given that we also have bright moonlight through mid-July, we must wait until the month’s final week to enjoy a truly dark midnight sky.
From a good vantage point, we may then see the Milky Way as it arches high across our eastern sky, culminating close to the star Deneb in Cygnus. Deneb occupies the top-left corner of the Summer Triangle which remains a feature of our high southern night sky until the autumn. The Triangle was so named by our much-missed Sir Patrick Moore and has its other corners marked by Vega in Lyra and Altair in Aquila.
Sunrise/sunset times for Edinburgh change from 04:32/22:01 BST on the 1st to 05:16/21:21 on the 31st, by which date nautical twilight persists for two hours before dawn and after dusk. The Moon is new on the 4th, at first quarter on the 12th, full on the 19th and at last quarter on the 26th.
As the twilight fades at present, the giant planet Jupiter shines brightly low in the west and Mars, only a little fainter but distinctly reddish in hue, hovers at much the same altitude in the south-south-west. Our third naked-eye planet, Saturn, stands 18° to the east (left) of Mars and is creeping westwards in the southern reaches of the constellation Ophiuchus as Mars begins to accelerate eastwards in Libra.
Jupiter is nearing the end of its apparition as it sinks lower in our evening sky on its way to conjunction on the Sun’s far side in September. Its altitude above Edinburgh’s western horizon one hour after sunset falls from 11° on the 1st to less than 2° on the 31st. By then it will be difficult to spot in the bright twilight, and we will not see it again in our evening sky for another six months.
Moving eastwards in southern Leo, Jupiter remains brighter than any star, though it does fade slightly from magnitude -1.9 to -1.7 as its distance grows between 862 million and 919 million km. Viewed telescopically, its disk appears 34 arcseconds across when it stands 6° to the right of the crescent Moon on the 9th.
Although Jupiter is well past its best for telescopic study, we can expect some of our sharpest views after NASA’s Juno probe enters a highly-eccentric orbit over the planet’s poles early on July 5th UK time – the engine firing to do so is due to last for 35 minutes and end at 04:53 BST on that day. Launched in 2011, and with the benefit of a gravity assist flyby of the Earth in 2013, Juno will have travelled for 2,800 million km to reach Jupiter, not far shy of the distance between the Sun and Uranus.
Juno’s initial orbit is to carry it around Jupiter in 53.5 days, but this is to be reduced by mid-October to one of 14 days that takes within 4,200 to 4,900 km of the equatorial cloud-tops. That path plunges through Jupiter’s hazardous radiation belts and, while it avoids their most deadly regions, Juno’s sensitive electronics need to be located in a first-of-its-kind radiation-shielded vault.
Jupiter owns some of the most interesting moons we know of, but Juno is focused firmly on learning as much as possible about Jupiter’s origins and structure, from its intense magnetosphere all the way down to its core. The probe’s trio of 9-metres long solar panels provide 500 watts of power, making it the first craft to rely on solar power so far from the Sun. If it survives, the plan calls for Juno to dive to a fiery destruction in Jupiter’s atmosphere in February, 2018.
Venus, brilliant at magnitude -3.9, stands closer to the Sun in our evening twilight than Jupiter and is unlikely to be seen from our latitudes. Mercury, much fainter, enters the same area of sky following its superior conjunction on the Sun’s far side on the 7th and is even less likely to be seen.
Mars dims from magnitude -1.4 to -0.8 this month as its distance grows from 86 million to 106 million km and its diameter shrinks from 16 to 13 arcseconds. Telescopes still show some detail on its rusty surface, but it, too, stands lower each evening and by the month’s end it sets before midnight BST. Look for Mars 7° below the gibbous Moon on the evening of the 14th.
The opposing motions of Mars and Saturn mean that their separation in the sky decreases to 11°, with Saturn fainter at magnitude 0.2 to 0.4 and noticeably above-left of Mars by the month’s end. The red supergiant star Antares in Scorpius lies 6° below Saturn while the Moon stands 5° above-right of Saturn on the 15th and 9° to the planet’s left on the 16th.
Viewed telescopically, Saturn appears 18 arcseconds wide at mid-month with the north face of the rings inclined 26° towards us and 40 arcseconds from side to side. Saturn’s main moon, Titan, shines at magnitude 8.5 and is best seen through a telescope as it orbits every16 days. Catch it 3 arcminutes west of Saturn on the 4th and 20th, and a similar distance east on the 11th and 27th.
It happens that my previous note was timely in its warning about noctilucent clouds. The first good displays were sighted within a couple of days, appearing as electric-blue cirrus-like banks low above the north-western horizon after dusk and shifting round into the north-east before dawn. Composed of ice-crystals some 82 km above the ground, we should expect further shows until mid-August.
This is a slightly-revised version of Alan’s article published in The Scotsman on July 1st 2016, with thanks to the newspaper for permission to republish here.
Saturn at its best as summer begins
The Sun reaches its most northerly place in the sky at the summer solstice on the 20th, regarded by many as the start of summer in our northern hemisphere. Contradictorily, though, the days around then are also classed as midsummer though the actual days of any midsummer celebrations vary from country to country. More sensibly, in my view, the Met Office defines summer to span the months of June to August which would place the middle of summer in mid-July and, consequently, means that summer begins on June 1.
The solstice occurs late on the 20th, at 23:34 BST, while sunrise/sunset times for Edinburgh change from 04:35/21:47 on the 1st, to 04:26/22:03 on the 20th and 04:31/22:02 on the 30th. Scotland’s nights remain twilight throughout, with little hope of spotting the fainter stars and, from the north of the country, only the brighter stars and planets may be seen.
One is the beautiful ringed world Saturn which stands opposite the Sun in the sky on June 3, only twelve days after Mars’ closest opposition since 2005. Both planets shine brightly in the south at our star map times as they track westwards across the sky. Unfortunately, Saturn climbs less than 14° above Edinburgh’s horizon and Mars is a degree or so lower still so telescopic views are hindered by their low altitudes.
Having stood at its closest (75 million km) on May 30, Mars fades from magnitude -2.0 to -1.5 as it recedes to 86 million km while telescopes show it contracting from almost 19 to 16 arcseconds in diameter, still large enough to show some detail on the disk. It tracks 5° westwards into the heart of Libra this month, its motion slowing to a halt on the 30th before resuming as an easterly progress that will persist for the next two years.
Saturn’s disk is similar in size, 18 arcseconds at opposition, but its rings are 42 arcseconds wide and have their north face tipped 26° towards us. Not since 2003 have the rings been so wide open to inspection. It dims slightly, from magnitude 0.0 to 0.2 as it creeps westwards in southern Ophiuchus about 7° above-left of Antares in Scorpius.
Third but not least in our planetary line-up, Jupiter is prominent at magnitude -2.0 in the south-west as the sky darkens at present, but sinks lower with each day and sets in the west a little more than one hour after our map times. Now moving eastwards below the main figure of Leo, it passes within 0.1° south of the magnitude 4.6 double star Chi Leonis on the 10th and dims a shade to magnitude -1.9 by the 30th.
Of the other naked-eye planets, Mercury stands 24° west of the Sun on the 4th and, while well placed for observers south of the equator, is swamped in our predawn twilight. Venus reaches superior conjunction on the Sun’s far side on the 6th and is not visible either.
The Moon is new on the 5th, close to Jupiter on the 11th, at first quarter on the 12th, above Spica in Virgo on the 14th, above-right of Mars on the 17th, close to Saturn on the 18th, full in the 20th and at last quarter on the 26th.
Our star charts show the stars of the Summer Triangle, Vega, Deneb and Altair, climbing in the east to south-east as the Plough stands high in the north-west. The curve of the Plough’s handle extends to the brightest star visible at our map times, Arcturus in Bootes. Look some 20° above and to the left of Arcturus for the pretty arc of stars that make up Corona Borealis, the Northern Crown, which, because it is incomplete, should perhaps be called the Northern Tiara.
Corona’s leading star has the dual names of Gemma, for an obvious reason, and Alphecca which derives from the Arabic for “the bright of the broken ring”. At magnitude 2.2, though, it was surpassed briefly and unexpectedly exactly 150 years ago, in 1866, by the appearance of a nova (“new star”) just beyond the crown’s south-eastern edge.
Now called T Coronae Borealis (or T CrB), this reached magnitude 2.0 but plunged below naked eye visibility after only eight days to became slightly variable in brightness as a telescopic object just fainter than the tenth magnitude. To much surprise it burst into prominence again in 1946 though this time it was already fading at magnitude 3.2 when it was first spotted.
T CrB thus earned its nickname as the Blaze Star and became the brightest known of ten such recurrent novae in the sky. Studies over the past year show it slightly brighter and bluer than usual and hint that a new outburst may occur at any time, so this is one to check regularly.
Another variable star, R CrB, is usually near the sixth magnitude and the brightest star within the crown. However, normally for a few weeks or months every few years, it fades to become a dim telescopic object when, so it is thought, clouds of soot form in its atmosphere and block its light. Strangely, it has yet to recover following a record-breaking fade in 2007 and was still near the 14th magnitude a few days ago.
Despite our summer twilight, Scotland is best placed to see noctilucent or “night-shining” clouds which may appear cirrus-like and often bluish low down between the north-west after sunset and the north-east before dawn. Formed by layers of ice-crystals near 82 km in height, these are Earth’s highest clouds and able to shine in the sunlight long after our normal clouds have dimmed to darkness.
This is a slightly-revised version of Alan’s article published in The Scotsman on June 1st 2016, with thanks to the newspaper for permission to republish here.
Venus and Jupiter converge for twilight rendezvous
The perpetual twilight during Scotland’s all-too-brief June nights means that the month is rarely a vintage one for stargazing. Indeed, from the north of the country, all but the brighter stars and planets are swamped by the “gloaming” or, for those in the Northern Isles, the “simmer dim”.
This year, though, we have two powerful excuses for staying up late. Not only is the beautiful world Saturn at its stunning best, but the two brightest planets, Venus and Jupiter, are converging in our western evening sky on their way to a spectacular close conjunction low down in the twilight at the month’s end. Just expect a flurry of UFO reports.
The Sun is at its furthest north over the Tropic of Cancer at 17:38 BST on the 21st, the moment of our summer solstice when days are at their longest over Earth’s northern hemisphere. For Edinburgh, sunrise/sunset times vary from 04:35/21:46 BST on the 1st, to 04:26/22:03 on the 21st and 04:30/22:02 on the 30th. The Moon is full on the 2nd, at last quarter on the 9th, new on the 16th and at first quarter on the 24th.
Venus is brilliant in our western evening sky and sets in the west-north-west just prior to our star map times. It reaches its greatest angular distance of 45° east of the Sun on the 6th and grows even brighter from magnitude -4.3 to -4.4 – bright enough to be glimpsed in broad daylight. However, its motion against the stars is taking it southwards in the sky so that its altitude at Edinburgh’s sunset plunges from 27° on the 1st to 16° by the 30th.
As Venus approaches from 113 million to 77 million km, a telescope shows its disk swelling from 22 to 32 arcseconds across while the sunlit portion falls from 53% to 32%. The planet is said to reach dichotomy when it is 50% illuminated on the 6th, but it seems that optical effects involving its deep cloudy atmosphere mean that observers see the phase occurring several days earlier than predicted when Venus is an evening star.
Venus lies below and left of the Castor and Pollux in Gemini as the month begins, but it tracks east-south-eastwards across Cancer and into Leo to pass 0.9° north of the Praesepe star cluster (use binoculars) on the 13th.
As it does so, it closes on the night’s second brightest planet, Jupiter, which creeps much more slowly from Cancer into Leo. Jupiter stands 21° to the left of Venus on the 1st but is barely 0.4°, less than a Moon’s breadth, above-left of Venus by the evening of the 30th. The giant planet dims slightly from magnitude -1.9 to -1.8 during the period and shrinks from 34 to 32 arcseconds as it recedes from 851 million to 909 million km.
Don’t forget that Jupiter’s four main moons can be followed through a telescope or decent binoculars as they orbit from side to side of the planet. Our own Moon is a 19% sunlit crescent on the 20th when it stands 5° below Jupiter which, in turn, is 6° left of Venus. On the next evening the Moon lies 5° below-left of the star Regulus in Leo which is about to set in the west-north-west at our map times as the Plough stands high above.
Mars and Mercury are not observable this month. Mars reaches conjunction on the Sun’s far side on the 14th while Mercury reaches 22° west of the Sun on the 24th but is swamped by our morning twilight.
The constellations of Hercules and Ophiuchus, both sparsely populated with stars, loom in the south at the map times while the Summer Triangle formed by Vega, Altair and Deneb is high in the east to south-east. Were we under darker skies a few degrees further south, in southern Europe for example, then we might spy the Milky Way flowing through the Triangle as it arches across the eastern sky from Sagittarius and Scorpius in the south. The latter are rich in stars and star clusters, but they hug Scotland’s southern horizon where only the bright yellowish Saturn and the distinctly red supergiant star Antares, half as bright and more than 11° below-left of the planet, stand out.
Saturn stood at opposition on May 23 but is still observable throughout the night as it moves from the south-east at nightfall to the south-west before dawn, peaking only 16° above Edinburgh’s southern horizon thirty minutes before our map times. As the planet edges 2° westwards in eastern Libra, it tracks away from the fine double star Graffias in Scorpius, below and to its left. Look for it close to the Moon on the evenings of the 1st and 28th.
This month Saturn fades a little from magnitude 0.1 to 0.3 but remains a striking telescopic sight. Its iconic ring system is tilted 24° towards us and spans 42 arcseconds around the rotation-flattened 18 arcseconds globe.
On the opposite side of our sky to Saturn is the star Capella in Auriga which transits low across the north from the north-west at dusk to the north-north-east before dawn. It is in this region of our sky that we sometimes see noctilucent clouds. Appearing like wisps, ripples and sheets of silvery-blue cirrus, these form as ice condenses around particles near altitudes of 82 km where they glow in the sunlight after our more familiar weather or troposphere clouds are in darkness. Best seen from latitudes between 50° and 60° N, ideal for Scotland, they appear for just a few weeks around the solstice, from about mid-May to early-August.
This is a slightly-revised version of Alan’s article published in The Scotsman on May 29th 2015, with thanks to the newspaper for permission to republish here.
Sun spotting in safety at solar maximum
With Scotland’s nights still awash with twilight, many people focus on the Sun during July. There are dangers involved, though, and I don’t just mean sunburn. Specifically, we must never look at the Sun directly through binoculars or any telescope. To do so invites serious eye damage. Instead, project the Sun’s image onto a white card held away from the eyepiece or obtain an approved solar filter to fit over the objective (rather than the eyepiece) end of your instrument.
The most obvious features on the solar disk are sunspots, cooler areas that are shaped by magnetic activity and last for a few hours to several weeks. Because the Sun rotates every 27 days with respect to the Earth, spots take two weeks to cross the Sun’s face, provided they survive as long.
Sunspot numbers ebb and flow in a solar cycle of about 11 years, although the actual period varies from about 9 to 14 years. The last peak in the Sun’s activity occurred in 2000 and, following an unusually prolonged minimum between 2007 and 2010 when very few spots were seen, we are back near solar maximum though at a lower level than in 2000. This also means that solar flares, and the auroral displays that they can produce, are also more frequent even if they are hard to see given our summer twilight
As I warned last time, though, silvery or bluish noctilucent clouds are sometimes visible low down in the northern quarter of the sky and Scotland enjoyed a nice display on the night of 19-20 June. They are formed by ice crystals near 82km and more can be expected until mid-August or so.
The Sun tracks 5° southwards during July and from the 12th onwards Edinburgh enjoys at least a few minutes of official nautical darkness around the middle of the night. We need to wait a few days more for the bright Moon to leave the scene, but when it does the fainter stars should once again be visible.
If light pollution is minimal, the Milky Way may be seen arching high across the east at our star map times. Marking the central plane of our galaxy, with the greater density of distant stars, it stretches from Capella in Auriga in the north through the “W” of Cassiopeia in the north-east before flowing by Deneb in Cygnus in the east and downwards towards Sagittarius near the southern horizon. Where it passes through the Summer Triangle formed by Deneb, Vega and Altair it is split into two by obscuring interstellar dust, the Cygnus Rift.
The red star Chi Cygni, 2.5° or five Moon-widths south-west of Eta in the neck of Cygnus, pulsates every 13 months or so between a naked eye object of the fifth magnitude and a dim telescopic one near magnitude 13. It reached an unusually bright peak of better than magnitude four last year and should be near maximum again about now, though recent observations suggest it may not even hit magnitude six this time.
The Earth is 152,114,000 km from the Sun, and at its farthest for the year, on the 4th. Sunrise/sunset times for Edinburgh change from 04:31/22:01 BST on the 1st to 05:15/21:22 on the 31st when nautical darkness lasts for almost four hours around the middle of the night. The Moon is at first quarter on the 5th, full on the 12th, at last quarter on the 19th and new on the 26th.
Jupiter is barely 6° above the west-north-western horizon at sunset on the 1st and is unlikely to be visible as it heads for conjunction on the Sun’s far side on 24th.
Mars, to the right of Spica in Virgo and low down in the south-west at nightfall, sinks to set in the west-south-west at our map times. Fading from magnitude 0.0 to 0.4 this month, it tracks to the left to pass 1.3° above Spica on the 14th – the final and closest of three conjunctions between them this year.
The young Moon lies below Regulus in Leo low in the west on the evening of the 1st and close to Mars on the 5th. The 7th finds it close to Saturn and even closer to the double star Zubenelgenubi in Libra, the three making for a superb sight through binoculars. Saturn dims only slightly from magnitude 0.4 to 0.5 and hardly moves against the stars, appearing telescopically as an 18 arcseconds disk with rings 40 arcseconds wide.
A brilliant morning star at magnitude -3.9, Venus rises at about 03:00 BST and stands 12° to 14° high in the east-north-east at sunrise. As it tracks eastwards through Taurus, use it as a pointer to Mercury which is less than 8° below and left of Venus from the 10th to the 23rd as it brightens from magnitude 0.8 to -0.8. Set your alarm to catch Venus 8° to the left of the 7% illuminated waning earthlit Moon before dawn on the 24th.
While many stars are larger than our Sun, including the vast majority of stars visible to the unaided eye, there are billions that are smaller. Indeed, red dwarf stars, from about half the Sun’s mass to 1/13th as massive, are thought to make up 75% of the more than 100 billion stars in our galaxy. The smallest known star, and probably close to the smallest star possible, is a red dwarf in the constellation Lepus, just south of Orion. Smaller than Jupiter, but more massive, it has surface temperature of 1,800C and a luminosity of 1/8,000th of our Sun so that we need a large telescope just to see it even though it is only 40 light years away.
This is a slightly-revised version of Alan’s article published in The Scotsman on July 1st 2014, with thanks to the newspaper for permission to republish here.
The mysterious noctilucent clouds of summer
If we are prepared to do battle with June’s night-long twilight, and provided the weather improves at last, there is plenty of interest in our June sky. Saturn is the pick of the planets while the bright star Vega in Lyra leads the onslaught as the constellations of summer invade from the east at our star map times. We also need to be alert for noctilucent clouds as they make their seasonal appearance low in our northern sky.
The Sun is furthest north at 11:51 BST on the 21st, the instant of our summer solstice. On that day, the Sun dips only 10.6° below Edinburgh’s northern horizon in the middle of the night, so that our sky remains bathed in twilight throughout the night while from further north in Scotland the sky is brighter still. This obviously impedes our ability to see the dimmer stars and “faint fuzzies” such as galaxies and nebulae. On the other hand, it means that satellites remain sunlit whenever they pass overhead. Indeed, the International Space Station is conspicuous two or three times each night until 10 June as it transits from west to east across Scotland’s southern sky – visit heavens-above.com for predictions customised for your location.
The Sun’s shallow sweep below our northern horizon overnight also allows us occasional views of noctilucent or “night-shining” clouds. Composed of tiny ice crystals in a thin layer at a height near 82 km, they catch the sunlight long after our usual low-level clouds are in darkness and can appear like chaotic banks of electric-blue cirrus, sometimes in a herringbone pattern. Their preferred direction follows the Sun around the horizon, so they are more commonly seen low in the north-west after nightfall and towards the north-east before dawn. They occur from mid-May to mid-August but why they are more frequent than they were a century ago remains a mystery. Could the rise be due to global warming, increased industrial pollution or even particles from rocket launches?
Sunrise/sunset times for Edinburgh change from 04:35/21:47 BST on the 1st to 04:26/22:03 on the 21st and 04:31/22:02 on the 30th. The Moon is at first quarter on the 5th, full on the 13th, at last quarter on the 19th and new on the 27th.
At magnitude -1.9, our brightest evening planet continues to be Jupiter, but we must look lower into the west to catch it below Pollux in Gemini as the twilight fades. Shining at magnitude -1.9, it stands 9° above-right of the Moon on the 1st. Jupiter sinks to set in the north-west almost three hours after the Sun as June begins but by the 30th it is only 6° high at sunset and may already be lost from view.
Mercury lies 18° below and to the right of Jupiter on the 1st but is one twentieth as bright at magnitude 1.4 and fading rapidly as it moves to pass through inferior conjunction between the Sun and Earth on the 19th.
The bright star Arcturus in Bootes stands high on the meridian at nightfall but has moved to the middle of our south-western sky by the map times. This leaves our high southern sky devoid of bright stars until we come to Vega in Lyra high in the east-south-east. Directly below Vega is Altair in Aquila while Deneb in Cygnus, almost due east, completes the Summer Triangle. The arc from Vega to Arcturus cuts through Hercules and Corona Borealis, the pretty semi-circular Northern Crown whose main star has the dual names of Alphecca or, perhaps more appropriately, Gemma.
Mars fades from magnitude -0.5 to 0.0 as it tracks eastwards in Virgo towards Spica. It also recedes from 119 million to 148 million km during the month as its small disk contracts from 12 to 9 arcseconds if viewed through a telescope. Look for its reddish light about 26° high in the south-west at nightfall and catch it above the Moon on the 7th. Our maps show it sinking towards the west where it sets two hours later.
Saturn, magnitude 0.2 to 0.4, stands almost 20° high in the south at nightfall at present and continues to creep westwards in Libra almost 4° above-left of the double star Zubenelgenubi. After standing close to Spica on the 8th, the Moon lies near Saturn on the 10th when the planet appears 18 arcseconds wide, its disk set within rings that span 41 arcseconds and have their north face inclined 21° towards us. Don’t miss an opportunity to observe it this month for it will soon be following Mars lower into the south-west at nightfall, and it stands even further south in our summer sky during every year until 2022.
Continuing as a brilliant morning star of magnitude -4.0 to -3.9, Venus rises above Edinburgh’s east-north-eastern horizon 61 minutes before the Sun tomorrow and in the north-east 102 minutes before sunrise on the 30th. Before dawn on the 24th, it lies 5° left of the slender waning Moon and 6° below the Pleiades in Taurus.
Last month, I reported the prediction that the Earth would slice through streams of particles from Comet 209P/LINEAR on the morning on 24 May and that the resulting meteor shower might be spectacular. In fact, it appears that the encounter occurred as forecast, but that the resulting display was disappointing with only a few bright meteors, even for observers in the Americas for whom the timing of the outburst was ideal. Radar studies suggest that the vast majority of meteoroids were unusually small and their meteors too dim to be seen by the unaided eye.