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Our nearest planet?

The BBC radio4 programme More or Less (broadcast weekly on Fridays; repeated on a Sunday) deals with claims involving numbers or statistics. Unusually, the episode broadcast on 11 January 2019 contained an astronomical question (‘Which is our nearest planet?). That arose from a remark by (Prof) Chris Lintott in a Sky at night TV programme, where he claimed that Mars is our nearest neighbour. That was odd since surely everyone knows that the orbit of Venus is nearer to us that the orbit of Mars.

Consequently the programme, presented by Tim Harford, went to work on the answer. Since the inner planets constantly change in their relationship to one another the answer is not obvious. The question had to be adjusted to ‘Which planet spends more time as our nearest neighbour for more time than any other planet?’

This task was given to a statistical expert (‘Oliver’) who wrote a computer program to calculate which planet on average is nearest to Earth than any other. This was then commented on by David Rothery, Professor of Planetary Geoscience at the Open University. He was as surprised as anyone that the answer turned out to be Mercury! The calculation showed that the nearest planet is Mars 18 per cent of the time, Venus 36 per cent of the time, but Mercury 46 per cent of the time. This may be because Mercury’s short orbital period means that it is more frequently on our side of the sun than the two other candidates, which often spend long periods on the far side.

Actually, at the time Chris Lintott made his claim, Mars was the nearest planet.

A podcast of the radio programme is available from the More of Less website, where the discussion starts 22 minutes in.

Steuart Campbell

This is a slightly expanded version of a presentation Steuart Campbell gave to the ASE on 1 February 2019. Steuart is a member of ASE and a science writer.

Scotland’s Sky in February, 2019

Orion and Winter Hexagon in prime-time view

The maps show the sky at 22:00 GMT on the 1st, 21:00 on the 15th and 20:00 on the 28th. An arrow depicts the motion of Mars. (Click on map to enlarge)

The maps show the sky at 22:00 GMT on the 1st, 21:00 on the 15th and 20:00 on the 28th. An arrow depicts the motion of Mars. (Click on map to enlarge)

Even though the two brightest planets, Venus and Jupiter, hover low in the south-east before dawn, the shortest month brings what many consider to be our best evening sky of the year. After all, the unrivalled constellation of Orion is in prime position in the south, passing due south for Edinburgh one hour before our star map times. Surrounding it, and ideally placed at a convenient time for casual starwatchers, are some of the brightest stars and interesting groups in the whole sky.

I mentioned some of the sights in and around Orion last time, including the bright stars Procyon, Betelgeuse and Sirius which are prominent in the south at the map times and together form the Winter Triangle.

Like the Summer Triangle, this winter counterpart is defined as an asterism which is a pattern of stars that do not form one of the 88 constellations recognised by the International Astronomical Union. Both triangles are made up of stars in different constellations, but we also have asterisms that lie entirely within a single constellation, as, for example, the Sickle of Leo which curls above Regulus in the east-south-east at our map times, and the Plough which comprises the brighter stars of the Ursa Major, the Great Bear, climbing in the north-east.

Yet another asterism, perhaps the biggest in its class, includes the leading stars of six constellations and re-uses two members of the Winter Triangle. The Winter Hexagon takes in Sirius, Procyon, Pollux in Gemini and Capella in Auriga which lies almost overhead as Orion crosses the meridian. From Capella, the Hexagon continues downwards via Aldebaran in Taurus and Rigel at Orion’s knee back to Sirius.

Edinburgh’s sunrise/sunset times change from 08:08/16:45 on the 1st to 07:07/17:44 on the 28th. The Moon is new on the 4th and at first quarter on the 12th when it stands 12° below the Pleiades in our evening sky. The 13th sees it gliding into the Hyades, the V-shaped star cluster that lies beyond Aldebaran. Both the Pleiades and the Hyades are open clusters whose stars all formed at the same time. Another fainter cluster, Praesepe or the Beehive in Cancer, is visible through binoculars to the left of the Moon late on the 17th. Full moon is on the 19th with last quarter on the 26th.

A number of other open star clusters lie in the northern part of the Hexagon, two of them plotted on our chart. At the feet of Gemini and almost due north of Betelgeuse is M35, visible as a smudge to the unaided eye but easy though binoculars and telescopes which begin to reveal its brighter stars. It lies 3,870 ly (light years) away, as compared with 440 ly for the Pleiades and 153 ly for the Hyades. Further north in Auriga is the fainter M37 (4,500 ly) which binoculars show 7° north-east of Elnath, the star at the tip of the upper horn of Taurus. M36 (4,340 ly) and M38 (3,480 ly) lie from 4° and 6° north-west of M37.

Mars dims a little from magnitude 0.9 to 1.2 but remains the brightest object near the middle of our south-south-western evening sky, sinking westwards to set before midnight. Mars is 241 million km distant when it stands above the Moon on the 10th, with its reddish 5.8 arcseconds disk now too small to show detail through a telescope. As it tracks east-north-eastwards against the stars, it moves from Pisces to Aries and passes 1° above-right of the binocular-brightness planet Uranus (magnitude 5.8) on the 13th.

The usually elusive planet Mercury begins its best evening apparition of 2019 in the middle of the month as it begins to emerge from our west-south-western twilight. Best glimpsed through binoculars, it stands between 8° and 10° high forty minutes after sunset from the 21st and sets itself more than one hour later still. It is magnitude -0.3 on the 27th when it lies furthest from the Sun in the sky, 18°, and its small 7 arcseconds disk appears 45% illuminated.

Venus, brilliant at magnitude 4.3, rises for Edinburgh at 05:11 on the 1st and stands 8° high by 06:30 as twilight begins to invade the sky. That morning also finds it 6° above and right of the waning earthlit Moon. A telescope shows Venus to be 19 arcseconds in diameter and 62% sunlit.

Jupiter is conspicuous 9° to the right of, and slightly above, Venus on the 1st though it is one ninth as bright at magnitude -1.9. Larger and more interesting through a telescope, its 34 arcseconds disk is crossed by bands of cloud running parallel to its equator while its four main moons may be glimpsed through binoculars. Edging eastwards (to the left) in southern Ophiuchus, it is 9° east of the celebrated and distinctly red supergiant star Antares in Scorpius, a star so big that it would engulf the Earth and Mars if it switched places with our Sun.

Our third predawn planet, Saturn rises at 06:38 on the 1st and is more of a challenge being fainter (magnitude 0.6) in the twilight. One hour before Edinburgh’s sunrise on the 2nd, it lies only 2° above the horizon and less than 10 arcminutes above-right of the Moon’s edge. Watchers in south-eastern England see it slightly higher and may glimpse it emerge from behind the Moon at about 06:31.

Venus speeds eastwards through Sagittarius to pass 1.1° north of Saturn on the 18th and shine at magnitude -4.1 even lower in the morning twilight by the month’s end. By then, the Moon has come full circle to stand above-right of Jupiter on the 27th and to Jupiter’s left on the 28th.

Diary for 2019 February

2nd          07h Moon 0.6° N of Saturn

4th           21h New moon

10th         16h Moon 6° S of Mars

12th         22h First quarter

13th         20h Mars 1.1° N of Uranus

14th         04h Moon 1.7° N of Aldebaran

18th         03h Moon 0.3° S of Praesepe

18th         14h Venus 1.1° N of Saturn

19th         13h Moon 2.5° N of Regulus

19th         16h Full moon

26th         11h Last quarter

27th         01h Mercury furthest E of Sun (18°)

27th         14h Moon 2.3° N of Jupiter

Alan Pickup

This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on January 31st 2019, with thanks to the newspaper for permission to republish here.

Scotland’s Sky in January, 2019

Rise early for a total lunar eclipse on the 21st

The maps show the sky at 21:00 GMT on the 1st, 20:00 on the 16th and 19:00 on the 31st. An arrow depicts the motion of Mars. (Click on map to enlarge)

The maps show the sky at 21:00 GMT on the 1st, 20:00 on the 16th and 19:00 on the 31st. An arrow depicts the motion of Mars. (Click on map to enlarge)

Any month that has the glorious constellation of Orion in our southern evening sky is a good one for night sky aficionados. Add one of the best meteor showers of the year, a total eclipse of the Moon, a meeting between the two brightest planets and a brace of space exploration firsts and we should have a month to remember

Orion rises in the east as darkness falls and climbs well into view in the south-east by our star map times. Its two leading stars are the blue-white supergiant Rigel at Orion’s knee and the contrasting red supergiant Betelgeuse at his opposite shoulder – both are much more massive and larger than our Sun and around 100,000 times more luminous.

Below the middle of the three stars of Orion’s Belt hangs his Sword where the famous and fuzzy Orion Nebula may be spied by the naked eye on a good night and is usually easy to see through binoculars. One of the most-studied objects in the entire sky, it lies 1,350 light years away and consists of a glowing region of gas and dust in which new stars and planets are coalescing under gravity.

The Belt slant up towards Taurus with the bright orange giant Aldebaran and the Pleiades cluster as the latter stands 58° high on Edinburgh’s meridian. Carry the line of the Belt downwards to Orion’s main dog, Canis Major, with Sirius, the brightest star in the night sky. His other dog, Canis Minor, lies to the east of Orion and is led by Procyon which forms an almost-equilateral triangle with Sirius and Betelgeuse – our so-called Winter Triangle.

The Moon stands about 15° above Procyon when it is eclipsed during the morning hours of the 21st. The event begins at 02:36 when the Moon lies high in our south-western sky, to the left of Castor and Pollux in Gemini, and its left edge starts to enter the lighter outer shadow of the Earth, the penumbra.

Little darkening may be noticeable until a few minutes before it encounters the darker umbra at 03:34. Between 04:41 and 05:46 the Moon is in total eclipse within the northern half of the umbra and may glow with a reddish hue as it is lit by sunlight refracting through the Earth’s atmosphere. The Moon finally leaves the umbra at 06:51 and the penumbra at 07:48, by which time the Moon is only 5° high above our west-north-western horizon in the morning twilight.

This eclipse occurs with the Moon near its perigee or closest point to the Earth so it appears slightly larger in the sky than usual and may be dubbed a supermoon. Because the Moon becomes reddish during totality, there is a recent fad for calling it a Blood Moon, a term which has even less of an astronomical pedigree than supermoon. Combine the two to get the frankly ridiculous description of this as a Super Blood Moon.

Sunrise/sunset times for Edinburgh change from 08:44/15:49 on the 1st to 08:10/16:43 on the 31st. New moon early on the 6th, UK time, brings a partial solar eclipse for areas around the northern Pacific. First quarter on the 14th is followed by full moon and the lunar eclipse on the 21st and last quarter on the 27th.

The Quadrantids meteor shower is active until the 12th but is expected to peak sharply at about 03:00 on the 4th. Its meteors, the brighter ones leaving trains in their wake, diverge from a radiant point that lies low in the north during the evening but follows the Plough high into our eastern sky before dawn. With no moonlight to hinder observations this year, as many as 80 or more meteors per hour might be counted under ideal conditions.

Mars continues as our only bright evening planet though it fades from magnitude 0.5 to 0.9 as it recedes. Tracking through Pisces and well up in the south at nightfall, it stands above the Moon on the 12th. Our maps show it sinking in the south-west and it sets in the west before midnight.

Venus, its brilliance dimming only slightly from magnitude -4.5 to -4.3, stands furthest west of the Sun (47°) on the 6th and is low down (and getting lower) in our south-eastern predawn sky. Look for it below and left of the waning Moon on the 1st with the second-brightest planet, Jupiter at magnitude -1.8, 18° below and to Venus’s left. As Venus tracks east-south-eastwards against the stars, it sweeps 2.4° north of Jupiter in an impressive conjunction on the morning of the 22nd while the 31st finds it 8° left of Jupiter with the earthlit Moon directly between them.

Saturn, magnitude 0.6, might be glimpsed at the month’s end when it rises in the south-east 70 minutes before sunrise but Mercury is lost from sight is it heads towards superior conjunction on the Sun’s far side on the 30th.

China hopes that its Chang’e 4 spacecraft will be the first to touch down on the Moon’s far side, possibly on the 3rd. Launched on December 7 and named for the Chinese goddess of the Moon, it needs a relay satellite positioned beyond the Moon to communicate with Earth.

Meantime, NASA’s New Horizons mission is due to fly within 3,500 km of a small object a record 6.5 billion km away when our New Year is barely six hours old. Little is known about its target, dubbed Ultima Thule, other than that it is around 30 km wide and takes almost 300 years to orbit the Sun in the Kuiper Belt of icy worlds in the distant reaches of our Solar System.

Diary for 2019 January

1st            06h New Horizons flyby of Ultima Thule

1st            22h Moon 1.3° N of Venus

2nd          06h Saturn in conjunction with Sun

3rd           05h Earth closest to Sun (147,100,000 km)

3rd           08h Moon 3° N of Jupiter

4th           03h Peak of Quadrantids meteor shower

6th           01h New moon and partial solar eclipse

6th           05h Venus furthest W of Sun (47°)

12th         20h Moon 5° S of Mars

14th         07h First quarter

17th         19h Moon 1.6° N of Aldebaran

21st         05h Full moon and total lunar eclipse

21st         16h Moon 0.3° S of Praesepe

22nd        06h Venus 2.4° N of Jupiter

23rd         02h Moon 2.5° N of Regulus

27th         21h Last quarter

30th         03h Mercury in superior conjunction

31st         00h Moon 2.8° N of Jupiter

31st         18h Moon 0.1° N of Venus

Alan Pickup

This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on December 31st 2018, with thanks to the newspaper for permission to republish here.

Scotland’s Sky in December, 2018

Comet sweeps near Earth as meteors streak from Gemini

The maps show the sky at 21:00 GMT on the 1st, 20:00 on the 16th and 19:00 on the 31st. Also indicated are the motions of both Mars and Comet Wirtanen. (Click on map to enlarge)

The maps show the sky at 21:00 GMT on the 1st, 20:00 on the 16th and 19:00 on the 31st. Also indicated are the motions of both Mars and Comet Wirtanen. (Click on map to enlarge)

December brings our longest and perhaps most interesting nights of the year. The two stand-out planets are Mars in the evening and Venus before dawn, the latter now as brilliant as it ever gets and the source of a flurry of recent UFO reports. We may also enjoy the rich and reliable Geminids meteor shower and Comet Wirtanen looks set to be the brightest comet of the year.

The comet’s progress is plotted on our charts, beginning low in the south near the Cetus-Eridanus border on the 1st and sweeping northwards and eastwards through Taurus to Auriga and beyond. A small comet with an icy nucleus possibly less than 1 km wide, Wirtanen was discovered in 1948 and orbits the Sun every 5.4 years between the Earth and Jupiter. It was the original destination of the European Space Agency’s Rosetta mission before delays forced the probe to target Comet Churyumov–Gerasimenko instead.

Comet Wirtanen reaches perihelion, its closest to the Sun and just beyond the Earth’s orbit, on the 12th. It is nearest the Earth on the 16th, passing only 11.6 million km away in the tenth closest approach of any observed comet since 1950. On that evening it lies 4° east (left) of the Pleiades and may appear as a large fuzzy ball lacking any obvious tail.

Predictions of its appearance at that time vary, but I suspect that its total brightness may be around the fourth magnitude, a little brighter than the fainter stars plotted on our charts. While this would normally put it well within naked-eye range, the fact that it is so close to the Earth is likely to mean that its light is spread out over an area even wider than the Pleiades. Unless we have a good dark sky, we may struggle to see its extended glow, and it is a pity that the gibbous Moon (63% sunlit) will also hinder observations before midnight. Only a week later, on the evening of the 23rd, it lies only 1° east-south-east of the bright star Capella but will be fading in still brighter moonlight.

The Sun reaches its most southerly point at the winter solstice at 22:23 GMT on the 21st as sunrise/sunset times for Edinburgh change from 08:19/15:44 GMT on the 1st to 08:42/15:40 on the 21st and 08:44/15:48 on the 31st. The Moon is new on the 7th, at first quarter on the 15th, full on the 22nd and at last quarter on the 29th.

Our charts show Andromeda and its Galaxy high in the south as Orion stands proudly in the south-east below Taurus and the Pleiades. Castor lies above Pollux in Gemini in the east and is close to the point in the sky that marks the radiant of the Geminids meteor shower.

The Geminids always produce an abundance of slow bright meteors which streak in all parts of the sky as they diverge from the radiant. The latter climbs to pass high in the south at around 02:00 and sinks into the west before dawn. The shower is active from the 8th to the 17th with the night of 13th-14th expected to be the best as meteor rates build to a peak at around dawn. An observer under an ideal dark sky with the radiant overhead may count upwards of 100 meteors per hour making the Geminids the highest-rated of our annual showers, though most of us under inferior skies may glimpse only a fraction of these.

Mars shines brightly some 25° high in the south as night falls for Edinburgh at present and is almost 10° higher by the month’s end after moving east-north-eastwards from Aquarius into Pisces. Our maps have it sinking in the south-west on its way to setting in the west before midnight. Although the brightest object in its part of the sky, it dims from magnitude 0.0 to 0.5 as it recedes from 151 million to 189 million km. When Mars stands above the Moon on the 14th, a telescope shows its ochre disk to be only 8 arcseconds across.

Saturn, magnitude 0.6, hangs just above our south-western horizon at nightfall as December begins but is soon lost in the twilight. Our other two evening planets, Uranus and Neptune, are visible through binoculars at magnitudes of 5.7 and 7.9 in Pisces and Aquarius respectively. Mars acts as an excellent guide on the evening of the 7th when Neptune stands about one quarter of a Moon’s breadth below-right of Mars.

Venus, now at its best as a dazzling morning star, rises in the east-south-east four hours before the Sun and climbs towards the south by dawn. This month it dims slightly from magnitude -4.7 to -4.5 as it tracks away from Virgo’s brightest star Spica in Virgo into the next constellation of Libra. Telescopes shows its crescent shrink from 40 to 26 arcseconds in diameter. Look for Venus below-left of the Moon on the morning of the 3rd and to the Moon’s right on the 4th.

Mercury is set to become as a morning star very low in the south-east and is soon to be joined by the even brighter Jupiter. Mercury rises more than 100 minutes before the Sun from the 5th to the 24th and stands between 5° and 9° high forty minutes before sunrise. It shines at magnitude 0.8 when it lies 7° below-left of the impressively earthlit Moon on the 5th, and triples in brightness to magnitude -0.4 by the 24th.

Jupiter, conspicuous at magnitude -1.8, emerges from the twilight and moves from 9° below-left of Mercury on the 11th to pass 0.9° south of Mercury on the 21st.

Diary for 2018 December

3rd            19h Moon 4° N of Venus

5th            21h Moon 1.9° N of Mercury

7th            07h New moon

7th           15h Mars 0.04° N of Neptune

9th           06h Moon 1.1° N of Saturn

12th         23h Comet Wirtanen closest to Sun (158m km)

14th         08h Peak of Geminids meteor shower

14th         23h Moon 4° S of Mars

15th         11h Mercury furthest W of Sun (21°)

15th         12h First quarter

16th         13h Comet Wirtanen closest to Earth (11.6m km) and 3.6° SE of Pleiades

20th         02h Jupiter 5° N of Antares

21st         08h Moon 1.7° N of Aldebaran

21st         15h Mercury 0.9° N of Jupiter

21st         22:23 Winter solstice

22nd        18h Full moon

23rd         18h Comet Wirtanen 0.9° SE of Capella

25th         05h Moon 0.3° S of Praesepe in Cancer

29th         10h Last quarter

Alan Pickup

This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on November 30th 2018, with thanks to the newspaper for permission to republish here.

Scotland’s Sky in November, 2018

InSight probe to land on bright evening planet Mars

The maps show the sky at 21:00 GMT on the 1st, 20:00 on the 16th and 19:00 on the 30th. An arrow depicts the motion of Mars. (Click on map to enlarge)

The maps show the sky at 21:00 GMT on the 1st, 20:00 on the 16th and 19:00 on the 30th. An arrow depicts the motion of Mars. (Click on map to enlarge)

The Summer Triangle, still high in the south at nightfall, shifts to the west by our map times as our glorious winter constellations climb in the east. Taurus with the Pleiades and its leading star Aldebaran (close to the Moon on the 23rd) stands well clear of the horizon while Orion is rising below and dominates our southern sky after midnight.

In the month that should see NASA’s InSight lander touch down on its surface, the planet Mars continues as a prominent object in the south at nightfall. Venus springs into view as a spectacular morning star but we must wait to see whether the Leonids meteor shower, which has produced some storm-force displays in the past, gives us any more than the expected few meteors this year.

InSight is due to land on the 26th on a broad plain called Elysium Planitia that straddles Mars’ equator. There it will place an ultra-sensitive seismometer directly onto the surface and cover it with a dome-like shell to shield it from the noise caused by wind and heat changes. This should be able of detect marsquakes and meteor impacts that occur all around Mars. Other InSight experiments will hammer a spike up to five metres into the ground to measure Mars’ heat flow, and further investigate the planet’s interior structure by using radio signals to track tiny wobbles in its rotation.

Until recently, Mars has remained low down as it performed a loop against the stars in the south-western corner of Capricornus. That loop, resulting entirely from our changing vantage point as the Earth overtook Mars and came within 58 million km on 31 July, took Mars more than 26° south of the sky’s equator and 3° further south than the Sun stands at our winter solstice.

Now, though, Mars is climbing east-north-eastwards on a track that will take it further north than the Sun ever gets by the time it disappears into Scotland’s night-long twilight next summer. One by-product of this motion is that Mars’ setting time is remarkably constant over the coming months, being (for Edinburgh) within 13 minutes of 23:42 GMT from now until next May.

This month sees Mars leave Capricornus for Aquarius and shrink as seen through a telescope from 12 to 9 arcseconds as it recedes from 118 million to 151 million km. Its path, indicated on our southern chart, carries it 0.5° (one Moon’s breadth) north of the multiple star Deneb Algedi, the goat’s tail, on the 5th. It almost halves in brightness, from magnitude -0.6 to 0.0, but its peak altitude above Edinburgh’s southern horizon early in the night improves from 16° to 25°, though by our map times it is sinking lower towards the south-west.

Mars is not our sole evening planet since Saturn shines at magnitude 0.6 low down in the south-west at nightfall. It is only a degree below-right of the young Moon on the 11th and sets more than 90 minutes before our map times. The two most distant planets, Neptune and Uranus, are also evening objects and may be glimpsed through binoculars at magnitudes 7.9 and 5.7 in Aquarius and Aries respectively.

Edinburgh’s sunrise/sunset times vary from 07:19/16:32 on the 1st to 08:17/15:45 on the 30th. The Moon is new on the 7th, at first quarter and below-right of Mars on the 15th, full on the 23rd and at last quarter on the 30th.

Jupiter is hidden in the solar glare as it approaches conjunction on the Sun’s far side on the 26th. Mercury stands furthest east of the Sun (23°) on the 6th but is also invisible from our northern latitudes.

Venus, though, emerges rapidly from the Sun’s near side into our morning twilight where it stands to the left of the star Spica in Virgo. Shining brilliantly at magnitude -4.1, the planet rises in the east-south-east only 29 minutes before the Sun on the 1st. By the 6th, though, it rises 80 minutes before sunrise and stands 8° below and right of the impressively earthlit waning Moon. Venus itself is 58 arcseconds wide and 4% illuminated on that morning, its slender crescent being visible through binoculars. By the 30th, Venus rises four hours before the Sun, climbs to stand 23° high in the south-south-east at sunrise and appears as a 41 arcseconds and 25% sunlit crescent.

It is just as well that my previous note led on the usually neglected Draconids meteor shower because observers, at least those under clear skies, were thrilled to see it provide perhaps the best meteor show of 2018. For just a few hours around midnight on 8-9th October, the sky became alive with slow meteors at rates of up to 100 meteors per hour or more.

Leonid meteors arrive this month between the 15th and 20th, with the shower expected to hit its usually-brief peak at around 01:00 on the 18th. Although they flash in all parts of the sky, they diverge from a radiant point in the so-called Sickle of Leo which rises in the north-east before midnight and climbs high into the south before dawn. No Leonids appear before the radiant rises, but even with the radiant high in a dark sky we may see fewer than 20 per hour – all of them very swift and many of the brighter ones leaving glowing trains in their wake.

Leonid meteoroids come from Comet Tempel-Tuttle which orbits the Sun every 33 years and was last in our vicinity in 1998. There has not been a Leonids meteor storm since 2002 and we may be a decade or more away from the next one, or are we?

Diary for 2018 November

2nd           05h Moon 2.1° N of Regulus

6th            16h Mercury furthest E of Sun (23°)

7th            16h New moon

11th         16h Moon 1.5° N of Saturn

15th         15h First quarter

16th         04h Moon 1.0° S of Mars

18th         01h Peak of Leonids meteor shower

23rd         06h Full moon

23rd         22h Moon 1.7° N of Aldebaran

26th         07h Jupiter in conjunction with Sun

26th         20h InSight probe to land on Mars

27th         09h Mercury in inferior conjunction on Sun’s near side

27th         21h Moon 0.4° S of Praesepe

30th         00h Last quarter

Alan Pickup

This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on October 31st 2018, with thanks to the newspaper for permission to republish here.

Scotland’s Sky in October, 2018

Draconid meteors glide away from the Dragon’s head

The maps show the sky at 23:00 BST on the 1st, 22:00 BST (21:00 GMT) on the 16th and at 20:00 GMT on the 31st. An arrow depicts the motion of Mars. Summer time ends at 02:00 BST on the 28th when clocks are set back one hour to 01:00 GMT. (Click on map to enlarge)

The maps show the sky at 23:00 BST on the 1st, 22:00 BST (21:00 GMT) on the 16th and at 20:00 GMT on the 31st. An arrow depicts the motion of Mars. Summer time ends at 02:00 BST on the 28th when clocks are set back one hour to 01:00 GMT. (Click on map to enlarge)

Mars dominates our southern evening sky but most of the other bright planets are poorly placed this month. Even so, our October nights are full of interest, from the Summer Triangle in the evening to the star-fest around Orion before dawn.

Although Mars dims from magnitude -1.3 to -0.6, its reddish light remains prominent as it moves from low in the south-south-east at nightfall to the south-south-west at our map times and onwards to set in the south-west a little before 01:00 BST (midnight GMT). As its distance grows from 89 million to 118 million km, and its diameter shrinks from 16 to 12 arcseconds, the planet speeds through Capricornus to climb 6° northwards and that much higher in our sky. Catch it to the left of the Moon on the 17th and below-right of the Moon on the 18th.

The Sun tracks 11° southwards as Edinburgh’s sunrise/sunset times change from 07:15/18:48 BST (06:15/17:48 GMT) on the 1st to 07:17/16:35 GMT on the 31st. The Moon is at last quarter on the 2nd, new on the 9th, at first quarter on the 16th, full (the Hunter’s Moon) on the 24th and back at last quarter on the 31st.

Our charts show the Plough in the north as it moves below Polaris, the Pole Star. Mizar, in the Plough’s handle, forms a famous double star with the fainter Alcor – the pair being separated by about one third the diameter of the Moon. Once held as a (not very rigorous) test of eyesight, they were dubbed “The Horse and Rider”.

Both lie 83 light years (ly) from us although we can’t be certain that they are tied together by gravity. In any case, we are not talking about just two stars, for Alcor has a faint companion and most telescopes show Mizar to be a binary star – the first to be discovered telescopically in the 17th century. Spectroscopes reveal that each of Mizar’s components is itself binary, so Mizar and Alcor, if they are truly associated, together form a sextuplet star system.

Mizar is the same brightness, magnitude 2.2, as Eltanin which lies 14° to the right of Vega and very high in the west at nightfall, falling into the north-west overnight. It is the brightest star in Draco and a member of a quadrilateral that marks the head of the Dragon whose body and tail twist to end between the Plough and Polaris. It lies 154 ly away but is approaching the Sun and will pass within 28 ly in another 1.5 million years to become the brightest star in Earth’s night sky.

Meteors from the Draconids shower diverge from a radiant point that lies close to Draco’s head (see our north map) between the 7th and 10th. Don’t expect a major display – perhaps no more than 10 meteors per hour, though all of them are very slow as they glide away from the radiant. The shower’s peak is due in a moonless sky around midnight on the 8th-9th and is worth checking because some years surprise us with strong displays and the shower’s parent comet, Comet Giacobini-Zinner, was visible through binoculars when it swept within 59 million km last month.

A better-known comet, Halley, is responsible for the meteors of the Orionids shower which lasts from the 16th to the 30th and has a broad but not very intense peak of fast meteors between the 21st and 24th. The radiant point, between Orion and Gemini, rises in the east-north-east soon after our map times and passes high in the south before dawn. Sadly, the peak coincides with the full moon, so don’t expect much of a show.

From high in the south at nightfall, the Summer Triangle (Vega, Deneb and Altair) tumbles into our western sky by the map times. By then, the less impressive and rather empty Square of Pegasus is in the south and Taurus and the Pleiades star cluster are climbing in the east. Orion rises below Taurus over the next two hours and crosses the meridian as the night ends.

Neptune and Uranus, now well placed in the evening, may be located through binoculars using better charts than I can provide here. A web search, for example for “Neptune finder chart”, should help. Neptune shines at magnitude 7.8 and lies in Aquarius at a distance of 4,342 million km on the 1st. Uranus is 2,824 million km away in Aries, near its border with Pisces, when it stands opposite the Sun in the sky (opposition) on the 24th. Although the full Moon stands close to it on that day, its magnitude of 5.7 makes it just visible to the unaided eye under a good dark and moonless sky.

October should see the launch of the European Space Agency’s BepiColombo mission to Mercury, but the planet itself is too low in our evening twilight to be seen. Venus sweeps around the Sun’s near side at inferior conjunction on the 26th and remains hidden in the Sun’s glare.

Jupiter is bright (magnitude -1.8) but less than 8° high in the south-west at sunset as the month begins. One of our last chances of spotting it in our bright evening twilight comes on the 11th when it lies 4° below-left of the young earthlit Moon.

Saturn, magnitude 0.5 and edging eastwards in Sagittarius, stands less than 10° high above Edinburgh’s south-south-western horizon as the sky darkens and sets in the south-west some 45 minutes before our map times. Look for it to the left of the Moon on the 14th.

Diary for 2018 October

Times are BST until the 28th

2nd           11h Last Quarter

9th            00h Peak of Draconids meteor shower

9th            05h New moon

11th         22h Moon 4° N of Jupiter

15th         04h Moon 1.8° N of Saturn

16th         19h First quarter

18th         14h Moon 1.9° N of Mars

21st – 24th         Peak of Orionids meteor shower

24th         02h Uranus at opposition at distance of 2,824m km

24th         18h Full moon

26th         15h Venus in inferior conjunction on Sun’s near side

28th         02h BST = 01h GMT End of British Summer Time

31st         17h GMT Last quarter

Alan Pickup

This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on September 29th 2018, with thanks to the newspaper for permission to republish here.

Scotland’s Sky in September, 2018

Summer Triangle stars as autumn evenings begin

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 depicts the motion of Mars. (Click on map to enlarge)

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 depicts the motion of Mars. (Click on map to enlarge)

We may be edging towards autumn, but the Summer Triangle, the asterism formed by the bright stars Vega, Altair and Deneb, looms high in the south as night falls and shifts into the high south-west by our star map times later in the evening. Vega, almost overhead as the night begins, is the brightest of the three and lies in the small box-shaped constellation of Lyra the Lyre.

The next brightest, Altair in Aquila the Eagle, stands lower in the middle of our southern sky and, at 16.7 light years (ly), is one of the nearest bright stars to the Sun – eight light years closer than Vega. Flanking Altair, like the two sides of a balance, are the fainter stars Alshain (below Altair) and Tarazed (above) whose names come from “shahin-i tarazu”, the Arabic phrase for a balance.

Deneb, 25° from Vega, lies very high in the south-east at nightfall and overhead at our map times. It marks the tail of Cygnus the Swan which is flying overhead with wings outstretched and its long neck reaching south-westwards to Albireo, traditionally the swan’s beak. Although it is the dimmest corner-star of the Triangle, Deneb is one of the most luminous stars in our galaxy. Current estimates suggest that it shines some 200,000 time more brightly than our Sun from a distance of perhaps 2,600 ly, but its power and distance are hard to measure and the subject of some controversy.

Also controversial is the nature of Albireo. Even small telescopes show it as a beautiful double star in which a brighter golden star contrasts with a dimmer blue one. The mystery concerns whether the pair make up a real binary, with the two stars locked in orbit together by gravity, or whether this is just the chance alignment of two stars at different distances. Now measurement by the European Space Agency’s Gaia spacecraft appear to confirm the chance alignment theory.

The Milky Way, the band of countless distant stars in the plane of our galaxy, flows through the Summer Triangle and close to Deneb as it arches across our evening sky. Scan it through binoculars to glimpse a scattering of other double stars and star clusters.

One interesting stellar group is the so-called Coathanger which lies 8°, a little more than a normal binocular field-of-view, south of Albireo. It is also easy to locate one third of the way from Altair to Vega. Its line of stars, with a hook of stars beneath, gives it the appearance of an upside-down coat hanger. For decades this was regarded as a true star cluster, whose stars formed together, and its alternative designations as Brocchi’s Cluster and Collinder 399 reflect this. In 1998, though, results from the Hipparcos satellite, Gaia’s predecessor, proved that the Coathanger’s stars are at very different distances so that it, like Albireo, is simply a fortuitous chance alignment.

The Sun sinks 11.5° southwards during September to cross the sky’s equator at 02:54 BST on the 23rd. This marks our autumnal equinox and, by one definition, the beginning of autumn in the northern hemisphere. Sunrise/sunset times for Edinburgh change from 06:17/20:07 BST on the 1st at 07:13/18:51 on the 30th. The Moon is at last quarter on the 3rd, new on the 9th, at first quarter on the 17th and full on the 25th.

Venus is brilliant at magnitude -4.4 and 45° from the Sun on the 1st but it is only 4° above Edinburgh’s west-south-western horizon at sunset and sets 35 minutes later as its evening apparition as seen from Scotland comes to an end.

The other inner planet, Mercury, is prominent but low in the east-north-east before dawn until about the 14th. Glimpse it at magnitude -1.1 when it lies 1° above-left of Regulus in Leo on the 6th and 9° below-left of the impressively earthlit waning Moon on the 8th.

Jupiter is conspicuous but very low in the south-west at nightfall, sinking to set in the west-south-west one hour before our map times. Look for it below-right of the Moon on the 13th.

Saturn and Mars are in the far south of our evening sky. Saturn, the fainter of the two at magnitude 0.4 to 0.5, stands above the Teapot of Sagittarius and is just below and right of the Moon on the 17th when a telescope shows that its rings span 38 arcseconds around its 17 arcseconds disk. It sets in the south-west some 70 minutes after our map times.

Mars stands more than 25° east (left) of Saturn, tracks 7° eastwards and northwards in Capricornus and stands near the Moon on the 19th and 20th. It is easily the brightest object (bar the Moon) in the sky at our map times though it more than halves in brightness from magnitude -2.1 to -1.3. As its distance increases from 67 million to 89 million km, its ochre disk shrinks from 21 to 16 arcseconds. The dust storm that blanketed the planet since June has now died down.

Finally, we have a chance to spot the Comet Giacobini-Zinner as it tracks south-eastwards past the bright star Capella in Auriga, low in the north-east at our map times but high in the east before dawn. The comet takes only 6.6 years to orbit the Sun and should appear in binoculars as a small oval greenish smudge only 0.9° to the right of Capella on the evening of the 2nd when it is 60 million km away. Moving at almost 2° per day, it passes less than 7° north-east of Elnath in Taurus (see chart) on the morning of the 11th, just a day after it reaches perihelion, its closest (152 million km) to the Sun.

Diary for 2018 September

Times are BST

2nd           10h Venus 1.4° S of Spica

3rd            03h Moon 1.2° N of Aldebaran

3rd            04h Last quarter

6th            11h Saturn stationary (motion reverses from W to E)

7th            04h Moon 1.1° S of Praesepe in Cancer

7th            19h Neptune at opposition

8th            23h Moon 0.9° N of Mercury

9th            19h New moon

10th         08h Comet Giacobini-Zinner closest to Sun (152 million km)

14th         03h Moon 4° N of Jupiter

16th         14h Mars closest to Sun (206,661,000 km)

17th         00h First quarter

17th         17h Moon 2.1° N of Saturn

20th         08h Moon 5° N of Mars

21st         03h Mercury in superior conjunction

23rd         02:54 Autumnal equinox

25th         04h Full moon

30th         09h Moon 1.4° N of Aldebaran

Alan Pickup

This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on August 31st 2018, with thanks to the newspaper for permission to republish here.

Scotland’s Sky in August, 2018

Perseid meteor shower peaks in planet-rich sky

The maps show the sky at midnight BST on the 1st, 23:00 on the 16th and 22:00 on the 31st. An arrow depicts the motion of Mars. (Click on map to enlarge)

The maps show the sky at midnight BST on the 1st, 23:00 on the 16th and 22:00 on the 31st. An arrow depicts the motion of Mars. (Click on map to enlarge)

The persistent twilight that has swamped Scotland’s night sky since May is subsiding in time for us to appreciate four bright evening planets and arguably the best meteor shower of the year.

The Perseid shower returns every year between 23 July and 20 August as the Earth cuts through the stream of meteoroids that orbit the Sun along the path of Comet Swift-Tuttle. As they rush into the Earth’s atmosphere at 59 km per second, they disintegrate in a swift streak of light with the brighter ones often laying down a glowing train that may take a couple of seconds or more to dissipate.

The shower is due to peak in the early hours of the 13th at around 02:00 BST with rates in excess of 80 meteors per hour for an observer under ideal conditions – under a moonless dark sky with the shower’s radiant point, the place from which the meteors appear to diverge, directly overhead. We should lower our expectations, however, for although moonlight is not a problem this year, most of us contend with light pollution and the radiant does not stand overhead.

Even so, observable rates of 20-40 per hour make for an impressive display and, unlike for the rival Geminid shower in December, we don’t have to freeze for the privilege. Indeed, some people enjoy group meteor parties, with would-be observers reclining to observe different parts of the sky and calling out “meteor!” each time they spot one. Target the night of 12th-13th for any party, though rates may still be respectable between the 9th and 15th.

The shower takes its name from the fact that its radiant point lies in the northern part of the constellation Perseus, see the north map, and climbs from about 30° high in the north-north-east as darkness falls to very high in the east before dawn. Note that Perseids fly in all parts of the sky – it is just their paths that point back to the radiant.

Records of the shower date back to China in AD 36 and it is sometimes called the Tears of St Lawrence after the saint who was martyred on 10 August AD 258, though it seems this title only dates from the nineteenth century.

Sunrise/sunset times for Edinburgh change this month from 05:17/21:20 BST on the 1st to 06:15/20:10 on the 31st. The Moon is at last quarter on the 4th, new on the 11th, at first quarter on the 18th and full on the 26th.

A partial solar eclipse on the 11th is visible from the Arctic, Greenland, Scandinavia and north-eastern Asia. Observers in Scotland north of a line from North Uist to the Cromarty Firth see a thin sliver of the Sun hidden for just a few minutes at about 09:45 BST. Our best place to be is Shetland but even in Lerwick the eclipse lasts for only 43 minutes with less than 2% of the Sun’s disk hidden at 09:50. To prevent serious eye damage, never look directly at the Sun.

Vega in Lyra is the brightest star overhead at nightfall and marks the upper right corner of the Summer Triangle it forms with Deneb in Cygnus and Altair in Aquila. Now that the worst of the summer twilight is behind us, we have a chance to glimpse the Milky Way as it flows through the Triangle on its way from Sagittarius in the south to Auriga and the star Capella low in the north. Other stars of note include Arcturus in Bootes, the brightest star in our summer sky, which is sinking in the west at the map times as the Square of Pegasus climbs in the east.

Of the quartet of planets in our evening sky, two have already set by our map times. The first and brightest of these is Venus which stands only 9° high in the west at Edinburgh’s sunset on the 1st and sets itself 68 minutes later. By the 31st, these numbers change to 4° and 35 minutes, so despite its brilliance at magnitude -4.2 to -4.4, it is becoming increasingly difficult to spot as an evening star. It is furthest east of the Sun (46°) on the 17th.

Jupiter remains conspicuous about 10° high in the south-west as darkness falls and sets in the west-south-west just before the map times. Edging eastwards in Libra, it dims slightly from magnitude -2.1 to -1.9 and slips 0.6° north of the double star Zubenelgenubi on the 15th. A telescope shows it to be 36 arcseconds wide when it lies below-right of the Moon on the 17th.

The two planets low in the south at our map times are Mars, hanging like a prominent orange beacon only some 7° high in south-western Capricornus, and Saturn which is a shade higher above the Teapot of Sagittarius almost 30° to Mars’ right. Mars stood at opposition on 27 July and is at its closest to the Earth (57.6 million km) four days later. A planet-wide dust storm has hidden much of the surface detail on its small disk which shrinks during August from 24 to 21 arcseconds as its distance increases to 67 million km. Although Mars dims from magnitude -2.8 to -2.1, so it remains second only to Venus in brilliance. Catch the Moon near Saturn on the 20th and 21st and above Mars on the 24th.

Finally, we cannot overlook Mercury which is a morning star later in the period. Between the 22nd and 31st, it brightens from magnitude 0.8 to -0.7, rises more than 90 minutes before the Sun and stands around 7° high in the east-north-east forty minutes before sunrise. It is furthest west of the Sun (18°) on the 26th.

Diary for 2018 August

Times are BST

4th            19h Last quarter

9th            01h Mercury in inferior conjunction on Sun’s near side

11th          11h New moon and partial solar eclipse

13th         02h Peak of Perseids meteor shower

14th         15h Moon 6° N of Venus

17th         12h Moon 5° N of Jupiter

17th         19h Venus furthest E of Sun (46°)

18th         09h First quarter

21st         11h Moon 2.1° N of Saturn

23rd         18h Moon 7° N of Mars

26th         13h Full moon

26th         22h Mercury furthest W of Sun (18°)

28th         11h Mars stationary (motion reverses from W to E)

Alan Pickup

This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on July 31st 2018, with thanks to the newspaper for permission to republish here.

Scotland’s Sky in July, 2018

Dust storm rages on Mars as it stands closest since 2003

The maps show the sky at 01:00 BST on the 1st, midnight on the 16th and 23:00 on the 31st. An arrow depicts the motion of Mars. (Click on map to enlarge)

The maps show the sky at 01:00 BST on the 1st, midnight on the 16th and 23:00 on the 31st. An arrow depicts the motion of Mars. (Click on map to enlarge)

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)

Alan Pickup

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.

Scotland’s Sky in June, 2018

Three planets outshine the stars during June’s twilit nights

The maps show the sky at 01:00 BST on the 1st, midnight on the 16th and 23:00 on the 30th. An arrow depicts the motion of Mars. (Click on map to enlarge)

The maps show the sky at 01:00 BST on the 1st, midnight on the 16th and 23:00 on the 30th. An arrow depicts the motion of Mars. (Click on map to enlarge)

Unless our passion is for observing the Sun, Scotland’s brief twilit nights can make June a frustrating month for stargazers. This month, though, three planets outshine all the stars, while a fourth, the handsome ringed world Saturn, is at its best for the year.

We are approaching the summer solstice, due this year at 11:07 BST on the 21st when the Sun is overhead at the Tropic of Cancer. On that day, it passes 57.5° high in the south for Edinburgh at 13:14 BST, the time of local noon.

The middle of the following night sees the Sun 10.6° below the northern horizon for Edinburgh and a mere 6.4° below for Lerwick in Shetland which is why, over northern Scotland in particular, only the brighter stars and planets may be glimpsed.

Edinburgh’s sunrise and sunset times 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 last quarter on the 6th, new on the 13th, at first quarter on the 20th and full on the 28th.

Our chart is timed for around the middle of the night at present and depicts three of those planets as they line up low across our southern sky. Even brighter, though, is the brilliant Venus which blazes at magnitude -4.0 low in the west-north-west after sunset and sinks to set in the north-west at 00:36 BST on the 1st and just before midnight by the 31st.

Although it is still drawing away from the Sun, Venus sinks lower each evening as it tracks further south in the sky, moving from below Castor and Pollux in Gemini to the western fringe of Leo by the 30th. Look for it 6° to the right of the young Moon on the 16th with the Praesepe star cluster in Cancer just above and to the Moon’s right. On that evening, the planet is 174 million km distant and appears through a telescope as a 75% illuminated disk of diameter 14 arcseconds.

Mercury joins Venus in the evening twilight later in the month but is a real challenge to spot through binoculars from our latitudes. For us, the little innermost planet shines at about magnitude 0.0 but stands only 2° high in the north-west one hour after sunset from the 20th onwards.

Foremost among the planets on our star chart is Jupiter which is prominent at magnitude -2.5 in Libra as it moves from low in the south-south-east at nightfall to the south-south-west by the map times. Having stood directly opposite the sun at opposition on 9 May, it dims slightly to magnitude -2.3 and shrinks to 41 arcseconds across by June’s end. Binoculars reveal its four main moons to either side and the interesting double star Zubenelgenubi less than a degree to its south over the coming nights. Catch it just below the Moon on the 23rd.

This month it is Saturn’s turn to reach opposition when it stands 1,354 million km away on the 27th when it also happens to lie close to the Moon. It passes less than 12 degrees high in the south as seen from Edinburgh in the middle of the night as Vega, the leading star in the Summer Triangle, passes just to the south of overhead.

Improving from magnitude 0.2 to 0.0 to equal Vega in brightness, Saturn is creeping slowly westwards just above the Teapot of Sagittarius though this asterism barely clears our southern horizon. Viewed telescopically, Saturn’s disk is 18 arcseconds broad at opposition while its rings span 41 arcseconds and have their north face tipped 26° towards us.

The night’s final planet, Mars, is rising above Edinburgh’s south-eastern horizon at our map times and climbs to lie 10° high in the south-south-east before dawn. Its orange hue is already conspicuous at magnitude -1.2 and it more than doubles in brightness to magnitude -2.1 by the 30th. Moving eastwards against the stars of Capricornus, it reaches a so-called stationary point on the 28th when its motion reverses to westerly.

Mars approaches from 92 million to only 67 million km during June while its orange-red disk swells from 15 to 21 arcseconds in diameter, becoming large enough for most decent telescopes to reveal something of its surface detail and that its icy south polar cap is tipped at 15° to our view. Mars lies near the Moon on the morning of the 3rd and to the left of the Moon on the 30th.

I mentioned solar observing at the beginning of this note since our long summer days give ample opportunities for viewing the Sun’s surface, or so we hope. Of course, I should repeat the serious warning that we must never look directly at the Sun through any binoculars or telescopes – to do so invites critical damage to the eyes, if not blindness. Instead it is possible to project the Sun’s image onto a card held away from the eyepiece. Alternatively, obtain an inexpensive but certified “solar filter” and follow the instructions carefully on how to employ this.

Of particular interest are sunspots, dark regions on the solar surface that last for anything from a day to several weeks and mark magnetic storms. Their numbers fluctuate in a cycle of roughly 11 years and, following a peak in activity in 2014, are low at present as we near a so-called sunspot minimum which might be due in 2020. However, sunspot numbers have plummeted in recent months and more than half the days in 2018 have been spotless so far, so it is suggested that the official minimum could occur rather earlier than expected.

Diary for 2018 June

Times are BST

1st            02h Moon 1.6° N of Saturn

3rd            13h Moon 3° N of Mars

6th            03h Mercury in superior conjunction on Sun’s far side

6th            20h Last quarter

13th          21h New moon

14th          14h Moon 5° S of Mercury

16th         14h Moon 2.3° S of Venus

16th         21h Moon 1.2° S of Praesepe in Cancer

20th         06h Venus 0.8° N of Praesepe

20th         12h First quarter

21st         11:07 Summer solstice

23rd         20h Moon 4° N of Jupiter

27th         14h Saturn at opposition at distance of 1,354 million km

28th         05h Moon 1.8° N of Saturn

28th         06h Full moon

28th         15h Mars stationary (motion reverses from E to W)

Alan Pickup

This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on May 31st 2018, with thanks to the newspaper for permission to republish here.