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Scotland’s Sky in November, 2017

Astronomers spot a mystery interstellar visitor

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

Comets have always been of particular interest. Appearing without warning, and sometimes with impressive tails, it was not surprising that they were regarded as portents of battles to be won or lost and of the passing of kings.

It was in 1705 that Edmond Halley first published the orbit of the comet that now bears his name. This, and the more than 5,000 comets that have been studied since, have all proved to be members of our solar system.

Some, like Halley, follow closed elongated orbits, returning to perihelion in the Sun’s vicinity every few years. Many more, though, trace almost parabolic paths as they dive towards the Sun from the Oort cloud, a spherical reservoir of icy worlds at the edge of the Sun’s influence – if they ever return to perihelion it may not be for millions of years. A handful, though, receive a sufficient gravitational boost as they pass a planet that they are flung beyond the Oort cloud into interstellar space, never to return.

Now astronomers have sighted a faint object which appears to have originated far beyond the Oort cloud, perhaps as an escapee from another star. Discovered by the Pan-STARRS 1 telescope in Hawaii on 18 October, it had already reached its perihelion within 38 million km of the Sun nine days before and passed 24 million km from the Earth on the 14th. Dubbed at first Comet/2017 U1 (PanSTARRS) because of its highly eccentric comet-like orbit, its name was changed to A/2017 U1 on 25 October when observers failed to detect any trace of a tail or hazy coma surrounding its small nucleus, probably less than 200 metres wide. So, for the moment, it is classed as an asteroid.

Its path though is certainly hyperbolic, having entered the solar system at a relative speed of 26 km per second from a direction close to the bright star Vega in the constellation Lyra. This is also close to the direction that our solar system is moving at 20 km per second with regard to the stars around us, so it may be expected that interstellar intruders, be they comets or asteroids, are most likely to appear from this region. As our first known visitor from interstellar space, frantic efforts are underway to investigate its spectrum and nature before it recedes forever from view in the direction of the Square of Pegasus.

Vega, itself, is the brightest object very high in the south-west at nightfall, falling into the west by our star chart times as Pegasus and Andromeda occupy our high meridian. Orion is rising in the east below Taurus whose brightest star, Aldebaran, is occulted by the bright Moon on the morning of the 6th. Use a telescope to watch it slip behind the Moon’s lower-left limb between 02:27 and 03:26 as seen from Edinburgh

Our sole bright evening planet, Saturn at magnitude 0.5, is easy to miss as it hangs low in the south-west at nightfall, sinking to Edinburgh’s horizon at 18:40 on the 1st and by 16:58 on the 30th. We may need binoculars to spy it in the twilight 5° left of the young earthlit Moon on the 20th and 8° below-right of the Moon a day later. Mercury stands 22° east of the Sun on the 24th but is unlikely to be visible from our latitudes.

The other naked-eye planets are all in our predawn sky. Mars rises in the east just before 04:00 throughout November, climbing to stand 15° to 20° high in the south-east before its magnitude 1.8 pinprick is swallowed by the twilight. This month, it tracks 19° east-south-eastwards in Virgo to pass 3° north of Virgo’s leading star Spica on the 28th. Mars stands to the right of the waning Moon on the 15th when a telescope show it as only 4 arcseconds wide – too small to see any detail.

Venus continues as a brilliant morning star of magnitude -3.9, but it stands lower each morning as it approaches the Sun’s far side. Currently above and left of Spica but speeding east-south-eastwards into Libra, it rises a little more than two hours before the Sun on the 1st and one hour before sunrise by the 30th.

Jupiter, about to emerge from the Sun’s glare below-left of Venus, climbs to pass a mere 16 arcminutes, or half the Moon’s diameter, below-right of Venus on the 13th. Conspicuous at magnitude -1.7, the Jovian disk appears 31 arcseconds wide as compared with only 10 arcseconds for Venus. On the 17th, the incredibly slim earthlit Moon lies above-left of Venus and to the left of Jupiter while the later stands 18° above-right of Venus by the 30th.

Sunrise/sunset times for Edinburgh change from 07:20/16:32 on the 1st to 08:18/15:45 on the 30th. The Moon is full on the 4th, at last quarter on the 10th, new on the 18th and at first quarter on the 26.

The annual Leonids meteor shower lasts from the 15th to the 20th and peaks on the night of the 17th-18th. Its meteors, all of them very fast and many leaving glowing trains in their wake, emanate from the Sickle, the reversed question-mark of stars above Regulus in Leo. This rises in the north-east at 22:00, with most Leonids visible during the predawn hours as it climbs through our eastern sky. The shower has given some spectacular meteor storms in the past, notably in 1966 and 1999, but the parent comet, Comet Tempel-Tuttle, is now near the farthest point of its orbit and rates may be around a dozen meteors per hour. For once, though, moonlight is no hindrance.

Alan Pickup

This is a slightly revised version of Alan’s article published in The Scotsman on October 31st 2017, with thanks to the newspaper for permission to republish here.
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Scotland’s Sky in October, 2017

Saturn at full tilt as Comet Halley’s meteors fly

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. Summer time ends at 02:00 BST on the 29th 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. Summer time ends at 02:00 BST on the 29th when clocks are set back one hour to 01:00 GMT. (Click on map to enlarge)

Our charts capture the sky in transition between the stars of summer, led by the Summer Triangle of Deneb, Vega and Altair in the west, and the sparkling winter groups heralded by Taurus and the Pleiades star cluster climbing in the east. Indeed, if we look out before dawn, as Venus blazes in the east, we see a southern sky centred on Orion that mirrors that of our spectacular February evenings. October also brings our second opportunity this year to spot debris from Comet Halley.

As the ashes of the Cassini spacecraft settle into Saturn, the planet reaches a milestone in its 29-years orbit of the Sun when its northern hemisphere and rings are tilted towards us at their maximum angle of 27.0° this month. In practice, our view of the rings’ splendour is compromised at present by its low altitude.

Although it shines at magnitude 0.5 and is the brightest object in its part of the sky, Saturn hovers very low in the south-west at nightfall and sets around 80 minutes before our map times. The rings span 36 arcseconds at mid-month while its noticeably rotation-flattened disk measures 16 arcseconds across the equator and 14 arcseconds pole-to-pole. Catch it below and to the right of the young crescent Moon on the 24th.

The Sun moves 11° further south of the equator this month as sunrise/sunset times for Edinburgh change from 07:16/18:48 BST (06:16/17:48 GMT) on the 1st to 07:18/16:34 GMT on the 31st, after we set our clocks back on the 29th.

Jupiter is now lost in our evening twilight as it nears the Sun’s far side on the 26th. Saturn is not alone as an evening planet, though, for both Neptune and Uranus are well placed. They are plotted on our southern chart in Aquarius and Pisces respectively but we can obtain more detailed and helpful diagrams of their position via a Web search for a Neptune or Uranus “finder chart” – simply asking for a “chart” is more likely to lead you to astrological nonsense.

Neptune, dimly visible through binoculars at magnitude 7.8, lies only 0.6° south-east (below-left) of the star Lambda Aquarii at present and tracks slowly westwards to sit a similar distance south of Lambda by the 31st. It lies 4,346 million km away on the 1st and its bluish disk is a mere 2.3 arcseconds wide.

Uranus reaches opposition on the 19th when it stands directly opposite the Sun and 2,830 million km from Earth. At magnitude 5.7 it is just visible to the unaided eye in a good dark sky, and easy through binoculars. Currently 1.3° north-west of the star Omicron Piscium and also edging westwards, it shows a bluish-green 3.7 arcseconds disk if viewed telescopically.

North of Aquarius and Pisces are Pegasus and Andromeda, the former being famous for its relatively barren Square while the fuzzy smudge of the Andromeda Galaxy, M31, lies 2.5 million light years away and is easy to glimpse through binoculars if not always with the naked eye.

Mercury slips through superior conjunction on the Sun’s far side on the 8th and is out of sight. Venus remains resplendent at magnitude -3.9 in the east before dawn though it does rise later and stand lower each morning. On the 1st, it rises for Edinburgh at 04:44 BST (03:44 GMT) and climbs to stand 20° high at sunrise. By the month’s end, it rises at 05:30 GMT and is 13° high at sunrise. Against the background stars, it speeds from Leo to lie 5° above Virgo’s star Spica by the 31st.

Mars is another morning object, though almost 200 times dimmer at magnitude 1.8 as it moves from 2.6° below-left of Venus on the 1st to 16° above-right of Venus on the 31st. The pair pass within a Moon’s breadth of each other on the 5th and 6th when Venus appears 11 arcseconds in diameter and 91% sunlit and Mars (like Uranus) is a mere 3.7 arcseconds wide.

Comet Halley was last closest to the Sun in 1986 and will not return again until 2061. Twice each year, though, the Earth cuts through Halley’s orbit around the Sun and encounters some of the dusty debris it has released into its path over past millennia. The resulting pair of meteor showers are the Eta Aquarids in early-May and the Orionids later this month. Although the former is a fine shower for watchers in the southern hemisphere, it yields only the occasional meteor in Scotland’s morning twilight.

The Orionids are best seen in the morning sky, too, and produce fewer than half the meteors of our main annual displays. This time the very young Moon offers no interference during the shower’s broad peak between the 21st and 23rd. In fact, Orionids appear throughout the latter half of October as they diverge from a radiant point in the region to the north and east of the bright red supergiant star Betelgeuse in Orion’s shoulder and close to the feet of Gemini. Note that they streak in all parts of the sky, not just around the radiant.

Orionids begin to appear when the radiant rises in the east-north-east at our map times, building in number until it passes around 50° high in the south before dawn. Under ideal conditions, with the radiant overhead in a black sky, as many as 25 fast meteors might be counted in one hour with many leave glowing trains in their wake. Rates were considerably higher than this between 2006 and 2009, so there is the potential for another pleasant surprise.

Alan Pickup

This is a slightly revised version of Alan’s article published in The Scotsman on September 30th 2017, with thanks to the newspaper for permission to republish here.

Scotland’s Sky in September, 2017

Cassini’s scheduled suicide at Saturn

The maps show the sky at 23:00 BST on the 1st, 22:00 on the 16th and 21.00 on the 30th. (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. (Click on map to enlarge)

The heroic Cassini mission to Saturn is set to reach its dramatic conclusion on 15 September. After a seven-year journey from Earth, the probe has been studying the planet, its glorious rings and its fascinating moons for the past thirteen years. Now, with its fuel running low, it is time for the NASA probe to plunge into the Saturnian atmosphere where, in the interest of so-called planetary protection, it will disintegrate and vaporise.

To leave it in orbit around the planet would run the risk of it colliding with the rings or one of the moons, with the outside possibility of contaminating them with microbes from the Earth. This was of little concern when Cassini’s mission was planned, and it carried and delivered the European-built Huygens probe which parachuted to the surface of Saturn’s largest moon, Titan. It touched down on a world in which rivers of liquid hydrocarbons, chiefly methane, flow into lakes in a landscape dominated by water-ice mountains.

Now, though, we realise that despite Saturn’s remoteness from the Sun, the possibility of alien life there cannot be discounted. Indeed, it seems clear that its small moon Enceladus has a subsurface watery ocean and there has been talk of sending a mission to search for organic compounds in the plumes of water erupting from geysers on its surface.

Recent orbits of Saturn have seen Cassini piercing the gap between Saturn and its rings, and even skimming the planet’s outer atmosphere. It will continue to collect data as it begins its final suicidal dive into Saturn’s atmosphere on the 15th, but its signal will be lost at around 13:00 BST as aerodynamic forces cause it to tumble and, eventually, break apart and burn up.

The Sun crosses southwards over the equator at 21:02 BST on the 22nd, the moment of our autumnal equinox. Sunrise/sunset times for Edinburgh change from 06:17/20:07 BST on the 1st to 07:14/18:50 on the 30th. The Moon is full on the 6th, at last quarter on the 13th, new on the 20th and at first quarter on the 28th.

Now that Scotland’s persistent summer twilight is behind us, our nights offer views of the Milky Way as it arches directly overhead from the south-west to the north-east at our chart times, carving through the Summer Triangle formed by Deneb, Altair and Vega which now lies just west of the high meridian.

To the east of the Triangle is the distinctive form of the celestial dolphin, Delphinus, where the celebrated English amateur astronomer George Alcock discovered a famous and unusual naked-eye nova fifty summers ago in 1967. I remember watching the stellar outburst as it took five months to reach its peak brightness at magnitude 3.5. Now assigned the variable-star tag HR Delphini, the star is still visible as a twelfth magnitude object through telescopes.

Another 13° east of Delphinus is the globular star cluster Messier 15, 4° north-west of Pegasus’s brightest star, Enif. A tightly packed globe of perhaps 100,000 stars, all very much older than our Sun, M15 lies around 34,000 light years away and looks like a fuzzy star through binoculars.

Saturn is the sole bright planet to appear on our star maps. Look for it as the brightest object low down in the south-south-west at nightfall and even lower in the south-west by our map times, only thirty minutes before it sets. Edging eastwards in Ophiuchus, it shines 4° below-left of the Moon on the 26th.

Jupiter is bright at magnitude -1.7 but hard to see very low in the west-south-west just after sunset. By mid-month it is likely to be lost in the twilight.

Our charts plot the two outer planets, the ice giant world Uranus in Pisces and its near-twin Neptune in Aquarius, though we probably need more detailed charts to identify them through binoculars or telescopes. At magnitude 5.7, Uranus is at the verge of naked-eye visibility, while Neptune reaches opposition on the 5th and is dimmer at magnitude 7.8.

The other planets are about to join Venus low down in our eastern sky at the end of the night. The brilliant morning star shines at magnitude -4.0 when it rises in the north-east at 03:04 for Edinburgh on 1 September, and climbs 25° high into the east by sunrise. Catch it through binoculars before the twilight intervenes on that day and look 1.2° to its left for the Praesepe or Beehive cluster of stars in Cancer. Leaving the cluster behind, Venus tracks east-south-eastwards into Leo to pass 0.5° (a Moon’s breadth) north of the star Regulus on the 20th.

Mercury emerges from the Sun’s glare to stand 18° west of the Sun and 11° below-left of Venus on the 12th. Between the 6th and 23rd it rises more than 80 minutes before sunrise and brightens eightfold from magnitude 1.1 to -1.1. On the 6th, in fact, Mercury lies 2.5° to the right of Regulus which, in turn, is 0.8° to the right of the fainter magnitude 1.8 planet Mars. As Regulus climbs above them, the two planets then converge to lie less than 0.5° apart on the 16th and 17th.

Early risers are in for a special treat when the waning earthlit Moon joins the party on the 17th. On that morning, Venus stands 10° below-left of the Moon and almost 4° above-right of Regulus, with the Mars-Mercury conjunction another 8° below and to the left. On the 18th, the line-up is even more compact as the Moon shifts to lie 0.7° below Regulus. By the 30th, Venus rises in the east-north-east at 04:41 and is 3° above-right of Mars.

Alan Pickup

This is a slightly-revised version of Alan’s article published in The Scotsman on August 31st 2017, with thanks to the newspaper for permission to republish here.

Scotland’s Sky in August, 2017

Countdown to the Great American Eclipse

The maps show the sky at 00:00 BST on the 1st, 23:00 on the 16th and 22:00 on the 31st. (Click on map to enlarge)

The maps show the sky at 00:00 BST on the 1st, 23:00 on the 16th and 22:00 on the 31st. (Click on map to enlarge)

With two eclipses and a major meteor display, August is 2017’s most interesting month for sky-watchers. Admittedly, Scotland is on the fringe of visibility for both eclipses while the annual Perseids meteor shower suffers moonlight interference.

The undoubted highlight is the so-called Great American Eclipse on the 21st. This eclipse of the Sun is total along a path, no more than 115km wide, that sweeps across the USA from Oregon at 18:17 BST (10:17 PDT) to South Carolina at 19:48 BST (14:48 EDT) – the first such coast-to-coast eclipse for 99 years.

Totality is visible only from within this path as the Moon hides completely the dazzling solar surface, allowing ruddy flame-like prominences to be glimpsed at the solar limb and the pearly corona, the Sun’s outer atmosphere, to be admired at it reaches out into space. At its longest, though, totality lasts for only 2 minutes and 40 seconds so many of those people fiddling with their gadgets to take selfies and the like may be in danger of missing the spectacle altogether.

The surrounding area from which a partial eclipse is visible even extends as far as Scotland. From Edinburgh, this lasts from 19:38 to 20:18 BST but, at most, only the lower 2% of the Sun is hidden at 19:58 as it hangs a mere 4° high in the west. Need I add that the danger of eye damage means that we must never look directly at the Sun – instead project the Sun through a pinhole, binoculars or a small ‘scope, or use an appropriate filter or “eclipse glasses”.

A partial lunar eclipse occurs over the Indian Ocean on the 7th as the southern quarter of the Moon passes through the edge of the Earth’s central dark umbral shadow between 18:23 and 20:18 BST. By the time the Moon rises for Edinburgh at 20:57, it is on its way to leaving the lighter penumbral shadow and I doubt whether we will see any dimming, It exits the penumbra at 21:51.

Our charts show the two halves of the sky around midnight at present. In the north-west is the familiar shape of the Plough while the bright stars Deneb in Cygnus and Vega in Lyra lie to the south-east and south-west of the zenith respectively. These, together with Altair in Aquila in the middle of our southern sky, make up the Summer Triangle. The Milky Way flows through the Triangle as it arches overhead from the south-west to the north-east where Capella in Auriga rivals Vega in brightness.

Of course, many of us have to contend with light pollution which swamps all trace of the Milky Way and we are not helped by moonlight which peaks when the Moon is full on the 7th and only subsides as last quarter approaches on the 15th. New moon comes on the 21st and first quarter on the 29th. The Sun, meantime, slips another 8° southwards during the month as sunrise/sunset times for Edinburgh change from 05:17/21:20 BST on the 1st to 06:15/20:09 on the 31st.

Meteors of the annual Perseids shower, the tears of St Lawrence, are already arriving in low numbers. They stream away from a radiant point in the northern Perseus which stands in the north-east at our map times, between Capella and the W-pattern of Cassiopeia. We spot Perseids in all parts of the sky, though, and not just around Perseus.

Meteor numbers are expected to swell to a peak on the evening of the 12th when upwards of 80 per hour might be counted under ideal conditions. Even though moonlight will depress the numbers seen this time, we can expect the brighter ones still to impress as they disintegrate in the upper atmosphere at 59 km per second, many leaving glowing trains in their wake. The meteoroids concerned come from Comet Swift-Tuttle which last approached the Sun in 1992.

Although Neptune is dimly visible through binoculars at magnitude 7.8 some 2° east of the star Lambda Aquarii, the only naked-eye planet at our map times is Saturn. The latter shines at magnitude 0.3 to 0.4 low down in the south-west as it sinks to set less than two hours later. It is a little higher towards the south at nightfall, though, where it lies below-left of the Moon on the 2nd when a telescope shows its disk to be 18 arcseconds wide and its stunning wide-open rings to span 40 arcseconds. Saturn is near the Moon again on the 29th.

Jupiter is bright (magnitude -1.9 to -1.7) but very low in our western evening sky, its altitude one hour after sunset sinking from 6° on the 1st to only 1° by the month’s end as it disappears into the twilight. Catch it just below and right of the young Moon on the 25th.

Venus is brilliant at magnitude -4.0 in the east before dawn. Rising in the north-east a little after 02:00 BST at present, and an hour later by the 31st, it climbs to stand 25° high at sunrise. Viewed through a telescope, its disk shrinks from 15 to 12 arcseconds in diameter as it recedes from 172 million to 200 million km and its gibbous phase changes from 74% to 83% sunlit.

As Venus tracks eastwards through Gemini, it passes below-right of the star cluster M35 (use binoculars) on the 2nd and 3rd, stands above-left of the waning earthlit Moon on the 19th and around 10° below Castor and Pollux as it enters Cancer a few days later. On the 31st it stands 2° to the right of another cluster, M44, which is also known as Praesepe or the Beehive.

Alan Pickup

This is a slightly-revised version of Alan’s article published in The Scotsman on July 31st 2017, with thanks to the newspaper for permission to republish here.

Scotland’s Sky in July, 2017

Pole stars of the future in the Summer Triangle

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

The Sun’s southerly motion since the solstice on 21 June has yet to gain speed and not until 12 July does it lie sufficiently far south for Edinburgh to enjoy any so-called nautical darkness, with the Sun more than 12° below the northern horizon in the middle of the night. Even then, moonlight is troublesome for a few more days to delay our first views of a dark summer night sky.

If there is one star-pattern that dominates our skies over the summer, it is the Summer Triangle. Formed by the bright stars Vega in the constellation Lyra, Deneb in Cygnus and Altair in Aquila, it occupies the upper part of our south star map, though its outline is not depicted. In fact, the projection used means that the Triangle’s proportions are squashed, because Vega and Deneb are significantly closer together in the sky than either are to Altair.

The leader and brightest of the Triangle’s stars is Vega which moves from high in the east at nightfall to stand even higher in the south at our map times. Blazing at magnitude 0.0 from a distance of 25 light years, it is a white star, twice as massive as our Sun but very much younger. Excess heat revealed by infrared astronomy indicates that Vega is encircled by a disk of dust which may be evidence that a planetary system is forming around it.

Set your time machine for about AD 13,700 and you will be able to glimpse Vega close to where we currently find Polaris, our current Pole Star. This is because the Earth’s axis is slowly toppling in space, taking 26,000 years to complete a 47° circle in the sky and carrying the axis to within 4° of Vega. Polaris happens to lie within 0.8° of the axis at present so that, as the Earth rotates once each day, it stays almost fixed in our sky and the other stars appear to circle counterclockwise around it

Altair is the second brightest of the Triangle’s stars and one of the closest bright stars at “only” 16.7 light years. Shining at magnitude 0.8, half as bright as Vega, it is 80% more massive than our Sun but, remarkably, spins on its axis in about nine hours as compared with the more leisurely 25 days taken by the Sun. As a result, it is noticeably oblate, measuring 20% wider across its equator than it does pole-to-pole.

Deneb’s magnitude of 1.2 makes it the dimmest of the Triangle’s corner stars but it is also one of the most luminous stars in our Milky Way Galaxy. Because its distance may be around 2,600 light years, it very difficult to measure the minuscule shift in its position when viewed from opposite sides of the Earth’s orbit around the Sun – the parallax technique that gives us accurate distances to Vega and Altair. Indeed, estimates of Deneb’s distance differ by well over 1,000 light years.

White-hot and shining at some 200,000 Sun-power, Deneb is large enough to engulf the Earth were it to swap places with the Sun. It is also burning its nuclear fuel at such a rate that it seems destined to disintegrate in a supernova within a few million years, although it should survive to be another of our future pole stars as it comes as close as 5° to the pole in AD 9,800.

The Sun eventually tracks 5° southwards during July as Edinburgh’s sunrise/sunset times change from 04:32/22:01 BST on the 1st to 05:15/21:22 on the 31st. The Moon is at first quarter on the 1st, full on the 9th, at last quarter on the 16th, new on the 23rd and returns to first quarter on the 30th.

At magnitude -2.0, Jupiter remains our brightest evening planet though it stands lower in the south-west to west as it sinks to set in the west just before our star map times. Above and to the right of the star Spica in Virgo, it lies to the right of the Moon in the south-west as the sky darkens on the 1st and is just below the Moon and much lower in the west-south-west on the 28th. The cloud-banded Jovian disk appear 39 arcseconds wide at mid-month if viewed telescopically, while binoculars allow glimpses of its four main moons.

Saturn is less conspicuous at magnitude 0.1 to 0.3 but continues as the brightest object low in our southern night sky. Creeping westwards against the stars of southern Ophiuchus, it crosses Edinburgh’s meridian at an altitude of 12° one hour before our map times and may be spotted 3° below-left of the Moon on the 6th. Binoculars show it as more than a round dot, while small telescopes reveal the beauty of ring system which is tilted wide open to our view and spans 41 arcseconds in mid-July.

Venus is brilliant at magnitude -4.1 in the east before dawn. After rising in the north-east at about 02:15 BST throughout the month. it climbs to stand 17° high at sunrise as the month begins and higher still by its end. Seen through a telescope, it is 16 arcseconds across and 70% illuminated when it lies to the left of waning (15% sunlit) and earthlit Moon on the 20th. Against the background stars of Taurus, the planet moves from 8° below-right of the Pleiades tomorrow to pass 3° above-left of Aldebaran on the 14th.

Of the other bright planets, Mars is out of sight as it reaches conjunction on the Sun’s far side on the 27th, while Mercury stands furthest east of the Sun (27°) on the 30th but is unlikely to be seen near our west-north-western horizon in the bright evening twilight.

Alan Pickup

This is a slightly-revised version of Alan’s article published in The Scotsman on June 30th 2017, with thanks to the newspaper for permission to republish here.

Scotland’s Sky in June, 2017

Saturn at its best as noctilucent clouds gleam

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

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.

Alan Pickup

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.

Scotland’s Sky in May, 2017

Cassini begins Grand Finale at Saturn

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

This month brings the final truly dark night skies for Scotland until mid-July or later. Our dwindling nights are dominated by Jupiter, bright and unmistakable as it passes about 30° high in our southern evening sky and sinks to the western horizon before dawn. Venus is brighter still but easily overlooked as it hovers low in our brightening eastern dawn twilight. Saturn is also best as a morning planet, though it rises at our south-eastern horizon a few minutes before our May star map times.

Saturn creeps westwards from the constellation Sagittarius into Ophiuchus this month and brightens a little from magnitude 0.3 to 0.1, making it comparable with the brightest stars visible at our map times – Arcturus, Capella and Vega. The ringed planet, though, climbs to only 12° high in the south by the time morning twilight floods our sky, which is too low for crisp telescopic views of its stunning rings. On the morning of the 14th, as Saturn stands only 3° below-right of the Moon, its rotation-squashed globe measures 18 arcseconds in diameter while its rings stretch across 41 arcseconds and have their northern face tipped at 26° to our view.

Saturn’s main moon, Titan, takes 16 days to orbit the planet and is an easy telescopic target on the ninth magnitude. It stands furthest west of the disk (3 arcminutes) on the 3rd and 19th and furthest east on the 11th and 27th.

The Cassini probe is now into the final chapter, its so-called Grand Finale, of its epic exploration of the Saturn system. On 22 April, it made its 127th and last flyby of Titan, while on 26 April it dived for the first time through the gap between the planet and its visible rings, successfully returning data from a region it has never dared to explore before. Cassini’s new orbit sees it make another 21 weekly dives until, come 15 September, its almost-20 years mission ends with a fiery plunge into the Saturnian atmosphere.

The Sun’s northwards progress during May, to within only 1.4° of its most northerly point at the summer solstice, changes the sunrise/sunset times for Edinburgh from 05:29/20:52 BST on the 1st to 04:36/21:46 on the 31st. The Moon reaches first quarter on the 3rd, full on the 10th, last quarter on the 19th and new on the 25th.

This crescent Moon on the 1st lies in the west, between the stars Pollux in Gemini and Procyon in Canis Minor, lower to its left, while on the 2nd it is 4° below-left of the Praesepe star cluster in Cancer, best viewed through binoculars. It lies near Regulus in Leo on the 3rd and 4th, and appears only 1.2° above the conspicuous Jupiter on the 7th.

The giant planet lies 10° above-right of Virgo’s leading star Spica and edges 2° to the west-north-west this month, drawing closer to the celebrated double star Porrima whose two equal stars orbit each other every 169 years but appear so close together at present that we need a good telescope to divide them.

Following its opposition on 7 April, Jupiter recedes from 678 million to 724 million km during May, dimming slightly from magnitude -2.4 to -2.2 as its diameter shrinks from 43 to 41 arcseconds. Any telescope should show its changing cloud-banded surface while its four main moons may be glimpsed through binoculars, although sometimes one or more disappear as they transit in front of the disk or are hidden behind it or in its shadow.

Some 30° above and to the left of Jupiter is the orange-red giant star Arcturus in Bootes the Herdsman. At magnitude -0.05, this is (just) the brightest star in the northern celestial hemisphere ahead of Capella in Auriga, low in the north-north-west at our map times, and Vega in Lyra, climbing in the east. It is also one of the closer stars to the Sun, but it is only a temporary neighbour for it is speeding by the solar system at 122 km per second at a distance of 36.7 light years. Even so, it takes 800 years to move a Moon’s breadth across our sky. It is also a corner star of a rarely-heralded asterism dubbed the Spring Triangle – the other vertices being marked by Spica and Regulus.

A useful trick for finding Arcturus is to extend a curving line along the handle of the Plough which passes overhead during our spring evenings but is always visible somewhere in our northern sky. That line, still pending, leads to Arcturus and then onwards to Spica. The traditional mnemonic for this is “Arc to Arcturus, spike to Spica” but, given current circumstances, we might amend this to “Arc to Arcturus, jump to Jupiter”.

Venus rises 65 minutes before the Sun on the 1st and climbs to stand 9° high at sunrise. By the 31st, these figures change only a little to 75 minutes and 10°, so it is far from obvious as a morning star, even though it blazes at magnitude -4.5 to -4.3. Through a telescope, it shows a crescent whose sunlit portion increases from 27% to 48% while its diameter shrinks from 38 to 25 arcseconds. Early rises, or insomniacs, can see it left of the waning Moon on the 22nd.

Mercury stands below and left of Venus but remains swamped by our dawn twilight. It is furthest west of the Sun (26°) on the 18th. Still visible, but destined soon to disappear into our evening twilight, is Mars. Shining at a lowly magnitude 1.6, it lies 7° above-right of Aldebaran as the month begins and tracks between the Bull’s horns as Taurus sinks below our north-western horizon in the early evening.

Alan Pickup

This is a slightly-revised version of Alan’s article published in The Scotsman on May 1st 2017, with thanks to the newspaper for permission to republish here.

Scotland’s Sky in April, 2017

Jupiter rules our April nights

The maps show the sky at midnight BST on the 1st, 23:00 on the 16th and 22:00 on 30th. An arrow shows the motion of Mars during the final week of the month. (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 30th. An arrow shows the motion of Mars during the final week of the month. (Click on map to enlarge)

Venus dominated our evening sky for the first quarter of 2017, but it is now Jupiter’s turn in the spotlight. The conspicuous giant planet lies directly opposite the Sun in the sky on the 7th so that it rises in the east at sunset, reaches its highest point in the south in the middle of the night and sets in the west at sunrise.

Our charts show it in Virgo to the east of south as Taurus and Orion dip beneath the western horizon and the Plough looms overhead, stretched out of its familiar shape by our map projection. Regulus in Leo is in the south-west and almost level with Arcturus in Bootes in the south-east. Vega in Lyra and Deneb in Cygnus are beginning their climb in the north-east.

Sunrise/sunset times for Edinburgh change from 06:43/19:51 BST on the 1st to 05:31/20:50 on the 30th. The Moon is at first quarter on the 3rd, full on the 11th, at last quarter on the 19th and new on the 26th.

Venus rises only a little more than one hour before sunrise and, though brilliant at magnitude -4.2, may be difficult to spot low in the east before dawn. However, the other inner planet, Mercury, remains nicely placed in the evening and stands furthest east of the Sun (19°) on the 1st.

Thirty minutes after Edinburgh’s sunset on that day, Mercury is 12° high in the west and shines at magnitude 0.0. It should be possible to spy it through binoculars and eventually with the unaided eye as the twilight fades and the planet sinks to set another 96 minutes later. By the 8th, though, it is a couple of degrees lower and a quarter as bright at magnitude 1.6 as it is engulfed by the twilight. Inferior conjunction on the Sun’s near side occurs on the 20th.

Mars, magnitude 1.5 to 1.6 and above and to Mercury’s left at present, tracks east-north-eastwards this month to pass 5° below the Pleiades on the 15th and a similar distance left of the star cluster on the 26th. By then it sets late enough to be plotted near our north-western horizon at the star map times.

Its opposition means that Jupiter is at its brightest and closest, shining more brightly than any star at magnitude -2.5 and a distance of 666 million km. It lies 6° north-west (above-right) of Virgo’s leading star Spica as the month begins and tracks 3.7° westwards during April to pass 10 arcminutes or a third of a Moon’s-width south of the fourth magnitude star Theta Virginis on the 5th.

Jupiter lies close to the full Moon on the night of the 10th-11th when the Jovian disk appears 44 arcseconds wide if viewed telescopically, one fortieth as wide as the Moon.

Jupiter’s clouds are arrayed in bands that lie parallel to its equator, the dark ones called belts and the intervening lighter hued ones called zones. There are numerous whirls and spots, the most famous being the Great Red Spot in the southern hemisphere. The planet spins in under ten hours, so a resolute observer might view the entire span of its clouds in a single April night. The four main moons, visible through decent binoculars and easy through a telescope, lie on each side of the disk and change their configuration from night to night.

The beautiful planet Saturn rises in the south-east less than three hours after our map times and is the brightest object (magnitude 0.4 to 0.3) less than 15° above Edinburgh’s southern horizon before dawn. It is a shame that its low altitude means that we miss the sharpest and most impressive views of it rings which span 39 arcseconds in mid-April, and are tilted at 26° around its 17 arcseconds disk. After appearing stationary on the 6th, Saturn begins to creep westwards against the stars of Sagittarius – look for it below and left of the Moon on the 16th and right of the Moon on the 17th.

It is not often that I advertise the annual Lyrids meteor shower. As one of the year’s lesser displays, it yields only some 18 meteors per hour at best, all of them swift and some leaving glowing trains in their wake as they diverge from a radiant point to the right of Vega. The event lasts from the 18th to the 25th and peaks on the 22nd when moonlight should not interfere unduly this year. The Lyrid meteoroids were released by Comet Thatcher, last seen in 1861.

Bright comets have been rare of late, but fainter ones are observed frequently. One such has the jaunty name of comet 41P/Tuttle–Giacobini–Kresák and takes 5.4 years to orbit between the paths of Jupiter and the Earth. It passes within 21 million km of us on the 1st as it nears perihelion, its closest point to the Sun, on the 12th. I glimpsed it through binoculars from a superb dark-sky site at Kielder Forrest, Northumberland, last week when it was a diffuse seventh magnitude smudge close to Merak, the southern star of the Pointers in the Plough.

Although its path is not depicted on our chart, the comet is poised to sweep close to three of the stars identified in Draco, between the Plough and Polaris, the Pole Star. It passes 0.6° north of Thuban on the night of the 2nd-3rd, 1.5° south-west of Eta on the 11th (sadly, in full moonlight) and 0.6° west of Beta on the 18th-19th. During past perihelia, it has been seen to flare by several magnitudes for a few days at a time, so, if we are lucky, it may reach naked-eye visibility.

Alan Pickup

This is a slightly-revised version of Alan’s article published in The Scotsman on March 31st 2017, with thanks to the newspaper for permission to republish here.

Scotland’s Sky in October, 2016

Mars bright in evenings as ExoMars probe arrives

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. Summer time ends at 02:00 BST on the 30th 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. Summer time ends at 02:00 BST on the 30th when clocks are set back one hour to 01:00 GMT. (Click on map to enlarge)

As we plunge into the final quarter of the year, our lengthening nights offer a procession of stellar views that stretch from the Summer Triangle in the evening to the stunning star-scapes around Orion during the morning hours. The brighter planets, though, are on show only low down around dusk and dawn.

The middle of the Summer Triangle stands some 60° high and due south as darkness falls tonight. Its brightest corner star, Vega in the constellation Lyra, lies just south-west of overhead, while Deneb in Cygnus is even higher in the south-east and Altair in Aquila lies below them on the meridian.

With no hindering moonlight over the next few evenings, now is a good time to spy the Milky Way as it arches almost overhead after dusk, climbing from Sagittarius on the south-south-western horizon and flowing through the heart of the Triangle on its way to Deneb and the “W” of Cassiopeia high in the north-east. Of course, unless we can find a dark site, away from the pollution of street lighting and the like, we may have trouble seeing the Milky Way or indeed any but the brighter stars on our chart.

Edinburgh’s sunrise/sunset times change this month from 07:16/18:47 BST (06:16/17:47 GMT) on the 1st to 07:18/16:34 GMT on the 31st after we set clocks back one hour with the end of BST on the morning of the 30th. The Moon is new on the 1st, at first quarter on the 9th, full on the 16th (the hunter’s moon), at last quarter on the 22nd and new again on the 30th.

Venus stands nearly 5° high in the south-west at sunset and sets itself only 43 minutes later on the 1st. By the 31st it is barely a degree higher in the south-south-west at sunset but remains visible for 73 minutes so is easier to spot if we enjoy an unobscured outlook. It blazes at magnitude -3.9 and stands 4° below-right of the slender earthlit Moon on the 3rd when its gibbous disk appears 12 arcseconds wide and 85% sunlit if viewed telescopically.

In the month that the first European-Russian ExoMars spacecraft reaches Mars, the planet is the brightest object low in the south-south-west as the twilight disappears. ExoMars consists of a Trace Gas Orbiter to study rare gases, and particularly methane, in Mars’ atmosphere and it also has the experimental Schiaparelli lander.

Mars fades slightly from magnitude 0.1 (almost equal to Vega) to 0.4 this month as it tracks 21° eastwards above the so-called Teapot of Sagittarius, clipping the top star of the Teapot’s lid (Kaus Borealis) on the 7th. The planet recedes from 160 million to 187 million km during October while its gibbous disk shrinks to 7.5 arcseconds in diameter which, with its low altitude, makes telescopic study all the more challenging. It lies below the Moon on the 8th.

A little fainter than Mars, and a little lower to Mars’ right in this evening’s sky, is the ringed planet Saturn. This shines at magnitude 0.6 in southern Ophiuchus and appears 16 arcseconds across, with its glorious rings spanning 36 arcseconds. Saturn lies to the left of the earthlit Moon on the 5th and dips lower with each evening until it is passed by Venus late in the month – catch Saturn 3° above Venus on the 29th.

By our map times, both Saturn and Mars have set and the Summer Triangle has toppled over into the west. High in the south is the Square of Pegasus, a line along its right-hand side pointing down to the southern bright star Fomalhaut in Piscis Austrinus the Southern Fish. Just to the right of this line, and 2° south-west (below-right) of the star Lambda Aquarii (magnitude 3.7), is the farthest of the Sun’s planets, Neptune. At magnitude 7.8 and a distance of 4,350 million km on the 1st, we need binoculars and a better chart to identify it, and probably a large telescope to glimpse its bluish disk only 2.3 arcseconds wide.

To the east of Aquarius lies the constellation of the two fish, Pisces, and the second most distant planet, Uranus, which stands directly opposite the Sun at opposition on the 15th at a distance of 2,835 million km. At magnitude 5.7 it is near the limit of naked-eye visibility under the darkest of skies, but is an easier binocular or telescope target with its diameter of 3.7 arcseconds.

Orion rises in the east less than two hours after our map times and strides across the meridian before dawn. To its north and east lies Gemini and between the two is the radiant point for the annual Orionids meteor shower. This is visible during our morning hours throughout the second half of the month and peaks at rates around 25 meteors per hour between the 21st and 24th. Its meteors are swift, with many leaving glowing trains in their wake, and represent the dusty debris laid down by Halley’s Comet.

The night ends with Mercury which is conspicuous at magnitude -0.7 and rises in the east 109 minutes before the Sun on the 1st, climbing to stand 9° high forty minutes before sunrise. By the 11th, as its favourable morning show draws to a close, it rises 76 minutes before sunrise. On that morning, the even brighter Jupiter lies only 0.7° below-right of Mercury as the giant planet climbs away from the Sun’s far side. By the 28th, Jupiter rises at about 05:40 BST and is an impressive sight 1.5° below the earthlit waning Moon.

Alan Pickup

This is a slightly-revised version of Alan’s article published in The Scotsman on October 1st 2016, with thanks to the newspaper for permission to republish here.  Journal Editor’s apologies for the lateness of the article appearing here.

Scotland’s Sky in September, 2016

Harvest moon eclipsed on the 16th

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 from the 21st. (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 from the 21st. (Click on map to enlarge)

Two eclipses and a couple of notable space exploration milestones make September an interesting month for astronomers. I’ll postpone until the close of this note, though, my thoughts on the exciting news that Proxima Centauri, the closest star to our Sun, has a planet which is probably rocky, slightly larger than the Earth and in the star’s so-called habitable zone where liquid water might exist.

The first eclipse, an annular or “ring” eclipse of the Sun, occurs on the 1st with the Moon too distant to hide the Sun completely. Instead, a dazzling ring of sunlight remains visible along a narrow path that stretches across Central Southern Africa into the Indian Ocean. Surrounding areas enjoy a partial solar eclipse but nothing is seen as far north as Europe

Of greater interest for us is a penumbral eclipse of the Moon on the 16th during which the Moon passes through the southern outer part of the Earth’s shadow, the penumbra. The event lasts from 17:55 to 21:54 BST although, as seen from Edinburgh, the Moon only rises in the east at 19:29. Maximum eclipse occurs 25 minutes later, at 19:54, when all but the southern 9% of the Moon is within the penumbra. Little darkening of the disk may be noticeable, except near the northern edge which is closest to the Earth’s umbra where all direct sunlight is extinguished.

Since this full moon is the one closest to the autumnal equinox, due at 15:21 BST on the 22nd, it is also called the harvest moon. The tradition is that the bright moon stands at a similar altitude in the eastern sky over several evenings at this time, so permitting the harvesting hours to be extended.

The Sun tracks 11.5° southwards during September to cross the celestial equator at the equinox when day and night have approximately equal lengths around the Earth. Sunrise/sunset times for Edinburgh change from 06:18/20:06 BST on the 1st to 07:14/18:50 on the 30th. The moon is new on the 1st, at first quarter on the 9th, full on the 16th, at last quarter on the 23rd and new again on 1 October.

Jupiter is now lost from view as it nears conjunction on the Sun’s far side on the 26th. It leaves Venus as an evening star, but even though Venus is brilliant at magnitude -3.9 it stands less than 5° above Edinburgh’s horizon at sunset and sets itself within the next 45 minutes. Catch it, if you can, in the west as September begins, shifting to the south-west by the month’s end.

Mars, Saturn and the star Antares in Scorpius form a triangle low in the south-west as darkness falls at present, with Saturn above Antares and Mars a few degrees to their left. Saturn is magnitude 0.5 while Mars is brighter and noticeably reddish, though it fades from magnitude -0.3 to 0.1 as it speeds 18° eastwards and further away. By month’s end, its motion brings it onto our chart and close to the so-called Teapot of Sagittarius, just setting in the south-west.

Look for the Moon close to Saturn on the 9th and above Mars on the 10th when, if viewed telescopically, the two planets appear 16 and 10 arcseconds wide respectively, with Saturn’s wide-open rings spanning 37 arcseconds.

Mercury begins its best morning appearance of the year late in the month. From the 24th onwards, it rises in the east more than 95 minutes before the Sun and reaches more than 8° high forty minutes before sunrise. It is furthest west of the Sun (18°) on the 28th and is magnitude -0.5 when it lies alongside the slender earthlit Moon on the 29th.

Just a day later, on the 30th, Europe’s Rosetta spacecraft is destined to end its mission when it collides with Comet Churyumov-Gerasimenko, the rubber-duck shaped body it has been orbiting and investigating since August 2014. The collision will be gentle but radio contact and data-collection is likely to be lost as the craft settles on the comet’s surface.

Earlier in the month, during a month-long launch window beginning on the 8th, NASA’s OSIRIS-REx spacecraft is due to embark on its seven-years mission to collect and return samples from the surface of Bennu, a small asteroid which has been given an outside chance of having a catastrophic impact with the Earth late in the next century.

Proxima Centauri lies at a distance of only 4.25 light years but is much too dim to be seen without a telescope, A small red dwarf star, it is less than 15% as massive and wide as our Sun and has less than 0.2% of the Sun’s energy output. Also called Alpha Centauri C, it was discovered in 1915 by the Edinburgh-born astronomer Robert Innes and lies 15° to the east of the Southern Cross in a part of the sky we never see from Britain. It is thought to form a triple star system with Alpha Centauri A and B, a tight binary of more Sun-like stars that lie 2° away in the sky.

The newly discovered world has been dubbed Proxima b but it is something of a stretch to call it Earth-like. It orbits its star in a year of 11.2 Earth-days at a distance of less than 8 million km where it is blasted by X-rays from dramatic flares that we see erupting on Proxima’s surface – far from ideal for life. It is also probably tidally locked – keeping its same face towards the star – and we do not even know (yet!) that it has water, never mind life.

Alan Pickup

This is a slightly-revised version of Alan’s article published in The Scotsman on September 1st 2016, with thanks to the newspaper for permission to republish here.