Astronomers spot a mystery interstellar visitor
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.
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.
Saturn at full tilt as Comet Halley’s meteors fly
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.
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.
Brilliant Venus plunges into the evening twilight
Stargazers will be hoping for better weather as Orion and the stars of winter depart westwards in our evening sky, Venus dives into the evening twilight and around the Sun’s near side, while all the other bright planets are on view too. Indeed, Venus has the rare privilege of appearing as both an evening star and a morning star over several days, provided our western and eastern horizons are clear.
Orion still dominates our southern sky at nightfall as Leo climbs in the east and the Plough balances on its handle in the north-east. The Sun’s northwards progress and our lengthening days mean that by nightfall at the month’s end Orion has drifted lower into the south-west, halfway to his setting-point in the west. He is even lower in the west-south-west by our star map times when it is the turn of Leo to reach the meridian and the Plough to be almost overhead.
Leo’s leading star, Regulus, sits at the base of the Sickle of Leo, the reversed question-mark of stars from which meteors of the Leonids shower stream every November. The star Algieba in the Sickle (see chart) appears as a glorious double star through a telescope. Its components are larger and much more luminous than our Sun and lie almost 5 arcseconds apart, taking some 510 years to orbit each other. The pair lie 130 light years away and are unrelated to the star less than a Moon’s breadth to the south which is only half as far from us.
The Sun travels northward across the equator at 10:28 GMT on the 20th, the moment of the vernal (spring) equinox in our northern hemisphere. On this date, nights and days are of roughly equal length around the globe. Sunrise/sunset times for Edinburgh change from 07:04/17:47 GMT on the 1st to 06:46/17:49 BST (05:46/18:49 GMT) on the 31st after we set our clocks forwards to BST on the morning of the 26th. The lunar phases change from first quarter on the 5th to full on the 12th, last quarter on the 20th and new on the 28th.
Look for the young earthlit Moon well to the left of the brilliant magnitude -4.6 Venus on the 1st when telescopes show the planet’s dazzling crescent to be 47 arcseconds in diameter and 16% sunlit. Venus’ altitude at sunset plummets from 29° in the west-south-west on that day to only 7° in the west on the 22nd as its diameter swells to 59 arcseconds and the phase shrinks to only 1% – indeed, a few keen-sighted people might be able to discern its crescent with the naked eye and this is certainly easy to spot through binoculars.
Venus dims to magnitude -4.0 by the time it sweeps 8° north of the Sun and only 42 million km from the Earth at its inferior conjunction on the 25th. This marks its formal transition from the evening to the morning sky, but because it passes so far north of the Sun as it does every eight years or so, Venus is already visible in the predawn before we lose it in the evening. In fact, it is 7° high in the east at sunrise on the 22nd, and it only gets better as the month draws to its close.
Before Venus exits our evening sky, it meets Mercury as the latter begins its best spell as an evening star this year. On the 20th, the small innermost planet lies 10° to the left of Venus, shines at magnitude -1.2 and sets at Edinburgh’s western horizon 78 minutes after the Sun. By the 29th, it is 10° high forty minutes after sunset and shines at magnitude -0.4, easily visible through binoculars and 8° to the right of the very young Moon.
Mars, near the Moon on the 1st and again on the 30th, dims from magnitude 1.3 to 1.5 this month as it tracks from Pisces into Aries. By the month’s end, it lies to the left of Aries’ main star Hamal and sets at our map times. It is now more than 300 million km away and its disk, less than 5 arcseconds across, is too small to be of interest telescopically.
The Moon has another encounter with the Hyades star cluster on the night of the 4th-5th, hiding several of its stars but setting for Scotland before it reaches Taurus’ main star Aldebaran. The latter, though, is occulted later as seen from most of the USA. The Moon passes just below Regulus on the night of the 10th-11th and meets the planet Jupiter on the 14th.
Jupiter, conspicuous at magnitude -2.3 to -2.5, rises in the east at 21:37 GMT on the 1st and only 31 minutes after Edinburgh’s sunset on the 31st. Now edging westwards above the star Spica in Virgo, it is unmistakable as it climbs through our south-eastern sky to cross the meridian in the small hours and lie in the south-west before dawn. Its disk, 43 arcseconds wide at mid-month, shows parallel cloud bands through almost any telescope, while its four moons may be glimpsed through binoculars as they orbit from one side to the other.
Saturn, the last of the night’s planets, rises in the south-east at 03:44 GMT on the 1st and almost two hours earlier by the 31st. Improving very slightly from magnitude 0.5 to 0.4 during March, it is the brightest object about 10° above the south-south-eastern horizon before dawn. Look for it 4° below-left of the Moon on the 20th.
This is a slightly-revised version of Alan’s article published in The Scotsman on February 28th 2017, with thanks to the newspaper for permission to republish here.
Venus highest and brightest as evening star
If you doubt that February offers our best evening sky of the year, then consider the evidence. The unrivalled constellation of Orion stands astride the meridian at 21:00 GMT tonight, and two hours earlier by February’s end. Around him are arrayed some of the brightest stars in the night sky, including Sirius, the brightest, and Capella, the sixth brightest which shines yellowish in Auriga near the zenith. This month also sees Venus, always the brightest planet, reach its greatest brilliancy and stand at its highest as an evening star.
By our map times, a little later in the evening, Orion has progressed into the south-south-west and Sirius, nipping at his heel as the Dog Star in Canis Major, stands lower down on the meridian. All stars twinkle as their light, from effectively a single point in space, is refracted by turbulence in the Earth’s atmosphere, but Sirius’ multi-hued scintillation is most noticeable simply because it is so bright. On the whole, planets do not twinkle since their light comes from a small disk and not a point.
I mentioned two months ago how Sirius, Betelgeuse at Orion’s shoulder and Procyon, the Lesser Dog Star to the east of Betelgeuse, form a near-perfect equilateral triangle we dub the Winter Triangle. Another larger but less regular asterism, the Winter Hexagon, can be constructed around Betelgeuse. Its sides connect Capella, Aldebaran in Taurus, Rigel at Orion’s knee, Sirius, Procyon and Castor and Pollux in Gemini, the latter pair considered jointly as one vertex of the hexagon.
Aldebaran, found by extending the line of Orion’s Belt up and to the right, just avoids being hidden (occulted) by the Moon on the 5th. At about 22:20 GMT, the northern edge of the Moon slides just 5 arcminutes, or one sixth of the Moon’s diameter, below and left of the star. Earlier that evening, the Moon occults several stars of V-shaped Hyades cluster which, together with Aldebaran, form the Bull’s face.
Sunrise/sunset times for Edinburgh change from 08:07/16:46 on the 1st to 07:06/17:45 on the 28th. The Moon is at first quarter on the 4th and lies to the west of Regulus in Leo when full just after midnight on the night of the 10th/11th. It is then blanketed by the southern part of the Earth’s outer shadow in a penumbral lunar eclipse. The event lasts from 22:34 until 02:53 with an obvious dimming of the upper part of the Moon’s disk apparent near mid-eclipse at 00:33. This time, the Moon misses the central dark umbra of the shadow where all direct sunlight is blocked by the Earth, but only by 160 km or 5% of its diameter.
Following last quarter on the 18th, the Moon is new on the 26th when the narrow track of an annular solar eclipse crosses the south Atlantic from Chile and Argentina to southern Africa. Observers along the track see the Moon’s ink-black disk surrounded by a dazzling ring of sunlight while neighbouring regions, but not Europe, enjoy a partial eclipse of the Sun.
Venus, below and to the right of the crescent Moon as the month begins, stands at it’s highest in the south-west at sunset on the 11th and 12th and blazes at magnitude -4.6, reaching its greatest brilliancy on the 17th. It stands further above-and to the right of the slim impressively-earthlit Moon again on the 28th.
Viewed through a telescope, Venus’ dazzling crescent swells in diameter from 31 to 47 arcseconds and the illuminated portion of the disk shrinks from 40% to 17%. Indeed, steadily-held binoculars should be enough to glimpse its shape. This month its distance falls from 81 million to 53 million km as it begins to swing around its orbit to pass around the Sun’s near side late in March.
Mars stands above and to the left of Venus but is fainter and dimming further from magnitude 1.1 to 1.3 during February. It appears closest to Venus, 5.4°, on the 2nd but the gap between them grows to 12° by the 28th as they track eastwards and northwards through Pisces. Both set before our map times at present but our charts pick them up at midmonth as they pass below-left of Algenib, the star at the bottom-left corner of the Square of Pegasus.
Mars shrinks below 5 arcseconds in diameter this month so few surface details are visible telescopically. This is certainly not the case with Jupiter, whose intricately-detailed cloud-banded disk swells from 39 to 42 arcseconds. We do need to wait, though, for two hours beyond our map times for Jupiter to rise in the east and until the pre-dawn hours for it to stand at its highest in the south. Second only to Venus, it shines at magnitude -2.1 to -2.3 and lies almost 4° due north of Virgo’s leading star Spica where it appears stationary on the 6th when its motion switches from easterly to westerly. Look for the two below-left of the Moon on the 15th and to the right of the Moon on the 16th.
Saturn is a morning object, low down in the south-east after its rises for Edinburgh at 05:25 on the 1st and by 03:48 on the 28th. At magnitude 0.6 to 0.5, it stands on the Ophiuchus-Sagittarius border where it is below-right of the waning Moon on the 21st. It is a pity that telescopic views are hindered by its low altitude because Saturn’s disk, 16 arcseconds wide, is set within wide-open rings which measure 16 by 36 arcseconds and have their northern face tipped 27° towards the Earth. Mercury remains too deep in our south-eastern morning twilight to be seen this month.
This is a slightly-revised version of Alan’s article published in The Scotsman on January 31st 2017, with thanks to the newspaper for permission to republish here.
Geminids suffer in the supermoonlight
The Sun reaches its farthest south at our winter solstice at 10:44 GMT on the 21st, as Mars and the brilliant Venus stand higher in our evening sky than at any other time this year. This is not a coincidence, for both planets are tracking eastwards and, more importantly, northwards in the sky as they keep close to the ecliptic, the Sun’s path over the coming weeks and months. Meantime, Jupiter is prominent during the pre-dawn hours while Orion is unmistakable for most of the night and strides proudly across the meridian at midnight in mid-December.
As the sky darkens this evening, Pegasus with its iconic, but rather empty, Square is nearing the meridian and the Summer Triangle (Vega, Deneb and Altair) stands high in the south-west.
By our map times, Altair is setting in the west and Orion stands in the south-east, the three stars of Belt pointing down to where Sirius, our brightest night-time star, will soon rise. Sirius, the red supergiant Betelgeuse at Orion’s shoulder and Procyon in Canis Minor, almost due east of Betelgeuse, form a near-equilateral triangle which has come to be known as the Winter Triangle.
Above Orion is Taurus, home to the Pleiades star cluster and the bright orange giant star Aldebaran, the latter located less than halfway between us and the V-shaped Hyades cluster.
Look for the almost-full Moon below the Pleiades and to the right of Aldebaran and the Hyades on the evening of the 12th and watch it barrel through the cluster during the night, occulting (hiding) several of the cluster’s stars on the way. As they dip low into the west on the following morning, the Moon occults Aldebaran itself, the star slipping behind the Moon’s northern edge between 05:26 and 05:41 as seen from Edinburgh. Even though this is the brightest star to be occulted this year, the Moon’s brilliance means we may well need a telescope to view the event.
Sunrise/sunset times for Edinburgh vary from 08:20/15:44 on the 1st to 08:42/15:40 on the 21st and 08:44/15:48 on the 31st. The Moon is at first quarter on the 7th and full on the 14th when, once again, it is near its perigee, its closest point to the Earth. Despite the fact that the Moon appears a barely perceptible 7% wider than it does on average, we can look forward to yet another dose of over-hyped supermoon hysteria in the media. The Moon’s last quarter comes on the 21st and it is new on the 29th.
Sadly, the Moon does its best to swamp the annual Geminids meteor shower which lasts from the 8th to the 17th and is expected to peak at about 20:00 on the 13th. Its meteors are medium-slow and, thankfully, there are enough bright ones that several should be noticeable despite the moonlight. Without the moonlight, and under perfect conditions, this might have been our best display of 2016, with 100 or more meteors per hour.
Geminids are visible in all parts of the sky, but perspective makes them appear to diverge from a radiant point near the star Castor in Gemini, marked near the eastern edge of our north map. This radiant climbs from our north-eastern horizon at nightfall to pass high in the south at 02:00.
Venus stands 10° above Edinburgh’s southern horizon at sunset on the 1st and shines spectacularly at magnitude -4.2 as it sinks to set in the south-west almost three hours later. The young earthlit Moon stands 10° above-right of Venus on the 2nd, 5° above the planet on the 3rd and, one lunation later, 20° below-right of the Moon on Hogmanay. By then, Venus is twice as high at sunset and (just) brighter still at magnitude -4.3. A telescope shows its dazzling gibbous disk which swells from 17 to 22 arcseconds in diameter as the sunlit portion shrinks from 68% to 57%.
As Venus speeds from Sagittarius to Capricornus, so Mars keeps above and to its left as it moves from Capricornus into Aquarius and into the region of sky above our south-western horizon at the map times. Mars is only a fraction as bright, though, and fades from magnitude 0.6 to 0.9. It also appears much smaller, only 6 arcseconds, so that telescopes now struggle to reveal any surface features. Spot Mars to the left of the Moon on the 4th and below-right of the Moon on the 5th.
Mercury is farthest east of the Sun, 21°, on the 11th but hugs our south-western horizon at nightfall and is unlikely to be seen. It reaches inferior conjunction between the Sun and Earth on the 28th by which time Saturn, which passes beyond the Sun on the 10th, might just be glimpsed low above the south-eastern horizon before dawn. On the 27th, it shines at magnitude 0.5 and lies 7° below-left of the slender waning Moon.
Jupiter is conspicuous at magnitude -1.8 to -1.9 and the real star of our morning sky. Rising in the east for Edinburgh at 03:04 on the 1st and 01:31 on the 31st, it climbs well up into our southern sky before dawn where it stands above Virgo’s leading star Spica and draws closer during the month.
Jupiter, Spica and the Moon form a neat triangle before dawn on the 23rd, when Jupiter is 850 million km away and appears 35 arcseconds wide through a telescope. Any decent telescope shows its parallel cloud belts, while binoculars reveal its four main moons which swap places from side to side of the disk as they orbit the planet in periods of between 1.8 and 17 days.
This is a slightly-revised version of Alan’s article published in The Scotsman on December 1st 2016, with thanks to the newspaper for permission to republish here.
Mars bright in evenings as ExoMars probe arrives
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.
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.
Smallest planet Mercury at its best for the year
It is surprising just how quickly our evening sky changes during April. If we look to the south-west as the twilight fades tonight, the foremost winter constellation of Orion stands well clear of the horizon, with Sirius sparkling to his left and Taurus and the Pleiades to the right, almost due west. By the month’s end, though, Orion has all-but-set as nautical twilight ends in the evening and only Betelgeuse at Orion’s shoulder remains (barely) in view, as shown by our monthly star chart. Taurus is setting, too, and Sirius has already gone.
Jupiter remains a striking object which is ideally placed for study in our evening sky as it slips westwards in the southern part of Leo, some 14° below and to the left of Regulus. Having stood at opposition, directly opposite the Sun, on March 8, the giant planet is unmistakable in the south-east at nightfall at present and passes 41° high in the S only thirty minutes before our map times.
Those maps have the Plough overhead, dragged out and distorted by the map projection used, while Virgo and the star Spica are nearing the meridian to the left of Jupiter. Spilling northwards from Virgo into the constellation of Coma Berenices is a region sometimes called the Realm of the Galaxies. This includes the Virgo cluster of well over 1,000 galaxies whose core lies some 54 million light years away and is roughly coincident with the “D” of “Denebola” on the chart.
More than a dozen of these Virgo galaxies are visible through medium-sizes telescopes and have entries in Charles Messier’s 18th century list of comet-like smudges in the sky. While it is impractical to plot their locations on our chart, a Web search and dark moonless skies over the next fortnight should allow some to be spotted.
The Sun climbs more than 10° northwards during April as sunrise/sunset times for Edinburgh change from 06:42/19:52 BST on the 1st to 05:30/20:51 on the 30th. New moon on the 7th is followed by first quarter on the 14th, full moon on the 22nd and last quarter on the 30th.
This month, Jupiter recedes from 676 million to 723 million km, dims only slightly from magnitude -2.4 to -2.3 and shrinks in diameter from 44 to 41 arcseconds. Binoculars show its four main moons and also show Jupiter passing only 7 arcminutes (one quarter of a Moon-breadth) above-left of the magnitude 4.6 star Chi Leonis on the 8th.
Jupiter loses its status as our sole evening planet this month. One of its usurpers is Mars which, as we’ll see, rises before midnight later in the period. The other is Mercury which emerges from the Sun’s glare over the coming week at the start of its best evening apparition of the year.
By the evening of the 8th, Mercury shines brightly at magnitude -0.9 and stands almost 8° high in the west-north-west 40 minutes after sunset. The very young crescent Moon, only 3% illuminated and brightly earthlit, lies 6° to its left but we will need a clear horizon, and perhaps even binoculars, to pick them out of the twilight. On the next evening, Mercury is 17° below-right of the still-spectacular earthlit Moon while, on the 10th, the Moon stands against the V-shaped Hyades star cluster in Taurus and sets as it draws close to the bright star Aldebaran.
As the Moon continues onwards, eventually to shine alongside Regulus on the 16th and Jupiter on the 17th, Mercury climbs to stand furthest east of the Sun (20°) on the 18th. By then, the innermost and smallest planet is 11° high 40 minutes after sunset and sets itself more than 90 minutes later still. It is fainter, though, at magnitude 0.2 and it dims further to magnitude 1.5 by the 25th when it is 2° lower and 7° below-right of the Pleiades. As Mercury dives towards the Sun’s near side, it is heading for a spectacular transit across the Sun’s face on May 9.
Mars is brightening rapidly as it draws closer to us on its way to opposition on May 22. It rises in the south-east about one hour after our chart times and from the 21st onwards rises before midnight as seen from Edinburgh. The best time to see it, though, is just before dawn when it reaches its highest point, admittedly only low down in the south. At magnitude -0.5 it is already the brightest object (after the Moon) down there, and by the month’s end it is more than twice as bright at magnitude -1.4.
Mars is currently in Scorpius, 6° north-north-west of the red supergiant star Antares, but it tracks 1.5° eastwards to a stationary point in Ophiuchus on the 17th before doubling back into Scorpius. Meantime, it approaches from 118 million to 87 million km and its disk swells from 12 to 16 arcseconds wide. Telescopes should reveal some markings on it desert surface, and perhaps its northern polar cap, but its low altitude is likely to make for poor observing conditions.
Not far to Mars’ left, and another victim of its low altitude, is the glorious ringed world Saturn. The second brightest object low in the south before dawn, it improves from magnitude 0.4 to 0.2 as it edges 1° westwards in Ophiuchus. Saturn lies almost 1,400 million km away in mid-April when its rotation-flattened disk is 18 arcseconds across and the rings span 40 arcseconds, their north face tipped 26° earthwards.
The Moon stands 4° above Mars before dawn on the 25th and a similar distance above-left of Saturn on the next morning.
This is a slightly-revised version of Alan’s article published in The Scotsman on April 1st 2016, with thanks to the newspaper for permission to republish here.
An extra day of superb February evening skies
February brings our best evening skies of the year and, with this being a leap year, we have one extra day to enjoy them. Pride of place must go to Orion which marches across our southern sky from the south-east at nightfall tonight to stand in the south-south-west by our star map times.
We are all familiar with the Summer Triangle of bright stars (Vega, Deneb and Altair) which graces our summer nights, but less well known is the Winter Triangle that follows close behind Orion. Consisting of the stars Betelgeuse at Orion’s shoulder, Procyon in Canis Minor which stands level with Betelgeuse to its left, and Sirius in Canis Major, the Winter Triangle is brighter than its summer counterpart and much more isosceles in form.
Sirius, found by extending Orion’s belt down and to the left, is the brightest star in our night sky largely because it is one of the closest to us at 8.6 light years. Indeed, viewed from the same distance as Betelgeuse, some 500 light years, it would be too dim to see without binoculars.
Because they are so obviously placed in the sky in the shape of a man, it is easy to regard the main stars of Orion as lying at similar distances from us. Although they are all highly luminous and far away, they stand at very different distances so that Orion’s impressive outline would change beyond recognition if we could view it from a different direction. A striking example concerns the three stars of Orion’s belt which, in order from the left, are Alnitak, Alnilam and (slightly fainter) Mintaka. Alnitak and Mintaka are thought to stand around 700 light years from us, but some estimates put Alnilam as distant as 2,000 light years, more than twice as far.
The Sun climbs almost 10° northwards during February as sunrise/sunset times for Edinburgh change from 08:08/16:45 on the 1st to 07:06/17:46 on the 29th. The Moon is at last quarter on the 1st, new on the 8th, at first quarter on the 15th and full on the 22nd. Because its path is inclined steeply in the south-west at nightfall, there is an excellent opportunity to spot the very young and brightly earthlit Moon low in the west-south-west on the evening of the 9th. It should still be spectacular over the following few evenings.
No bright planets are visible until the conspicuous Jupiter begins its climb through our eastern and south-eastern sky as Orion crosses the meridian. It lies in south-eastern Leo, 22° below and left of Regulus, and is creeping westwards against the stars as it draws towards its opposition in March. This month it brightens from magnitude -2.4 to -2.5, approaches from 694 million to 665 million km and swells from 42 to 44 arcseconds in diameter.
Any telescope should show Jupiter’s two main dark cloud belts, appearing symmetrically and in parallel on either side of its pale equatorial zone. Spots and streaks in the clouds, including the famous Red Spot in its southern hemisphere, drift from east to west across the Jovian disk as the planet rotates in just under ten hours. Of course, we need only binoculars to spot Jupiter’s four main moons as they change their relative positions on either side of the disk.
The second bright planet of the night stands low in the south-east as Jupiter reaches the meridian some five hours after our map times. The reddish, or perhaps salmon-pink, Mars lies below the Moon and just above the double star Zubenelgenubi in Libra on the morning of the 1st.
Mars spends February sliding eastwards though Libra and brightening from magnitude 0.8 to 0.3 as it approaches from 205 million to 161 million km. Its small slightly-gibbous disk grows from 7 to 9 arcseconds and is starting to reveal detail through good telescopes, particularly if we catch it just before dawn as it passes less than 20° high in the south.
If we look before dawn and take a line from Jupiter, well over in the west-south-west, to Mars in the south and onwards to the left we reach the almost equally-bright Saturn (magnitude 0.6 to 0.5) which is slow-moving in southern Ophiuchus, 8° above-left of the red supergiant star Antares in Scorpius. The Moon stands above Antares and above-right of Saturn on the morning of the 3rd when Saturn’s disk appears 16 arcseconds wide, with its rings spanning 36 arcseconds and tipped 26° to our view – a stunning sight.
The line-up of Jupiter, Mars and Saturn may be extended to Venus and Mercury, hugging our south-eastern horizon, and has led to widespread claims of a spectacular planetary alignment in our morning sky. In fact, the term “planetary alignment” is more usually applied to those occasions when several planets collect together in the same region of sky. There was one such tight alignment of Venus, Mars and Jupiter before dawn in October and similar events have been preceded by apocalyptic pronouncements in the crackpot community.
The current alignment stretches over more than 100° of sky and is better appreciated by observers further south and particularly by those in the southern hemisphere. For Scotland, though, Venus is uncomfortably low in our bright predawn twilight and although it is brilliant at magnitude -4.0 it is sinking ever lower – its altitude at Edinburgh’s sunrise being 7° on the 1st and half that by the month’s end. Mercury, much fainter near magnitude 0.0 and farthest from the Sun on the 7th, is a few degrees to the lower-left of Venus and very difficult from our latitudes. Both stand below the slender waning Moon on the 6th.
This is a copy of Alan’s article to be published in The Scotsman on February 1st 2016, with thanks to the newspaper for permission to reproduce here.
Quadrantids bring New Year fireworks on the 4th
If one of our resolutions for the New Year is to get to grips with the sky at night, then we could hardly do better than start with our January evenings. The unmistakable constellation of Orion the Hunter rises in the east at nightfall and is the centrepiece of a star-strewn region in the south-south-east by our star map times. On the other hand, most of the brighter planets, and what may be our brightest comet of 2016, are best seen in the morning sky.
Just as last month brought the Geminids as the best meteor shower of 2015, so the imminent Quadrantids shower may provide our best display of 2016. Lasting from today until the 6th, but with most of its activity in the hours before dawn on the 4th, its medium speed meteors are seen in all parts of the sky but diverge from a radiant point below and left of the Plough’s handle. The Plough itself lies in the north at nightfall and climbs through the north-east and east to lie overhead before dawn.
Most of the constellation figures show little relation to the things, persons or animals they represent. Orion is a striking exception, for he has conspicuous stars at his shoulders and knees and an iconic line of three stars to define the belt around his waist. Admittedly, his head is marked only by a knot of fainter stars, although if we look carefully we can find an arc of other faint stars to represent the shield he holds in the face of the charging bull, Taurus. Another line hangs below his belt to form his sword.
Use binoculars or a telescope to inspect the sword and it is easy to spot the Orion Nebula, a cloud of gas and dust that lies some 1,350 light years away. This miasma of greens, reds and blues is a region where new stars are forming, together with their nascent planetary systems.
The line of Orion’s belt slants downwards to the brightest star Sirius in Canis Major, the larger of Orion’s two dogs. Extend the line the other way and we reach Taurus with its leading star Aldebaran in and the Pleiades star cluster. As Orion sinks towards our western horizon early on the morning of the 20th, Aldebaran is once again occulted by the Moon. As seen from Edinburgh, the star disappears behind the upper edge of the Moon just before 03:24.
It may be hard to believe, but the Earth is closest to the Sun for the year (147,100,176 km) when it reaches perihelion late tomorrow. Sunrise/sunset times for Edinburgh vary from 08:44/15:49 today to 08:10/16:42 on the 31st, while the Moon is at last quarter tomorrow, new on the 10th, at first quarter on the 16th and full on the 24th.
Jupiter rises at Edinburgh’s eastern horizon at 22:39 tonight and two hours earlier by the 31st. Now in south-eastern Leo and already twice as bright as Sirius, it brightens from magnitude -2.2 to -2.4 this month and reaches a so-called stationary point on the 8th when its easterly motion reverses to westerly. If you did get a telescope for Christmas, then enjoy the view of its fascinating cloud-banded disk which swells in diameter from 39 to 42 arcseconds. Jupiter stood near the Moon last night and the two are even closer on the 28th-29th.
Mars rises in the east-south-east by 02:15 and lies to the left of Spica in Virgo as they pass 25° high in the S before dawn tomorrow. The Moon is nearby on Sunday and even closer on 1 February, by which time Mars has travelled east-south-eastwards into Libra where it lies just above the double star Zubenelgenubi. Mars improves from magnitude 1.3 to 0.8 to overtake Spica in brightness, but is shows only a small 6 arcseconds disk through a telescope.
Venus continues as a brilliant morning star (magnitude -4.1 to -4.0) though its altitude in the south-east at sunrise sinks from 15° today to 8° by the 31st. It lies to the right of the waning Moon on the 7th when a telescope shows its disk to be 79% sunlit and 14 arcseconds wide. Venus is just 2° to the right of Saturn on that morning and within 7 arcminutes of Saturn on the 9th. At magnitude 0.5, Saturn is much the fainter of the two as it creeps eastwards in southern Ophiuchus.
Mercury has a few more days as a difficult evening star. It is bright at magnitude -0.2 tonight, but it hugs our south-western horizon at nightfall and sets less than 100 minutes after the Sun. As the month ends it is back in our morning twilight, a few degrees to the left of Venus.
Comet 2013 US10 Catalina has remained stubbornly below naked eye brightness in our morning sky, though photographs reveal a striking divergence between its tails of dust and ionized gas, the latter being torn and billowed by the solar wind.
Following perihelion 123 million km from the Sun in mid-November, the comet is closest to Earth (108 million km) on the 17th. Likely to appear as a small greenish fuzzy blob through binoculars, it moves from less than 0.5° west of the conspicuous star Arcturus in Bootes this morning to lie 1.2° east of Alkaid, the star at the end of the Plough’s handle, before dawn on the 15th. It is currently around the sixth magnitude but may be a magnitude dimmer by the month’s end as it sweeps within 9° of Polaris and recedes on a trajectory that will never bring it back towards the Sun.
This is a slightly-revised version of Alan’s article published in The Scotsman on January 2nd 2016, with thanks to the newspaper for permission to republish here. Journal Editor’s apologies for the lateness of the article appearing here.
Get ready for a memorable meteor display
Experience tells us that the coldest night of the winter is unlikely to occur during December, but the month does bring our longest ones as the Sun dips to its farthest south at the winter solstice, due this year at 04:48 GMT on the 22nd.
Those long nights begin with Pegasus nearing the meridian but, by our star map times, its famous Square is in the south-west and our eastern sky has been claimed by the sparkling constellations of winter. Orion is unmistakable, his three Belt stars aligned almost vertically and pointing up to Aldebaran in Taurus and on to the Pleiades cluster.
There is another occultation of Aldebaran by the Moon on the 23rd with the star blinking out at the Moon’s limb just before 18:18 as viewed from Edinburgh, and reappearing by 19:15. The Moon’s glare means that we will probably need a telescope to view the event.
Sunrise/sunset times for Edinburgh vary from 08:18/15:44 on the 1st, to 08:42/15:40 on the 22nd and 08:44/15:47 on the 31st. The Moon’s last quarter on the 3rd is followed by new on the 11th, first quarter on the 18th and full on the 25th.
Our evening sky remains devoid of bright planets at present, but the return of the annual Geminids meteor shower is ample compensation. Now regarded as our best meteor display, this is active from the 8th to the 17th with its peak predicted for about 13:00 on the 14th with meteor rates of perhaps 120 per hour for an observer under an ideal dark sky. This is, of course, during our daylight but, unlike some other showers, meteor activity remains high for more than 24 hours and the nights of 13th/14th and 14th/15th could both be memorable. Just be careful to wrap up well to get your fill of long, bright, medium-slow meteors.
The radiant, the point in the sky from which the meteors appear to diverge, is plotted close to the star Castor in Gemini on the eastern side of our North map. Gemini lies north and east of Orion and as Orion marches across our southern sky so the radiant climbs to pass high in the south at 02:00. Remember that the meteors are visible in all parts of the sky, not just near Gemini – it is their streaks that point back to the radiant.
As Orion crosses our meridian some four hours after our map times, so the first bright planet of the night rises in the east. Jupiter brightens further from magnitude -2.0 to -2.2 as it creeps 2° or four Moon-breadths east-south-eastwards in south-eastern Leo, some 20° below and left of the star Regulus.
As the most conspicuous object in the middle of our southern sky before dawn, Jupiter stands just above the Moon on the 4th and to the Moon’s left on the 31st. By the month’s end, it rises more than one hour before midnight and its interesting cloud-banded disk has swollen in diameter from 36 to 39 arcseconds as seen telescopically.
The night’s second naked-eye planet, Mars, lies 20° east-south-east (below-left) of Jupiter and just below the star Porrima in Virgo as the month begins. At magnitude 1.5, but improving to 1.3, it, too, tracks east-south-eastwards to pass 4° north of Spica on the 21st. Look for it close to the waning Moon before dawn on the 6th but don’t expect your telescope to show much if any detail on its tiny 5 arcseconds disk.
The third planet is the brightest of all. Venus climbs above Edinburgh’s eastern horizon at 03:53 on the 1st and, at magnitude -4.2, may still be visible 25° high in the south-south-east at sunrise. It is then 4° north-east of Spica, but it speeds through Virgo and much of Libra so that, by the 31st, it rises in the south-east at 05:26 and is 15° high in the south at sunrise.
As Venus recedes, its gibbous disk shrinks from 17 to 14 arcseconds in diameter. Its motion takes it 2° above Zubenelgenubi in Libra on the 17th and to within a similar distance of the Graffias in Scorpius on the 31st. Venus is occulted for observers over much of N America as it is overtaken by the Moon next Monday.
Saturn, magnitude 0.5, emerges from the morning twilight to hover low in the south-east, below and to the left of Venus, during the final ten days of the year. On those same days, but in the evening, it might just be possible to spot Mercury as it shines at magnitude -0.5 some 5° high in the south-west only 30 minutes after sunset.
Comet 2013 US10 Catalina is likely to be a binocular object as it climbs into our south-eastern sky before dawn. Thought to be an asteroid when it was discovered in 2013, hence its odd name, it was closest to the Sun (123 million km) on November 15 and is due to pass closest to the Earth (108 million km) on January 17. There has been speculation that it might become a naked eye object of the fourth magnitude or better.
However, having spent weeks hidden in the Sun’s glare, it was a disappointing sixth magnitude object when it was recovered a couple of weeks ago. I fear it may not get much better than this, though the fact that it has two, or even three, tails will make for some interesting photographs. From 11° below-left of Venus as the month begins, it tracks almost due northwards to stand only 4° to the right of Venus next Monday (with the Moon nearby) and lie a mere 2° south of the bright star Arcturus in Bootes by the 31st.