Geminid meteors sparkle during long December nights
December brings us spectacular night skies and arguably the richest meteor shower of the year, the Geminids. We still have the Summer Triangle of bright stars, Vega in Lyra, Deneb in Cygnus and Altair in Aquila, high in the south-west at nightfall while the unmistakable figure of Orion dominates the midnight hours, surrounded by his cohort of familiar winter constellations. By the predawn, the Plough sails overhead and the night’s only conspicuous planets shine to the south of east.
Our longest nights, of course, occur around the winter solstice when the Sun reaches its most southerly point in its annual trek around the sky. This occurs at 16:28 GMT on the 21st when Edinburgh’s night, measured from sunset to sunrise, lasts for 17 hours and 3 minutes, which no less than 10 hours and 39 minutes longer than at June’s summer solstice.
Sunrise/sunset times for Edinburgh during December vary from 08:19/15:44 on the 1st to 08:42/15:40 on the 21st and 08:44/15:48 on the 31st. The Moon is full on the 3rd, at last quarter on the 10th, new on the 18th and at first quarter on the 26th,
By our map times, the Summer Triangle has toppled low into the west and is being followed by the less impressive Square of Pegasus. The Square’s top-left star, Alpheratz, belongs to Andromeda whose other main stars, Mirach and Almach, line up to its left. A spur of fainter stars above Mirach leads us to the Andromeda Galaxy, whose oval glow reaches us from 2.5 million light years away.
Orion is in the east-south-east, his Belt pointing up Aldebaran and the Pleiades in Taurus and down to where the brightest nighttime star, Sirius in Canis Major, rises less than one hour later.
The Moon lies to the right of Aldebaran and below the Pleiades on the night of 2nd-3rd, to the left of Aldebaran a day later and comes around again to occult the star in the early hours of the 31st. We need a telescope to see Aldebaran wink out at the Moon’s limb at 01:01 and reappear at 01:57 as seen from Edinburgh.
It is from a radiant point near Castor in Gemini, north-east of Orion, that meteors from the Geminids shower diverge between the 8th and 17th although, of course, the meteors fly in all parts of the sky. With negligible moonlight this year, and given decent weather, we are in for a stunning display of sparkling long-trailed meteors whose paths point back to the radiant. Rates for an observer under an ideal dark sky could peak at more than 100 per hour at the shower’s peak on the night of the 13th-14th, though most of us may glimpse only a fraction of these.
Although most meteors originate as cometary debris, the Geminids appear to be rocky splinters from the 5 km-wide asteroid, Phaethon, which dives within 21 million km of the Sun every 523 days. In what is its closest approach to the Earth since its discovery in 1983, Phaethon sweeps only 10.3 million km from the Earth on the 16th when a telescope might show it as a tenth magnitude speck speeding past Alpheratz.
December’s second shower, the Ursids, derives from Comet Tuttle and is active between the 17th and 25th, peaking on the 23rd. Typically it yields fewer than ten meteors per hour so I rarely mention it here – I believe my last time was 37 years ago – but very occasionally it rivals the Geminids in intensity, if only for a few hours. The radiant point lies near the star Kochab in Ursa Minor and is plotted on our northern chart.
The unprecedented interstellar asteroid, discovered using a telescope in Hawaii and featured here hast time, has now been called 1I/’Oumuamua. This indicates that it is our first known interstellar visitor and employs the Hawaiian word ’Oumuamua to reflect its supposed status as a scout from the distant past. Further observations imply that it is remarkably elongated, being at least five times longer than it is wide.
Venus shines brilliantly at magnitude -3.9 very low in the south-east as the night ends, but is soon lost from view as it dives towards the Sun’s far side. It leaves Jupiter as our most prominent (magnitude -1.7 to -1.8) morning object. The giant world rises at Edinburgh’s east-south-eastern horizon at 05:31 on the 1st and 04:07 on the 31st, climbing southwards in the sky to stand some 15° high before dawn. Tracking eastwards in Libra, it passes 0.7° north of the celebrated double star Zubenelgenubi on the 21st.
Mars, fainter at magnitude 1.7 to 1.5, lies 16° above-right of Jupiter on the 1st when it is also about half as bright as Virgo’s star Spica, 3° below and to its right. As Mars tracks east-south-eastwards from Virgo to Libra it almost keeps pace with the Sun, so that it rises at around 03:50 throughout the month. By the 31st, it stands 3° from Jupiter, with Zubenelgenubi below and to Mars’ left in the same binocular field of view. The waning Moon forms a nice triangle with Mars and Spica on the 13th and with Mars and Jupiter on the 14th.
Saturn sets in our bright evening twilight as it heads towards conjunction beyond the Sun on the 21st. Mercury slips around the Sun’s near side on the 13th to become best placed as a morning star between Christmas and New Year. Between the 21st and 31st it brightens between magnitude 0.8 and -0.3, rises 100 or more minutes before Edinburgh’s sunrise and stands around 8° high in the south-east thirty minutes before sunrise.
This is a slightly revised version of Alan’s article published in The Scotsman on November 30th 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.
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.
This is a slightly-revised version of Alan’s article published in The Scotsman on December 1st 2015, with thanks to the newspaper for permission to republish here.
Jupiter outstanding as the Geminids meteors fly
December brings our longest nights of the year and what may be 2014’s richest meteor shower. Indeed, there is an argument for ranking December nights as the most spectacular of the year if only because Orion, and the sparkling constellations that attend him, stand at their highest near the meridian at midnight. Of the bright planets, Jupiter outshines every star and is well placed from mid-evening onwards, but the others are lurking shyly near the Sun and require a little more effort.
Jupiter is unmistakable from the moment it rises in the east-north-east some 35 minutes after our star map times. Improving in brightness from magnitude -2.3 to -2.5 this month, it climbs to pass high in the south and onwards into the south-west before dawn. We find it in Leo, to the right of the Sickle and less than 8° above-right of Regulus. It is here that it reaches a stationary point on the 9th before beginning a westerly motion which carries it back into Cancer just a day before its opposition in early February.
With its large disk and changing cloud-patterns, Jupiter is always an rewarding telescopic sight while the motions from side to side of its four main moons may be followed using nothing more than decent binoculars. When Jupiter lies near the Moon on the night of the 11th-12th, it is 717 million km distant and its globe appears 41 arcsec in diameter.
Orion stands clear of the horizon in the east-south-east at the map times. Its main stars, the blue-white supergiant Rigel at Orion’s knee and the contrasting red supergiant Betelgeuse at his shoulder, are among the ten brightest. the trio of stars between them form Orion’s Belt while hanging below the Belt is Orion’s Sword and the fuzzy glow of the Orion Nebula where new stars and planets are forming, albeit slowly, before our eyes.
A line upwards along the Belt extends to Aldebaran (close to the Moon on the 5th-6th) and onwards to the Pleiades or Seven Sisters star cluster. Carry the line downwards towards Sirius which rises one hour after our map times and is our brightest star after the Sun.
North and east (above-left) of Orion lies Gemini with its twins Castor and Pollux, while close to Castor (see chart) is the radiant point for the annual Geminids meteor shower. Bright medium-slow meteors streak in all parts of the sky between the 8th and 17th but all radiate away from this point as they follow parallel paths into the upper atmosphere. The radiant climbs from the north-north-east horizon at nightfall to pass high in the south at about 02:00. Meteor rates are expected to be highest during the 24 hours around 07:00 on the morning of the 14th when more than 80 Geminids per hour might be counted under ideal conditions. The Moon is much less obtrusive than during the Geminids last year.
The Square of Pegasus crosses the high meridian in the early evening and shifts to the south-west by our map times as Andromeda stretches up from its upper-left corner. High in the south are the two smaller constellations of Triangulum the Triangle and Aries the Ram. Aries’ main star, Hamal, is identical in brightness to Polaris, the Pole Star, but lies perhaps five times closer to us at 66 light years, It also appears to have a planet that is larger than Jupiter and takes 381 days to orbit at a distance slightly greater than that between the Earth and the Sun.
Aries also gives its name to the celestial counterpart of the Greenwich meridian. Longitudes in the sky are measured eastwards from the so-called First Point of Aries where the Sun crosses the sky’s equator at the spring or vernal equinox. When the Greek astronomer Hipparchus assigned the name more than two thousand years ago this point was located in Aries. However, the Earth wobbles on its axis over a period of 26,000 years with the result that the First Point of Aries has slipped more than 30° westwards against the stars and now lies to the south of the Square of Pegasus in the dim constellation of Pisces.
The Sun is furthest south in the sky at 23:03 GMT on the 21st, the moment of our winter solstice. Sunrise/sunset times for Edinburgh change from 08:19/15:44 on the 1st, to 08:43/15:40 on the 21st and 08:44/15:48 on the 31st. Nautical twilight persists for around 94 minutes at dawn and dusk. The Moon is full on the 6th, at last quarter on the 14th, new on the 22nd and at first quarter on the 28th.
Mars, the best of the planets after Jupiter, is the brightest object low in the south-south-west at nightfall and climbs a little higher from night to night as it slides northwards in relation to the Sun. It does, though, dim from magnitude 1.0 to 1.1 as it tracks eastwards through Capricornus. It sets at about 19:15 and stands left of the young earthlit Moon on Christmas Eve.
By mid-month, and provided we have a clear south-western horizon, we may be able to spot the brilliant (magnitude -3.9) evening star Venus just after sunset. At Hogmanay, Venus stands 6° high at sunset and sets itself 76 minutes later. Mercury slips around the Sun’s far side on the 8th and is destined to join Venus as an evening star in the New Year.
Saturn is emerging as a pre-dawn object low in the south-east where it shines at magnitude 0.5 as it tracks from Libra into Scorpius. Catch it 7° below-left of the waning Moon on the 19th.
This is a slightly-revised version of Alan’s article published in The Scotsman on November 28th 2014, with thanks to the newspaper for permission to republish here.
Saturn’s opposition in the Balance
Our days lengthen during May until the period of true nighttime darkness dwindles to almost nothing by the month’s end. You might think that astronomers would be tempted to mothball their telescopes, but if they did they would miss the year’s best views of Saturn.
The beautiful ringed planet comes to opposition at a distance of 1,331 million km on the 10th when it lies in Libra, the Balance or Scales, and stands in the south in the middle of the night. The ochre deserts and white north polar cap of Mars are also observable, as are all the other brighter planets at one time or another. There may also be a spectacular meteor shower that has never been seen before.
Look overhead at nightfall to find the Plough and extend a curving line along its handle to reach the star Arcturus shining brightly in Bootes well up in the east-south-east. Continue that line, still bending, into the south-east where Mars is conspicuous and reddish in Virgo, above-right of Virgo’s leading star Spica. By our star map times, the Plough has moved to stand high in the west, Arcturus is high in the south, and Mars is in the south-west.
Following its own opposition on 8 April, Mars is now receding from us, from 96 million to 119 million km during May, and although it halves in brightness from magnitude -1.2 to -0.5 it still outshines Arcturus. Viewed telescopically, its disk shrinks from 15 to 12 arcseconds and only in moments of steady “seeing” can we discern its surface detail. The Red Planet’s slow westerly progress below the famous binary star Porrima halts on the 21st when it reaches a so-called stationary point before tracking eastwards again.
Saturn, creeping westwards in the middle of Libra and bright at magnitude 0.1, stands close to the horizon and beneath Arcturus at nightfall. By our map times, though, it is almost due south at an altitude of nearly 19° as seen from Edinburgh. This is 12° lower than Mars when it transits the meridian, so we see it through more of the Earth’s atmosphere and the seeing is likely to be worse. On the other hand, Saturn’s disk is bigger at 19 arcseconds while its superb ring system spans 42 arcseconds and has its north face tipped 22° towards us. This is a good time to look for the Cassini Division, the 4.800 km gap between the two main rings.
Binoculars show the star Zubenelgenubi, 5° to the west of Saturn, to be an obvious double star, while Zubeneschamali, to Saturn’s north, is held (perhaps mistakenly) by some observers to be one of the few greenish-hued stars in the sky. The Arabic names for these stars mean Southern and Northern Claw respectively and date from an era when they were also associated with the brighter nearby constellation of Scorpius the Scorpion. Use binoculars to scan 11° north of Zubeneschamali for the fuzzy blob of M5, a globular cluster of up to 500,000 stars at a distance of about 25,000 light years. Some observers rate it more highly than the more familiar M13 globular in Hercules and M3 in Canes Venatici, 12° to the north-west of Arcturus.
Jupiter remains prominent, and brighter than any star, in the west at nightfall but is close to setting in the north-west by our map times. At magnitude -2.0, it is tracking eastwards in the middle of Gemini, below Castor and Pollux, and shows a 34 arcseconds disk at midmonth.
Mercury is an evening star as it climbs to stand furthest east of the Sun, 23°, on the 25th. Between the 13th and 29th it stands about 10° high in the west-north-west forty minutes after sunset though it may be hard to spy without binoculars in the slowly-fading twilight. It dims from magnitude -0.6 to 1.0 between these dates. Venus is a brilliant morning star on magnitude -4.1 which rises in the east fifty minutes before the Sun on the 1st and one hour before sunrise on the 31st.
Sunrise/sunset times for Edinburgh change from 05:29/20:52 BST on the 1st to 04:36/21:45 on the 31st. Nautical twilight at dusk and dawn lasts for 105 minutes on the 1st and for all but the middle 24 minutes of the last night of May.
The Moon is at first quarter on the 7th, full on the 14th, at last quarter on the 21st and new on the 28th. The Moon is strongly earthlit when it stands just above Aldebaran in Taurus on the 1st evening. Catch it again below-left of Jupiter on the 4th, near Mars on the nights of the 10th and 11th and Saturn on the 13th and 14th.
The morning of the 24th may see slow meteors streaming away from a radiant point in the dim constellation of Camelopardalis the Giraffe, see north map. The prediction is made by analysts who have back-tracked the motion of a small comet whose official name is Comet 209P/LINEAR. Discovered as recently as 2004, its path carries it between the orbits of the Earth and Jupiter every 5.1 years and it is to pass harmlessly only 8,290,000 km from the Earth on the 29th, the ninth closest approach by a comet on record.
Only a few days earlier, it is thought that the Earth may encounter several streams of particles that were released by the comet between 1803 and 1924. Meteor rates could hit many hundreds per hour, if not storm force, though the peak of activity is predicted between 08:00 and 09:00 BST on the 24th, during daylight for Britain but ideal for observers in N America. Our pre-dawn hours could still be interesting, though.