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.
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.