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.
Nights begin with Venus and end at Jupiter
The end of British Summer Time means that we now enjoy six hours of official darkness before midnight, though I appreciate that this may not be welcomed by everyone. The starry sky as darkness falls, however, sees only a small shift since a month ago, with the Summer Triangle, formed by the bright stars Vega, Deneb and Altair, now just west of the meridian and toppling into the middle of the western sky by our star map times.
Those maps show the Square of Pegasus high in the south. The star at its top-left, Alpheratz, actually belongs to Andromeda whose other main stars, Mirach and Almach, are nearly equal in brightness and stand level to its left. A spur of two stars above Mirach leads to the oval glow of the Andromeda Galaxy, M31, which is larger than our Milky Way and, at 2.5 million light years, is the most distant object visible to the unaided eye. It is also approaching us at 225 km per second and due to collide with the Milky Way in some 4 billion years’ time.
Binoculars show M31 easily and you will also need them to glimpse more than a handful of stars inside the boundaries of the Square of Pegasus, even under the darkest of skies. In fact, there are only four such stars brighter than the fifth magnitude and another nine to the sixth magnitude, close to the naked eye limit under good conditions. How many can you count?
Mars is the easiest of three bright planets to spot in tonight’s evening sky. As seen from Edinburgh, it stands 11° high in the south as the twilight fades, shining with its customary reddish hue at a magnitude of 0.4, and appearing about half as bright as the star Altair in Aquila, 32° directly above it.
Now moving east-north-eastwards (to the left), Mars is 5° below-right of the Moon on the 6th and crosses from Sagittarius into Capricornus two days later. Soon after this, it enters the region covered by our southern star map, its motion being shown by the arrow. By the 30th, Mars has dimmed slightly to magnitude 0.6 but is almost 6° higher in the south at nightfall, moving to set in the west-south-west at 21:00. It is a disappointingly small telescopic sight, though, its disk shrinking from only 7.5 to 6.5 arcseconds in diameter as it recedes from 188 million to 215 million km.
We need a clear south-western horizon to spy Venus and Saturn, both low down in our early evening twilight. Venus, by far the brighter at magnitude -4.0, is less than 4° high in the south-west thirty minutes after sunset, while Saturn is 4° above and to its right, very much fainter at magnitude 0.6 and only visible through binoculars. The young earthlit Moon may help to locate them – it stands 3° above-right of Saturn on the 2nd and 8° above-left of Venus on the 3rd.
Mercury is out of sight in the evening twilight and Saturn will soon join it as it tracks towards the Sun’s far side. However, Venus’ altitude thirty minutes after sunset improves to 9° by the 30th when it sets for Edinburgh at 18:30 and is a little brighter at magnitude -4.1. Viewed telescopically, Venus shows a dazzling gibbous disk that swells from 14 to 17 arcseconds as its distance falls from 178 million to 149 million km.
Sunrise/sunset times for Edinburgh change from 07:20/16:31 on the 1st to 08:18/15:44 on the 30th. The Moon reaches first quarter on the 7th, full on the 14th, last quarter on the 21 and new on the 28th.
The full moon on the 14th occurs only three hours after the Moon reaches its perigee, the closest point to the Earth in its monthly orbit. As such, this is classed as a supermoon because the full moon appears slightly (7%) wider than it does on average. By my reckoning, this particular lunar perigee, at a distance of 356,509 km, is the closest since 1948 when it also coincided with a supermoon.
Of the other planets, Neptune and Uranus continue as binocular-brightness objects in Aquarius and Pisces respectively in our southern evening sky, while Jupiter, second only to Venus in brightness, is now obvious in the pre-dawn.
Jupiter rises at Edinburgh’s eastern horizon at 04:28 on the 1st and stands more than 15° high in the south-east as morning twilight floods the sky. It outshines every star as it improves from magnitude -1.7 to -1.8 by the 30th when it rises at 03:07 and is almost twice as high in the south-south-east before dawn.
Currently close to the famous double star Porrima in Virgo, Jupiter is 13° above-right of Virgo’s leader Spica and draws 5° closer during the period. Catch it less than 3° to the right of the waning earthlit Moon on the 25th. Jupiter’s distance falls from 944 million to 898 million km during November while its cloud-banded disk is some 32 arcseconds across.
The annual Leonids meteor shower has produced some stunning storms of super-swift meteors in the past, but probably not this year. Active from the 15th to 20th, it is expected to peak at 04:00 on the 17th but with no more than 20 meteors per hour under a dark sky. In fact, the bright moonlight is likely to swamp all but the brightest of these this year. Leonids diverge from a radiant point that lies within the Sickle of Leo which climbs from low in the east-north-east at midnight to pass high in the south before dawn.
This is a slightly-revised version of Alan’s article published in The Scotsman on November 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.
Europe’s Philae probe to attempt first touchdown on comet
In an exciting month in astronomy and space exploration, November should bring the first soft landing on a comet when the European Space Agency’s Philae craft detaches from the Rosetta probe and drops gently onto the icy nucleus of Comet Churyumov-Gerasimenko.
Our sky at nightfall s similar to that of a month ago although, with our return to GMT, darkness arrives more than two hours earlier in the evening. Mars continues as the only bright planet at these times, visible low in Edinburgh’s south-south-western sky and fading only a little from magnitude 0.9 to 1.0 as it tracks eastwards above the Teapot of Sagittarius.
However, even though Mars is drawing closer to the Sun, its altitude at the end of nautical twilight improves from 5° to 9° during November as the Sun plunges more than 7° southwards in the sky and Mars edges almost 3° northwards. This also means that Mars-set in the south-west occurs at about 19:05 throughout the period. It stands below the young crescent Moon on the 26th.
Sunrise/sunset times for Edinburgh change from 07:19/16:33 GMT on the 1st to 08:17/15:45 on the 30th as the duration of nautical twilight at dawn and dusk extends from 83 to 93 minutes. The Moon is full on the 6th, at last quarter on the 14th, new on the 22nd and at first quarter on the 29th.
Comet Churyumov-Gerasimenko lies 6° south-east of Mars on the 12th but is a very dim telescopic object some 450 million km from the Sun. On that day Philae is due to unlatch from Rosetta and take about seven hours to fall 22.5km, coming to rest on tripod legs at about 16:00 GMT atop the head of the comet’s strange “rubber-duck” shape. To stop itself bouncing off into space in defiance of the comet’s feeble gravitational pull, it should then fire a tethered harpoon to anchor itself to the surface.
The comet’s 6-year orbit is carrying it closer to the Sun, eventually to reach perihelion at a distance of 186 million km next August. Meantime, its activity is picking up and Rosetta is imaging jets of dust and gas emerging, mainly from the duck’s neck region at present. With Philae in position to also monitor conditions at the surface, and even below the crust using sonar, seismographs and permittivity probes, our knowledge of what makes comets tick should soon be transformed.
The Summer Triangle of Vega, Deneb and Altair, lies in the west at our map times as Orion rises in the east below Taurus and the Pleiades. The Square of Pegasus stands high on the meridian with the three main stars of Andromeda, Alpheratz, Mirach and Almach, leading off from its top-left corner. The Andromeda Galaxy, M31, could hardly be better placed, being visible to the naked eye in a decent sky and not difficult at all through binoculars. It stands 2.5 million light years (ly) away and appears as an oval smudge some 8° above Mirach.
A line through the Square’s two right-hand stars points the way to Fomalhaut, bright but very low in the south. I mentioned last time that it may have at least a couple of planets. In fact, the first so-called extrasolar planet circling a solar-type star was discovered in 1995 and is about half the size of Jupiter yet orbits in only 4.2 days at a distance only one seventh of that of Mercury from the Sun. The star concerned is 51 Pegasi, magnitude 5.5 and 50 ly distant, which is unmistakable through binoculars just 1.5° or 3 Moon-widths to the right of the Scheat-Markab line.
Of the 1,800-plus extrasolar planets now known, no less than four orbit Upsilon Andromedae, a fourth magnitude star at 44 ly that stands between Mirach and Almach (see chart).
Jupiter, is creeping eastwards to the right of the famous Sickle of Leo. Rising in the east-north-east at about 23:20 on the 1st and as early as 21:40 on the 30th, it is prominent until dawn as it climbs through our south-eastern sky to pass about 50° high on our meridian before dawn. The Jovian disk is 38 arcseconds across when Jupiter lies near the Moon on the night of 13/14th.
The annual Leonids meteor shower lasts from the 15th to the 20th, building to a sharp peak on the morning of the 18th. Its super-swift meteors flash in all parts of the sky, though their paths radiate from a point in the Sickle. There is little moonlight interference this year, but meteor rates may be well down on what they were a few years ago when the shower’s parent comet was in the vicinity.
Venus sets too soon after the Sun to be seen, and with Saturn reaching conjunction on the Sun’s far side on the 18th, our only other observable bright planet is Mercury, fortunately putting on its best morning show of 2014.
On the 1st Mercury rises two hours before the Sun and shines at magnitude -0.5 as it climbs to an altitude of 10° in the east-south-east forty minutes before sunrise. Although it soon brightens to magnitude 0.8, it also slips back towards the Sun, so that by the 14th it rises 89 minutes before the Sun and is 6° high forty minutes before sunrise. Given a clear horizon, though, binoculars should show it easily and it should be a naked-eye object until it is swamped by the brightening twilight. Look for Virgo’s leading star, Spica, climbing from below Mercury to pass 5° to its right on the 7th.