Elusive Mercury is second evening star alongside Venus
Orion is striding proudly across the meridian as darkness falls, but, even before the twilight dims, we have our best chances this year to spot Mercury low down in the west and close to the more familiar brilliant planet Venus.
Both evening stars lie within the same field-of-view in binoculars for much of March, so the fainter Mercury should be relatively easy to locate using Venus as a guide. Provided, of course, that we have an unobstructed horizon. Mercury never strays far from the Sun’s glare, making it the most elusive of the naked-eye planets – indeed, it is claimed that many astronomers, including Copernicus, never saw it.
Blazing at magnitude -3.9, Venus hovers only 9° above Edinburgh’s western horizon at sunset on the 1st and sets 64 minutes later. Mercury, one tenth as bright at magnitude -1.3, lies 2.0° (four Moon-breadths) below and to its right and may be glimpsed through binoculars as the twilight fades. Mercury stands 1.1° to the right of Venus on the 3rd and soon becomes a naked eye object as both planets stand higher from night to night, becoming visible until later in the darkening sky.
By the 15th, Mercury lies 4° above-right of Venus and at its maximum angle of 18° from the Sun, although it has more than halved in brightness to magnitude 0.2. The slender young Moon sits 5° below-left of Venus on the 18th and 11° above-left of the planetary pairing on the 19th. Earthshine, “the old Moon in the new Moon’s arms”, should be a striking sight over the following few evenings.
On the 22nd, the 30% illuminated Moon creeps through the V-shaped Hyades star cluster and hides (occults) Taurus’ leading star Aldebaran between 23:31 and 00:14 as they sink low into Edinburgh’s west-north-western sky.
Falling back towards the Sun, Mercury fades sharply to magnitude 1.4 by the 22nd when it passes 5° right of Venus and becomes lost from view during the following week. At the month’s end, Venus stands 15° high at sunset and sets two hours later.
The Sun climbs 12° northwards in March to cross the sky’s equator at the vernal equinox at 16:15 on the 20th, which is five days before we set our clocks forward at the start of British Summer Time. Sunrise/sunset times for Edinburgh change from 07:04/17:47 GMT on the 1st to 06:46/19:49 BST (05:46/18:49 GMT) on the 31st. The Moon is full on the 2nd, at last quarter on the 9th, new on the 17th, at first quarter on the 24th and full again on the 31st.
Orion is sinking to our western horizon at our star map times while the Plough, the asterism formed by the brighter stars of Ursa Major, is soaring high in the east towards the zenith. To the south of Ursa Major, and just reaching our meridian, is Leo which is said to represent the Nemean lion strangled by Hercules (aka Heracles) in the first of his twelve labours. Leo appears to be facing west and squatting in a similar pose to that of the lions at the foot of Nelson’s Column in Trafalgar Square.
Leo’s Sickle, the reversed question mark that curls above Leo’s brightest star Regulus, outlines its head and mane and contains the famous double star Algieba whose two component stars, both much larger than our Sun, take more than 500 years to orbit each other and may be seen through a small telescope. Regulus, itself, is occulted as they sink towards Edinburgh’s western horizon at 06:02 on the morning of the 1st.
Jupiter, easily our brightest morning object, rises at Edinburgh’s east-south-eastern horizon at 00:47 GMT on the 1st and at 23:41 BST (22:41 GMT) on the 31st, climbing to pass around 17° high in the south some four hours later. Brightening from magnitude -2.2 to -2.4, it is slow moving in Libra, being stationary on the 9th when its motion reverses from easterly to westerly. Jupiter is obvious below the Moon on the 7th when a telescope shows the Jovian disk to be 40 arcseconds wide.
If we look below and to the left of Jupiter in the south before dawn, the three objects that catch our attention are the red supergiant star Antares in Scorpius and, further from Jupiter, the planets Mars and Saturn.
Mars lies in southern Ophiuchus, between Antares and Saturn, and is heading eastwards into Sagittarius and towards a conjunction with Saturn in early April. The angle between the two planets falls from 17° to only 1.5° this month as Mars brightens from magnitude 0.8 to 0.3 and its distance falls from 210 million to 166 million km. Mars’ disk swells from 6.7 to 8.4 arcseconds, becoming large enough for surface detail to be visible through decent telescopes. Sadly, Mars (like Saturn) is so far south and so low in Scotland’s sky that the “seeing” is unlikely to be crisp and sharp.
Incidentally, on the morning of the 19th Mars passes between two of the southern sky’s showpiece objects, being a Moon’s breadth below the Trifid Nebula and twice this distance above the Lagoon Nebula. Both glowing clouds of hydrogen, dust and young stars appear as hazy patches through binoculars but are stunning in photographs.
Saturn, creeping eastwards just above the Teapot of Sagittarius, improves from magnitude 0.6 to 0.5 and has a 16 arcseconds disk set within its superb rings which span 37 arcseconds at midmonth and have their northern face tipped towards us at 26°. The waning Moon lies above-left of Mars on the 10th and close to Saturn on the 11th.
Diary for 2018 March
Times are GMT until March 25, BST thereafter.
1st 06h Moon occults Regulus (disappears at 06:02 for Edinburgh)
2nd 01h Full moon
4th 14h Neptune in conjunction with Sun
5th 18h Mercury 1.4° N of Venus
7th 07h Moon 4° N of Jupiter
9th 10h Jupiter stationary (motion against stars reverses from E to W)
9th 11h Last quarter
10th 01h Moon 4° N of Mars
11th 02h Moon 2.2° N of Saturn
15th 15h Mercury furthest E of Sun (18°)
17th 13h New moon
18th 01h Mercury 4° N of Venus
18th 18h Moon 8° S of Mercury
18th 19h Moon 4° S of Venus
20th 16:15 Vernal equinox
23rd 00h Moon occults Aldebaran (23:31 to 00:14 for Edinburgh)
24th 16h First quarter
25th 01h Start of British Summer Time
27th 02h Moon 1.8° S of star cluster Praesepe in Cancer
31st 14h Full moon
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on February 28th 2018, with thanks to the newspaper for permission to republish here.
Orion and Jupiter are unmistakable at nightfall
March sees Jupiter high and conspicuous in our southern sky at nightfall as Mars brightens considerably and rises well before midnight on its way to opposition in April.
Meanwhile, the Sun’s climb northwards means that it is already two and a half times higher in Edinburgh’s sky at midday than it was at our winter solstice on 21 December and by the end of March it will stand 38° high, almost four times higher than it did at midwinter. The moment when it crosses the equator comes this year at 16:57 GMT on the 20th and marks our spring or vernal equinox. Although this is often cited as the first day of spring, meteorologists now use 1 March as this milestone.
The days are lengthening, too, and the sunrise/sunset times for Edinburgh change from 07:04/17:47 GMT on the 1st to 05:46/18:49 GMT on the 31st. We set our clocks forwards to British Summer Time on the 30th, so the latter times translate to 06:46/19:49 BST. With nautical twilight persisting for 84 minutes, effective darkness does not arrive until 21:13 BST as the month ends, less than one hour after our map times.
Another consequence is that our sky at nightfall is changing quickly. The glorious constellation of Orion the Hunter, for example, stands proudly in the south at nightfall at present but has shifted lower into the south-west by the 31st, taking with him Taurus and his faithful companion, Sirius the Dog Star. Our maps show him even lower in the west-south-west as his place near the meridian has been claimed by Leo the Lion whose main star Regulus shines in the handle of the reversed question-mark of stars known as the Sickle.
Meanwhile, Ursa Major is soaring from the east to overhead. As I mentioned last time, it was in the galaxy M82 in Ursa Major that a group of students in London discovered one of the brightest and closest supernovae for several years. After peaking as an easy telescopic object near magnitude 10.5 in early February, that stellar explosion has now dimmed to be closer to the twelfth magnitude.
It is Jupiter that really catches the eye during our March evenings. As the brightest object high in the southern sky at nightfall, it is slow-moving against the stars of Gemini, above and to the left of Orion and just 1.8° to the south of the third magnitude star Mebsuta. In fact, it reaches a so-called stationary point on the 6th when its westerly or retrograde progress against the stars reverses to a more usual easterly or direct motion. Such apparent changes in motion result from our changing vantage point on the moving Earth.
The giant planet recedes from 695 million to 767 million km and dims slightly from magnitude -2.4 to -2.2. Binoculars show its four main moons while telescopes sometimes reveal the inky shadows of one or other of the moons on its cloud-banded globe which shrinks from 42 to 38 arcseconds. Chances to view Jupiter at its sharpest while high in the sky are beginning to run out – by our map times it is already sinking towards the west and it sets in the north-west before dawn.
Our second conspicuous evening planet is Mars which rises in the east-south-east one hour before our map times and crosses our lower southern sky during the early hours. After its own stationary point on the 1st, 6° north-east of Spica in Virgo, it moves to lie 5° north of Spica on the 31st, as indicated by the arrow on our chart. Spica is a blue-white star of magnitude 1.0 and considerable fainter than the distinctively reddish hue of Mars which again doubles in brightness from magnitude -0.5 to -1.3.
Due to reach opposition in April, Mars approaches from 121 million to 95 million km during March as its diameter swells from 12 to 15 arcseconds, large enough for surface markings to be glimpsed through decent telescopes. The northern hemisphere of Mars experienced its own midsummer in mid-February and the small white button of the northern polar ice cap is tipped 20° towards us in mid-March.
Saturn, magnitude 0.4 to 0.3 and at a stationary point in Libra on the 3rd, rises in the east-south-east less than two hours after our map times and trails some 25° behind Mars, and slightly lower, as it crosses our southern sky before dawn. Venus continues as a brilliant morning star though its altitude in the south-east at sunrise falls from 12° to 8° and it fades a little from magnitude -4.6 to -4.3. Viewed telescopically, it shrinks from 33 to 22 arcseconds in diameter and changes from a crescent to slightly gibbous in form. While Venus is furthest west of the Sun (47°) on the 22nd, Mercury lies 28° west of the Sun on the 14th but is probably too low in the predawn twilight to be seen from Scotland.
The Moon is new on the 1st, at first quarter on the 8th, full on the 16th, at last quarter on the 24th and new again on the 30th. Look for the young earthlit Moon low in the west-south-west at nightfall on the 3rd and 4th. It lies south of the Pleiades on the 6th and against the stars of the Hyades near Aldebaran in Taurus on the 7th. After passing south of Jupiter on the 10th, it lies below Regulus on the 14th and between Mars and Spica as they rise on the 18th. It has a close conjunction with Saturn on the morning of the 21st and stands just above Venus on the 27th.
This is a slightly-revised version of Alan’s article published in The Scotsman on February 28th 2014, with thanks to the newspaper for permission to republish here.
London students spot nearby bright supernova
One of the brightest and closest supernovae since 1987 was discovered by a student group from University College London at an observatory in north London on 21 January. Meanwhile, Jupiter is unmistakable in the best evening sky of the year and both Mars and Venus are conspicuous before dawn.
The supernova, the catastrophic disintegration of a white dwarf star, is located in the galaxy M82, some 11.5 million light years away in the constellation of Ursa Major. At its brightest, perhaps as February begins, it may be shining at about magnitude 10.0. This is too dim to target through binoculars, unless you use large ones under a perfect sky, but it is easily seen through most amateur-owned telescopes provided we know just where to look.
At the star map times, M82 and its sister galaxy M81 are located 8° above the star Lambda high in the north-east at the end of the winding constellation of Draco. M81 lies 0.6° south (right) of M82 and is larger and brighter at about the seventh magnitude. M82 is the more interesting of the two because it appears to be a spiral galaxy in the throes of unusually rapid star formation – indeed it is classed as a starburst galaxy. Perhaps triggered by a close encounter with its neighbour, the episode means that M82 has a surfeit of luminous young stars and star clusters and, consequently, may host more than its share of supernovae.
We may now expect the current supernova, dubbed SN 2014J, to dwindle to obscurity over the coming months. Eventually, though, its debris may add another twist to the complex network of dusty filaments that do their best to hide M82’s spiral structure. It is interesting to note that all four of the brightest supernovae since 1993 have occurred in different galaxies in Ursa Major.
Jupiter stood at opposition on 5 January and is conspicuous as it climbs from the east at nightfall to stand high on the meridian at our star map times. Meanwhile the glorious shape of Orion the Hunter marches from the south-east to the south-south-west, followed by Sirius which lies 40° almost due south of Jupiter and is less than half as bright. Orion’s Belt points upwards to Aldebaran and the iconic Pleiades cluster and, as Orion stands at his highest in the south, look almost overhead for the bright star Capella in Auriga.
Besides the Pleiades, three other open star clusters are plotted on our southern star map. Praesepe, or the Beehive cluster, in Cancer is the brightest of these and best seen through binoculars. Look also for M35 near the feet of Gemini, and currently 10° to the west of Jupiter, and the slightly brighter M41 4° due south of Sirius.
There is still a chance to spot Mercury as it nears the end of its best evening show in 2014. Forty minutes after sunset on the 1st it stands almost 9° high in the south-west and 7° below the slender young Moon. Use binoculars to find it at magnitude -0.4, although it may become a naked-eye object before it sets in the west-south-west another 70 minutes later. By the 8th, though, the small innermost planet is 2.5° lower and one fifth as bright at magnitude 1.4 as it disappears into the twilight on its way to inferior conjunction on the near side of the Sun on the 15th.
Sunrise/set times for Edinburgh change from 08:07/16:46 on the 1st to 07:07/17:44 on the 28th. The Moon is at first quarter on the 6th, full on the 14th and at last quarter on the 22nd. It was new on 30 January and as it emerges in our south-western sky in early February, expect earthshine (“the Old Moon in the Young Moon’s Arms”) to be impressive. It is caused, of course, by the night side of the Moon’s disk being illuminated by the almost-full Earth in the lunar sky. The phenomenon will have disappeared before the Moon stands 7° below the Pleiades on the 7th, close to Aldebaran on the 8th and right of Jupiter on the 10th.
Jupiter dims from magnitude -2.6 to -2.4 as it creeps westwards in Gemini and shrinks to 42 arcseconds if viewed telescopically. With its active meteorology and four bright moons, it is a favourite for amateur observers, particularly now that it is highest in the evenings. The magnitude 3.6 star Lambda Geminorum, 9° south-east of Jupiter, disappears behind the southern limb of the Moon on the 11th. As seen from Edinburgh, the occultation lasts from 19:55 until 20:51.
Mars doubles in brightness from magnitude 0.2 to -0.5 as its small ochre disk swells from 9 to 12 arcseconds this month. The Red Planet is tracking eastwards 5° to the north of Spica in Virgo, rises in the east about ninety minutes after our map times and crosses Edinburgh’s meridian at a height of 26° almost six hours later. Saturn follows Mars across our southern morning sky to pass 17° high in the south at 06:50 on the 1st and almost two hours earlier by the 28th. The Moon is near Mars and Spica on the 19th and 20th and closest to Saturn on the 21st when Saturn is magnitude 0.5 and 17 arcseconds wide, with the rings tipped at 23° and 39 arcseconds broad.
Venus, at its brilliant best at magnitude -4.6 on the 11th, rises above Edinburgh’s horizon in the east-south-east at 05:58 on the 1st and 51 minutes earlier by the 28th. Look for it low in the south-east before dawn and catch it close to the waning Moon on the 26th.