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.
Mars meets Regulus as Jupiter dominates before dawn
Our main interests this month lie in our predawn sky where Jupiter shines brighter than any star and where Mars is in conjunction with the star Regulus in Leo. Sweeping close to Mars is Comet ISON which remains dim at present but may yet brighten to become an impressive sight later in the year.The Summer Triangle of Vega, Altair and Deneb still looms high on the meridian at dusk but has tumbled westwards by our star map times. Trailing behind it is Delphinus where a nova flared in August. That stellar outburst was still just visible through binoculars in late September but was perhaps on the verge of plunging much fainter as is becomes shrouded in dust forming in the wake of the explosion.
Our charts show the Square of Pegasus approaching the meridian as the Plough rotates counterclockwise below Polaris in the north and the “W” of Cassiopeia nears the zenith. Taurus and the Pleiades are climbing in the east while Gemini is rising in the north-east with the Twins, Castor and Pollux, one above the other.
Jupiter stands 8° below and to the right of Pollux and rises less than 30 minutes after our map times, climbing to prominence high in the south-south-east to south before dawn. The planet creeps 2° eastwards during October, passes only 7 arcminutes north of the magnitude 3.5 star Delta Geminorum on the 4th and is above the Moon on the 26th. Jupiter improves from magnitude -2.2 to -2.4 this month and swells from 38 to 41 arcseconds wide if viewed telescopically.
Our other pre-dawn planet, Mars, stands above-left of the Moon on the 1st and again on the 30th. Rising for Edinburgh in the east-north-east at 02:27 BST on the 1st and by 01:18 GMT on the 31st, it is climbing well up into the south-east before dawn. From 9° above-right of Leo’s leading star Regulus as the month begins, it speeds eastwards to pass 1.0° north of Regulus late on the 14th and lie 9° below-left of the star at month’s end. It improves slightly from magnitude 1.6 to 1.5 but remains just fainter than the magnitude 1.4 of Regulus. Note, though, the contrast in appearance with Mars being steady and reddish while Regulus is bluish-white and twinkling. Through a telescope, the planet’s tiny ochre disk is 4 to 5 arcseconds wide.
Comet ISON remains something of an enigma. Discovered just over a year ago when it lay beyond the orbit of Jupiter, it has been diving towards the Sun on a path that carries it 1,100,000 km above the Sun’s surface on 28 November. Some predictions have it as bright as the full moon at that point, albeit swamped in the Sun’s glare. In fact, its brightening has been slower than most were expecting and it was still a dim 12th magnitude object in late September. Hopes remain that it will be a naked-eye object in mid-November and again during December when it may well sport an impressive tail.
Its orbit takes it within 10.5 million km of Mars on the 1st and it is already being observed by spacecraft at the planet. It stands 2.0° above-left of Mars in our morning sky on the 2nd, moving to lie within 0.9° of Mars on the 18th and 6° below-left of the planet by the 31st. We can only hope that it might be visible through binoculars by the month’s end.
An unfortunate fact concerning our autumn sky is that planets that lie to the east of the Sun are hugging our horizon at sunset. Take Venus, for example. As seen from Edinburgh at sunset on the 1st, the brilliant magnitude -4.2 evening star stands 135 million km away and 45° away from the Sun but is only 5° high in the south-west. It sets 53 minutes later and should be obvious as the twilight fades, but only if our horizon is clear. Contrast this with Australia where Venus is a stunning object 43° high in the W at sunset and remains visible for almost four hours.
The reason, of course, is that the planets never stray far from the ecliptic, the Sun’s apparent annual path against the stars. At present the ecliptic slants low across Scotland’s south-western sky at nightfall as it traces the Sun’s southerly motion until midwinter.
By the 31st, Venus stands 5° above Edinburgh’s south-south-western horizon at sunset, shines a little brighter at magnitude -4.4 and is 6° below-right of the Sun’s midwinter position against the stars. As Venus approaches to 101 million km this month, its telescopic diameter swells from 19 to 25 arcseconds while the dazzling sunlit part of its disk changes from 63% to 50%. Look for the planet 4° below the young crescent Moon on the 8th and 1.5° above the red supergiant Antares in Scorpius on the 16th.
We have no chance of seeing Saturn or Mercury which are both fainter and closer to the Sun in the evening sky than Venus.
This month the Sun tracks 11° southwards 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. Nautical twilight persists for about 82 minutes at dawn and dusk. The Moon is new on the 4th, at first quarter on the 12th, full on the 19th and at last quarter on the 27th.
The southern 76% of the Moon’s disk slips through the fringe of the Earth’s shadow on the night of the 18th/19th to cause a penumbral lunar eclipse. Although only a slight dimming may be noticed, at least the Moon is well placed being in Pisces in the middle of our southern sky. The eclipse lasts from 22:51 to 02:50 BST.