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.
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.
Moon between Venus and Mars on the 2nd
The new year opens with the Moon as a slim crescent in our evening sky, its light insufficient to hinder observations of the Quadrantids meteor shower.
Lasting from the 1st to the 6th, the shower is due to reach its maximum at about 15:00 GMT on the 3rd. Perhaps because of the cold weather, or a lingering hangover from Hogmanay, this may be the least appreciated of the year’s top three showers. It can, though, yield more than 80 meteors per hour under the best conditions, with some blue and yellow and all of medium speed. It can also produce some spectacular events – I still recall a Quadrantids fireball many years ago that flared to magnitude -8, many times brighter than Venus.
Although Quadrantids appear in all parts of the sky, perspective means that their paths stream away from a radiant point in northern Bootes. Plotted on our north map, this glides from left to right low across our northern sky during the evening and trails the Plough as it climbs through the north-east later in the night. The shower’s peak is quite narrow so the optimum times for meteor-spotting are before dawn on the 3rd, when the radiant stands high in the east, and during the evening of that day when Quadrantids may follow long trails from north to south across our sky.
Mars and Venus continue as evening objects, improving in altitude in our south-south-western sky at nightfall and, in the case of Venus, becoming still more spectacular as it brightens from magnitude -4.3 to -4.6. Mars, more than one hundred times fainter, dims from magnitude 0.9 to 1.1 but is obvious above and to Venus’ left, their separation falling from 12° to 5° during the month as they track eastwards and northwards from Aquarius to Pisces.
On the evening of the 1st, Mars stands only 18 arcminutes, just over half a Moon’s breadth, above-left of the farthest planet Neptune though, since the latter shines at magnitude 7.9, we will need binoculars if not a telescope to glimpse it. At the time, Neptune, 4,556 million km away, is a mere 2.2 arcseconds wide if viewed telescopically and Mars appears 5.7 arcseconds across from a range of 246 million km. On that evening, the young Moon lies 8° below and right of Venus, while on the 2nd the Moon stands directly between Mars and Venus. The pair lie close to the Moon again on the 31st.
As its distance falls from 115 million to 81 million km this month, Venus swells from 22 to 31 arcseconds in diameter and its disk changes from 56% to 40% sunlit. In theory, dichotomy, the moment when it is 50% illuminated like the Moon at first quarter, occurs on the 14th. However, the way sunlight scatters in its dazzling clouds means that Venus usually appears to reach this state a few days early when it is an evening star – a phenomenon Sir Patrick Moore named the Schröter effect after the German astronomer who first reported it. Venus stands at its furthest to the east of the Sun, 47°, on the 12th.
The Sun climbs 6° northwards during January and stands closer to the Earth in early January than at any other time of the year. At the Earth’s perihelion at 14:00 GMT on the 4th the two are 147,100,998 km apart, almost 5 million km less than at aphelion on 3 July. Obviously, it is not the Sun’s distance that dictates our seasons, but rather the Earth’s axial tilt away from the Sun during winter and towards it in summer.
Sunrise/sunset times for Edinburgh change from 08:43/15:49 on the 1st to 08:09/16:44 on the 31st. The Moon is at first quarter on the 5th, full on the 12th, at last quarter on the 19th and new on the 28th.
The Moon lies below the Pleiades on the evening of the 8th and to the left of Aldebaran in Taurus on the next night. Below and left of Aldebaran is the magnificent constellation of Orion with the bright red supergiant star Betelgeuse at his shoulder. Soon in astronomical terms, but perhaps not for 100,000 years, Betelgeuse will disintegrate in a supernova explosion.
The relics of a supernova witnessed by Chinese observers in AD 1054 lies 15° further north and just 1.1° north-west of Zeta Tauri, the star at the tip of Taurus’ southern horn. The 8th magnitude oval smudge we call the Crab Nebula contains a pulsar, a 20km wide neutron star that spins 30 times each second.
The conspicuous planet in our morning sky is Jupiter which rises at Edinburgh’s eastern horizon at 01:27 on the 1st and at 23:37 on the 31st. Creeping eastwards 4° north of Spica in Virgo, it brightens from magnitude -1.9 to -2.1 and is unmistakable in the lower half of our southern sky before dawn. Catch it just below the Moon on the 19th when a telescope shows its cloud-banded disk to be 37 arcseconds broad at a distance of 786 million km. We need just decent binoculars to check out the changing positions of its four main moons.
Saturn, respectable at magnitude 0.5, stands low in our south-east before dawn, its altitude one hour before sunrise improving from 3° to 8° during the month. Look to its left and slightly down from the 6th onwards to glimpse Mercury. This reaches 24° west of the Sun on the 19th and brightens from magnitude 0.9 on the 6th to -0.2 on the 24th when the waning earthlit Moon stands 3° above Saturn.
This is a slightly-revised version of Alan’s article published in The Scotsman on December 31st 2016, with thanks to the newspaper for permission to republish here.
November nights end with planets on parade
With the return of earlier and longer nights, astronomy enthusiasts have plenty to observe in November. As in October, though, the real highlight is the parade of bright planets in our eastern morning sky.
The first to appear is Jupiter which rises above Edinburgh’s eastern horizon at 02:04 GMT on the 1st and by 00:35 on the 30th. More conspicuous than any star, it brightens from magnitude -1.8 to -2.0 this month as it moves 4° eastwards in south-eastern Leo. It lies 882 million km away and appears 33 arcseconds wide through a telescope when it stands 4° to the left of the waning Moon on the 6th.
Following close behind Jupiter at present is the even more brilliant Venus. This rises 34 minutes after Jupiter on the 1st and stands 5° below and to its left as they climb 30° into the south-east before dawn. In fact, the two were only 1° apart in a spectacular conjunction on the morning of October 26 and Venus enjoys an even closer meeting with the planet Mars over the first few days of November.
On the 1st, Venus blazes at magnitude -4.3 and lies 1.1° to the right of Mars, some 250 times fainter at magnitude 1.7. The pair are closest on the 3rd, with Venus only 0.7° (less than two Moon-breadths) below-right of Mars, before Venus races down and to Mars’ left as the morning star sweeps east-south-eastwards through the constellation Virgo. Catch Mars and Venus 2° apart on the 7th as they form a neat triangle with the Moon, a triangle that contains Virgo’s star Zavijava.
Venus lies only 4 arcminutes above-left of the star Zaniah on the 13th, and 1.1° below-left of Porrima on the 18th. The final morning of the month finds it 4° above-left of Virgo’s leading star Spica. By then Mars is 14° above and to the right of Venus and 1.3° below-right of Porrima, while Jupiter is another 19° higher and to their right.
Venus dims slightly to magnitude -4.2 during November, its gibbous disk shrinking as seen through a telescope from 23 to 18 arcseconds as its distance grows from 110 million to 142 million km. Mars improves to magnitude 1.5 and is only 4 arcseconds wide as it approaches from 329 million to 296 million km.
Neither Mercury nor Saturn are observable during November as they reach conjunction on the Sun’s far side on the 17th and 30th respectively.
More than 15° above and to the right of Jupiter is Leo’s leading star Regulus, while curling like a reversed question-mark above this is the Sickle of Leo from which meteors of the Leonids shower diverge between the 15th and 20th. The fastest meteors we see, these streak in all parts of the sky and are expected to be most numerous, albeit with rates of under 20 per hour, during the morning hours of the 18th.
The Sun plunges another 7.5° southwards during November as sunrise/sunset times for Edinburgh change from 07:19/16:33 GMT on the 1st to 08:18/15:44 on the 30th. The Moon is at last quarter on the 3rd, new on the 11th, at first quarter on the 19th and full on the 25th.
As the last of the evening twilight fades in early November, the Summer Triangle formed by bright stars Vega, Deneb and Altair fills our high southern sky. By our star map time of 21:00 GMT, the Triangle has toppled into the west to be intersected by the semicircular border of both charts – the line that arches overhead from east to west and separates the northern half of our sky from the southern.
The maps show the Plough in the north as it turns counterclockwise below Polaris, the Pole Star, while Cassiopeia passes overhead and Orion rises in the east.
The Square of Pegasus is high in the south with Andromeda stretching to its left as quintet of watery constellations arc across our southern sky below them. These are Capricornus the Sea Goat, Aquarius the Water Bearer, Pisces the (Two) Fish, Cetus the Water Monster and Eridanus the River.
One of Pisces’ fish lies to the south of Mirach and is joined by a cord to another depicted by a loop of stars dubbed the Circlet below the Square. Like the rest of Pisces, they are dim and easily swamped by moonlight or street-lighting. Just to the left of the Circlet, one of the reddest stars known is visible easily though binoculars. TX Piscium is a giant star some 760 light years away and has a surface temperature of perhaps 3,200C compared with our Sun’s 5,500C.
Omega Piscium, to the left of the Circlet, is notable because it sits only two arcminutes east of the zero-degree longitude line in the sky – making it one of the closest naked-eye stars to the celestial equivalent of our Greenwich Meridian. The celestial counterparts of latitude and longitude are called declination and right ascension. Declination is measured northwards from the sky’s equator while right ascension is measured eastwards from the point at which the Sun crosses northwards over the equator at the vernal equinox.
That point lies 7° to the south of Omega but drifts slowly westwards as the Earth’s axis wobbles over a period of 26,000 years – the effect known as precession.
Below Pisces lies Cetus, the mythological beast from which Perseus rescued Andromeda. Its brightest stars, Menkar and Deneb Kaitos, are both orange-red giants, the latter almost identical in brightness to Polaris at magnitude 2.0. Another, Mira, takes 11 months to pulsate between naked-eye and telescopic visibility and is currently near its minimum brightness.