Blog Archives

Scotland’s Sky in February, 2017

Venus highest and brightest as evening star

The maps show the sky at 22:00 GMT on the 1st, 21:00 on the 15th and 20:00 on the 28th. Arrows depict the motions of Mars during the month, and of Venus from the 14th. (Click on map to enlarge)

The maps show the sky at 22:00 GMT on the 1st, 21:00 on the 15th and 20:00 on the 28th. Arrows depict the motions of Mars during the month, and of Venus from the 14th. (Click on map to enlarge)

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.

Alan Pickup

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.
Advertisements

Scotland’s Sky in February, 2016

An extra day of superb February evening skies

The maps show the sky at 22:00 GMT on the 1st, 21:00 on the 15th and 20:00 on the 29th.  (Click on map to enlarge)

The maps show the sky at 22:00 GMT on the 1st, 21:00 on the 15th and 20:00 on the 29th. (Click on map to enlarge)

February brings our best evening skies of the year and, with this being a leap year, we have one extra day to enjoy them. Pride of place must go to Orion which marches across our southern sky from the south-east at nightfall tonight to stand in the south-south-west by our star map times.

We are all familiar with the Summer Triangle of bright stars (Vega, Deneb and Altair) which graces our summer nights, but less well known is the Winter Triangle that follows close behind Orion. Consisting of the stars Betelgeuse at Orion’s shoulder, Procyon in Canis Minor which stands level with Betelgeuse to its left, and Sirius in Canis Major, the Winter Triangle is brighter than its summer counterpart and much more isosceles in form.

Sirius, found by extending Orion’s belt down and to the left, is the brightest star in our night sky largely because it is one of the closest to us at 8.6 light years. Indeed, viewed from the same distance as Betelgeuse, some 500 light years, it would be too dim to see without binoculars.

Because they are so obviously placed in the sky in the shape of a man, it is easy to regard the main stars of Orion as lying at similar distances from us. Although they are all highly luminous and far away, they stand at very different distances so that Orion’s impressive outline would change beyond recognition if we could view it from a different direction. A striking example concerns the three stars of Orion’s belt which, in order from the left, are Alnitak, Alnilam and (slightly fainter) Mintaka. Alnitak and Mintaka are thought to stand around 700 light years from us, but some estimates put Alnilam as distant as 2,000 light years, more than twice as far.

The Sun climbs almost 10° northwards during February as sunrise/sunset times for Edinburgh change from 08:08/16:45 on the 1st to 07:06/17:46 on the 29th. The Moon is at last quarter on the 1st, new on the 8th, at first quarter on the 15th and full on the 22nd. Because its path is inclined steeply in the south-west at nightfall, there is an excellent opportunity to spot the very young and brightly earthlit Moon low in the west-south-west on the evening of the 9th. It should still be spectacular over the following few evenings.

No bright planets are visible until the conspicuous Jupiter begins its climb through our eastern and south-eastern sky as Orion crosses the meridian. It lies in south-eastern Leo, 22° below and left of Regulus, and is creeping westwards against the stars as it draws towards its opposition in March. This month it brightens from magnitude -2.4 to -2.5, approaches from 694 million to 665 million km and swells from 42 to 44 arcseconds in diameter.

Any telescope should show Jupiter’s two main dark cloud belts, appearing symmetrically and in parallel on either side of its pale equatorial zone. Spots and streaks in the clouds, including the famous Red Spot in its southern hemisphere, drift from east to west across the Jovian disk as the planet rotates in just under ten hours. Of course, we need only binoculars to spot Jupiter’s four main moons as they change their relative positions on either side of the disk.

The second bright planet of the night stands low in the south-east as Jupiter reaches the meridian some five hours after our map times. The reddish, or perhaps salmon-pink, Mars lies below the Moon and just above the double star Zubenelgenubi in Libra on the morning of the 1st.

Mars spends February sliding eastwards though Libra and brightening from magnitude 0.8 to 0.3 as it approaches from 205 million to 161 million km. Its small slightly-gibbous disk grows from 7 to 9 arcseconds and is starting to reveal detail through good telescopes, particularly if we catch it just before dawn as it passes less than 20° high in the south.

If we look before dawn and take a line from Jupiter, well over in the west-south-west, to Mars in the south and onwards to the left we reach the almost equally-bright Saturn (magnitude 0.6 to 0.5) which is slow-moving in southern Ophiuchus, 8° above-left of the red supergiant star Antares in Scorpius. The Moon stands above Antares and above-right of Saturn on the morning of the 3rd when Saturn’s disk appears 16 arcseconds wide, with its rings spanning 36 arcseconds and tipped 26° to our view – a stunning sight.

The line-up of Jupiter, Mars and Saturn may be extended to Venus and Mercury, hugging our south-eastern horizon, and has led to widespread claims of a spectacular planetary alignment in our morning sky. In fact, the term “planetary alignment” is more usually applied to those occasions when several planets collect together in the same region of sky. There was one such tight alignment of Venus, Mars and Jupiter before dawn in October and similar events have been preceded by apocalyptic pronouncements in the crackpot community.

The current alignment stretches over more than 100° of sky and is better appreciated by observers further south and particularly by those in the southern hemisphere. For Scotland, though, Venus is uncomfortably low in our bright predawn twilight and although it is brilliant at magnitude -4.0 it is sinking ever lower – its altitude at Edinburgh’s sunrise being 7° on the 1st and half that by the month’s end. Mercury, much fainter near magnitude 0.0 and farthest from the Sun on the 7th, is a few degrees to the lower-left of Venus and very difficult from our latitudes. Both stand below the slender waning Moon on the 6th.

Alan Pickup

This is a copy of Alan’s article to be published in The Scotsman on February 1st 2016, with thanks to the newspaper for permission to reproduce here.