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.
Geminids suffer in the supermoonlight
The Sun reaches its farthest south at our winter solstice at 10:44 GMT on the 21st, as Mars and the brilliant Venus stand higher in our evening sky than at any other time this year. This is not a coincidence, for both planets are tracking eastwards and, more importantly, northwards in the sky as they keep close to the ecliptic, the Sun’s path over the coming weeks and months. Meantime, Jupiter is prominent during the pre-dawn hours while Orion is unmistakable for most of the night and strides proudly across the meridian at midnight in mid-December.
As the sky darkens this evening, Pegasus with its iconic, but rather empty, Square is nearing the meridian and the Summer Triangle (Vega, Deneb and Altair) stands high in the south-west.
By our map times, Altair is setting in the west and Orion stands in the south-east, the three stars of Belt pointing down to where Sirius, our brightest night-time star, will soon rise. Sirius, the red supergiant Betelgeuse at Orion’s shoulder and Procyon in Canis Minor, almost due east of Betelgeuse, form a near-equilateral triangle which has come to be known as the Winter Triangle.
Above Orion is Taurus, home to the Pleiades star cluster and the bright orange giant star Aldebaran, the latter located less than halfway between us and the V-shaped Hyades cluster.
Look for the almost-full Moon below the Pleiades and to the right of Aldebaran and the Hyades on the evening of the 12th and watch it barrel through the cluster during the night, occulting (hiding) several of the cluster’s stars on the way. As they dip low into the west on the following morning, the Moon occults Aldebaran itself, the star slipping behind the Moon’s northern edge between 05:26 and 05:41 as seen from Edinburgh. Even though this is the brightest star to be occulted this year, the Moon’s brilliance means we may well need a telescope to view the event.
Sunrise/sunset times for Edinburgh vary from 08:20/15:44 on the 1st to 08:42/15:40 on the 21st and 08:44/15:48 on the 31st. The Moon is at first quarter on the 7th and full on the 14th when, once again, it is near its perigee, its closest point to the Earth. Despite the fact that the Moon appears a barely perceptible 7% wider than it does on average, we can look forward to yet another dose of over-hyped supermoon hysteria in the media. The Moon’s last quarter comes on the 21st and it is new on the 29th.
Sadly, the Moon does its best to swamp the annual Geminids meteor shower which lasts from the 8th to the 17th and is expected to peak at about 20:00 on the 13th. Its meteors are medium-slow and, thankfully, there are enough bright ones that several should be noticeable despite the moonlight. Without the moonlight, and under perfect conditions, this might have been our best display of 2016, with 100 or more meteors per hour.
Geminids are visible in all parts of the sky, but perspective makes them appear to diverge from a radiant point near the star Castor in Gemini, marked near the eastern edge of our north map. This radiant climbs from our north-eastern horizon at nightfall to pass high in the south at 02:00.
Venus stands 10° above Edinburgh’s southern horizon at sunset on the 1st and shines spectacularly at magnitude -4.2 as it sinks to set in the south-west almost three hours later. The young earthlit Moon stands 10° above-right of Venus on the 2nd, 5° above the planet on the 3rd and, one lunation later, 20° below-right of the Moon on Hogmanay. By then, Venus is twice as high at sunset and (just) brighter still at magnitude -4.3. A telescope shows its dazzling gibbous disk which swells from 17 to 22 arcseconds in diameter as the sunlit portion shrinks from 68% to 57%.
As Venus speeds from Sagittarius to Capricornus, so Mars keeps above and to its left as it moves from Capricornus into Aquarius and into the region of sky above our south-western horizon at the map times. Mars is only a fraction as bright, though, and fades from magnitude 0.6 to 0.9. It also appears much smaller, only 6 arcseconds, so that telescopes now struggle to reveal any surface features. Spot Mars to the left of the Moon on the 4th and below-right of the Moon on the 5th.
Mercury is farthest east of the Sun, 21°, on the 11th but hugs our south-western horizon at nightfall and is unlikely to be seen. It reaches inferior conjunction between the Sun and Earth on the 28th by which time Saturn, which passes beyond the Sun on the 10th, might just be glimpsed low above the south-eastern horizon before dawn. On the 27th, it shines at magnitude 0.5 and lies 7° below-left of the slender waning Moon.
Jupiter is conspicuous at magnitude -1.8 to -1.9 and the real star of our morning sky. Rising in the east for Edinburgh at 03:04 on the 1st and 01:31 on the 31st, it climbs well up into our southern sky before dawn where it stands above Virgo’s leading star Spica and draws closer during the month.
Jupiter, Spica and the Moon form a neat triangle before dawn on the 23rd, when Jupiter is 850 million km away and appears 35 arcseconds wide through a telescope. Any decent telescope shows its parallel cloud belts, while binoculars reveal its four main moons which swap places from side to side of the disk as they orbit the planet in periods of between 1.8 and 17 days.