February sky in starring role
Watch for Leonardo da Vinci’s lunar glow from the 11th, says Alan Pickup
Now that we are in the awards season, the prize for the best evening sky of the year surely goes to the month of February itself. It is just as well that we have a day longer to savour February’s superiority this leap year and we can only hope for some clear skies after the dire storms of recent weeks.
Orion, of course, takes centre stage. Its familiar pattern of stars lies in the southeast as darkness falls and stands proudly in the south one hour before our star map times.
Accompanying Orion is Taurus the Bull with the iconic Pleiades star cluster, and Gemini with the Twins, Castor and Pollux. Orion’s leading stars, Rigel and Betelgeuse, count among the ten brightest in Earth’s night sky. Two even brighter ones, Sirius and Capella, blaze in adjacent constellations, with Sirius below and left of Orion and Capella soaring almost overhead in Auriga the Charioteer.
If we persist with our awards theme, then the one for “planet in a leading role” for February belongs to Jupiter. The giant planet is conspicuous high in the south at nightfall but is sinking in the west by our map times as it tracks to its setting-point on the west-north-western horizon some three hours later. By the month’s end it sets before midnight, but to get the sharpest views through a telescope of its fascinating cloud-banded disk, and of its four main moons, it would be best to catch it even before our map times. Jupiter dims a little from magnitude -2.4 to -2.2 (twice as bright as Sirius) as it recedes from 743 million to 810 million km and shrinks in apparent diameter to 36 arcseconds.
Saturn, nearing the end of its spell in our night sky and shining at magnitude 1.0, stands only 9° high in the south-western evening twilight one hour after sunset tomorrow. This falls to 3° by the 10th as it disappears on its way to conjunction on the Sun’s far side on the 28th.
Venus is brilliant at magnitude -4.0 but hugs our south-eastern horizon before dawn, being less than 3° high one hour before Edinburgh’s sunrise tomorrow and rising itself only 33 minutes before the Sun by the 29th. Both Mars and Mercury are much fainter and lie even deeper in the dawn twilight where they are unlikely to be seen from our northern latitudes. The Ingenuity mini-helicopter, delivered to Mars with Nasa’s Perseverance rover three years ago, has finally reached the end of its mission. Intended only as a brief technological demonstration for no more than a few weeks, it ended up making 72 flights and travelling 18 km before damage to its rotor blades forced it to retire.
As the Sun climbs almost 10° degrees northwards during February, Edinburgh’s sunrise/sunset times change from 08:09/16:45 tomorrow to 07:06/17:46 on the 29th.
The waning gibbous Moon stands
close to the star Spica in Virgo tomorrow morning and reaches last quarter late on the 2nd in Libra. Look for its crescent very low in the south-south-east before dawn on the 5th when it lies 3° below-left of Antares in Scorpius. We lose the Moon before it passes south of Venus on the 7th on its way to new on the 9th.
The Moon makes an impressive return to our evening sky as an extremely thin crescent low down in the south-west after sunset on the 11th. Only 5% sunlit, and with bright earthshine (“The Old Moon in the Young Moon’s Arms”), it stands 9° above-left of Saturn on that evening.
Earthshine, of course, arises when the darker side of the lunar disk is illuminated by the almost-full Earth rather than the Sun. It is occasionally called the “Da Vinci glow” after Leonardo da Vinci, who sketched it in the early-16th century and speculated that it originated from sunlight reflected by terrestrial oceans, though now we realise Earth’s clouds have the greater role.
Expect the effect to fade as the Moon climbs higher and lunar crescent thickens over the next few days, probably vanishing by the time the Moon stands to the right of Jupiter on the 14th and above-left of the planet on the 15th.
First quarter comes on the 16th as the Moon skims the bottom of the Pleiades on its way into Taurus. The 20th finds the Moon close to Pollux, while on the 23rd it is just above Regulus, the leading star of Leo which is climbing in the eastsouth-east
at our map times. Full moon occurs further on in Leo on the 24th and the Moon returns to the vicinity of Spica for the nights of the 27th and 28th.
By our map times, Orion has progressed into the south-south-west and Sirius twinkles at its highest point 17° above Edinburgh’s southern horizon. With a name that comes from the Greek for “scorching”, Sirius outshines every other star, except for the one we call the Sun.
Although the Sun appears 13 billion times brighter, if we viewed it from the same distance as Sirius, 8.6 light years, the latter would be the winner by a factor of 25.
Despite this, Sirius’ stellar ranking owes more to the fact that it is the tenth closest star.
Indeed, most of our naked-eye stars are intrinsically brighter than our Sun, with all seven of the leading stars of Orion shining with the power of many thousands of Suns from hundreds of light years.
Sirius is also the Dog Star since it is the leading star in Canis Major, the Greater Dog, one of two dogs that accompany Orion the Hunter around the sky. The other is Canis Minor, the Lesser Dog, with its main star Procyon, another near neighbour at 11.5 light years that shines at seven Sun-power. As our chart shows, we can link Sirius and Procyon with Betelgeuse in Orion’s shoulder to form the asterism of the almost-equilateral Winter Triangle.