The Night Sky
Ian Morison tells us what we can see in the northern hemisphere night sky during February 2017.
Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during February 2017.Kia ora and welcome to the February Jodcast from Space Place at Carter Observatory in Wellington, New Zealand.
This month we'll start to see some changes in our evening skies. Bright Venus, which has been dominating in the west for some months, is now beginning its journey back towards the Sun. Whilst still visible in the dusk skies, it will be setting as twilight ends, around an hour and a half after the Sun, at the beginning of the February, but by the end of the month it will be dropping below the horizon just 30 minutes after sunset. Fainter red Mars is a little above, holding its position well as it moves through the constellation of Pisces. At the end of the month, Mars will pass within 34 arcminutes of faint Uranus, with both visible in the same binocular field of view, and well worth a look, particularly as this also coincides with the new moon on the 27th, although by the time it gets fully dark from our location the pair will right on the horizon.
On the opposite side of the sky, golden Jupiter is now moving into our evening skies, rising just before midnight at the start of the month and by around 10pm, as twilight ends, at the end.
Orion is now high in the north after dark, with Sirius, or Takurua, the brightest star in our night-time sky, even higher.
Below and to the right, and forming a triangle with Sirius and Betelgeuse, is Procyon, the brighter of the two main stars that form the constellation of Canis Minor, Orion's small hunting dog. Procyon is the eighth brightest star in the night-time sky and, like Sirius (at ~9 ly distant), is one of our Sun's nearest neighbours at just 11 light years away. Also like Sirius, it is in fact a binary system, with a 1.5 solar mass primary and a faint white dwarf companion.
Just over a third of the way between Sirius and Procyon, in the constellation of Monoceros, is M50, a pretty, heart-shaped open cluster of stars, visible in binoculars.
Around a third of the way from Betelgeuse to Procyon is NGC2244, a rectangular cluster of stars that is embedded in a faint nebula called the Rosette. Whilst the cluster is visible in binoculars and small telescopes, the nebula is more of a challenge and is best seen photographically.
Below Canis Minor sit another pair of stars, Castor and Pollux, marking the heads of Gemini, the twins. Pollux, the higher and brighter of the two stars, is the 17th brightest star in our night sky. It is about 35 light years away from us, whilst Castor is in fact a sextuple star system located 52 light years from Earth.
Nearby to Eta Geminorum, at the foot of the twin of Castor, is the open star cluster M35, covering an area almost the size of the full moon. Under good conditions it can be seen with the unaided eye as a hazy star, but binoculars or a wide-field telescope will reveal more detail and are the best way to view this lovely cluster.
Next to Gemini is the faint zodiac constellation of Cancer, the crab. At the centre of Cancer is a lovely open cluster of stars known as M44, Praesepe (the Manger) or the Beehive. At magnitude 3.7, the cluster is visible to the naked eye as a hazy nebula, and has been know since ancient times. It was one of the first objects Galileo studied when he turned his telescope to the skies in 1609.
Galileo was able to pick out around 40 stars, but today we know that Praesepe contains over 1000 individual members, with a combined mass of between 500 and 600 times that of the Sun. As one of the closest open star clusters to our Solar System, M44 is a great target for binoculars or small telescopes, which will easily reveal a number of individual stars within it.
Higher, and to the east of Canis Major is Puppis, representing the Poop deck of the great ship Argo, which we explored last month. Inside Puppis are two lesser known Messier Objects, M46 and M47.
Messier 46 (also known as M 46 or NGC 2437) is a rich open cluster at a distance of about 5,500 light-years away. M46 is estimated to contain around 500 stars, of which around 150 of magnitude 10-13. Estimated to be only 300 million years old, this is a young cluster, and a lovely sight in binoculars or a small telescope. Astronomer John Herschel described it in his General Catalogue of Nebulae and Clusters of Stars as 'Remarkable, cluster, very bright, very rich, very large, involving a planetary nebula'. This planetary nebula, located near the cluster's northern edge, is NGC 2438.
A planetary nebula is formed when a low or intermediate mass star comes to the end of its life, ejecting its outer layers into space as a glowing shell of ionized gas.
Whilst NGC 2438 appears to lie within the cluster, it is probably just a chance line of sight effect as the vadial velocities are quite different. NCG 2438 is estimated to lie somewhat closer than M46 at around 2900 ly away.
Located around 1 degree west is another open cluster, M47. The two fit easily within one binocular field of view, and are often referred to as sisters.
Messier 47 or NGC 2422 has actually been discovered several times. The first was some time before 1654 by Giovanni Batista Hodierna and then independently by Charles Messier on February 19, 1771. William Herschel also independently rediscovered it on February 4, 1785, and it was included as GC 1594 in John Herschel's General Catalogue of Nebulae and Clusters of Stars (the precursor to Dreyer's New General Catalogue) in 1864.
Due to a sign error by Messier, the cluster was considered a 'lost Messier Object' for many years, as no cluster could be found at the position of Messiers original coordinates. It wasn't until 1959 that Canadian astronomer T. F. Morris identified that the cluster was in fact NGC2422, and realized Messier's mistake.
M47 lies at a distance of around 1,600 light-years from Earth with an estimated age of about 78 million years. M47 is described as a course, bright cluster containing around 50 stars, scattered over an area around the same size as the full moon in the sky. It is bright enough to be glimpsed with the naked eye under good observing conditions, but best viewed with binoculars or a small telescope.
There are a couple of other excellent binocular targets in Puppis, including open cluster NGC2477 - a wonderful, rich cluster of over 300 stars, described by American Astronomer Robert Burnham as 'probably the finest of the galactic clusters in Puppis' along with its neighbor NGC 2451, both located close to the second magnitude star Zeta Puppis.
Also known as Naos, this blue supergiant is one of the hottest, most luminous stars visible to the naked eye. It has a bolometric (total) luminosity of at least 500,000 times that of the Sun, but with most of its radiation emitted in the ultraviolet it is visually around 10,000 times brighter. It is also one of the closest stars of its kind to our Sun, at a distance of around 1,080 ly.
Wishing you clear skies from the team here at Space Place at Carter Observatory.
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