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The night sky for February 2018

The Night Sky This Month - Tue, 06/02/2018 - 10:00
Northern Hemisphere

Ian Morison tells us what we can see in the Northern Hemisphere night sky during February 2018.

  • Jupiter - Jupiter rises around 2 am at the beginning of the month and just before midnight by month's end. Initially it has a 36 arcsecond disk, shining at a magnitude of -2 but as the month progresses, its apparent diameter increases to 39 arcseconds and it brightens to magnitude -2.2. Jupiter will transit before dawn and so will enable the giant planet to be seen with the equatorial bands, sometimes the Great (but reducing in size) Red Spot and up to four of its Gallilean moons visible in a small telescope. Sadly, Jupiter, lying in Libra during the month, is heading towards the southern part of the ecliptic and will only have an elevation of ~20 degrees when crossing the meridian. Atmospheric dispersion will thus hinder our view and it might be worth considering purchasing the ZWO Atmospheric Dispersion Corrector to counteract its effects.

  • Saturn - Saturn, at the start of its new apparition, rises at around 5 am at the start of the month and just after 3 am at its end. With an angular size of ~15.5 arc seconds it climbs higher before dawn and so becomes easier to spot as the month progresses. Its brightness remains at +0.6 magnitudes. The rings were at their widest a few months ago and are still, at 26 degrees to the line of sight, well open. Saturn, lying in Sagittarius, is just 3 degrees above the topmost star of the 'teapot'. Sadly, even when at opposition later in the year it will only reach an elevation of just over 15 degrees above the horizon when crossing the meridian. Atmospheric dispersion will thus greatly hinder our view and it might be worth considering purchasing the ZWO Atmospheric Dispersion Corrector to counteract its effects.

  • Mercury - Mercury passes through superior conjuction (between us and the Sun) on the 17th February so will be lost in the Sun's glare until the very end of the month when it might just be glimpsed after sunset with its ~5 arc second disk having an unusually bright magnitude of -1.5.

  • Mars - Mars starts the month moving quickly eastwards in Scorpius close to Beta Scorpii (Graffias) but moves into Ophiuchus on the 8th of the month. Now a morning object at the start of its new apparition, it rises four hours or so earlier than the Sun. During the month, Mars has a magnitude which increases from +1.2 to +0.8 and an angular size of just 5.6, increasing to 6.6, arc seconds so no details will be seen on its salmon-pink surface. It will only reach an elevation of ~14 degrees before dawn at the start of the month and just 12 degrees by month's end.

  • Venus - Venus passed through superior conjunction (on the far side of the Sun) on January 9th and so, at the beginning of February will be lost in the Sun's glare, setting less than half an hour after the Sun. However, by month's end, shining with a magnitude of -3.9, it will set around an hour after the Sun and its 10 arc second disk should be easy to spot 30 minutes or so after sunset. However a low western horizon will be needed as it will then only have an elevation of ~5 degrees some way to the south of west.

  • Highlights
  • February 8th before dawn: A waning Moon close to Jupiter - with Mars nearby. If clear before dawn on the 8th, a waning moon between Full Moon and Last Quarter lies close to Jupiter. Down to the left is Mars lying above Antares in Scorpius.

  • February 9th before dawn: Mars and a waning Moon. If clear before dawn on the 9th and looking to the South-southeast, Mars, at magnitude +1, will be seen to the lower right of a waning crescent Moon.

  • February 17th after sunset: Venus and a thin crescent Moon. Looking West-Southwest after sunset on the 17th and given a very low western horizon, one might be able to spot Venus at the start of its new evening apparition. A very thin crescent Moon, just two days after new, will be seen up to its left. Binoculars may well be needed, but please do not use them before the Sun has set. A very tough observing challenge!

  • February 23rd/24th evening: The Moon in a beautiful skyscape. In the evenings of the 23rb and 24th of the month, the Moon, coming towards first quarter, will pass through Taurus and Orion. On the 23rd, it will lie close to Aldebaran and on the 24th lie above Orion.

  • February 6th and 22nd evening: The Hyginus Rille. For some time a debate raged as to whether the craters on the Moon were caused by impacts or volcanic activity. We now know that virtually all were caused by impact, but it is thought that the Hyginus crater that lies at the centre of the Hyginus Rille may well be volcanic in origin. It is an 11 km wide rimless pit - in contrast to impact craters which have raised rims - and its close association with the rille of the same name associates it with internal lunar events. It can quite easily be seen to be surrounded by dark material. It is thought that an explosive release of dust and gas created a vacant space below so that the overlying surface collapsed into it so forming the crater.

  • In her final broadcast for the Jodcast, Claire Bretherton from the Carter Observatory in New Zealand tells us what we can see in the Southern Hemisphere night sky during February 2018.

    Kia ora and welcome to the February Jodcast from Space Place at Carter Observatory in Wellington, New Zealand.

  • Lunar Eclipse - Whilst the Earth blocks all direct light from the Sun, some light passes though the Earth's atmosphere and is bent or refracted towards the surface of the Moon. Light with shorter wavelengths, towards the blue end of the spectrum, is scattered more strongly, so only the redder light gets through, giving the eclipsed moon a telltale reddish glow.

  • Partial Solar Eclipse - Whilst New Zealand won't see it, some parts of the southern hemisphere will also experience a partial solar eclipse this month, on the morning of the 16th NZ time. From parts of Chile and Argentina the moon will cover some 25% of the Sun's disk, whilst from Antarctica around 49% will be covered.

  • Orion - Orion is now high in the north after dark, with Sirius, or Takurua, the brightest star in our night-time sky, even higher.

  • Procyon - 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.

  • Clusters and Nebulae - 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 in long exposure photographs.

    Below Canis Minor sits 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 ways 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 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.

    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. It 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.

  • Planets - Our evening skies are still bereft of bright planets. Jupiter is the first to rise at around 1 am at the start of the month. Mars follows shortly afterwards, and the two are joined by Saturn around 3:30 am. You may spot Mercury briefly at the start of February, rising in the dawn twilight around an hour before the Sun, but it will soon disappear from view as it heads back towards the Sun. By months end Jupiter has moved into our evening skies, rising at 11 pm, Mars around 12:30 am and Saturn by 2 am, making a diagonal line down the eastern morning sky.

  • Farewell - After 8 years at Space Place at Carter Observatory, and being involved with the Jodcast for almost as long, I am moving on to a new role in February and so sadly this will be my last southern skies section. It's been a great pleasure bringing you a little taster of our wonderful New Zealand stars and some of the amazing stories within them over the past few years. I wish you clear skies and all the very best for the future. So farewell from me, Claire Bretherton, and the team here at space Place at Carter Observatory.

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