Northern Hemisphere
Ian Morison tells us what we can see in the Northern Hemisphere night sky during February 2020.
The Planets
- Jupiter As February begins, Jupiter rises more than 90 minutes before the Sun shining at magnitude of -1.9. During the month it brightens to magnitude -2.0 whilst its angular size increases slightly from 32.5 to 34.1 arc seconds. A low south-eastern horizon will be needed and our views of the giant planet and its Gallilean moons will be hindered by the depth of atmosphere through which it will be observed.
- Saturn passed directly behind the Sun on the 13th of January and, as February begins, will rise less than one hour before the Sun. Then, equipped with binoculars and a very low south-eastern horizon, it might be glimpsed at magnitude +0.58 in the pre-dawn sky - but please do not use binoculars after the Sun has risen. As February progresses, its magnitude actually reduces very slightly to +0.66 as it angular size increases from 15.1 to 15.5 arc seconds. Saturn crosses the Ecliptic (the path of the Sun across the heavens) in a southerly direction on the 13th, just 13 days before Jupiter reaches this point whilst Mars reaches it on the 1st of February. (Stellariun shows them beautifully aligned along the ecliptic this month.)
- Mercury passed in front of the Sun (superior conjunction) on the 10th of January and, on the 10th of February, comes to its greatest elongation east, some 18.2 degrees in angle from the Sun. Mercury starts the month at magnitude -1 and dims to magnitude +0.2 by the 14th and will then soon be lost in the Sun's glare. From the 1st to the 14th, its angular size increases from 5.6 to 8.1 arc seconds but its phase (the % illuminated disk) falls from 85% to just 32% - hence the fall in magnitude. On the 1st of the month, it will set about 70 minutes after the Sun and will have an elevation, low in the west-southwest, of ~9 degrees. This will increase until the 10th before it begins to fall back towards the Sun. Binoculars may well be needed, but please do not use them until after the Sun has set.
- Mars can be seen towards the southeast in the pre-dawn sky at the start of the month. It then rises some three hours before the Sun and will be best seen at around 7am having an elevation of ~8 degrees. It will have a magnitude of +1.4 and a 4.3 arc second, salmon-pink, disk. By month's end it will be seen further round towards the south before dawn and its magnitude will have increased slightly to +1.1. Its angular size will have increased to 5.5 arc seconds but no markings will be seen unless you have access to the Hubble Space Telescope. Lying along the ecliptic it is moving eastwards above the 'Teapot' of Sagittarius and will lie just above its 'lid' on the 24th.
- Venus is now dominating the south-western twilight sky and appears higher each night, climbing from ~29 degrees above the horizon to more than 38 degrees at sunset. During the month its angular size increases from 15.3 to 18.6 arc seconds but, at the same time, it phase (the percentage of the disk illuminated) decreases from 73% to 63% and so the brightness only increases slightly from -4.1 to -4.3 magnitudes.
Highlights
- February: find M31 - The Andromeda Galaxy - and perhaps M33 in Triangulum. In the evenings when the Moon is not prominent, the galaxy M31 in Andromeda will be visible high in the south. There are two ways of finding it:
1) Find the square of Pegasus. Start at the top left star of the square - Alpha Andromedae - and move two stars to the left and up a bit. Then turn 90 degrees to the right, move up to one reasonably bright star and continue a similar distance in the same direction. You should easily spot M31 with binoculars and, if there is a dark sky, you can even see it with your unaided eye. The photons that are falling on your retina left Andromeda well over two million years ago!
2) You can also find M31 by following the "arrow" made by the three rightmost bright stars of Cassiopeia down to the lower right.
Around new Moon (23rd February) - and away from towns and cities - you may also be able to spot M33, the third largest galaxy after M31 and our own galaxy in our Local Group of galaxies. It is a face on spiral and its surface brightness is pretty low so a dark, transparent sky will be needed to spot it using binoculars (8x40 or, preferably, 10x50). Follow the two stars back from M31 and continue in the same direction sweeping slowly as you go. It looks like a piece of tissue paper stuck on the sky just a bit brighter than the sky background. Good Hunting!
- February 3rd - evening: the Moon between the Hyades and Pleiads Clusters. In the evening one could see the waxing Moon, moving towards full, lying to the right of the Hyades Cluster. Aldeberan is a red giant star far closer to us than the Hyades.
- February 7th - after sunset: Venus lies above Mercury. After sunset, low in the southwest, Venus will lie above Mercury. Venus will not be missed, but to spot Mercury which lies down to its lower right, a low horizon just south of west and perhaps binoculars will be needed - but please do not use them until the Sun has set.
- February 18th - before dawn: a thin crescent Moon lies just to the right of Mars. If clear around 7 am on the 18th, one will see a thin cresent Moon lying over to the right of Mars. This could be a nice photo opportunity.
- February 27th - after sunset: a very thin crescent Moon lies down to the lower left of Venus. After sunset on the 27th, and given a low horizon towards the west, you may be able to spot a very thin crescent Moon lying down to the lower left of Venus.
- February 29th - before dawn: a lineup of Saturn, Jupiter and Mars. If clear around 6:30 am on the 29th, one will see a nice lineup of, from left to right, Saturn, Jupiter and Mars. A low horizon towards the southeast will be needed to spot Saturn.
- February 1st and 14th evening: The Hyginus Rille. During these evenings the terminator lies close so making it more obvious. 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 contast 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.
Haritina Mogosanu and Samuel Leske from the Carter Science Centre in New Zealand speaks about the Southern Hemisphere night sky during February 2020.
