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Constellations of the month




Saturn passed behind the Sun on December 21st (superior conjunction) and reappears in the pre dawn sky this month at the start of its new apparition. It is unlikely to be seen in the first week of January, but climbs higher and so becomes easier to spot as the month progresses and its brightness increases up to +0.6 magnitudes. The rings were at their widest a few months ago and are still well open.


Jupiter is now a pre-dawn object rising some three and a half hours before the Sun at the beginning of the month with its 33 arc second disk, shining at a magnitude of -1.8, to be seen under clear skies. As the month progresses, its apparent diameter increases to 35.8 arc seconds and it brightens to magnitude -2. The elevation before dawn will then be sufficiently high to enable crisp views of 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.


Mars. At the start of the month Mars lies in Libra but moves down into Scorpius at the end 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 increasing from 1.5 to 1.2 and an angular size of just 4.8, increasing to 5.6, arc seconds so no details will be seen on its salmon-pink surface. Moving eastwards, Mars has a very close conjunction with Jupiter on the 7th of January.


Venus, passes through superior conjunction (on the far side of the Sun) on January 9th and so cannot be observed this month.


Mercury reaches greatest elongation west on New Year's Day shining at magnitude -0.3. It will be seen low in the Southeast before dawn and will be visible for a couple of weeks before sinking back towards the Sun. Its angular diameter reduces from 6.7 to 4.9 arc seconds but, as the percentage illuminated surface area increases from 62% to 95%, its brightness remains constant throughout the month.

The Night Sky In and Around Swindon January 2018

Slide Presentation

The following presentation was given at our meeting on the 17th November, 2017 by Rob Slack

The constellation Taurus

Taurus is one of the most beautiful constellations and you can almost imagine the Bull charging down to the left towards Orion. His face is delineated by the "V" shaped cluster of stars called the Hyades, his eye is the red giant star Aldebaran and the tips of his horns are shown by the stars beta and zeta Tauri. Although alpha Tauri, Aldebaran, appears to lie amongst the stars of the Hyades cluster it is, in fact, less than half their distance lying 68 light years away from us. It is around 40 times the diameter of our Sun and 100 times as bright.

The Hyiades and Pleiades. Copyright: Alson Wong

More beautiful images by Alson Wong : Astrophotography by Alson Wong

To the upper right of Taurus lies the open cluster, M45, the Pleiades. Often called the Seven Sisters, it is one of the brightest and closest open clusters. The Pleiades cluster lies at a distance of 400 light years and contains over 3000 stars. The cluster, which is about 13 light years across, is moving towards the star Betelgeuse in Orion. Surrounding the brightest stars are seen blue reflection nebulae caused by reflected light from many small carbon grains. These relfection nebulae look blue as the dust grains scatter blue light more efficiently than red. The grains form part of a molecular cloud through which the cluster is currently passing. (Or, to be more precise, did 400 years ago!)

VLT image of the Crab Nebula
Close to the tip of the left hand horn lies the Crab Nebula, also called M1 as it is the first entry of Charles Messier's catalogue of nebulous objects. Lying 6500 light years from the Sun, it is the remains of a giant star that was seen to explode as a supernova in the year 1056. It may just be glimpsed with binoculars on a very clear dark night and a telescope will show it as a misty blur of light.

Lord Rosse's drawing of M1
Its name "The Crab Nebula" was given to it by the Third Earl of Rosse who observed it with the 72 inch reflector at Birr Castle in County Offaly in central Ireland. As shown in the drawing above, it appeared to him rather lile a spider crab. The 72 inch was the world's largest telelescope for many years. At the heart of the Crab Nebula is a neutron star, the result of the collapse of the original star's core. Although only around 20 km in diameter it weighs more than our Sun and is spinning 30 times a second. Its rotating magnetic field generate beams of light and radio waves which sweep across the sky. As a result, a radio telescope will pick up very regular pulses of radiation and the object is thus also known a Pulsar. Its pulses are monitored each day at Jodrell Bank with a 13m radio telescope.
The constellation Orion

Orion, perhaps the most beautiful of constellations, will be seen in the south at around 11 - 12 pm during January. Orion is the hunter holding up a club and shield against the charge of Taurus, the Bull up and to his right. Alpha Orionis, or Betelgeuse, is a read supergiant star varying in size between three and four hundred times that of our Sun. The result is that its brightness varies somewhat. Beta Orionis, or Rigel, is a blue supergiant which, at around 1000 light years distance is about twice as far away as Betelgeuse. It has a 7th magnitude companion. The three stars of Orion's belt lie at a distance of around 1500 light years. Just below the lower left hand star lies a strip of nebulosity against which can be seen a pillar of dust in the shape of the chess-board knight. It is thus called the Horsehead Nebula. It shows up very well photographically but is exceedingly difficult to see visually - even with relativly large telescope.

The Horsehead Nebula: Anglo Australian Observatory
Beneath the central star of the belt lies Orion's sword containing one of the most beautiful sights in the heavens - The Orion Nebula. It is a region of star formation and the reddish colour seen in photographs comes from Hydrogen excited by ultraviolet emitted from the very hot young stars that make up the Trapesium which is at its heart. The nebula, cradling the trapesium stars, is a beautiful sight in binoculars or, better still, a telescope. To the eye it appears greenish, not red, as the eye is much more sensitive to the green light emitted by ionized oxygen than the reddish glow from the hydrogen atoms.

The Orion Nebula: David Malin
January 26th: Two great Lunar Craters: Tycho and Copernicus
Around the 17th of January (with no Moon in the sky): find M31 - The Andromeda Galaxy - and perhaps M33 in Triangulum

How to find M31
Image: Stellarium/IM

In the evening, the galaxy M31 in Andromeda is visible in the south The chart above provides 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 as shown on the chart.

Around new Moon (17th Jan) - 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!

Compiled by Ian Morison - Jodrell Bank Centre for Astrophysics
January 6th before dawn: Mars and Jupiter up close

Jupiter in conjunction with Mars

If clear before dawn on the 6th and looking to the South-southeast, Mars, at magnitude 1.4, will be seen just to the right of Jupiter shining at magnitude -1.8. At their closest they will be just 23 arc seconds apart.

The planets this month
Supermoon 1st/2nd January and Blue Moon 31st January

There will be a big bright Full Moon to open the year when our satellite will be at its closest to Earth at 356,567 km away and will be 14% brighter than when the Moon is furthest away. This takes place on the night of 1st/2nd January.

The 'Blue Moon' on the 31st January suffers a lunar eclipse; because some of the Sun's reddish light is bent round into the Earth's shadow, it will actually appear red.

With special thanks to Heather Couper & Nigel Henbest for this guide, from 'Stargazing 2018' published by Philip's.