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Constellations of the month

 

 
CURRENT MOON

Saturn

Saturn might just be glimpsed in the first few days of December very low in the southwest around 16:45, but soon disappears into the Sun's glare as it moves towards superior conjunction on January 2nd. It will have a disk of ~15 arc seconds and a magnitude of +0.5.

Jupiter

Jupiter passed behind the Sun on November 26th and will appear low in the eastern pre-dawn sky around the 12th of the month. It will have a magnitude of ~-1.8 and a disk ~32 arc seconds across. Not a good month to observe it due to its low elevation.

Mars

Mars, though fading from magnitude -0.0 to +0.4 during the month remains prominent in the southern sky as it starts the month in Aquariusat an elevation of 27 degrees. It will lie due south around 6 pm. It moves eastwards into Pices on the 21st; slightly higher in elevation at ~32 degrees when due south around 5:30 pm. Its angular size falls from 9.3 arc seconds to 7.5 arc seconds during the month so it will become harder to spot any details, such as Syrtis Major, on its salmon-pink surface.
Venus

Venus begins December at an elevation of ~32 degrees and a dazzling magnitude of -4.9. Its angular size reduces from 40.7 to 26.6 arc seconds during the month as it moves away from the Earth but, at the same time, the precentage illuminated disk (its phase) increases from 26% to 47% - which is why the brightness only reduces from -4.9 to -4.6 magnitudes. It will reach greatest elongation from the Sun on January 6th.

Mercury

Mercury passed between us and the Sun (inferior conjunction) on the 27th of November but appears in the pre-dawn sky around the 6th of the month. It will then have a magnitude of +0.5 which increases to magnitude 0.0 by the 8th. Mercury reaches its greatest elongation (west) of the Sun on the 16th, then 21 degrees away, and rises over an hour and a half before the Sun when it is ~60% lit. As the morning ecliptic is at a steep angle to the horizon at this time of the year, this is an excellent apparition. Do not miss (when hopefully clear) its conjunction with Jupiter as described above.

The Night Sky In and Around Swindon December 2018

Slide Presentation

The following presentation was given at our last meeting by Rob Slack

December 3rd - before dawn: Venus below a very thin crescent Moon


Venus below a thin crescent Moon.
Image: Stellarium/IM

Looking southeast before dawn one should, if clear, be able to easily spot brilliant Venus lying below a very thin crescent Moon. Spica is over to the right of Venus making a nice photo opportunity.
Compiled by Prof. Ian Morison
The planets this month
The constellations of Pegasus and Andromeda
Pegasus

The Square of Pegasus is in the south during the evening and forms the body of the winged horse. The square is marked by 4 stars of 2nd and 3rd magnitude, with the top left hand one actually forming part of the constellation Andromeda. The sides of the square are almost 15 degrees across, about the width of a clentched fist, but it contains few stars visibe to the naked eye. If you can see 5 then you know that the sky is both dark and transparent! Three stars drop down to the right of the bottom right hand corner of the square marked by Alpha Pegasi, Markab. A brighter star Epsilon Pegasi is then a little up to the right, at 2nd magnitude the brightest star in this part of the sky. A little further up and to the right is the Globular Cluster M15. It is just too faint to be seen with the naked eye, but binoculars show it clearly as a fuzzy patch of light just to the right of a 6th magnitude star.

Andromeda

The stars of Andromeda arc up and to the left of the top left star of the square, Sirra or Alpha Andromedae. The most dramatic object in this constellation is M31, the Andromeda Nebula. It is a great spiral galaxy, similar to, but somewhat larger than, our galaxy and lies about 2.5 million light years from us. It can be seen with the naked eye as a faint elliptical glow as long as the sky is reasonably clear and dark. Move up and to the left two stars from Sirra, these are Pi amd Mu Andromedae. Then move your view through a rightangle to the right of Mu by about one field of view of a pair of binoculars and you should be able to see it easily. M31 contains about twice as many stars as our own galaxy, the Milky Way, and together they are the two largest members of our own Local Group of about 3 dozen galaxies.


M31 - The Andromeda Nebula
M33 in Triangulum

If, using something like 8 by 40 binoculars, you have seen M31 as described above, it might well be worth searching for M33 in Triangulum. Triangulum is the small faint constellation just below Andromeda. Start on M31, drop down to Mu Andromedae and keep on going in the same direction by the same distance as you have moved from M31 to Mu Andromedae. Under excellent seeing conditions (ie., very dark and clear skies) you should be able to see what looks like a little piece of tissue paper stuck on the sky or a faint cloud. It appears to have uniform brightness and shows no structure. The shape is irregular in outline - by no means oval in shape and covers an area about twice the size of the Moon. It is said that it is just visible to the unaided eye, so it the most distant object in the Universe that the eye can see. The distance is now thought to be 3.0 Million light years - just greater than that of M31.
M33


M33 in Triangulum - David Malin
 
December 13th onwards - late evening: Comet 46P/Wirtanen could be visible to the unaided eye

Track of 46P/Wirtanen
Looking southeast late evening one should, if clear, be able to spot a naked eye comet. Its location is shown on the chart. Let's hope it is clear on the night of the 15th/16th when it passes between th Hyades and Pleiades cluster in Taurus. It lies very close to Capella in Auriga on the 23rd, but, sadly that night is close to Full Moon. It is hoped that it will reach a magnitude of +3.

December 14th and 15th after midnight: the Geminid Meteor Shower

The Geminid Meteor shower
Image:Stellarium/IM
The early mornings of December 14th and 15th will give us the chance, if clear, of observing the peak of the Geminid meteor shower. The Moon is at First Quarter and will set around 11 pm so, when Gemini is highest in the sky, its light will not hinder our view. The Geminids can often produce near-fireballs and so the shower is well worth observing if its clear. An observing location well away from towns or cities will pay dividends. The relatively slow moving meteors arise from debris released from the asteroid 3200 Phaethon. This is unusual, as most meteor showers come from comets. The radiant - where the meteors appear to come from - is close to the bright star Castor in the constellation Gemini as shown on the chart. If it is clear it will be cold - so wrap up well, wear a woolly hat and have some hot drinks with you.
December 16th (late night) and 17th: Two Great Lunar Craters
Two great Lunar Craters: Tycho and Copernicus

This is a great night to observe two of the greatest craters on the Moon, Tycho and Copernicus, as the terminator is nearby. Tycho is towards the bottom of Moon in a densely cratered area called the Southern Lunar Highlands. It is a relatively young crater which is about 108 million years old. It is interesting in that it is thought to have been formed by the impact of one of the remnents of an asteroid that gave rise to the asteroid Baptistina. Another asteroid originating from the same breakup may well have caused the Chicxulub crater 65 million years ago. It has a diameter of 85 km and is nearly 5 km deep. At full Moon - seen in the image below - the rays of material that were ejected when it was formed can be see arcing across the surface. Copernicus is about 800 million years old and lies in the eastern Oceanus Procellarum beyond the end of the Apennine Mountains. It is 93 km wide and nearly 4 km deep and is a clasic "terraced" crater. Both can be seen with binoculars.

Illustration: Tycho and Copernicus: Ian Morison
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.

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 (M42). 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
Compiled by Ian Morison - Jodrell Bank Centre for Astrophysics