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« November 2019


The Night Sky December 2019


Compiled by Ian Morison




This page, updated monthly, will let you know some of the things that you can look out for in the night sky.  It lists the phases of the Moon, where you will see the naked-eye planets and describes some of the prominent constellations in the night sky during the month.


New(ish)

The author's: Astronomy Digest

which, over time, will provide useful and, I hope, interesting articles for all amateur astronomers.   A further aim is to update and add new material to link with the books recently published by Cambridge University Press and which are described on the home page of the digest.   It now includes nearly 70 illustrated articles.



Image of the Month

Moons

Saturn's Moons
Image: Cassini Imaging Team, SSI, JPL, NASA.

Saturn now holds the record for having the most detected moons within the Solar System with a known total of 82 as compared to Jupiter's 79.   All of the 20 newly found satellites are very small, 5 km or so in diameter.   The Cassini image shows 5 of the moons: left to right are Janus and Pandora (179 and 81 km across), 504 km diameter Enceladus and Mimas at 396 km diamater.   Cut off at the right hand side of the image is Rhea, Saturn's second largest moon, some 1,528 km across.

Highlights of the Month


December - still a chance to observe Saturn.

Saturn
Saturn in the evening Sky

Saturn is now low (at an elevation of ~13 degrees) just west of south as darkness falls lying above the 'teapot' of Sagittarius.   Held steady, binoculars should enable you to see Saturn's brightest moon, Titan, at magnitude 8.2.   A small telescope will show the rings with magnifications of x25 or more and one of 6-8 inches aperture with a magnification of ~x200 coupled with a night of good "seeing" (when the atmosphere is calm) will show Saturn and its beautiful ring system in its full glory.

As Saturn rotates quickly with a day of just 10 and a half hours, its equator bulges slightly and so it appears a little "squashed".   Like Jupiter, it does show belts but their colours are muted in comparison.

The thing that makes Saturn stand out is, of course, its ring system.   The two outermost rings, A and B, are separated by a gap called Cassini's Division which should be visible in a telescope of 4 or more inches aperture if seeing conditions are good.   Lying within the B ring, but far less bright and difficult to spot, is the C or Crepe Ring.

Due to the orientation of Saturn's rotation axis of 27 degrees with respect to the plane of the solar system, the orientation of the rings as seen by us changes as it orbits the Sun and twice each orbit they lie edge on to us and so can hardly be seen.   This last happened in 2009 and they are currently at an angle of 25 degrees to the line of sight.   The rings will continue to narrow until March 2025 when they will appear edge-on again.

See more of Damian Peach's images: Damian Peaches Website"




Saturn
Saturn imaged in April 2012 by Damian Peach



December, evening: the Double Cluster and the 'Demon Star', Algol.

Algol
Algol and the Double Cluster.
Image: Stellarium/IM

December is a good time to look high in the Southeast after dark towards the constellations of Cassiopea and Perseus.   Perseus contains two interesting objects; the Double Cluster between the two constellations and Algol the 'Demon Star'.   Algol in an eclipsing binary system as seen in the diagram below.   Normally the pair has a steady magnitude of 2.2 but every 2.86 days this briefly drops to magnitude 3.4.

Double Cluster
Double Cluster imaged by IM and the Algol Light Curve




December: find Uranus.

Uranus
Uranus in Aries.
Image: Stellarium/IM

This month is a still good time to find the planet Uranus in the late evening as it reached opposition on October 28th.   With a magnitude of 5.7, binoculars will easily spot it and, from a really dark site, it might even be visible to the unaided eye.   A medium aperture telescope will reveal Uranus's 3.7 arc second wide disk showing its turquoise colour.   It lies in Aries, close to the boarders of Pisces and Cetus as shown on the chart.

December: find M31 - The Andromeda Galaxy - and perhaps M33 in Triangulum

M31
How to find M31
Image: Stellarium/IM

In the evenings when the Moon is not prominent, the galaxy M31 in Andromeda will be visible in the south The chart 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 (26th December) - 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!



December 1st - before dawn: Mercury, Mars and Spica.

Mercury
Mercury, Mars and Spica.
Image: Stellarium/IM

If clear before dawn and looking southeast, one could see a nice lineup of Mercury, Mars and Spica.   Arcturus will be seen high up to their left.

December 10th - after sunset: Venus lies below Saturn.

Venus
Venus lies below Saturn
Image: Stellarium/IM

After sunset, low in the southwest, Venus will lie just 2 degrees below Saturn.

December 10th - evening: the Moon lies between the Pleiades and Hyades Clusters.

Moon
The Moon lies between the Pleiades and Hyades clusters.
Image: Stellarium/IM

In the evening one could see the Moon, close to full, lying between the Pleaides and Hyades Clusters.   Aldeberan is a red giant star far closer to us.

December 12th - before dawn: Mars and the double star Alpha Librae.

Mars
Mars closeto the souble star Alpha Librae.
Image: Stellarium/IM

If clear before dawn on the 12th, one will see Mars (magnitide +1.67) just above the double star Alpha Librae (Magnitudes +2.74 and +5.15) or Zubwnelgenubi.   Despite its name it is the second brightest star in Libra.   This would make a nice image using a small telescope.

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

Dec14th
The Geminid Meteor shower
Image:Stellarium/IM

The Geminids

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 22nd/23rd - late evenings: the Ursid Meteor Shower

Ursid meteor Shower
The Ursid meteor shower
Image: Stellarium/IM
The late evenings of the 22nd and 23rd of December are when the Ursid meteor shower will be at its best - though the peak rate of ~10-15 meteors per hour is not that great.   Sadly, this year Full Moon is on the 21st, so its light will greatly hinder our view.   The radiant lies close to the star Kochab in Ursa Minor (hence their name), so look northwards at a high elevation.   Occasionally, there can be a far higher rate so its worth having a look should it be clear.

December - Evenings of the 5th and 18th: The Straight Wall

Moon
Location of the Straight Wall: IM.

The Straight Wall
The Straight Wall, or Rupes Recta, is best observed either 1 or 2 days after First Quarter or a day or so before Third Quarter.   To honest, it is not really a wall but a gentle scarp - as Sir Patrick has said "Neither is it a wall nor is it straight!"

The Straight Wall
The Straight Wall at Sunrise and Sunset.













M109 imaged with the Faulkes Telescope

M109
Messier 109
Image: Daniel Duggan
Faulkes Telescope North.

The Galaxy M109, imaged by Daniel Duggan.
This image was taken using the Faulkes Telescope North by Daniel Duggan - for some time a member of the Faulkes telescope team.   It shows the barred spiral galaxy M109 that lies at a distance of 83 million light years in the constellation of Ursa Major.   It is the brightest galaxy in the Ursa Major group of some 50 galaxies.   Our own Milky Way galaxy is now thought to be a barred spiral like M109.

Learn more about the Faulkes Telescopes and how schools can use them: Faulkes Telescope"

















Observe the International Space Station

The International Space Station
The International Space Station and Jules Verne passing behind the Lovell Telescope on April 1st 2008.
Image by Andrew Greenwood

Use the link below to find when the space station will be visible in the next few days. In general, the space station can be seen either in the hour or so before dawn or the hour or so after sunset - this is because it is dark and yet the Sun is not too far below the horizon so that it can light up the space station. As the orbit only just gets up the the latitude of the UK it will usually be seen to the south, and is only visible for a minute or so at each sighting. Note that as it is in low-earth orbit the sighting details vary quite considerably across the UK. The NASA website linked to below gives details for several cities in the UK. (Across the world too for foreign visitors to this web page.)

Note: I observed the ISS three times recently and was amazed as to how bright it has become.

Find details of sighting possibilities from your location from: Location Index

See where the space station is now: Current Position


The Moon

3rd Quarter Moon
The Moon at 3rd Quarter. Image, by Ian Morison, taken with a 150mm Maksutov-Newtonian and Canon G7.
Just below the crator Plato seen near the top of the image is the mountain "Mons Piton".   It casts a long shadow across the maria from which one can calculate its height - about 6800ft or 2250m.
`
new moon first quarter full moon third quarter
December 26th December 4th December 12th December 19th

Some Lunar Images by Ian Morison, Jodrell Bank Observatory: Lunar Images

A World Record Lunar Image

World record Lunar Image
The 9 day old Moon.

To mark International Year of Astronomy, a team of British astronomers have made the largest lunar image in history and gained a place in the Guinness Book of Records!   The whole image comprises 87.4 megapixels with a Moon diameter of 9,550 pixels.  The resolution of ~0.4 arc seconds allows details as small as 1km across to be discerned!   The superb quality of the image is shown by the detail below of Plato and the Alpine Valley.  Craterlets are seen on the floor of Plato and the rille along the centre of the Alpine valley is clearly visible.  The image quality is staggering! The team of Damian Peach, Pete lawrence, Dave Tyler, Bruce Kingsley, Nick Smith, Nick Howes, Trevor Little, David Mason, Mark and Lee Irvine with technical support from Ninian Boyle captured the video sequences from which 288 individual mozaic panes were produced.   These were then stitched together to form the lunar image.

Plato and the Alpine valley
Plato and the Alpine Valley.

Please follow the link to the Lunar World Record website and it would be really great if you could donate to Sir Patrick Moore's chosen charity to either download a full resolution image or purchase a print.









The 8 day old Moon

Lunar Image
The 8 day old Moon imaged by Ian Morison.

This image was taken by the author on a night in March 2018 when the Moon was at an elevation of ~52 degrees and the seeing was excellent.   This enabled the resolution of the image to be largely determined by the resolution of the 200 mm aperture telescope and the 3.75 micron pixel size of the Point Grey Chameleon 1.3 megapixel video camera.   The use of a near infrared filter allowed imaging to take place before it was dark and also reduced the effects of atmospheric turbulence.   The 'Drizzle' technique developed by the Hubble Space Telescope Institute (HSTI) was used to reduce the effective size of the camera's pixels to allow the image to be well sampled.   Around 100 gigabytes of data, acquired over a 2 hour period, was processed to produce images of 54 overlapping areas of the Moon which were then combined to give the full lunar disk in the free 'stitching' program Microsoft ICE.   A further HSTI development called 'deconvolution sharpening' was then applied to the image.   The Moon's disk is ~6,900 pixels in height and has a resolution of 0.6 to 0.7 arc seconds.   Interestingly, as seen in the inset image, the rille lying along the centre of the Alpine Valley is just discernable and this is only ~0.5 km wide!   [Due to size limitations the large image is 2/3 full size.]









The Planets

 A montage of the Solar System
A montage of the Solar System. JPL / Nasa

Jupiter

Jupiter
A Cassini image of Jupiter . Nasa

Jupiter, shining on the 1st at magnitude -1.8 and with an angular size of 32 arc seconds, can be seen very low in the southwest as darkness falls at the start of December but, soon after, will be lost in the Sun's glare.   Jupiter lies in the southeastern part of Ophiuchus and is heading towards the southernmost part of the ecliptic so, as it appears in the twilight, will only have an elevation of ~6 degrees.   With its low elevation, atmospheric dispersion will take its toll and an atmospheric dispersion corrector would greatly help to improve our views of the giant planet and it four Gallilean moons.



Saturn

Saturn
The planet Saturn. Cassini - Nasa

Saturn, will be seen west of south as darkness falls at the start of the month.   Then, its disk is ~16 arc seconds across and its rings - which are still, at ~24 degrees, nicely tilted from the line of sight - spanning some 36 arc seconds across.   During the month its brightness remains +0.6 with an angular size of 15.4 arc seconds.   Sadly, now in Sagittarius and lying on the south-eastern side of the milky way, it is at the lowest point of the ecliptic and will only have an elevation of ~12 degrees after sunset.   As with Jupiter, an atmospheric dispersion corrector will help improve our view.




Mercury

Mercury.
Messenger image of Mercury Nasa

Mercury. Following its transit of the Sun and reaching greatest elongation west on the 28th of November, can be seen in the pre-dawn sky low in the southeast at the start of December.   On the 1st it will have a magnitude +0.29 and will rise around an hour before the Sun.   It will then have an elevation of some 9 degrees before being lost in the Sun's glare.   With an angular size of ~5 arc seconds, it will then fall back towards the Sun and be lost from view by the middle of the month.






Mars

Mars showing Syrtis major.
A Hubble Space Telescope image of Mars.
Jim Bell et al. AURA / STScI / Nasa

Mars can be seen towards the southeast in the pre-dawn sky at the start of its new apparition.   It rises some two and a half hours before the Sun at the start of the month and will have an elevation of ~15 degrees before it is lost in the Sun's glare.   It then has a magnitude of +1.7 and a 3.9 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 +1.6.




Venus

Venus
Venus showing some cloud structure

Venus may just be glimpsed in the south-west at the start of the month, but will be difficult to see due to the fact that the ecliptic is at a shallow angle to the horizon and so Venus will have a very low elevation.   As the month progresses, it will rise higher in the sky and on the 31st will have reached an elevation of 14 degrees as darkness falls.   During December, its magnitude remains at about -4 and its disk increases from 11.6 to 13 arc seconds across.   A low horizon and possibly binoculars will be needed to spot Venus, but please do not use them until after the Sun has set.

Radar Image of Venus
Radar image showing surface features









The Early Evening December Sky

Early Evening December Sky
The December Sky in the south - early evening

The Late Evening December Sky

Late Evening December Sky
The December Sky in the south - late evening

The maps shows the constellations seen towards the south in the early and late evening. Setting towards the west in early evening is the beautiful region of the Milky Way containing both Cygnus and Lyra. Below is Aquilla. The three bright stars Deneb (in Cygnus), Vega (in Lyra) and Altair (in Aquila) make up the "Summer Triangle". East of Cygnus is the great square of Pegasus - adjacent to Andromeda in which lies M31, the Andromeda Nebula. To the north lies "w" shaped Cassiopeia and Perseus. The map shows the constellation Taurus, with its two lovely clusters, the Hyades and the Pleaides, and is also described in more detail below.   As the evening draws on, Orion, the Hunter, follows Taurus into the eastern sky with the constellations Auriga, above, and Gemini, to the upper left. Later Sirius, in Canis Major will be seen to the lower left of Orion. Due to its brightness and scintillations caused by the atmosphere it often appears as a rainbow of colours flashing in the sky.

The constellations Pegasus and Andromeda

Pegasus and Andromeda
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.

M 31 - The Andromeda Nebula
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

The constellation Taurus

Taurus
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 Hyades and Pleiades
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!)

The Crab Nebula
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.

The Crab Nebula
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
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 Orion Nebula
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
The Orion Nebula: David Malin