December Observing Guide

OBSERVING GUIDE
(Please note all times are UT and are based on an observing location of Belfast and covers the month of December)

The Sun

At the start of the month the Sun rises at 08:25 and sets at 16:20. By the end of the month, it rises at 08:45 and sets at 16:25.

The Planets

Jupiter and Venus lie close together for the first week of the month. On the evening of the 1st, Jupiter lies two degrees to the North of Venus. Venus is occultated by the moon in the early evening of the 1st (Details below in the Moon Section).

Venus and Neptune lie close together from just short of Christmas through to the end of the month. A 16% illuminated waxing crescent moon joins the pair on the evening of New Years Eve, to the North of Venus and to the East of Neptune.

Jupiter and Mercury lie close together for the last few days of the month. On the evening of 29th, they are joined by a 4% illuminated waxing crescent moon, lying three degrees to the East of Jupiter with Mercury within three degrees to the South-West of Jupiter.

Mercury was at superior conjunction last month and is only observable towards the end of the month when it becomes an evening object. At month’s end it sets at 17:50, over an hour after the sun and is mag -0.7 and can be located in Sagittarius.

Venus is an evening object this month and is currently moving away from the Sun. It should be well placed for observation in the West after sunset as the end of the month approaches. It sets more than two hours after the sun at the start of the month at 19:10 and by month’s end; it sets more than four hours after the Sun at 20:35. It brightens from mag -4.1 to mag -4.3 and can be located in Capricornus during the month.

Mars is at conjunction on the 5th and is not visible this month.

Ceres can be found this month in Leo. It will be magnitude +8 and moves between Delta and Theta Leonis (mag +2.6 and mag +3.3) in an Easterly direction.

Jupiter can be found in Sagittarius. It is currently low down in the sky and as a result poorly placed for observation. It slips further westward this month. At the start of the month, it rises during daylight hours and sets at 19:20. By month’s end, it sets at 18:00. It fades from mag -2.0 to mag -1.9 during the month. The four Galilean moons – Io, Europa, Ganymede and Callisto are visible with 10x50 binoculars or a small telescope and are worth a look.

Saturn can be located in Leo this month. It rises at 00:50 at the start of the month and by month’s end; it rises at 22:50. It brightens from mag +1.0 to mag +0.9 during the month. With the planet’s ring plane almost edge on, this is not a good time to try and observe the rings. It is however a good time to try and observe the smaller satellites and details on the planet’s surface with the rings out of the picture.

Uranus can be found in Aquarius and is well placed for observation. At the start of the month, it rises during daylight hours and sets at 00:45. By month’s end it sets at 22:50. It is just within naked eye visibility and fades from mag +5.8 to mag +5.9 during the month. It can be located close to Phi Aquarii (mag +4.2). Between the 5th and the 15th, it lies just to the East of the star, close to 96 Aquarii (mag +5.5).

Neptune can be found in Capricornus. At the start of the month, it rises during daylight hours and sets at 22:10 and by month’s end it sets at 20:15. The planet lies to the North and slightly to the West of the pair of stars Delta and Gamma Capricorni (mag +2.9 and mag +3.7). It fades from mag +7.9 to mag +8.0 during the month.


The Moon

The first quarter moon is on the 5th with the full moon on the 12th. The last quarter moon is on the 19th with the new moon on the 27th.

On the early evening of the 1st, Venus is occultated by a 14% illuminated waxing crescent moon. The planet disappears behind the East North-Easterly dark limb of the moon at approximately 15:37 and reappears from behind the West South-West bright limb at approximately 17:07. As the planet disappears behind the moon during daylight, the Sun will still above the horizon and all precautions should be taken to observe this safely.

On the evening of the 3rd, a 30% illuminated waxing crescent moon lies to the West of Neptune.

Meteors

The ZHR or Zenithal Hourly Rate is the number of meteors an observer would see in one hour under a clear, dark sky with a limiting apparent magnitude of 6.5 and if the radiant of the shower were in the zenith. The rate that can effectively be seen is nearly always lower and decreases as the radiant is closer to the horizon. The Zenith is the overhead point in the sky for an observer. The radiant is the point in the sky, from which (to a planetary observer) meteors appear to originate, i.e. the Perseids, for example, are meteors which appear to come from a point within the constellation of Perseus. A fireball is defined by the International Astronomical Union as a meteor brighter than any of the planets, i.e. magnitude -4 or brighter. The International Meteor Organisation alternatively defines it as a meteor which would have a magnitude of -3 or brighter at the zenith.

There are five showers this month. The first two showers of the month both peak on the 11th. They are the Sigma Hydrids and the Monocerotids. Both are minor showers with ZHRs of 3 and 2 respectively. Lunar conditions are very poor for these showers with a 99% illuminated waxing gibbous moon present all night in Taurus. The radiants for the two showers rise around 04:00 on the morning of 12th and 23:00 on the evening of the 11th respectively.

The major shower of the month is the Geminids. They peak on the 13th at around 18:00 with a ZHR of 100. It is often one of the best showers of the year with its slow moving meteors which travel on average at 22 miles/second. Unfortunately lunar conditions are poor this year with the just past full moon present all night in Gemini, close to the radiant.

The next shower is the Ursids. They peak on the 22nd at around 07:00 with a ZHR of 10. Lunar conditions are good for this shower with a 24% illuminated waning crescent moon only rising at 03:55 on the morning of the 22nd. The radiant is close to Kocab (Beta Ursa Minoris) and rate enhancements have occurred in the past. There is a possibility of increased activity this year of up to a ZHR of 50. Its parent comet 8/P Tuttle is at perihelion in January and it is not known whether this will have any impact on the activity.

The final shower is the Coma Berenicids. They peak on the 29th with a ZHR of 5. Lunar conditions are perfect for this shower with a moonless night on the 29th. The radiant rises around midnight.

Comets

Comet 2006 OF2 Broughton moves out of Lynx during December in a North-Westerly direction, passing into Camelopardalis in the last week of the month. It is circumpolar and thus well placed for observation. Current predictions estimate its brightness at mag +10 with it expected to fade slowly. The comet lies close to the East of star 2 Lyn (mag +4.5) around the 19th / 20th.

Comet 2006 W3 Christensen moves out of Cepheus and heads in a Northerly direction, following a path similar to that of the Lacerta / Cygnus boundary. It is also circumpolar and is predicted to remain around mag +10 for the month. It passes within two degrees of NGC 7128, a mag +10 open cluster in Cygnus at around 01:00 on the morning of the 9th. On the evening of the 10th at around 19:00, it passes within three degrees of IC 1434, a mag +9 open cluster in Lacerta and at around 02:00 on the morning of Boxing day (St. Stephens day), it passes within a degree of IC 5146 (The Cocoon Nebula) in Cygnus which is mag +7.

Comet/2008 A1 (McNaught) is currently estimated at mag +8 with it predicted to fade to mag +9 by month’s end. During December it moves out of Ophiuchus in a North-Westerly direction, passing into Hercules mid-month. It is visible both in the early evening after sunset low in the West and in the early morning before sunrise low in the East. On the morning of the 13th at around 06:00, it lies within two degrees of NGC 6574, a mag +12 galaxy in Hercules.


Deep Sky

On the deep sky front this month, galaxies M81 and M82 can be observed in Ursa Major. In Andromeda, M31 – The Andromeda galaxy can be observed along with its satellite galaxies M32 and M110. In Perseus, there is the open cluster M34 and the excellent Double Cluster – NGC 869 and 884. In Triangulum, there is the galaxy M33. In Auriga there are three open clusters M36, M37 and M38 and also M35 in Gemini. Taurus has the excellent Pleiades – M45, the Hyades and also M1 – The Crab Nebula. In Orion there is M42 – The Great Orion Nebula and also NGC 1980 and 1981.In Canis Major there is the open cluster M41. Another open cluster M50 can be found in Monoceros and also Cancer has its open clusters with M44 – The Beehive Cluster and M67.

For further observing information, check out www.eaas.co.uk/stargazers.html

General Notes

Always keep an eye out for Aurorae. Check out www.stronge.org.uk/spaceweather.html for the most up-to-date information on the aurorae. The winter solstice is on the 21st which sees the shortest day of the year and after this date the nights shorten and the days lengthen.

Other interesting naked eye phenomena to look out for include the Zodiacal Light and the Gegenschein. Both are caused by sunlight reflecting off dust particles which are present in the solar system. The Zodiacal Light can be seen in the West after evening twilight has disappeared or in the East before the morning twilight. The best time of year to see the phenomenon is late-Feb to early-April in the evening sky and September/October in the morning sky -- it's then that the ecliptic, along which the cone of the zodiacal light lies, is steepest in our skies. The Gegenschein can be seen in the area of the sky opposite the sun. To view either, you must get yourself to a very dark site to cut out the light pollution. When trying to observe either of these phenomena, it is best to do so when the moon is below the horizon. If you are observing them when the moon has risen, restrict your efforts to the period 4 days either side of the new moon as otherwise the moonlight will be sufficient to drown them out.

Finally check out www.heavens-above.com for the latest passes of the International Space Station and satellites, details of Space Shuttle launches and passes and for details of Iridium Flare activity.

Clear Skies

Neill McKeown

Information Sources Used

www.skyviewcafe.com - Used for the Sun and Planets section. Also partly used for the Moon Section

Sky at Night Magazine Observing Guide and Interactive Planetarium

www.aerith.net and cometchasing.skyhound.com – Used for the Comet Section for information and finder charts

www.imo.net – Used in the Meteor section

BAA Handbook

Stardust Magazine

Sky Guide 2008 – South Dublin Astronomical Society

Excellent stuff.
Many thanks Neill.

Hi Neill,

An update on your December 2008 Observing Guide:

Comet 17P/Holmes is now, once again, a very faint object. Recently, it was imaged at about magnitude 20.

Comet 85P/Boethin has not brightened as expected. It is still about mag 18-20.

John

Info on Comets Broughton, McNaught and Christensen updated.