December 11 Observing Guide

Hi all,

Guide for December is below:

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

The Sun

At the start of the month, the Sun rises at 08:20 and sets at 16:00. By month's end, it rises at 08:45 and sets at 16:05.

The Planets

Mercury is at inferior conjunction on the 4th and at greatest western elongation on the 23rd. This means it is visible as a morning object in the second half of the month. At mid-month, it rises at 06:45 and is mag +0.0, by month’s end; it rises at 07:10 and is mag -0.4.

Venus is visible in the evening sky during the month. At the start of the month, it sets at 17:35 and by month’s end sets at 19:00. It maintains its brightness at mag -3.9 during the month.

Mars is in Leo during the month and is at western quadrature on the 2nd. It rises at 23:25 at the start of the month and at 22:30 by month’s end. It brightens from mag +0.7 to mag +0.2 during the month.

Jupiter is an evening object this month and moves from Aries into Pisces during the month. It rises during daylight hours during the month and sets at 02:45 by month’s end. It fades from mag -2.8 to mag -2.6 during the month.

Saturn is a morning object this month and can be found in Virgo. It rises at 04:00 at the start of the month and at 02:20 by month’s end. It maintains its brightness at mag +0.7 during the month.

Uranus is an evening object this month and is at eastern quadrature on the 22nd. It can be found in Pisces, SE of the Circlet asterism. It can be located half way between Omega (ω) Piscium (mag +4.0) and Iota (ι) Ceti (mag +3.5). It rises during daylight hours during the month and sets at 23:50 by month’s end. It fades from mag +5.8 to mag +5.9 during the month. Don’t expect to see much detail - it will be like a green-blue star.

Neptune is an evening object and can be found in Aquarius, near to Iota (ι) Aquarii (mag +4.3). It rises during daylight hours during the month and sets at 20:40 by month’s end. It maintains its brightness at mag +7.9 during the month. You’ll see even less detail than on Uranus: It will appear like a faint bluish star.

The Moon

The first quarter moon is on the 2nd with the full moon on the 10th. The last quarter moon is on the 18th with the new moon on the 24th.

There is a lunar eclipse on the 10th, but don’t get too excited. Sunset and moonrise are both at around 16:00, but the total phase of the eclipse will have already finished and the partial phase ends at 16:17 with the faint penumbral phase ending at 17:29. The next lunar eclipse in which mid-totality will be visible from Ireland is not until 2015 and it will probably be cloudy that day!! :evil:

On the evening of the 1st, the waxing crescent moon lies to the N of Neptune at around 20:00.

On the evening of the 3rd, the waxing gibbous moon lies 6° to the NW of Uranus at around 20:00.

On the evenings of the 6th and 7th, the waxing gibbous moon lies near to Jupiter. On the 6th, it lies to the N of the planet and on the 7th to its E. On both evenings, look around 20:00.

On the evening of the 8th, the waxing gibbous moon lies 5° to the W of M45 – The Pleiades at around 20:00.

On the evening of the 9th, the waxing gibbous moon lies to N of Aldebaran (Alpha (α) Tauri, mag +0.9) at around 20:00.

On the evening of the 15th, the waning gibbous moon lies 6° to the W of Regulus (Alpha (α) Leonis, mag +1.4) at around midnight.

On the morning of the 17th, the waning gibbous moon lies to the W of Mars at around 01:00.

On the morning of the 20th, the waning crescent moon lies to the S of Spica (Alpha (α) Virginis, mag +1.0) and to the SW of Saturn at around 05:00.

On the mornings of the 22nd and 23rd, the waning crescent moon lies near to Mercury. On the 22nd, it lies to the W of it and on the 23rd to its S. On both mornings look between 07:00 and 08:00 low in the East and BE SURE TO WATCH FOR THE RISING SUN ON THE HORIZON.

On the evenings of the 26th and 27th, the waxing crescent moon lies near to Venus. On the 26th, it lies to the W of it and on the 27th to its N. On both evenings, look around 17:00.

On the evening of the 28th, the waxing crescent moon lies 6° to the W of Neptune at around 19:00.

On the evenings of the 30th and 31st, the waxing crescent moon lies near to Uranus. On the 30th, it lies to the W of it and on the 31st to its N. On both evenings, look around 19:00.

Meteors

The best time to observe meteor showers is when the moon is below the horizon; otherwise its bright glare limits the number you will see especially the fainter ones. Below is a guide to this month's showers.

The Geminids peak during the day on the 14th with a ZHR of 120. It is therefore best to look on the nights of the 13th and the 14th for the shower. The radiant rises around 20:00, but a waning gibbous moon on both nights spoils the view. On the 13th, it rises at around 19:15 in Gemini and on the following night, at around 20:30 in Cancer.

The Ursids peak on the 22nd with a ZHR of 10. The radiant in Ursa Minor is visible as soon as darkness falls and the moon is out of the way, making for excellent meteor watching conditions.

There are additional minor showers this month, details of which can be found at meteorshowersonline.com/calendar.html or www.imo.net/calendar/2011

Comets

Comet C/2009 P1 (Garradd) is in Hercules in December, heading N during the month. It is visible as soon as darkness falls, low in the N and is currently around mag +7 with a predicted peak of mag +6 in the new year.

Finder charts and further information about the above comet and other fainter comets can be found at www.aerith.net , cometchasing.skyhound.com , www.ast.cam.ac.uk/%7Ejds/ , kometen.fg-vds.de/fgk_hpe.htm and www.rasnz.org.nz in the source list below.

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. Orion returns to our skies with M42 – The Great Orion Nebula and also Cancer with M44 – The Beehive Cluster.


General Notes

Always keep an eye out for Aurorae. The winter solstice is on the 22nd which sees the shortest day of the year and after this date the nights shorten and the days lengthen. This also sees the beginning of winter. 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. A new appendix has been added explaining some of the more technical terms used in the guide.

Clear Skies

Neill McKeown

Information Sources Used and Links

www.skyviewcafe.com ; Sky at Night Magazine Observing Guide and CD; www.aerith.net ; cometchasing.skyhound.com ; www.ast.cam.ac.uk/%7Ejds/ ; kometen.fg-vds.de/fgk_hpe.htm ; www.rasnz.org.nz ; Stardust Magazine;
Philip's Stargazing 2011; Patrick Moore's 2011 Yearbook of Astronomy; www.heavens-above.com ; www.spaceweather.com ; meteorshowersonline.com/calendar.html ; www.timeanddate.com/astronomy/ ; www.imo.net/calendar/2011 - International Meteor Organisation; seds.org/messier/ - The Messier Catalogue website; www.seds.org/messier/xtra/ngc/ngc.html - NGC Catalogue website; www.irishastronomy.org - Irish Federation of Astronomy Societies Website; irishastro.org.uk - Irish Astronomical Association website; www.eaas.co.uk - Northern Ireland Amateur Astronomy Society; www.koshko.com/almanako/oppositions_quadratures.shtml ;

Appendix

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.

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. When the radiant is quoted as “circumpolar”, it is never below the horizon and visible all night, otherwise the times quoted are when the constellation in which the radiant lies rises above the horizon in the East.

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.

The ° symbol in the guide is that for degrees. A degree is two full moon widths to give an idea for judging any distances quoted in the guide.

An asterism is a collection of stars seen in Earth's sky which form simple patterns which are easy to identify, i.e. the Big Dipper. They can be formed from stars within the same constellation or by stars from more than one constellation. Like the constellations, they are a line of sight phenomenon and the stars whilst visible in the same general direction, are not physically related and are often at significantly different distances from Earth.

Mag is short for magnitude which is the measure of an object’s brightness. The smaller the number, the brighter the object. The brightest object in the sky is the Sun at mag -26, the full moon is mag -12 and Venus the brightest planet is mag -4. The brightest stars are mag -1. If there is a 1 mag difference between two objects – there is a difference in brightness of a factor of 2.5 between the two objects. For example the full moon is eight magnitudes brighter than Venus on average which means it is 1,526 times brighter than Venus. Objects down to mag +6 can be seen with the naked eye under very dark skies.

Local time is always quoted in the guide and this means for November – February – universal time (UT)/GMT is used and for April to September – daylight savings time (DST, = GMT+1). For the months of March and October when the clocks go forward/back respectively, both times will be used and attention should be paid to any times at the end of these months for that change.

Deep Sky Objects such as galaxies, nebulae and star clusters are classified in catalogues such as the Messier catalogue for objects like M44 – M for Messier. Another example of a catalogue would the New General catalogue whose objects have the prefix NGC. There are links for websites to both catalogues in the section above.

The Planets

From Earth - Mercury and Venus are the inner planets in the solar system and Mars, Jupiter, Saturn, Uranus and Neptune are the outer planets. Below is a short guide as to how both the inner and outer planets move around the sun. The above pictorial guide should hopefully help in this.

The Inner Planets

These are best seen when at Greatest Eastern/Western elongation and are not visible when at either Inferior/Superior conjunction. Greatest Eastern elongation is when the inner planet is at its furthest point east from the sun as seen from Earth and visible in the evening sky in the West after sunset, Western elongation is when its at its furthest point west from the sun as seen from Earth and visible in the morning sky in the East before sunset. Inferior conjunction occurs when the inner planet is between the Sun and the Earth. Superior conjunction occurs when the inner planet is on the other side of the Sun as seen from Earth.

From our Northerly latitudes, the ecliptic, along which the planets move, lies at a very shallow angle to the horizon after sunset in the autumn and before sunrise in the spring. This means that any of the planets will be difficult to see when fairly close to the Sun in the evening sky in the autumn or in the morning sky in the spring. In particular, Mercury is more or less invisible from here when at Eastern elongation in the autumn, or at Western elongation in the spring, because it lies so close to the horizon and is never above the horizon except in daylight or bright twilight.

The normal cycle for an inner planet is Superior Conjunction – Greatest Eastern Elongation – Inferior Conjunction – Greatest Western Elongation - Superior Conjunction. After superior conjunction, the planet moves away from the Sun as seen from Earth and becomes visible in the evening sky after a period of time. It then moves past the point of Greatest Eastern Elongation and moves back towards the Sun as seen from Earth until a point when it is not visible and at Inferior Conjunction. After this the planet appears in the morning sky for a time, before again slipping into the Sun’s glare as seen from Earth. The duration of this cycle will depend on the planet’s closeness to the Sun, i.e. Mercury completes the above cycle in around 4 months.

The Outer Planets

These are best seen when at opposition and are not visible when at conjunction. Opposition occurs when the earth is between the sun and the outer planet. It is the best time to observe them because the planet is visible all through the night and it is due South and at its highest at about midnight. The planet is also at its closest point in its orbit to Earth – making it appear brighter. Conjunction occurs when the outer planet is on the other side of the Sun as seen from Earth.
If the planet is at or near it furthest point South along the ecliptic, then it won’t get very high in the sky even at opposition – just as the Sun never gets high in the sky in midwinter. This happens when opposition occurs near midsummer when the planet is opposite the Sun in the sky and in midsummer the Sun is high, so the planet will be low. The opposite of course applies in winter.
The normal cycle for an outer planet is Conjunction – Western Quadrature – Opposition – Eastern Quadrature - Conjunction. After conjunction, the planet moves away from the Sun as seen from Earth and becomes visible again. The planet from this point on rises earlier and earlier in the morning sky and eventually becomes visible in the evening sky. At Western Quadrature it is at its highest at sunrise and by opposition it is in the same position by midnight. By Eastern Quadrature, it is past its best and is at its highest at sunset, meaning it is rising in daytime and setting earlier and earlier until a point when it sets too close to the Sun as seen from Earth and is no longer visible. The duration of this cycle will depend on the planet’s closeness to the Sun, i.e. Jupiter completes the above cycle in around 13-14 months.