Skynotes for December 2012

jfSDAS

hi all,

Hope you've got that Santa list written

There's plenty of celestial goodies though this month and as always, feel free to get in touch if any queries about the sky notes or errors found.

Clear skies,

John


Skylights for December2012
This month is a busy one for sky watchers with Jupiter well placed for viewing, a nice comet to round out the year, some asteroids to sweep up, meteors galore from the Geminids, and a celestial ballet in the morning sky. As such, we are not picking one particular highlight but instead giving a detailed overview of these and other celestial happenings in December.


The Sun
The winter solstice falls this year on December 21st at 11:12am. Although the shortest day of the year, this is not the date of latest sunrise from Ireland. That isn't until the 29th at 8:41am while the earliest sunset is December 13th at 4:06pm. Why is this so?

Well, the difference is mostly due to the Earth's axial tilt and our motion around the Sun. Although our timepieces regulate a standard 24 hour day, the length of time between when the Sun is exactly due south one day and the next can vary (what is called the solar day). This difference is well known to sundial lovers and can lead to a dial running fast or slow compared to a standard clock. More details about this intriguing phenomenon can be found at http://curious.astro.cornell.edu/question.php?number=208


The Moon
Last Quarter Moon falls on December 6th, New Moon occurs on the 13th, First Quarter is on the 20th, and the last Full Moon of the year is on December 28th.

Observers along a line from Mayo to Wexford will see a grazing occultation of the magnitude 5.6 star 45 Cancri at 2:55am on the morning of December 31st.

• On the morning of the 10th, the waning crescent moon lies 6° to the lower right of Saturn before sunrise.
• On the morning of the 11th, the waning crescent moon lies 4° to the right of Venus before sunrise.
• Look low in the south-western sky as dusk falls on the evening of the 15th to find Mars as a magnitude 1.2 "star" about 6½° below the Moon.
• On Christmas night, the waxing gibbous moon lies 3° to the right of Jupiter during the early evening. The pair are nestled amongst the stars of Taurus at the moment and the nearby Pleiades cluster enhances the scene.
  
  

The Planets
Mercury is well placed in the morning sky at the beginning of December and can be seen low in the south-east before sunrise up to about mid-month. The diminutive planet reaches greatest western elongation(20.6°) on the 4th. It shines at magnitude -0.4 and rises at 6am on this date. Mercury is to the lower left of Venus during its visibility period but is much fainter than the dazzling Morning Star.

Venus dominates the crisp December mornings but is rising slightly later as the month progresses so that by the 31st it will still be quite low when the sky brightens. During the lead up to this though it willbe unmistakable and is joined by both Mercury and Saturn to delight even the most casual observer. Venus shows a 94% sunlit disk through a small telescopeby the end of the year but don't expect to see any detail due to the planet's opaque atmosphere.

Mars moves from Sagittarius into Capricornus during December and remains a dim magnitude 1.2 object very low above the south-western horizon after sunset. The planet is setting around 6pm and there is little of interest to see on the tiny disk for the telescopic observer.

The month belongs to Jupiter which reaches opposition in Taurus on December 3rd. The magnitude -2.8 planet is then 609 million kilometres distant and the disk measures 48.25 arcseconds in diameter. The planet is currently retrograding and passes close to Aldebaran. Jupiter's current declination of +21° means it lies almost 60° above the horizon when due south and can be observed throughout the hours of darkness. The gas giant spins in less than ten hours which affords the opportunity follow it through a complete rotation in a single night this month. Keen observers therefore often attempt to sketch or image Jupiter in a single session to create a strip chart or movie clip. Any takers this year?

Saturn is also a morning object this month and crosses from Virgo to Libra in early December. The magnitude 0.6 world lies 5° to the upper right of Venus on the 1st and the pair slowly drift apart over the next few days. Telescope users will see the magnificent ring system tipped 19° Earthward at the moment.


Comets
C/2012 K5 (LINEAR) is expected to reach a peak brightness of around magnitude 8 over the Christmas period. It starts the month though as a magnitude 9.1 object nestled in the northwest corner of Coma Berenices and crosses into Ursa Major by the end of the first week of December.The comet then spends nearly two weeks gliding along the Plough asterism from the tip of the handle (eta UMa) to the top rightmost star of the share (alpha UMa)and will be visible throughout the hours of darkness during this time. By Christmas Day the celestial snowball should be near maximum brightness and easy in giant binoculars or a small telescope. The comet's trajectory then continues into Lynx where it ends the year.

More details can be found at http://www.ast.cam.ac.uk/~jds/or http://kometen.fg-vds.de/fgk_hpe.htm


Meteors
The Geminids are now considered the richest shower of the year and peak on the evening of the 13th at around 23h. Maximum coincides with New Moon, making for perfect observing conditions. The rates are quite rich (ZHR 110) because the stream has been perturbed in recent years towards Earth. However, the dynamics will change again in a few decades when a gravitational tussle with Jupiter will cause the denser regions of the swarm to miss Earth and the current rates to decline.

The Ursids peak on the morning of the 22nd at around 08h with a ZHR of 10. The radiant near Kocab is circumpolar but the waxing gibbous moon in Pisces does not set until after 2:30am on the morning of the 22nd, making observation of all but the brighter meteors difficult until the small hours.

Details of meteor showers during the year can be found at http://www.imo.net or http://meteorshowersonline.com/calendar.html


Asteroids
It's a busy month for tracking asteroids as 1 Ceres and 4 Vesta both reach opposition in Taurus, while 9 Metis can be spotted too. Moderate-sized telescopes will also be able to follow the near-Earth asteroid 4179 Toutatis as it swings within 0.046 astronomical units of our planet.

4 Vesta is at opposition on December 9th and is an easy magnitude 6.3 object in binoculars. You may have to plot its position over a few nights though to be sure you've snared the asteroid. It can be found mid-way between Aldebaran and zeta Tauri on the night of opposition, and within 1° of the magnitude 4.9 star 104 Tauri.

9 Metis shines at magnitude 8.9 this month and lies just two arc-minutes southwest of the magnitude 5.8 star 47 Geminorum on the night of December 12th. An opportunity to spot the first asteroid to be discovered from Ireland perhaps?

The dwarf planet 1 Ceres can also be found in Taurus and reaches magnitude 6.6 when at opposition on the 18th -- this is the object's best apparition until 2018. See http://www.skyandtelescope.com/observing/objects/asteroids/Ceres-and-Vesta-July-2013-148149915.html for Ceres and Vesta finder charts.

4179 Toutatis is an elongated chuck of rock measuring 4.5 x 2.4 x 1.9 km that comes close to Earth every four years. Not all approaches are at the same distance and this one will be about 6.9 million kilometres. The asteroid is gravitationally perturbed by both the Earth and Jupiter though which may ultimately cause it to be ejected from the solar system. Closest approach is during daylight hours on the 12th from Ireland (when the asteroid is magnitude 10.9) but you can follow Toutatis during the evenings of the encounter period as it sails through Cetus, then briefly clips Pisces before continuing across the celestial sea monster into Aries, where it can be found as a magnitude 10.3 object on December 16th. A finder chart is on page 53 of the December 2012 issue of Sky and Telescope magazine.


Spaceflight
The Chinese Chang'e 2 spacecraft is expected to make a close flyby of 4179 Toutatis on December 13th. The probe was first launched in 2010 to conduct research and map the lunar surface from orbit. It then departed for the Sun-Earth L2 Lagrangian point in June 2011 as a test of the Chinese deep-space tracking network. Chang'e 2 then left the L2 point and was put on a course to encounter 4179 Toutatis later this month.

The ultra-secret US Air Force X-37B space plane is next expected to be launched on December 11th for another long duration flight. Amateur astronomers have successfully tracked it in orbit on previous missions but details of the craft's purpose are in the realm of the internet's conspiracy rooms. However, more reasoned heads speculate these technology tests are to help consolidate the military's own space-based reconnaissance program and showcase the ability to manoeuvre in orbit -- a problem with ordinary spy satellites whose track can be predicted and then targeted by unfriendly nations. More on the X-37B at http://www.bbc.com/future/story/20121123-secrets-of-us-military-spaceplane

See http://en.wikipedia.org/wiki/2012_in_spaceflight and also the Planetary Society blog at http://www.planetary.org/blogs/emily-lakdawalla/ after the start of each month for updates on the status of unmanned missionsacross the solar system.


Exploring further
The following web sites are also a great resource for information about what’s on view in our skies during the month;

www.skymaps.com — superb charts you can download

www.jb.man.ac.uk/astronomy/nightsky/

www.guardian.co.uk/science/series/starwatch

www.telegraph.co.uk/news/newstopics/nightsky/

www.heavens-above.com — space station predictions

http://dcford.org.uk/index.php -- the Digital Astrolabe

http://earthsky.org/astronomy-essentials -- absolutely essential reading for what's up

www.jodcast.net — monthly night sky tour for MP3 players

www.spaceweather.com – details of transitory events during the month as well as aurora alerts

http://spaceflightnow.com — mission launches and other news (click “Launch Schedule” too)

www.skymania.com – astronomy and space news

www.universetoday.com – more astronomy and space news

www.nightskyobserver.com/the-sky-this-month.php -- Gary Nugent’s astronomy and space news

ZeRoY

Awesome summary, thanks!! Defo keeping an eye out for Geminids and C/2012 K5 Linear

Zubeneschamali

jfSDAS wrote: »

Saturn is also a morning object this month and crosses from Virgo to Libra in early December. The magnitude 0.6 world lies 5° to the upper right of Venus on the 1st and the pair slowly drift apart over the next few days.

It's a lot closer than that right now, it's less than a degree away!

Very cool sight.

jfSDAS

Zubeneschamali wrote: »

It's a lot closer than that right now, it's less than a degree away!

Very cool sight.

Aaarrgghhh!!! I should really read my own sky notes If I had looked back on November's post it would have helped

Cheers for pointing out the even closer pairing of the two planets this week!

John

DubOnHoliday

Great notes!!! I'm looking forward to tracking that Comet.