The Sky for December 2013

The chart below shows the southern sky mid December at 9pm EDT. The same view will be seen at 10pm on Dec 1st and 9pm on Dec 31st.
December_2013_AllSky_Chart
Comet ISON (c2012 s1) will be visible in the eastern predawn skies starting about Dec 4th at 6am. For a more detailed description including finder charts, see the Comet ISON Finder for December 2013 article.

Pegasus and Andromeda are now south-west of the meridian (the line defining south) in the evening sky. The constellations due south are more challenging than others to identify as the figures they define are not as obvious as others and the stars they encompass are on the dim side for urban or semi-rural viewing (mag 3-5) . Perseus is at the zenith (directly overhead) and is identified by the relatively bright mag 1.8 star Mirfak, but otherwise the constellation is hard to identify. Cetus is a rather ramshackle arrangement of stars near the celestial equator (red line) and marked by the mag 2.5 star Menkar at the top left and mag 2.0 Deneb Kaitos on the bottom right. Among this group though is the tiny constellation Triangulum – a distinctive group of 3 stars in an elongated triangle about 15° south of the zenith. It measures a little less than 7° on the long side and only 2° at the base. Still, its easy to spot.

M33_Pinwheel_2010-02-08_v3_SJMThe galaxy Triangulum (M33) lies about 4° west of the point star Rasalmothallah. M33 is difficult to see , even though some people have claimed to see it unaided from a dark site. A more realistic expectation is to be able to see it from a relatively dark semi-rural site sky using binoculars or a medium sized telescope (100mm +).

M33 is part of our “Local Group” and is therefore in our celestial backyard.

South east in the sky is the constellation Taurus (the Bull) marked by the bright orange mag 0.8 Star Aldebaran. And to the East is the spectacular constellation Orion. Rigel, mag 0.15, marks the bottom right corner of Orion and Betelgeuse, a mag 0.43 red giant, marks the upper left corner. Notice the three star star which mark Orion’s belt and the 3 stars hanging down below the belt which outline the sword. The middle star of the Sword is a complex structure of many stars and the Orion Nebula. More about that next month.

Rigel is a challenging double star observable in amateur telescope and actually has a third member which is beyond the reach for amateurs. Although the companion is 9arc-sec away (large for doubles), it is challenging to see because Rigel, being the 7th brightest star, overwhelms its mag 6.8 companion. However, even with a small telescope (70-100mm) it is possible to separate the double under stable seeing.

The brightest object in the night sky (other than the moon) is the star Sirius (the Dog Star) measuring a blinding (lol) mag -1.47. Mid-month at 9pm it will be low in the eastern sky (ESE). Sirius is the brightest star in the sky – north and south and in all seasons.

There is a smudge of a tight grouping of stars between Taurus and the meridian. If you look closely, even without a telescope, you might be able to make some sense of the grouping. With binoculars it appears as a mini dipper composed of 9 bright stars and several fainter stars. This grouping is the Pleiades (M45) – an open cluster – also named the Seven Sisters (plus two parents). An open cluster is a group of star that not only look closely connected visually, but are in the same region of space and gravitationally bound to each other. The Pleiades spans 1.8° and so is best viewed in binoculars or a low power, wide-field telescope.
M45_Pleiades_2010-02-10_v3_SJM
A long exposure photograph shows a reflection nebula – light from the bright blue stars reflecting off dust in the surrounding area. To the south of the cluster, an emission nebula composed of ionized hydrogen gas glows faintly red. These features aren’t visible in a telescope though.

Jupiter_Finder_December_2013Looking high to SW, the Gemini twins Castor and Pollux are a pair of bright stars marking the constellation Gemini (mag 1.56 and 1.15). The third bright object near the twins is the planet Jupiter. For reference, the separation between Castor and Pollux is 4°. Jupiter lies about 11° west of Pollux.

With 7×50 binoculars on a tripod or held firmly against a stabilizing structure (tree or post) the moons of Jupiter can be clearly seen. Even in binoculars Jupiter will appear as a discernible disk, although no surface structures will be visible. A 70mm scope will start to show some of the horizontal cloud patterns. When viewed through a 280mm scope (11″ SCT) some structure to the cloud patterns begins to emerge.

The Double Cluster (NGC 869 and 884) is still a feature of the the north sky and will continue to be visible for several more months. Double_Cluster_Finder_1_December_2013
I like objects that catch my attention with the unaided eye and then show up as as impressive object in binoculars or a small telescope. The Pleiades and the double cluster are great examples. While casually scanning the northern sky at this time of year, my attention is always drawn to the faint, just discernible fuzzy patch between the constellation Cassiopeia and Perseus (the bright star Mirfak).

Double_Cluster_Finder_2_December_2013
Looking north, Cassiopeia will be an upside-down /W/ with Mag 2.6 Ruchabah marking the right point of the upside down /W/. The bright star Mag 1.8 Mirfak will be close to the Zenith. The double cluster lies approximately mid-way between these two reference points and a little closer to Cassiopeia. Just point the binoculars at either of the two reference stars and scan towards the other.

Planets and the Moon

Uranus is a little east of due south by mid month and positioned at declination 2° so is well placed to view it. It’s magnitude 5.8 so requires a small telescope. It’s small so the disc is not discernible but it will appear blueish green in large telescope.

Neptune is further to the west and lower in that sky at declination -11°. At mag 7.9 it will be challenge to find in medium sized telescopes.

Jupiter mentioned above is in the eastern sky. Its declination is 22° and mag -2.6. By mid-month is transits at 2:45am. So its too early to good views. Wait a couple of months when it will be high in the south in the late evening sky.

At the start of the month Venus is low in the ssw sky at declination -24° (elevation 15° at 6pm). It’s about as bright as it gets at mag 4.65 and outshines everything except the moon. By late month Venus has moved closet to the sun and sets at 6:45pm in the sww sky.

By the end of December, Saturn will be seen in the pre-dawn sky. It will be few months yet before even an early morning view will high enough in the sky for good seeing.

The new moon is on Dec 3rd. Try looking for the slim crescent on Dec 5th. Dec 4th is a little too early with the moon only 1.3days old. The 1st quarter is on the 10th. This is best time to view the moon as it’s high in the sky in the evening and the terminator provides high contrast views of craters and other features. The full moon in on Dec 17th, but it will appear full on the 18th as well. The 3rd quarter is on Dec 25th.

Telescope Targets

Objects suitable for larger diameter scopes from a dark site.

Photography Targets

Objects suitable for astrophotography