The "Great Square" forms the body of the Winged Horse. To connect the rest of Pegasus, you'll need to use the right side of the "square." Pegasus is flying upside down across the sky. From Markab (lower right corner) extends the head of the Winged Horse. The two front legs of Pegasus can be found off the star Scheat (upper right corner). The star Alpheratz is shared by two constellations, Pegasus and Andromeda. The star is actually considered to be a star of Andromeda.
51 Pegasi, a star in this constellation, is the first Sun-like star known to have an extrasolar planet. IK Pegasi is the nearest supernova candidate.
In Andromeda is the most famous deep sky object , M31.This is the Andromeda Galaxy, one of the most distant objects visible to the naked eye. It is an enormous spiral galaxy much like the Milky Way and is approximately 2.5 million light-years away.
Andromeda is the largest galaxy of the Local Group, which consists of the Andromeda Galaxy, the Milky Way Galaxy, the Triangulum Galaxy, and about 30 other smaller galaxies. Although the largest, it may not be the most massive, as recent findings suggest that the Milky Way contains more dark matter and may be the most massive in the grouping. However, recent observations by the Spitzer Space Telescope revealed that M31 contains one trillion (1012) stars, greatly exceeding the number of stars in our own galaxy. 2006 estimates put the mass of the Milky Way to be ~80% of the mass of Andromeda, which is estimated to be 7.1×1011 solar masses.
Bright Mars rises a little later that night, making its closest approach to Earth since 2005. Not often do we get a close look at Mars. It’s a small world to begin with, about half the diameter of Earth, and it spends most of the time far away on the other side of its orbit from us. Mars usually ranks as one of the most disappointing objects in amateur astronomy — a tiny, featureless orange blob. The only time we get a decent look at its surface markings, clouds, dust storms, and changing polar caps is for a couple of months every two years, when Mars comes closest (around its date of opposition).
This time around, Mars maxes out at 15.9 arcseconds when it passes closest to Earth on December 18th. That's nowhere near its record-breaking apparent diameter of 25.1" in August 2003. Even so, it's bigger than Mars will appear again until 2016.
Contrary to rumor, Comet 17P/Holmes has not faded away. From any dark starry-skied observing site, it remains visible to the naked eye. Although the comet is not as bright as it was when it exploded in late October, it makes up for its lack of surface brightness by sheer size: the comet is huge! It looks like a faint Moon-sized puff of cloud in the middle of the constellation Perseus--a really splendid sight.
For patient and wakeful people, the Geminid meteor shower can be viewed the night of December 13–14, with good prospects the following night as well.