On the northern hemisphere, December is the month when the days are shortest and the nights longest. This means the planets of our solar system and the stars of our galaxy are more noticeable than during other times of the year. If you are struggling to recognize and name the various constellations, you can get some help from applications like Stellarium.
Stellarium is free and open source software for generating realistic views of the sky on your Linux or Windows PC, similar to what you would see in a planetarium. It is great as an educational tool since it demonstrates various astronomic principles and provides the names and positions of stars, constellations, nebulae, and other galactic objects.
Stellarium is easy to use and renders skies just like you would see them with your eyes or binoculars. The basic use involves setting your current location on the earth so that the system can generate the animated views from that particular position. The mouse and arrow keys can be used to zoom in and out, to select objects, and to center on selected objects. The speed of the animations can be increased, decreased, and even reversed.
Stellarium's default catalogue includes some 600,000 stars. Additional catalogues are available with more than 200 million stars. It can display nebulae from the Messier catalogue, the milky way, and constellations from various cultures.
Now, if you ever dreamed of flying to those distant places, check out the software Celestia, and get ready for the ride. It's a free software package that graphically simulates celestial objects ranging from the earth and our solar system to distant constellations and galaxies. Simulating motions, light and shadow in three dimensions, the program generates amazing 3D images and allows the user to travel to any place in the universe and visit planets, comets, and other objects in the solar system.
You can follow the paths of satellites and space probes and observe to numerous stars and galaxies. It is based on the Hipparcos Catalogue and represents more than 100,000 stars and 10,000 galaxies. The software supports multiple star systems and uses advanced technologies for shading.
Celestia can be extended for example by adding high resolution images of planet surfaces. The program is licensed under GPL and can be downloaded from the Celestia web site. Versions are available for Linux, Windows, and Mac OS X. Stellarium can be freely downloaded for all major operating system as well.