Galactic Plane
The Galactic Plane is the plane in which the majority of a disk-shaped galaxy's mass lies. In the case of the Milky Way, it is the plane of the galaxy's disk, encompassing the spiral arms, stars, gas, and dust. This plane is used as the reference for the galactic coordinate system.
Source: asd.gsfc.nasa.gov
APODs including "Galactic Plane"
NGC 4565: Galaxy on the Edge
28/04/2009
Is our Galaxy this thin? We believe so. Magnificent spiral galaxy NGC 4565 is likely similar to our own spiral galaxy, but viewed edge-on from far away. Also known as the Needle Galaxy for its narrow profile, bright NGC 4565 is a stop on many telescopic tours of the northern sky as it lies in the faint but well-groomed constellation Coma Berenices. This sharp color image reveals the galaxy's bulging central core dominated by light from a population of older, yellowish stars. The core is dramatically cut by obscuring dust lanes which lace NGC 4565's thin galactic plane. NGC 4565 lies about 30 million light-years distant and spans over 100,000 light-years in diameter. Visible through a small telescope, some sky enthusiasts consider NGC 4565 to be a prominent celestial masterpiece Messier missed.