M42, also known as the Orion Nebula or the Great nebula of Orion, is a gigantic cloud of gas and dust over 30 light years in diameter. It is located about 1,500 light years from the Earth. M42 is a site of active star formation, and the stars within this nebula cause it to shine with a magnitude of 4. This makes it one of the few nebulae that can be seen with the naked eye. The most famous of these stars is a small cluster known as the Trapezium.