Orion Nebula. Mosaic of images taken by the Hubble Space Telescope showing the Orion Nebula. The colors approximate to natural tones. This view, about 2.5 light years across, shows most of the visible light parts of the nebula. Just left of center are four massive, young stars known as the Trapezium. Ultraviolet radiation from these hot stars ionizes the gas of the nebula, causing it to glow. Stellar winds add to the pressure of this radiation to 'blow' dust and gas away from the center, forming large 'shock waves' such as the Great Wall (lower left). This is a mosaic of 45 exposures made during January 1994 to March 1995.