Astronomy Picture of the Day

Explanation: Moving left to right near the centre of this beautifully detailed colour composite, the thin, bright, braided filaments are actually long ripples in a sheet of glowing gas seen almost edge on. The interstellar shock wave plows through space at over 500,000 kilometres per hour. Catalogued as NGC 2736, its elongated appearance suggests its popular name, the Pencil Nebula. The Pencil Nebula is about 5 light-years long and 800 light-years away, but represents only a small part of the Vela supernova remnant. The Vela remnant itself is around 100 light-years in diameter, the expanding debris cloud of a star that was seen to explode about 11,000 years ago. Initially, the shock wave was moving at millions of kilometres per hour but has slowed considerably, sweeping up surrounding interstellar material. In the narrowband, wide field image, red and blue-green colours track the characteristic glow of ionized hydrogen and oxygen atoms.