The Christmas Tree Cluster
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	Common Name: The Christmas Tree Cluster Other Names: Cone Nebula RA: Dec Constellation: Orion Distance: Magnitude: Telescope: Orion ED80 Camera: SBig ST-8 Filters: CBVR Exposure: Date: 2006 Software acquisition: acquired with ccdsoft Processing Software: Maxim DL, Where: Tenby Observatory, Coonabarabran Lat: 31 16 35.05 S, Long 149 11 33.99 E, Elevation 547metres Notes: The Dumbbell Nebula is the brightest planetary nebula in the sky and the first one to be discovered in 1764 by Charles Messier. Planetary Nebula are the remains of the outershell of sunlike stars that have ended their lives as a white dwarf star. The name planetary nebula was given by Messier. In this nebula there are 2 shells of expanding gas. One is made of oxygen and is moving at 15km/sec. The other is a nitrogen shell moving at speeds of 30km/sec. Planetary Nebula aquire their name as they appeared to look like the planets neptune an Uranus through low power telescopes. Planetary Nebulae are quite common with 1500 known in our galaxy alone. They are relatively short lived phenomena and disspipate into the interstellar medium within 20 000 years. The Dumbbell is thought to be between 3000 to 4000 years old. Most of the light from planetary nebulae are emitted at 500.7nm and hence the blue - green colour. Our eyes see this colour very well however is dimmer photographically. At the time this was discovered there was no known element to create this emission line so an element was made up called nebulium. It was later found to be the forbidden lines of [OIII] double ionised oxygen. The central star is visible in this photo and has a magnitude of 13.5. It is type O7 so has a surface temperature of 85000 degrees C. It also has a fainter companion, a yellow star at magnitude 17.