Pear Tree Observatory

Quite often, astronomers adopt a common name for a celestial object based on what it ‘looks’ like to them. Just as often it takes a very vivid imagination to see what the astronomer saw. Most of the common names were based on photography using fairly primitive cameras, equipment and techniques. Modern imagery taken with today’s CCD cameras and processed with computer software, look nothing like the common names associated with the celestial objects.

This is not one of those times.

This nebula quite obviously has a bubble blown in it. The star right of the bubble’s center and slightly above and right of the bright knot of gas is the guilty party. This young star has about 20 times the mass of the Sun and its energy output is several hundred thousand times that of our star. This is what is blowing the bubble in to the surrounding molecular cloud. The cloud of gas and dust is more dense on the right side of the bubble and thus is constraining the expansion more on that side.

 The nebula is located in the constellation Cassiopeia and is about 7,100 LY from the solar system. It was discovered in 1787 by German born British astronomer William Herschel. The bubble is about 7 LY in diameter and is expanding at a rate of 25 km/s (54,000 mph). The temperature at the bubbles boundary is about 8180 K (14,264 °F).

Since I am now waiting for the reprogrammed mount control panel to return I have some time to catch up with some archived imagery.

Once thought to be a supernova remnant, this nebula is now known to be an old planetary nebula. It was discovered by renowned astronomer George Abell in 1955. This is one of the first objects in the Sharpless catalog that I have imaged.

Using Palomar Sky Survey plates as source material, US Naval Observatory astronomer Stewart Sharpless published two catalogs of H II regions. The catalogs also contain some planetary nebulae and supernova remnants. This nebula is one of those and the 274th item in his second catalog.

The nebula is located in the constellation Gemini on the border with Canis Minor. It is estimated to be about 1500 light years distant. Deeper exposures than this show the nebula to have a braided appearance hence the Greek mythology Medusa name reference. The nebula is also cataloged as PK 205+14.1 in the catalogue of galactic planetary nebulae published by Czech astronomers Luboš Perek and Luboš Kohoutek.