May 25, 2008

After a long, long siege of rainy, cloudy weather and clear nights ruined by a bright moon, clear dark skies return.

The LXD75 was aligned with Polaris and Vega, now rising above the tree line by 9:30pm.

M20

I decided to use the DSI-C (a color camera) and the focal reducer to capture a wide-angle view of the nebula. While the DSI Pro (a monochrome camera) is much more sensitive and give better resolution, the Tridid's beautiful interplay of colors simply demands a color image.

M20 is composed of both a bright emission nebula (the red part) and a dimmer reflection nebula (the blue-ish cloud below the red), which actually surrounds the emission nebula. Messier discovered the nebula in 1764, describing it as a cluster of young stars surrounded by a nebula. Herschel noted its segmented nature – caused by dark dust lanes which extend in front of the emission nebula - and listed it as four separate items. It was Herschel who gave the nebula is famous name.

Estimates on the nebula's distance vary, but 5,200 light years is a commonly accepted number.

M17

Commonly known as the “Swan Nebula” because of its distinctive shape, M17 was first discovered by Phillippe Cheseaux some years before Messier rediscovered it and listed it in his catalog in 1764.

The nebula is illuminated by hot, young stars inside it. Estimated to be 40 light years across and about 5,000 light years away, the Swan is occasionally visible to the naked eye as a faint smudge in the constellation called Sagittarius.