Swan Nebula (M17, NGC 6618)

M17 was first named by Sir John Herschel and he called it the Omega Nebula, but he used the name Horseshoe and Omega interchangeably and it seems his later sketches emphasized the horseshoe shape. But somewhere along the line, it obtained the name Swan and all three names are still used today. Be that as it may, the Swan Nebula is about 15 light-years across and around 5000 light-years from Willingboro, NJ.

The Swan Nebula is a vast interstellar cloud of dust and gas giving birth to young, hot stars and has undergone three waves of star formation. During the first wave (2 to 5 million years ago) roughly 2000 stars were formed. This led to a increase in the density of the interstellar gas which, about 2 million years ago, caused the birth of an additional 12,000 stars, and these stars make up the huge NGC 6618 star cluster. However, these stars remain mostly hidden within the H II gas cloud. Even though the second wave is still ongoing, a third wave has started, and it, too, is still ongoing and has given birth to about 1000 stars so far.