Observing deep sky objects

How ”deep” is a deep sky object?

 

M7 (NGC 6475) as seen in the eyepiece of my C6 NGT, taken with Nikon D90 for a few minutes exposure

M7 (NGC6475) is the first deep sky object (DSO) that I could observe with my C6. It was in April 2008 when I noticed a crowd of tiny stars filling in the eyepiece between Shaula (in Scorpius) and Kaus Australis (in Sagittarius). M7 was already spotted by Ptolemeus in around 130 BC, but the first serious observation of this object was done by Hodiernes in 1654, and he counted 30 stars in the crowd.  Messier listed this object as number 7 in his list on May 23, 1764, and I could only see this object with my own eyes 244 years later. M7 is located about 800 light years. This means I had just seen a light from year 1200s! M7 remains my favorite DSO object until now.

The night sky in May 2008 was exceptionally clear. Before dawn, I scanned again the tail region of Scorpius towards Sagittarius. This is a DSO-rich region, the center of the Milky Way. On the “right’ side of M7, I noted two crowds which I believed were M8 (NGC6523 also known as Lagoon Nebula) and M20 (NGC6514 known as Trifid Nebula). Both DSOs are famous for their beautiful colors, which could be seen on long-exposure shots.    

I learned from Stellarium (www.stellarium.org), that M20 has its neigbor: M21 (NGC6531). M21, together with M20, was first noticed by Messier in 1794. Its distance from us is around 3,000 light years. That night, I saw the light from M21 touched my retina from year 1,000 BC!