by Anthony Ayiomamitis
Open cluster IC 4725 in Sagittarius depicted below is a rich dense cluster comprised of about 100 member stars which are of varying brightness and well detached from the rich background sky and includes a handful of giants of spectral type M. The cluster spans 32 arc-minutes in diameter, lies at a distance of 2,000 light-years away while spanning 19 light-years across and is dated at about 90 million years-old and as evidenced by the predominance of white hot stars in the image below and based on the presence of a δ-Cepheid variable (U Sgr). The cluster is best observed using low magnifications (50-100x) during mid-summer as it appoaches the southern meridian near midnight. IC 4725 was discovered by Swiss astronomer and mathematician Philippe Loys de Cheseaux (1718-51) and in 1745 and later observed by Charles Messier in 1764.
Technical Details:
Date: May 14, 2010 @ 02:30 - 04:45 UT+3
Location: Athens, Greece (38.2997° N, 23.7430° E)
Equipment: AP 160 f/7.5 StarFire EDF, AP 1200GTO GEM, SBIG ST-10XME, SBIG CFW10, SBIG LRGB filters
Integrations: LRGB @ 36:30:30:30 using 3-/6-min subs, 1x1 binning, 1.17"/pixel, -17.5d C
Further details are available here.