(IAAC) Obj: M25 (IC 4725) - Inst: 12.5" f/6.5 Cave equatorial Newtonian

Observer: Dave Mitsky
Your skills: Intermediate (some years)
Date/time of observation: 6/18/98 05:33 UT
Location of site: Naylor Observatory, PA http://www.msd.org/obs.htm (Lat 40.1d N, 76.9d W, Elev 570')
Site classification: Exurban
Sky darkness: ~5.0 <Limiting magnitude>
Seeing: 8 <1-10 Seeing Scale (10 best)>
Moon presence: None - moon not in sky
Instrument: 12.5" f/6.5 Cave equatorial Newtonian
Magnification: 121x
Filter(s): None
Object(s): M25 (IC 4725)
Category: Open cluster.
Class: I 2 p
Constellation: Sagittarius
Data: mag 4.6  size 32.0'
Position: RA 18:31.6  DEC -19:15
M25 is the only Messier object with an Index Catalog designation.  It is a large
but scattered open star cluster that lies some 580 parsecs from the solar system.
It is sparsely populated (30 to 80 stars) and has a concentration of stars near
its center.  M25 is about 89 million years old and has a diameter of appromimately
20 light years.  Within the cluster is the Cepheid variable U Sagittarii, which
has a period of 6.75 days and varies between 6.3 and 7.1 magnitude.
M25 was seen as a large and sparse open cluster with 4 bright stars at its center. 
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