NGC 6664 rating MEDIUM
open cluster in Scutum
RA 18h 36.7m Dec -08d 13.5' (2000)
Magnitude 7.8
When it comes to open star clusters, the small Milky Way constellation of Scutum is best known for M11. But in fact, there are at least a dozen open clusters in Scutum. One of these, NGC 6664, is an easy find because it sits just 20' east of 4th-magnitude Alpha Scuti.
NGC 6664 is a sparse cluster embedded in a rich part of the Milky Way, and covers an area about one quarter that of the full Moon. It looks like a partially resolved cloud in a 2.4-inch refractor. In a 6-inch you can see about 35 stars in a 25' area, with the brighter ones mostly on the north side.
A 10-inch scope at medium powers will show 60 or more stars, all fainter than 10th magnitude. Overall, the cluster has no central condensation and is highly-elongated north to south.
A study by Halton Arp of reddening of cluster members reveals a cluster distance of 1,450 parsecs, or about 450 light-years. The cluster contains a Cepheid variable star as a member: EV Scuti varies from 9.9 to 10.3 over a 3.09-day period.
NGC 6629 rating HARD
planetary nebula in Sagittarius
RA 18h 25.7m Dec -23d 12.3' (2000)
Magnitude 11.3
This challenging little planetary lies in Sagittarius roughly 2 degrees north, and just a bit west, of 3rd-magnitude Lambda Sgr, which marks the top of the Sagittarius teapot. Closer in, you'll find it 7' south of 8th-magnitude SAO 186800. This is a difficult planetary for small scopes, even through an OIII filter, but it can be detected with averted vision.
In larger scopes, such as an 8-inch at 110x, NGC 6629 looks like a very faint round diffuse ball with no discernable edges. In a 10-inch scope at 100x, it looks like a 10th-magnitude star. At 250x its about 15" in diameter, fading abruptly at the edge.
The magnitude of the central star is 12.9
