M39
Open Cluster in Cygnus
About
A loose open cluster in Cygnus, about 1,010 light-years away and 280 million years old, spanning roughly the width of the full Moon. About two dozen members show in a small telescope at low power.
Imaging tips
- About 32′ across: 760–1,260 mm on APS-C frames it with space around it, and its bright stars stand out against a dense Milky Way background.
- Forgiving on time: one imager got a good result from about an hour of 3-minute subs on a fast f/3.9 astrograph; another stacked 3.6 hours of 7.5-minute RGB subs at f/7.
- Rich Milky Way star fields surround it, so a wider frame gives a natural setting; the Cocoon Nebula (IC 5146) is nearby but one write-up says it will not share the view.
- No nebulosity, so broadband or a one-shot colour camera is enough. Best in July and August.
Facts
- Size
- 32′
- Magnitude
- 4.6
- Coordinates
- RA 21h 31.6m, Dec +48° 15′
- Framing, APS-C
- 760–1260 mm
- Framing, full frame
- 1160–1930 mm
- Best months
- Jul, Aug
- Peak altitude
- 88° from 50°N, 77° from 35°N