When to photograph NGC 4609 (Coalsack Cluster)
NGC 4609, the Coalsack Cluster, is an open cluster in Crux, 5′ across at magnitude 6.9. Also listed as C 98.
When to photograph it
From 45° N it never rises.
From 35° S the best months are March to May, with up to 10.0 hours of astronomical darkness above 30° in April. It reaches 62° at its highest. It never sets from this latitude, so some imaging is possible all year.
Framing
Its long axis is 5′. It fills 35 to 80% of the short side of an APS-C sensor at about 3480 to 7950 mm, and of a full-frame sensor at about 5350 to 12220 mm.
Filters and the moon
Clusters are broadband targets, but bright ones tolerate some moonlight and light pollution. Short subs keep the brightest stars from clipping. The dark sky calendar shows which nights this month are moon-free where you are.
Plan it for tonight
Dates and times depend on your exact location. The imaging planner shows NGC 4609's altitude through tonight, its transit time and its distance from the moon. For sub length, use the exposure calculator.
Nearby targets
- C 99 Coalsack Nebula 1.4° away
- NGC 4755 Herschel's Jewel Box 3.0° away
- IC 2944 Running Chicken Nebula 7.5° away
- NGC 3766 Pearl Cluster 7.8° away
- NGC 4833 8.1° away
- NGC 4372 9.8° away
Gear that suits NGC 4609
NGC 4609 is only 5.4′ across, so it stays small in any amateur telescope. The longest focal length gives it the most pixels.
- Celestron C8 OTA 2032 mm f/10: fills 20% of an APS-C frame's short side View at High Point Scientific
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