M6 — Butterfly Cluster
Open Cluster in Scorpius
About
The Butterfly Cluster, an open cluster of about 120 stars in Scorpius, roughly 1,590 light-years away and about 94 million years old. Most of its bright stars are hot and blue; the brightest is the orange giant BM Scorpii.
Imaging tips
- At 970–1,620 mm on APS-C (1,490–2,480 mm on full frame) the cluster spans a third to half of the frame, about 25′ across.
- The cluster is bright: one imager stacked 244 twenty-second subs at ISO 3200 on a 130 mm refractor, about 81 minutes, from a Bortle 7 balcony.
- Declination is about −32°, so it is hard from the north: the same imager caught it only about 6° above the horizon, and its maximum altitude is about 8° from 50°N.
- Best around June; from 35°N it reaches about 23°, so a southern site helps a lot.
Facts
- Size
- 25′
- Magnitude
- 4.2
- Coordinates
- RA 17h 40.1m, Dec −32° 13′
- Framing, APS-C
- 970–1620 mm
- Framing, full frame
- 1490–2480 mm
- Best months
- Jun
- Peak altitude
- 8° from 50°N, 23° from 35°N