M4
Globular Cluster in Scorpius
About
The nearest globular cluster to the Solar System, about 6,000 light-years away in Scorpius, and about as wide on the sky as the Moon. It lies 1.3° west of Antares and has a bar of stars across its core.
Imaging tips
- At 930–1,550 mm on APS-C (1,430–2,380 mm on full frame) the cluster spans a third to half of the frame. It is loosely concentrated, and modest telescopes begin to resolve its stars.
- Antares is 1.3° away, beyond the 57′ field at those focal lengths. A wide refractor puts both in view, and shows the Rho Ophiuchi gas around the star.
- Low altitude is the main problem: it stays below 14° from 50°N. One team shot it just above the mountains and wished they had imaged it higher and longer.
- One imager took 30 s LRGB subs for 1 h 15 min with a 70 mm refractor; the cluster looked fine, but the nebulosity came out weak.
- Best in May and June.
Facts
- Size
- 26′
- Magnitude
- 5.6
- Coordinates
- RA 16h 23.6m, Dec −26° 32′
- Framing, APS-C
- 930–1550 mm
- Framing, full frame
- 1430–2380 mm
- Best months
- May, Jun
- Peak altitude
- 14° from 50°N, 29° from 35°N
Nearby
- Cr302 · 0.6′ away