IC 4628 (Nebula)
A large glowing cloud in Scorpius north of Zeta Scorpii, lit by the young stars of Scorpius OB1. Its distance is borrowed from the cluster NGC 6231 in the same group, 1.6° away.
Nebula in Scorpius.
Can you see it from Guyana?
From Georgetown (6.8° N) it climbs to 43° above the southern horizon at its highest; from Lethem (3.4° N), to 46° above the southern horizon. It is highest at midnight on the night of 3 Jun, in the middle of its season. The page works out tonight's rise, highest point and set for both towns in Guyana time (UTC-4), and where the Moon is.
What you'll see
- Your eyes: Not visible to the eye. It lies 6.3° south of Larawag.
- 10x50 binoculars: Hard: a faint glow from a dark site, near NGC 6231.
- A small telescope (80 to 100 mm): Too big and faint for most telescopes; a camera target.
- A camera: Spans about 40% of an APS-C frame at 400 mm (field 3.4° × 2.2°); needs a tracking mount. The photo above also shows NGC 6231, 1.6° away.
How big, how bright, how far
- Size on the sky: 89.1′ × 58.9′, 2.9 Moons across (the Moon is about 31′ wide).
- Distance: 5,100 light-years. The light reaching your eye left it about 5,100 years ago.
- True size: 130 light-years across its catalogued outline; light crosses it in 130 years.
Apparent size from OpenNGC (Mattia Verga), CC-BY-SA-4.0.
What it is made of
- Type
- Emission nebula
What is in it, not measured:
- Ionised hydrogen: glows red where hot stars light it
- Helium and heavier gases: with traces of oxygen, nitrogen and sulphur
- Dust: in dark lanes
- Young hot stars: that light it
How we know: Distance from the young stars of Scorpius OB1 around it: its own star HD 152723 has a 31% parallax error, so the distance of the NGC 6231 cluster at the heart of the same group is borrowed: Hunt & Reffert 2024, A&A 686, A42 (Gaia DR3 cluster catalogue, VizieR J/A+A/686/A42), retrieved 2026-10-21: NGC 6231 1,553 pc; Yalyalieva et al. 2020 (arXiv:2004.13418) trace one young population from IC 4628 down to NGC 6231. True size: the apparent size times the distance (apparent size: OpenNGC (Mattia Verga, CC BY-SA 4.0), commit 4e2398a2).
More deep-sky objects: Rho Ophiuchi Nebula (IC 4604) · Lagoon Nebula (M8) · Trifid Nebula (M20) · R Coronae Australis Nebula (NGC 6729) · Omega Nebula (M17) · Eta Carinae Nebula (NGC 3372)