Checkmark Nebula
M 17
Scientific overview
Checkmark Nebula is a nebula in the constellation Sagittarius. It shines at apparent magnitude 7 and spans about 12.6 arcminutes of sky.
Observation guide
Guidance follows standard observing practice, derived from the object's real magnitude and position. A dark, moonless sky always helps.
Location in the sky
Precision measurements
Distances and velocities from SIMBAD · NGC 6618
| Distance | 5,916 ly | SIMBAD · catalogued |
| Physical size (major axis) | 21.68502 ly | SIMBAD · derived |
| Radial velocity | -44.577 ± 0.682 km/s | SIMBAD · measured |
| Right ascension (ICRS) | 275.195833 deg | SIMBAD · measured |
| Declination (ICRS) | -16.171667 deg | SIMBAD · measured |
Full field-level provenance
- Distance: Centre de données astronomiques de Strasbourg (CDS) · SIMBAD · mesDistance · dist · 2017AstBu..72..257L · catalogued value · source value 1814 pc · retrieved 2026-07-11
- Physical size (major axis): Centre de données astronomiques de Strasbourg (CDS) · derived (OpenNGC angular size × SIMBAD distance) · physical size = angular size × distance (small-angle); angular size from OpenNGC, distance from SIMBAD mesDistance · derived · retrieved 2026-07-11
- Radial velocity: Centre de données astronomiques de Strasbourg (CDS) · SIMBAD · basic · rvz_radvel · 2014A&A...562A..54C · direct catalogue measurement · retrieved 2026-07-11
- Right ascension (ICRS): Centre de données astronomiques de Strasbourg (CDS) · SIMBAD · basic · ra · 2009MNRAS.399.2146W · direct catalogue measurement · retrieved 2026-07-11
- Declination (ICRS): Centre de données astronomiques de Strasbourg (CDS) · SIMBAD · basic · dec · 2009MNRAS.399.2146W · direct catalogue measurement · retrieved 2026-07-11
Physical size is derived from the OpenNGC angular size and the catalogued distance (small-angle: size = angle × distance). This is a Galactic object: its Doppler shift is shown as a radial velocity, not a cosmological redshift. Fields a source did not provide are omitted, never invented.
Other objects in Sagittarius
| Object | Type | Mag | Size (′) |
|---|---|---|---|
| M 25M 25 | Open cluster | 4.6 | 14.1 |
| NGC 6530NGC 6530 | Cluster with nebulosity | 4.6 | 6 |
| M 23M 23 · NGC 6494 | Open cluster | 5.5 | 16.8 |
| Lagoon NebulaM 8 · NGC 6523 | Nebula | 5.8 | 45 |
| M 21M 21 · NGC 6531 | Open cluster | 5.9 | 6 |
| M 22M 22 · NGC 6656 | Globular cluster | 6.17 | 12.6 |
| M 55M 55 · NGC 6809 | Globular cluster | 6.49 | 12 |
| M 18M 18 · NGC 6613 | Open cluster | 6.9 | 6 |
Sources
The primary and reference sources this topic draws on.
- OpenNGCOpenNGC (M. Verga) — NGC/IC, Messier, and Caldwell catalogue data
Openly-licensed deep-sky catalogue: object types, positions, magnitudes, sizes, morphology, and cross-identifiers.