NGC 6645
Scientific overview
NGC 6645 is an open cluster in the constellation Sagittarius. It shines at apparent magnitude 8.5 and spans about 5.4 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 6645
| Distance | 5,903 ly | SIMBAD · catalogued |
| Physical size (major axis) | 9.273087 ly | SIMBAD · derived |
| Radial velocity | -3.53 ± 0.29 km/s | SIMBAD · measured |
| Right ascension (ICRS) | 278.157917 deg | SIMBAD · measured |
| Declination (ICRS) | -16.918056 deg | SIMBAD · measured |
Full field-level provenance
- Distance: Centre de données astronomiques de Strasbourg (CDS) · SIMBAD · mesDistance · dist · 2021A&A...651A.104P · distance indicator: paral · catalogued value · source value 1810 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 · 2021A&A...647A..19T · direct catalogue measurement · retrieved 2026-07-11
- Right ascension (ICRS): Centre de données astronomiques de Strasbourg (CDS) · SIMBAD · basic · ra · 2021A&A...647A..19T · direct catalogue measurement · retrieved 2026-07-11
- Declination (ICRS): Centre de données astronomiques de Strasbourg (CDS) · SIMBAD · basic · dec · 2021A&A...647A..19T · 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.