OVERVIEW
] NEBULACheckmark Nebula is a nebula in the constellation Sagittarius, 5500 from Earth, shining at apparent magnitude 7.00 (). It is catalogued as Lobster Nebula, Swan Nebula and HD 168520, among 11 designations in total. It was discovered in 1745.
One of the brightest and most massive star-forming regions in the galaxy, its glowing bar of gas shaped like the swan it is named for.
- WHAT IT IS
- Nebula
- HOW FAR
- 5500
- HOW BIG ON THE SKY
- 12.6
- HOW BRIGHT (V)
The light arriving now left it that long ago.
About 0.4 of the full Moon's width.
Binoculars reach it; the naked eye does not.
IMAGES
] 4 FRAMES- ESO/INAF-VST/OmegaCAM
CC BY 4.0 - European Southern Observatory
CC BY 4.0 - NASA, ESA and J. Hester (ASU)
Public domain - NASA/SOFIA/Lim, De Buizer, & Radomski et al.; ESA/Herschel; NASA/JPL-Caltech
CC0
OBSERVING
] FROM WHERE YOU AREWhat it takes to see Checkmark Nebula for yourself. Everything in this part of the page is worked out for a real horizon, a real night and the equipment you say you have.
Say where you are, and this line says when Checkmark Nebula is worth going out for.
THROUGH AN EYEPIECE
] 150 MM TELESCOPE · 25 MM EYEPIECEToo faint for your eyes alone. Binoculars reach it. Checkmark Nebula covers 12.6′ of sky against a of 1.08°, so at 48× it is comfortably framed.
- 48×
- 1.08
- 1.25
- 13.0
- SIZE ON THE SKY
- 12.6
- FILLS OF THE FIELD
- 19% of the width
- APPARENT MAGNITUDE ()
- 7.00 · within reach
Checkmark Nebula is not a point of light, so the limit above is the wrong one to hold it against: the same brightness spread over 12.6′ of sky is harder than a star of it, and goes first. Catalogued sizes are measured to a photographic contour, and the part an eye sees is usually smaller.
APPARENT PLACE
] EQUINOX J2026.7Where a telescope has to be pointed today, which is not quite where the catalogue records the object: the coordinate grid itself has turned since the year 2000 the catalogue is referred to.
- RIGHT ASCENSION
- DECLINATION
- GRID TURNED SINCE
- 22.3
- PROPER MOTION SINCE
- none published
Computed for 2026-08-27 00:00 UT. No proper motion is published for Checkmark Nebula, so nothing here moves the object; what separates this from the catalogued position above is the coordinate grid turning under it — about fifty arcseconds a year of precession since 2000, and the small nodding of the Earth’s axis on top of that. Aberration and refraction are not included, and neither is parallax; each is under an arcminute, which is also about as well as the catalogued position is known. The same figure for any date.
CATALOG DATA
] 10 FIELDSThe raw catalogue values, as the source published them, with the error bars where one was published — sorted by what each set of figures is about rather than by the order they happened to be stored in.
HOW BRIGHT IT IS
What the light adds up to, measured through one filter at a time. A magnitude is a brightness on a backwards scale — the smaller the number, the brighter the object.
- Apparent magnitude ()
- Apparent magnitude ()
WHERE IT IS AND HOW IT MOVES
Position, motion across the sky and the size it covers on it. These are measurements of the object as seen from here, so every one of them depends on where here is.
- Radial velocity
- −45
- Redshift (z)
- Major axis
- 12.6
WHEN IT WAS FOUND
Who first saw it, from where, and by what method.
- Discovered by
- Jean-Philippe de Cheseaux
OTHER NAMES AND NUMBERS
The identifiers other catalogues file this object under, for anyone joining this data to theirs.
- Also known as
- Horseshoe Nebula, Lobster Nebula, Swan Nebula
- OpenNGC type code
- Neb
- Wikidata item
- Q11357
- Wikipedia article
- Omega Nebula
ALSO KNOWN AS
] 11 DESIGNATIONS- Common name Checkmark Nebula
- Common name Lobster Nebula
- Common name ω Nebula
- Common name Swan Nebula
- HD HD 168520
- IAU cluster C 1817-162
- LBN LBN 60
- Lynds LBN 015.28-00.67
- Messier M 17
- MWSC MWSC 2896
- NGC NGC 6618
LOOK IT UP ELSEWHERE
] 3 SERVICESEach link carries the identifier printed beside it. Nothing on this page is a measurement of our own, so a number that disagrees with one of these is worth reporting — and a service that has never catalogued this object under this name will say so plainly.
- SIMBADM 17
Cross-identifications, measured values and the reference behind each of them.
- ADSobject:"M 17"
Papers indexed against this object rather than against the string, newest first.
- VizieR378″ around 275.1963 -16.1715
Every published table with a row at this position, searched by coordinates rather than by name.
CITE THIS PAGE
] DR1This page is live and its numbers move when an upstream refreshes, so the citation names the release the rows belong to rather than the day you read them. The release itself is frozen, republished as a bundle, and is what a data-availability statement should point at.
SpaceCatalog. Checkmark Nebula [catalogue entry]. Data release DR1 (2026-08-21). https://spacecatalog.org/object/m17
@misc{spacecatalog_m17,
author = {{SpaceCatalog}},
title = {{Checkmark Nebula}},
howpublished = {SpaceCatalog, data release DR1 (2026-08-21)},
year = {2026},
url = {https://spacecatalog.org/object/m17},
note = {Catalogue entry, data release DR1 (2026-08-21). Values from OpenNGC.}
}The values above were taken from OpenNGC — CC-BY-SA-4.0. Citing this page does not replace citing that catalogue, and its licence is share-alike: the terms reach whatever you build from these rows.
RECENT ACTIVITY
] 1 ITEMS- The early evolution of young massive clusters. II. The kinematic history of NGC 6618 / M 172023-11-07 · arXiv · PAPER · Mitchel Stoop, Annelotte Derkink, Lex Kaper, Alex de Koter, Ciaran Rogers, Maria Claudia Ramírez-Tannus
arXiv · UPDATED DAILY