Blue and orange stars glitter across the image, interwoven with dark clouds of brown dust and bright, glowing regions of blue. — Hubble · Messier 17 · Image credit: NASA, ESA, and A. Kraus (The University of Texas at Austin); Processing: Gladys Kober (NASA/Catholic University of America)

Checkmark Nebula

Nebula in Sagittarius · 5,500 light-years

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Type	Nebula
Constellation	Sagittarius
Right ascension	18h 20m 47s
Declination	−16° 10′
Object distance	5,500 light-years
Apparent magnitude	7
Apparent size	12.6′ (arc-minutes)
Approx. true diameter	20.2 light-years across
Also known as	M17 · NGC 6618 · Lobster Nebula · Swan Nebula · omega Nebula

Messier 17, popularly known as the Checkmark Nebula, is a nebula (also catalogued as NGC 6618) in Sagittarius — a glowing cloud of interstellar gas and dust. It was recorded by Charles Messier in his famous catalogue of 110 deep-sky objects. It spans roughly 12.6 arc-minutes on the sky. At about magnitude 7, it is an easy target for binoculars and small telescopes.

Although it appears about 12.6′ wide on the sky, its real span is roughly 20.2 light-years — the difference is a measure of how far away it lies.

Observing Checkmark Nebula

Checkmark Nebula lies in the constellation Sagittarius and is best placed in the evening sky around June. Its maximum altitude above the horizon depends on your latitude. Lying near the celestial equator, it can be seen from both hemispheres. It is a comfortable target for binoculars and small telescopes. Note that the listed magnitude is spread across the whole object — diffuse galaxies and nebulae are often harder to see than the number alone suggests, so dark, moonless skies help a great deal.

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Sources

Position, magnitude and angular size from the OpenNGC catalogue (Mattia Verga).
Object identity cross-referenced with SIMBAD (CDS, Strasbourg).
Image credits and the original observation source are linked with each photograph.

Related objects

Orion Nebula — nebula
Ring Nebula — nebula
Eagle Nebula — nebula
Carina Nebula — nebula
Lagoon Nebula — nebula