A portion of a nebula, made of variously colored layers of dust clouds. One upper layer is dark reddish dust which is dense and obscures light, in places so dense that it appears black. A middle layer holds pale clouds that are thick like curling wisps of smoke. They form a broad bow across the center of the image. Many small, bright stars lie throughout the nebula. They appear as blue, purple or red depending on depth. — Hubble · Caldwell 103 · ESA/Hubble & NASA, C. Murray

30 Dor Cluster

Nebula in Dorado · 160,000 light-years

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Type	Nebula
Constellation	Dorado
Right ascension	5h 38m 42s
Declination	−69° 06′
Object distance	160,000 light-years
Apparent magnitude	7.3
Apparent size	16′ (arc-minutes)
Approx. true diameter	744.7 light-years across
Also known as	C103 · NGC 2070 · Tarantula Nebula

Caldwell 103, popularly known as the 30 Dor Cluster, is a nebula (NGC 2070) in Dorado — a luminous cloud of interstellar gas and dust. It appears as number 103 in the Caldwell catalogue, Sir Patrick Moore's 1995 list of 109 bright deep-sky objects for amateur astronomers. It spans roughly 16 arc-minutes on the sky. At about magnitude 7.3, it is a rewarding binocular and small-telescope target.

Although it appears about 16′ wide on the sky, its real span is roughly 744.7 light-years — the difference is a measure of how far away it lies.

Observing 30 Dor Cluster

30 Dor Cluster lies in the constellation Dorado and is best placed in the evening sky around December. Its maximum altitude above the horizon depends on your latitude. It sits far enough south to be circumpolar from mid-southern latitudes, and never rises for most of the northern hemisphere. 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