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Caldwell 17
Hubble · Caldwell 17 · NASA, ESA, and A. Ferguson (University of Edinburgh, Institute for Astronomy); Processing: Gladys Kober (NASA/Catholic University of America)

Caldwell 17

Galaxy in Cassiopeia · 2.4 million light-years

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TypeGalaxy
ConstellationCassiopeia
Right ascension0h 33m 12s
Declination+48° 31′
Object distance2.4 million light-years
Apparent magnitude9.7
Apparent size9.4′ (arc-minutes)
Approx. true diameter6,562 light-years across
Also known asC17 · NGC 147
Caldwell 17 is a galaxy (NGC 147) in the constellation Cassiopeia — a distant island of stars far beyond the Milky Way. It appears as number 17 in the Caldwell catalogue, Sir Patrick Moore's 1995 list of 109 bright deep-sky objects for amateur astronomers. It spans roughly 9.4 arc-minutes on the sky. At about magnitude 9.7, it shows up in a small backyard telescope.

Although it appears about 9.4′ wide on the sky, its real span is roughly 6,562 light-years — the difference is a measure of how far away it lies.

Observing Caldwell 17

Caldwell 17 lies in the constellation Cassiopeia and is best placed in the evening sky around September. Its maximum altitude above the horizon depends on your latitude. It is best placed for observers in the northern hemisphere, and sits low for those far south. A small backyard telescope will show it; binoculars may hint at it under dark skies. 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.

See Caldwell 17 in Universe Finder

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