NGC 2403

NGC 2403 (also known as Caldwell 7) is an intermediate spiral galaxy in the constellation Camelopardalis. It is an outlying member of the M81 Group,[2] and is approximately 8 million light-years distant. It bears a similarity to M33, being about 50,000 light years in diameter and containing numerous star-forming H II regions.[3] The northern spiral arm connects it to the star forming region NGC 2404.[2] NGC 2403 can be observed using 10×50 binoculars.[2] NGC 2404 is 2000 light-years in diameter, making it one of the largest known H II regions, even larger than Tarantula Nebula in Large Magellanic Cloud. This H II region represents striking similarity with NGC 604 in M33, both in size and location in galaxy.

NGC 2403
A Hubble Space Telescope (HST), and Subaru image of NGC 2403. NGC 2404 is visible
Observation data (J2000 epoch)
ConstellationCamelopardalis
Right ascension 07h 36m 51.4s[1]
Declination+65° 36′ 09″[1]
Redshift131 ± 3 km/s[1]
Distance8 Mly (2.5 Mpc)[2]
Apparent magnitude (V)8.9[1]
Characteristics
TypeSAB(s)cd[1]
Apparent size (V)21′.9 × 12′.3[1]
Other designations
UGC 3918,[1] PGC 21396,[1] Caldwell 7

Supernovae

There have been two reported supernovae in the galaxy: SN 1954J, which attained a magnitude of 16 at its brightest, and SN 2004dj. SN 2004dj was the nearest and brightest supernovae in the past 17 years. It remains nearest and brightest supernova in 21st century.

History

The galaxy was discovered by William Herschel in 1788. Edwin Hubble detected Cepheid variables in NGC 2403 using the Hale telescope, making it the first galaxy beyond the Local Group within which a Cepheid was discovered.[2] He derived a distance of 8,000 light years.[2] Today, it is thought to be a thousand times further away at about 8,000,000 light-years (2.5 Mpc).

  • RGB image of the galaxy NGC 2403 from the Liverpool Telescope
  • SN2004dj
  • LRGBHa image of NGC 2403 from W4SM, 17" PlaneWave CDK

References
  1. "NASA/IPAC Extragalactic Database". Results for NGC 2403. Retrieved 2006-11-21.
  2. Kepple, George Robert; Glen W. Sanner (1998). The Night Sky Observer's Guide. 1. Willmann-Bell, Inc. p. 73. ISBN 978-0-943396-58-3.
  3. Ho, Luis C.; Filippenko, Alexei V.; Sargent, Wallace L. W. (October 1997). "A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies". Astrophysical Journal Supplement. 112 (2): 315–390. arXiv:astro-ph/9704107. Bibcode:1997ApJS..112..315H. doi:10.1086/313041.


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