| 词条 | NGC 2403 |
| 释义 |
| image = NGC 2403HST.jpg | image_size = 250px | caption = A Hubble Space Telescope (HST) image of NGC 2403 Credit: HST/NASA/ESA | name = NGC 2403 | epoch = J2000 | type = SAB(s)cd[1] | ra = {{RA|07|36|51.4}}[1] | dec = {{DEC|+65|36|09}}[1] | dist_ly = 8 Mly (2.5 Mpc)[4] | z = 131 ± 3 km/s[1] | appmag_v = 8.9[1] | size_v = 21′.9 × 12′.3[1] | constellation name = Camelopardalis | notes = | names = UGC 3918,[1] PGC 21396,[1] Caldwell 7 }}{{Sky|07|36|51.4|+|65|36|09|1000000}}NGC 2403 (also known as Caldwell 7) is an intermediate spiral galaxy in the constellation Camelopardalis. NGC 2403 is an outlying member of the M81 Group,[2] and is approximately 8 million light-years distant. It bears a striking 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] SupernovaeAs of late 2004, there had been two reported supernovae in the galaxy: SN 1954J, which attained a magnitude of 16 at its brightest, and SN 2004dj. HistoryThe galaxy was discovered by William Herschel in 1788. Allan Sandage detected Cepheid variables in NGC 2403 using the Hale telescope, giving it the distinction of being the first galaxy beyond the Local Group within which a Cepheid was discovered.[2] He derived a distance of a mere 8 thousand light years.[2] Today, it is thought to be a thousand times further away at about 8 million light years (2.5 Mpc). See also
References1. ^1 2 3 4 5 6 7 {{cite web| title=NASA/IPAC Extragalactic Database| work=Results for NGC 2403| url=http://nedwww.ipac.caltech.edu/| accessdate=2006-11-21 }} 2. ^1 2 3 4 5 {{cite book |last= Kepple |first= George Robert |author2=Glen W. Sanner |title= The Night Sky Observer's Guide |volume= 1 |publisher= Willmann-Bell, Inc. |date= 1998 |isbn= 978-0-943396-58-3 |page=73}} 3. ^{{cite journal | last1 = Ho | first1 = Luis C. | last2 = Filippenko | first2 = Alexei V. | last3 = Sargent | first3 = Wallace L. W. | title = A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies | date = October 1997 | periodical = Astrophysical Journal Supplement | volume = 112 | issue = 2 | pages = 315–390 | arxiv = astro-ph/9704107 | bibcode = 1997ApJS..112..315H | doi = 10.1086/313041 | postscript = }} External links{{commons|NGC 2403}}
9 : Intermediate spiral galaxies|M81 Group|Camelopardalis (constellation)|NGC objects|UGC objects|Principal Galaxies Catalogue objects|Caldwell objects|Astronomical objects discovered in 1788|Discoveries by William Herschel |
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