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Arp Peculiar Object Number 026 - Spiral Galaxy With One Heavy Arm
NGC 5457 (M101 = PGC 50063 = Arp 26), The Pinwheel Galaxy
Discovered (Mar 27, 1781) by Pierre Méchain
Recorded (without observational verification) by Charles Messier as M101
Also observed (later in 1781) by Charles Messier
Also observed (May 4, 1831) by John Herschel
A magnitude 7.9 spiral galaxy (type SAB(rs)cd?) in Ursa Major (RA 14 03 12.4, Dec +54 20 58)
Historical Identification: Per Dreyer, NGC 5457 (= GC 3770 = JH 1744, M101, 1860 RA 13 58 14, NPD 34 58.6) is "pretty bright, very large, irregularly round, very suddenly much brighter middle with bright small nucleus". The position precesses to RA 14 03 11.5, Dec +54 20 58, essentially dead center on the galaxy listed above and the description fits, so the identification is certain.
Discovery Information: Usually Messier verified discoveries reported to him by Méchain, and listed both his friend's prior discovery and his own observation. However, at the time of Méchain's observation of what became M101, the deadline for additions to the 1784 publication of Messier's last Catalog was fast approaching, so he did not verify the observation until later. Messier's description of the object was only recorded (without the date of his observation) in a handwritten note in his personal copy of the printed version. (A similar situation applies to M102 and M103, the last objects recorded by Messier.)
Physical Information: Listed in Halton Arp's Atlas of Peculiar Galaxies as Arp 26, an example of a spiral galaxy with one heavy arm. M101's recessional velocity of only 240 km/sec is too small in comparison to peculiar (non-Hubble-expansion) velocities to provide a reliable estimate of its distance. Redshift-independent distance estimates range from 18 to 29 million light years. Given that and its apparent size of 28 by 26 arcmin (nearly the same size as the full moon), M101 is nearly 200 thousand light years across.
"Excerpt courtesy of Courtney Seligman"
cseligman.com/text/atlas/ngc54a.htm#5457
Image... Cherryvalley Observatory (I83). Telescope: 0.2-m SCT & SBIG STL-1301E CCD Camera @f7.6. Image Scale 2.17 arcsec/pixel, Field of View 46 x 37 arcmins.
Flat field and dark subtract calibration frames. Combined Stack of three images of 120 seconds each unfiltered and unbinned. CCD operating temperature: -35 degrees. Image acquisition and processing: CCD Soft v5, TheSky6 Professional and Mira Pro v7. February 18th 2016.
Dr. Halton Arp originally compiled the Atlas of peculiar galaxies with photographs he made mainly using the Palomar 200-inch telescope and the 48-inch Schmidt telescope between the years 1961 to 1966. Original image can be found here: ned.ipac.caltech.edu/level5/Arp/Figures/big_arp26.jpeg
Arp Peculiar Object Number 026 - Spiral Galaxy With One Heavy Arm
NGC 5457 (M101 = PGC 50063 = Arp 26), The Pinwheel Galaxy
Discovered (Mar 27, 1781) by Pierre Méchain
Recorded (without observational verification) by Charles Messier as M101
Also observed (later in 1781) by Charles Messier
Also observed (May 4, 1831) by John Herschel
A magnitude 7.9 spiral galaxy (type SAB(rs)cd?) in Ursa Major (RA 14 03 12.4, Dec +54 20 58)
Historical Identification: Per Dreyer, NGC 5457 (= GC 3770 = JH 1744, M101, 1860 RA 13 58 14, NPD 34 58.6) is "pretty bright, very large, irregularly round, very suddenly much brighter middle with bright small nucleus". The position precesses to RA 14 03 11.5, Dec +54 20 58, essentially dead center on the galaxy listed above and the description fits, so the identification is certain.
Discovery Information: Usually Messier verified discoveries reported to him by Méchain, and listed both his friend's prior discovery and his own observation. However, at the time of Méchain's observation of what became M101, the deadline for additions to the 1784 publication of Messier's last Catalog was fast approaching, so he did not verify the observation until later. Messier's description of the object was only recorded (without the date of his observation) in a handwritten note in his personal copy of the printed version. (A similar situation applies to M102 and M103, the last objects recorded by Messier.)
Physical Information: Listed in Halton Arp's Atlas of Peculiar Galaxies as Arp 26, an example of a spiral galaxy with one heavy arm. M101's recessional velocity of only 240 km/sec is too small in comparison to peculiar (non-Hubble-expansion) velocities to provide a reliable estimate of its distance. Redshift-independent distance estimates range from 18 to 29 million light years. Given that and its apparent size of 28 by 26 arcmin (nearly the same size as the full moon), M101 is nearly 200 thousand light years across.
"Excerpt courtesy of Courtney Seligman"
cseligman.com/text/atlas/ngc54a.htm#5457
Image... Cherryvalley Observatory (I83). Telescope: 0.2-m SCT & SBIG STL-1301E CCD Camera @f7.6. Image Scale 2.17 arcsec/pixel, Field of View 46 x 37 arcmins.
Flat field and dark subtract calibration frames. Combined Stack of three images of 120 seconds each unfiltered and unbinned. CCD operating temperature: -35 degrees. Image acquisition and processing: CCD Soft v5, TheSky6 Professional and Mira Pro v7. February 18th 2016.
Dr. Halton Arp originally compiled the Atlas of peculiar galaxies with photographs he made mainly using the Palomar 200-inch telescope and the 48-inch Schmidt telescope between the years 1961 to 1966. Original image can be found here: ned.ipac.caltech.edu/level5/Arp/Figures/big_arp26.jpeg