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M 101 is a large, face-on spiral galaxy that was discovered by Mechain in 1781. It was added to Messier catalog that same year and it was one of its last entries. Despite its magnitude, +7.9, its surface brightness is low (its light is spread over 30×27 arcmin) and it is not easy to observe or capture. M 101 is a quite large galaxy, about twice the Milky Way’s diameter. M 101 is part of a group of several galaxies (it is the brightest member) and the gravitational encounters with other members of the group may have provided the current “asymmetrical” appearance that can be seen today. It has many HII regions, more than 3000 can be seen in pictures, meaning a high star-birthrate.
Additional Information
Object
Name(s): M 101. NGC 5457. Pinwheel Galaxy.
Type: Spiral galaxy
RA: 14h 03m 11s
Dec: +59º 21’ 06”
Constellation: Ursa Major
Size (arcmin): 30×27
Magnitude: +7.9
Distance: 27 Mly
Image
Date: 2014-04-23
Location: iTelescope.net, Mayhill, NM, USA
Size (arcmin): 49×33
Telescope: 17” f/4.5
Camera: SBIG STL 11000M (4008x2672pix)
Guiding: yes
Total exposure: 68 min (L. 24min; RGB 44 min)
Processing: CCDStack, Photoshop CC 2016 and PixInsight