Object: M101 (NGC 5457)
Type: Spiral Galaxy (morphological classification SAB (rs) cd)
Constellation: Ursa Major
Distance: 20.9 million light years
Date: March 29th, 2019
Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD
Subframes: 16 x 300s each for RGB, flats but no darks (hot pixel removal in Astroart). Above is a 50% crop of the original image.Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD
Messier 101 (M101), also known as the Pinwheel Galaxy, is a spiral galaxy located in the constellation Ursa Major. It has the designation NGC 5457 in the New General Catalogue. Discovered by Pierre Méchain on March 27, 1781, it was communicated to Charles Messier who verified its position for inclusion in the Messier Catalogue as one of its final entries.
M101 lies at a distance of 20.9 million light years from
Earth. The galaxy appears face-on and occupies an area of 28.8 by 26.9 arc
minutes of apparent sky (about the same size as a full moon), which corresponds
to a linear diameter of about 170,000 light years, similar to our Milky Way
galaxy.
Its location in the sky is easy to find, forming an equilateral
triangle with Mizar and Alkaid, two of the bright stars in the “handle” of the
Plough (see the Stellarium map opposite). Despite this, the galaxy has a low
surface brightness that renders it difficult to see from suburban locations.
M101 has around a trillion stars, more than twice the number
of stars in the Milky Way. The galaxy has an unusually high number of H II
regions, where new stars form, and many of these regions are bright and large,
ionized by many extremely luminous and hot young stars. Some of the larger and brighter ones can be
seen in the above image.
Sky conditions were not good on the night of the 29th. Although cloud and moon-free, unusually calm
conditions had allowed a build-up of a rather unpleasant pollution haze in the
Medway Valley, with particulates exceeding recommended annual means as
evidenced on the local UKAIR
monitoring site (by a factor of four on
the 30th – which mercifully dispersed with the advent of
northerly winds next day). This gave a sickly
orange colour to the sky, making it very difficult to pull out luminance data
from the background sky glow, to the point where I gave up and stuck with the
RGB filtered sub-frames, which were not so badly contrast-compromised.
If I get the opportunity, I will try and improve the brightness and resolution of this image by the acquisition of some longer (and hopefully cleaner) luminance exposures.
If I get the opportunity, I will try and improve the brightness and resolution of this image by the acquisition of some longer (and hopefully cleaner) luminance exposures.
