M101 Pinwheel Galaxy

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2016/05/06 - After a long break, we're back in business. We've updated the QSI with new firmware to fix the banding issue, which is gone. We had some issues with the focuser, but that's fixed. We had some good nights in France and this image is the result.

The Pinwheel Galaxy is a face-on spiral galaxy distanced 21 million light-years away in the constellation Ursa Major, first discovered by Pierre Méchain on March 27, 1781, and communicated to Charles Messier who verified its position for inclusion in the Messier Catalogue as one of its final entries.

Pierre Méchain, the discoverer of Messier 101, described it as a "nebula without star, very obscure and pretty large, 6' to 7' in diameter, between the left hand of Bootes and the tail of the great Bear. It is difficult to distinguish when one lits the wires." William Herschel noted in 1784 that "M101 in my 7, 10, and 20-feet reflectors shewed a mottled kind of nebulosity, which I shall call resolvable; so that I expect my present telescope will, perhaps, render the stars visible of which I suppose them to be composed." Lord Rosse observed M101 in his 72-inch Newtonian reflector during the second half of the 19th century. He was the first to make extensive note of the spiral structure and made several sketches.

To observe the spiral structure in modern instruments requires a fairly large instrument, very dark skies, and a low power eye piece.

M101 is a relatively large galaxy compared to the Milky Way. With a diameter of 170,000 light-years it is seventy percent larger than the Milky Way. It has a disk mass on the order of 100 billion solar masses, along with a small bulge of about 3 billion solar masses. Another remarkable property of this galaxy is its huge and extremely bright H II regions, of which a total of about 3,000 can be seen on photographs. H II regions usually accompany the enormous clouds of high density molecular hydrogen gas contracting under their own gravitational force where stars form. H II regions are ionized by large numbers of extremely bright and hot young stars.

On photographs M101 can be seen to be asymmetrical on one side. It is thought that in the recent past M101 underwent a near collision with another galaxy and the associated gravitational tidal forces caused the asymmetry. In addition, this encounter also amplified the density waves in the spiral arms of M101. The amplification of these waves leads to the compression of the interstellar hydrogen gas, which then triggers strong star formation activity.


Object information
Name : M101 Pinwheel Galaxy
Type : Galaxy
Constellation : Ursa Major
Distance : 20.900K light-year
Apparent dimensions : 28'.8 x 26'.9
Apparent magnitude : 7.86

Image information
Image date : 2016/05/06, 2016/05/05, 2016/05/04, 2016/05/03, 2016/05/02, 2016/05/01, 2016/04/29
Right ascension : 14:3:12.908
Declination : 54°20' 56.95"
Focal length : 1686.46 mm
Focal ratio : f/6.64
Image resolution : 0.660 arcsec/pixel
Field of view : 36' 8.9" x 27' 8.0"
Sky quality : 21.77 mag/arcsecond2
Sensor temperature : -20°C
Light frames : 24 hours, 45 minutes total exposure time
31x 900 sec. luminance unbinned
24x 900 sec. red unbinned
20x 900 sec. green unbinned
24x 900 sec. blue unbinned
Image acquisition with ACP Observatory Control Software, ACP Scheduler and Maxim DL
Auto-guiding with Maxim DL
Auto-focusing with FocusMax
Bias frames : 100x unbinned
Dark frames : None
Flat frames : 20x luminance unbinned
15x RGB unbinned
Automated sky twilight flats with ACP
Processing : PixInsight for calibration, alignment and integration.
Adobe Photoshop CS6 for final touch.

Equipment information
Telescope : Orion Optics 10" ODK
Corrector : None
Focuser : Baader SteelTrack with SteelDrive
Mount : Mesu Mount 200 with Sidereal Technology SiTech Controller
Camera : QSI 683wsg-8 cooled CCD camera with Kodak KAF-8300 sensor and Off Axis Guide (OAG) port
Guidecamera : Starlight Xpress Lodestar autoguider
Filters : Astrodon Tru-Balance E-Series LRGB & Astrodon 3nm H-α, 3nm O-III, 3nm S-II and 3nm N-II
Observatory site : www.sunstarfrance.com, Hautes-Alpes, France