M101 Pinwheel Galaxy

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2013/04/18 - It was a windy night, but the ASA DDM60 didn't have any problems with that, I only saw some guiding corrections, that I normally don't see. CCDInspector indicated that seeing was between 2.07" and 2.77". The total session was automated with CCDAutoPilot.

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 : 2013/04/18
Right ascension : 14:3:19.004
Declination : 54°21' 41.67"
Focal length : 1381.40 mm
Focal ratio : f/5.44
Image resolution : 0.806 arcsec/pixel
Field of view : 42' 14.2" x 31' 24.3"
Guiding rms : 0.29 arcsec
Sensor temperature : -30°C
Light frames : 6 hours total exposure time
9x 600 sec. luminance unbinned
9x 600 sec. RGB unbinned
Image acquisition with CCDAutoPilot and Maxim DL
Auto-guiding with Maxim DL
Auto-focusing with FocusMax
Bias frames : 100x unbinned
Dark frames : None, only used outlier rejection.
Flat frames : 5x luminance unbinned
5x RGB unbinned
Created with Gerd Neumann Aurora flatfield panel
Processing : PixInsight for calibration (bias frames and flat frames), alignment and integration.
Adobe Photoshop CS6 for final touch.

Equipment information
Telescope : Robtics 10" 2000mm f/8 Ritchey Chretien
Corrector : Astro-Physics CCDT67 Focal Reducer
Focuser : Moonlite CS Ritchey Chretien focuser with high resolution stepper motor
Mount : ASA DDM60 Pro direct drive german equatorial mount controlled with AutoSlew
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 : Etten-Leur, The Netherlands