Galaxies & clusters




Solar system

Narrow band

Wide field






Canon 40D Baader mod (RGB) @ISO1600

Original                          Old       

The Pinwheel galaxy (or M101 or NGC5457) was discovered by Pierre Méchain in March 1781.

M101 is a relatively large galaxy compared to the Milky Way. With a diameter of 170,000 light-years it is nearly twice the size of 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 (speaking in galactic terms) 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.

Text taken from Wikipedia.

Event though I managed to get a fair number of hours to stack, the background contained some strange noise patterns. The reason for the delayed "publishing" is the difficulty I have had in processing the image while keeping the background under control. Thus there are faint dust arms going out from the galaxy present that I did not manage to show by stretching without also stretching the noise pattern.

In order to "hide" the noise pattern I also had to apply a little too much smoothing to the background, making it look a little artificial.

Also I found that the 5min subs where substantially better than the 3min subs. The reason may be due to different seeing conditions at different nights but I suspect that 3min subs are a little too short for the f-number used.

I am not completely happy with the result considering the long integration time, but still M101 has a very low surface brightness and if this would have been a five hour image I would have been satisfied with the result :-)

By "mouse over" on the blue text just below the image you can see:

  • Original: the most recently processed image.

  • Old: the previously processed image. I got the comment from Bob Gilette that this one had a green cast which led me to re-process (using a different white balance). Thank you Bob!

An enlarged (50% of original) can be viewed here.

 The following software has been used. MaximDL (image acquisition and guiding), CCDStack (calibration and de-convolution), PixInsight (cropping, background correction, colour corrections) and Photoshop CS5 (all the rest, incl Noel Carbonis Astronomy Tools).

This image was processed in February 2011 (the "old" was processed in January 2011).




Celestron C8 at f6.3 (using

FLATNER/REDUCER: Ted Agos adapter w x6.3 reducer
MOUNT:  Celestron CGE
IMAGE: 126x180s + 36x300s (9hr 18min total) @ISO1600
IMAGE SCALE: 0.88 arcsec/pixel
FIELD OF VIEW: 39' 2" x 20' 48"


Autoguiding with MaximDL


William Optics 66Zenith Star


Orion Deep Space Star Shooter


64 Darks/32Flats


March 10 to April 13, 2010

LOCATION: Älta, Sweden

Copyright: All images © 2010 Matts Sporre. All Rights Reserved