M101 – The Pinwheel Galaxy

A beautiful face-on spiral galaxy, M101 is about 21 million light years away in Ursa Major. In fact it forms an equilateral triangle with two stars of The Plough, Alkaid and Mizar. Although the galaxy is well below naked eye visibility, binoculars will reveal it as a misty patch, depending on sky clarity and light pollution. Because of its relatively low surface brightness, a large amateur telescope is needed to clearly see the spiral structure visually.

The  galaxy itself is about 170,000 light years  across – almost twice the size of the Milky Way.

As can be seen from the above image, M101 has numerous H-II regions glowing with the red light of the H-α spectral line at 656.3 nm. The neutral hydrogen has been ionized by radiation from nearby hot young blue stars in the spiral arms.

Equipment: Planewave CDK 14″ reflector on 10Micron GM2000 mount. FLI Proline P09000 CCD camera with Astrodon LRGB and Hα filters.

Exposure times: Lum 12 hrs, R 11 hrs, G 11 hrs, B 10 hrs, Hα 16 hrs.

Data acquired with ACP Expert/Maxim DL and processed in PixInsight.