M101, also known as the Pinwheel Galaxy, is a spiral galaxy located in the constellation Ursa Major. To find it locate the star Alkaid, the last star in the handle of the Big Dipper. Above it is M101, with M51 below (the subject of a previous post). It has taken 21 million years for the light from the Pinwheel to travel through space and reach the sensor on my camera.

M101 is about 1.7 times the size of our own Milky Way. It sits 21 million light years away and is 170,000 light years across. It is estimated to contain over 1 trillion stars, twice as many as found in our galaxy. The arms of M101 are dotted with large, star forming nebulae. Many of these are large enough to have been categorized as their own NGC objects! An annotated version of the picture is shown, with many of these objects labeled.

This latest photo is a little over 14 hours of exposure time. I used a monochrome camera with Red, Green, Blue, and Hydrogen Alpha filters. Exposure times were 10 seconds to 1 minute for RGB, and 4 to 5 minutes for Ha. Total times were Red: 181 minutes, Green: 154 minutes, and Blue: 113 minutes. An additional 419 minutes Ha was added to capture the faint regions, enhancing the red in the Pinwheel.

In total over 1300 images were combined. This is because many images were taken during a full moon. To prevent too much light from the moon I kept the exposures to 10 seconds for the first couple nights. A lot of 10 second exposures can be captured over a 6 hour period.

The final M101, Pinwheel Galaxy image was produced by calibrating and stacking the images using PixInsight. The images from the separate filters were combined to form a color image and then the detail was pulled out using the tools in PixInsight. The final image was left wide to show some of the objects in the surrounding area. (I am particularly fond of NGC 5422, the small galaxy you can see if you zoom in near the lower right.)