M101 – Pinwheel Galaxy – Ha

Acquisition Date: February 17, 2019

This is a work in progress with the goal being a color image. As more data becomes available I will post updates.

Spiral galaxies like M101 contain ionized hydrogen regions. This is where star formation occurs and it is mainly found in the arms of the galaxy. There is a type of narrowband filter which is designed to pass the Hydrogen Alpha (Ha) emission line. This photo was taken with an Ha filter.

One of the advantages of imaging in narrowband is that it can be performed during all phases of the Moon. In fact, the Moon was 91% illuminated when I acquired this image. The downside is that the required exposure is quite long: 3 minutes 20 seconds for each of the 32 frames in this case. Wideband imaging, by comparison, typically uses exposures in the range of 30 to 60 seconds but images will be washed out by the light of the Moon. Wideband filters are typically named Luminance, Red, Green, and Blue (i.e. LRGB).

As this project matures to color I will provide more detailed technical information. The image shown above is a screenshot of Astro Pixel Processor (APP).