NGC 6946, The Fireworks Galaxy
Optics:   Ritchey–Chrétien 20" F/8.2 (4166mm FL) Processing:   PixInsight, Photoshop
Camera:   SBIG STXL-11000 with Adaptive Optics Date:   September 2019
11 Megapixel (4008 x 2672 16-bit sensor) Location:   Columbus, Texas
Exposure:   LRGB = 590:100:80:100 minutes Imager:   Kent E. Biggs
NGC 6946, also called the Fireworks Galaxy, lies in the direction of not just one, but two constellations! At about one-third the visible size of the full moon, half of this galaxy visually sits in the constellation Cepheus (a king from Greek mythology) and the other is in the constellation Cygnus (the swan, also Northern Cross). At over 25 million light-years away, it is 10 times more distant than our neighbor, the Andromeda Galaxy. At about 40,000 light-years across, the diameter of NGC 6946 is one-third the size of our own Milky Way Galaxy. Since this galaxy is so close to the Milky Way’s galactic plane, many stars, gas, and dust significantly obscure the galaxy from optimal view. Consequently, in order to eke out its true details and hidden information, we employ substantial image processing. In the image above, as in nearly all astronomy images, each one of the thousands of stars visible is a part of our own Milky Way Galaxy. The obscured image is certainly incredible, with bright blue and red arms, but the detail of the galaxy’s extended arms remains largely invisible. By hovering the mouse over the image, as if my magic, most of the foreground stars disappear revealing the extended faint galaxy arms.

Even though NGC 6946 has only half the number of stars as our own galaxy, it has produced supernovae (death of massive stars) at ten times our rate. In the 20th and 21st centuries, we have seen 10 of these events and this has given it the name of the Fireworks Galaxy, since in the astronomical since, this activity level is like rapid fireworks explosions. More supernovae have been recorded in this galaxy than in any other!

What do astronomers do when they run out of nebula to study in our own galaxy? Simple, study other galaxies. Hovering over the first image below with a mouse, reveals such nebula enlarged. The blue areas are regions of new hot stars, quickly burning through their stellar food. Red regions are called HII (“H-two”) regions where light from surrounding stars excite hydrogen gas to emit specific wavelengths of red light and often times become stellar nurseries for future stars. As a bonus, the lowest enlarged inset is a much more distant galaxy, likely of similar size to NGC 6946, yet visibly far far younger and distant due to the billion or so years it took that light to reach us. There are a dozen or more such galaxies visible in this image, can you find them all?

Click here for a continuous video showing the full animation!

Finally the bottom image below, was the best image obtained of NGC 6946, using the old Celestron-11 telescope, 3 megapixel camera, and old workflow.