Fireworks galaxy (NGC 6946)

 

Fireworks-DSS2-PS1-web

Fireworks galaxy, NGC 6946, in the constellations Cepheus and Cygnus. Torrey, 6/4/2016 (revised color)

It is new moon early June and the nights are dark but short. Summer solstice is only two weeks off and it does not get dark enough for observing until 10:40 PM. It will start getting light again in just five and half hours. Dark enough for observing is known as astronomical twilight and technically starts when the sun is 18 degrees below the horizon or almost two hours after sunset. Before astronomical twilight comes nautical twilight, defined by the old mariners as when the horizon at sea is still barely discernible. Before nautical twilight comes civil twilight. During civil twilight there is enough natural light to carry on outdoor activities. The end of civil twilight is called civil dusk and is the start of nautical twilight. At nautical dusk astronomical twilight starts and I can get started with tasks like using stars to align the telescope with the earth’s axis. There is something romantic about sitting up 7,000 feet high on the Colorado Plateau and imagining the horizon of the sea as it slowly fades from view and the stars overhead become so bright they create shadows.

In early June, as I set up the telescope and camera equipment, the Milky Way is just coming up on the eastern horizon. The advent of the Milky Way marks the end of galaxy viewing season. Our galaxy is a disk or plate shaped swirl of stars. All of the stars we can see by naked eye are in our galaxy but the swath of light through the night sky that we call the Milky Way is what we see when we look out through the plate and not straight up from it. Looking straight up from the plane of the galaxy is where it is easiest to see out of the galaxy and therefore see things like other galaxies.

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Fireworks galaxy is in the square in the center of the frame. The frame is roughly the area of sky captured in my entire image.

NGC 6946 ( New General Catalogue of Nebulae and Clusters of Stars), nicknamed the Fireworks galaxy, sits right on the edge of the visual Milky Way. It is close enough to it that it is partially obscured by galactic stuff including stars and dust. Look at the number of stars in my image versus the Black Eye galaxy I shot a few months ago looking straight up and out. I have never captured an object that is identified as being in two constellations, Cepheus and Cygnus in this case. But as small as it appears in the view from earth, it sits right on the border. The entire image above takes up about the amount of sky you would see looking through a drinking straw, so you can see the galaxy had to do some sharp shooting to hit in both constellations.

As the fiery colors came through while I was processing this image I thought no wonder it is called Fireworks. But then I learned it has had more supernovas in the last 100 years than any other galaxy we can observe. It is less than half as big at the Milky way and has had nine supernovas compared to the Milky Way’s one or two. Supernovas are hands down the ultimate fireworks. NGC 6946 is 18 million light years from Earth and about 40 ,000 light years across, around a third of that of the Milky Way.

  • My image is a total of two hours four minutes composed of 31 sub-frames of four minutes each at 1600 ISO. 12 each of dark, flat and bias compensation frames.
  • Celestron vintage “Orange Tube” C8 SCT, f/6.3 reducer
  • Losmandy G-11 mount
  • Guiding: Orion ST80, SSAG, PHD
  • Gary Honis full spectrum modification Canon T1i (Jan. 2015)
  • BackyardEOS, DSS, Photoshop CS5
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