Challenge #1 – C12, Fireworks Galaxy

Target	Type	R. A.	Dec.	Constellation	Magnitude	Size
C12 (NGC 6946)	Spiral Galaxy	20h 34m 53s	+60° 09′ 13″	Cygnus	8.9	11.4×10.8 arcmins

Overview

The Fireworks Galaxy is a fabulously appropriate name for this distant world first discovered by William Herschel in September 1798.

As galaxies go, this one is relatively close by, at just 22 million light-years distant. It’s face-on spirals are about 40,000 light-years across and lay exactly on the boundary between Cygnus and Cepheus. In fact, the boundary is so odd in that region that you’ll probably be surprised that C12 doesn’t belong to Cepheus, it looks like it should.

C12 is an active starburst galaxy, so called for the large amount of star formation occurring within its dusty arms. It’s also quite famous for the amount of supernovae we’ve detected within its boundaries: nine between 1917 and 2008, which is the actual reason for its evocative name.

C12, the Fireworks Galaxy is a spiral galaxy in Cygnus (source).

Finder Charts

C12 is classed as being part of Cygnus but it’s actually much closer visually to Cepheus.

This first sky chart, from SkySafari 6, shows the sky looking west at 10:00 p.m. in mid-October. Stars on this chart are shown to magnitude 5.0 and the moon and planets are not shown. On it, I’ve circled the obvious constellations of Cygnus the swan and Ursa Minor, home of the Pole Star.

Between them is Cepheus, to my mind looking like a young child’s drawing of a house. C12 is shown as a green oval and labelled as NGC 6946.

[C12-1] Locate Cepheus between the obvious Swan and Ursa Minor. Click for full-screen.

Zooming in to the region around the Fireworks Galaxy, you can see Deneb in Cygnus – a very bright star – and three stars in Cepheus that are all comfortably visible to the naked eye.

C12 (NGC 6946) forms one corner of an equilateral triangle with the stars Eta and Theta Cephei.

[C12-2] Imagine Eta and Theta Cephei as two corners of an equilateral triangle with C12 as the third. Click for full-screen.

In this third chart, stars are shown to magnitude seven, comfortably visible in binoculars and magnifying finderscopes. Just over a degree south of Eta Cephei, you’ll see two magnitude-six stars. The most southwesterly of these, HR 7925, is inside the same 1° field of view as the Fireworks Galaxy.

[C12-3] NGC 6946 fits inside the same 1° field of view as magnitude six HR 7925. Click for full-screen or download the pdf below.

Now you have this faint face-on galaxy in your eyepiece, what should you expect to see?

Individual Telescope Views

The following views will help you find C12 in different telescope types by presenting the images as your telescope will show them. The first image is with a black sky and white stars, the second picture is the same image but presented in inverse monochrome. Black stars on a white background is often easier to use at the telescope. Stars are shown to magnitude 10.0 and Eta Cephei and the two magnitude-six stars are shown, along with a circle with a 1° field of view.

Each image can be clicked on for a full-screen version.

Upright View – This is what your eyes see unaided and through a reflex or red-dot finderscope

Upside-down view – This is what reflectors and magnifying finders show, and refractors / Cassegrains without a star diagonal

Mirrored View – Refractors and Cassegrain models with a star diagonal show this view

Observation

As glorious as the astrophotography images of this object are, and although its magnitude is brighter than nine, this is still a very faint object. Remember that the light it emits is spread over a relatively large area, so its surface brightness is low.

That’s why we need to spy it at low magnification, because higher levels diffuse the little light we have too much and leave nothing left to see in smaller scopes. At that low magnification, we can see the obvious ghostly marker of this galaxy that brightens towards its center. With patience and averted vision, some structure can be glimpsed.

If you’re lucky enough to own a larger model where more light is being gathered, it’s possible to dial up the magnification a little when the seeing is good and show more elements of this distant world.

PDFs for Printing

Each of the star maps above is reproduced as a pdf below. Each star map has a number in [square brackets] beneath it which corresponds to the file number below. If you want image [C12-1], for example, click the ‘download’ button next to it below and you’ll be able to open it as a printable pdf.

October 2024