Through a scope of 8 inches or larger, this astronomical wonder will delight you.
The Fireworks Galaxy (NGC 6946) is in a good place to view during autumn in the Northern Hemisphere.
Credit: Dietmar Hager
- Despite its unified magnitude of 9.6, the spiral galaxy NGC 6946 exhibits low surface brightness due to its pronounced angular extent and position near the galactic plane, requiring an aperture of at least 8 inches for detailed observation.
- Discovered by Sir William Herschel in 1798, NGC 6946 is colloquially known as the “Fireworks Galaxy” due to its unusually high frequency of supernova events.
- This phenomenon is evidenced by the observation of ten supernovae within the last century, including a particularly bright event in 2017 that reached magnitude 12.8.
- Located at the junction of the constellations Cepheus and Cygnus, NGC 6946 is observable as a deep-sky object, with detailed structural features such as its bright core and multiple spiral arms, becoming apparent with progressively larger telescope apertures.
How can a celestial object be bright and dim at the same time? The answer depends on the brightness of its surface. In the case of the spiral galaxy NGC 6946, its overall brightness, magnitude 9.6, is high for a galaxy. Unfortunately, that light is spread over 1/20th of 1°. For comparison, that area is one-quarter of the area covered by the full moon.
Another obstacle to NGC 6946’s visibility is its location near the plane of the Milky Way in Cepheus and Cygnus. So, unless you are using at least an 8-inch telescope, the overall impression of NGC 6946 is that of a blurry object.
a suitable name
NGC 6946 was discovered by Sir William Herschel on September 9, 1798. But its common name, Fireworks Galaxy, has recently been given. Why? For some unknown reason, this galaxy is a hotbed of supernova activity.
In the past century, ten supernovae have occurred, in 1917, 1939, 1948, 1968, 1969, 1980, 2002, 2004, 2008, and 2017. The most recent supernova was the brightest, reaching magnitude 12.8 on September 30.
find it and inspect it
As far as its location is concerned, the Fireworks Galaxy is one of the few deep-sky objects that lie on the border of two constellations: Cepheus the King and Cygnus the Swan. To find NGC 6946, look 2.1° southwest of the 3.4 star Eta Cephei.
Smaller telescopes now will let you explore the galaxy, but you won’t be able to see much detail through apertures smaller than 8 inches. When you observe it, notice that the galaxy’s core appears bright and extends to about 10 percent of its diameter. An 11-inch scope shows two spiral arms, and you’ll see four from a 16-inch or larger instrument.
and who knows? Depending on its explosive history, you may be witnessing a supernova!
