NGC 6946 - Spiral Galaxy

Designations:	NGC 6946, Caldwell C12, H IV 76, UGC 11 597, ARP 29, PGC 65001
Object Type:	Spiral Galaxy
Constellation:	Cepheus
RA:	20 hr 34 min 49.2 sec	Dec:	+60° 9 min 38 sec
Magnitude:	8.9	Size:	9 arcminutes
Distance:	18 million light years

Although NGC 6946 is one of the nearest galaxies to us ( beyond the Local Group that is) it is a difficult object visually. This is because its position in our sky is close to the plane of the Milky Way, which results in it being partially obscured and much reduced in contrast by foreground stars. The nucleus is also small and faint but represents the best chance to spot it. Certainly from suburban skies with a 10 inch (25 cm) telescope that was all I could detect, although there are sightings of an outer haze with an 8 inch (20 cm) from darker locations. To see the five main spiral arms, a large Dobsonian and pristine skies are required. Despite its faintness it is surprisingly easy to locate its position. This is because the open cluster NGC 6939 is nearby. This cluster is a splendid sight in any size telescope and a low power field can include both. NGC 6946 is 1° south-east of the cluster and 2° south-west of Eta Cephei (mag.3.4). NGC6946 was for many years classed as an Sc Galaxy i.e. similar to M33 with loose open arms and small nucleus. However it has recently been categorized as an SAB(rs)cd galaxy. This classification refers to the presence of a small core with multiple well-defined arms (cd), a poorly-developed bar across the middle(AB) and an inner confused ring (rs). It is undergoing a starburst phase in its nuclear region. Engelbract et al. (1996) concluded that much of the starburst is masked by dust and that it has had a duration of around 20 million years. Elmegreen et al. (1998), observing in the infra-red, found evidence for a bar like structure that could be fuelling the starburst. There have been several supernovae observed in NGC 6946 and it also has the brightest X-ray supernova remnant (SNR) known anywhere Blair et al. (1997) postulated colliding SNRs but Dunne et al. (1999) preferred a supernova explosion inside a dense interstellar bubble as an explanation. NGC 6946 is thought to be about 18 million light years away.

Telescope:	TMB 152 F8 APO refractor
Focal Length:	1200 mm
Mount:	Takahashi NJP 160
Camera	SBIG ST10XME
Guider:	SBIG ST402ME
Exposures:	14 7-minute exposures luminance and 5 8-minute exposures for each color (Red, Green and Blue)
Location:	Cicero, IN
Software:	CCDSoft for image acquisition, processed with CCDStack and Photoshop CS2