Spiral Galaxy NGC 1643

This is a 7 minute exposure with an ST-6 CCD camera thru Kopernik's 20-inch F/8.1 Ritchey Chretien Cassegrain telescope. The field of view is about 5x7 arc minutes with North at the top.

Dreyer's description in the New General catalog(NGC):

Faint, very small, irregularly round, brighter middle.

There is little that is certain about NGC 1643 except that it is a spiral galaxy, or perhaps a barred spiral. In the north arm there is a bright H II region or companion galaxy of 16th magnitude. There is also a 18th magnitude companion galaxy at 0.7 arc minutes to the south. If the galaxy is at its estimated distance of 255 million light years, it must have a diameter of around 82,000 light years.

NGC 1643 was the site of supernovae in 1995 (SN1995g) and 1999 (SN1999et). In fact the latter supernova was reported to be visible at the time of the Kopernik image. However, it was only 18th magnitude and very close to the nucleus of the galaxy. This makes it impossible to see it in our picture.

• NGC 1643
• Magnitude: 14.0
• Constellation: Eridanus
• RA: 04h 43m 44.0s
• Dec: -05° 19' 10" Epoch 2000
• Size (mins): 1.1
• Classification: SB?(r?)bc pec?
                          Barred Spiral, Inner ring, peculiar, all uncertain
  
  

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George Normandin, KAS

December 8th, 1999