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NGC 147, Galaxie

NGC 147 is an elliptical dwarf galaxy located at a distance of about 2.6 million light-years in the constellation Cassiopeia. It was discovered in 1829 by the British astronomer John Herschel. With an apparent brightness of 8.4mag and a size of 13.2'x7.8' the galaxy seems to be an easy object, but its surface brightness is only 14.5mag/'², so it requires a rather dark sky to see it.

From its distance and position in the sky, it can be concluded that NGC 147 could be a companion of the large Andromeda Galaxy. However, it took until 1944 when the first individual stars could be resolved in the halo by W. Baade, confirming its extragalactic nature. The dwarf galaxy of Hubble- Type "E5" is only about 300,000 light years away from Messier 31 and is also gravitationally bound to NGC 185.

The galaxy's longitudinal extent is just 10,000 light-years and it contains between 100 million and one billion stars. The last major phase of star formation occurred 3 billion years ago, so NGC 147 contains almost exclusively older stars. The absolute magnitude is M= -15.5mag, which is about one hundredth of the luminosity of our Milky Way.

So far two supernovae have been observed in NGC 147: "SN 1954J" and "SN 2002kg".

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In my 20" telescope a pale, oval brightening of low surface brightness is visible at a magnification of 210x. However, the galaxy is easily visible with indirect vision. Towards the center the halo becomes slightly brighter, in which several fainter stars can be seen. Further details are not visible.