NGC 147
NGC 147 (also known as DDO3 or Caldwell 17) is a dwarf spheroidal galaxy about 2.58 Mly away in the constellation Cassiopeia. NGC 147 is a member of the Local group of galaxies and a satellite galaxy of the Andromeda Galaxy (M31). It forms a physical pair with the nearby galaxy NGC 185, another remote satellite of M31. It was discovered by John Herschel in September 1829. Visually it is both fainter and slightly larger than NGC 185 (and therefore has a considerably lower surface brightness). This means that NGC 147 is more difficult to see than NGC 185, which is visible in small telescopes. In the Webb Society Deep-Sky Observer's Handbook, the visual appearance of NGC 147 is described as follows:
Large, quite faint, irregularly round; it brightens in the middle to a stellar nucleus.
| NGC 147 | |
|---|---|
Hubble Space Telescope image of NGC 147 | |
| Observation data (J2000 epoch) | |
| Constellation | Cassiopeia |
| Right ascension | 00h 33m 12.1s |
| Declination | +48° 30′ 32″ |
| Redshift | -193 ± 3 km/s |
| Distance | 2.53 ± 0.11 Mly (780 ± 30 kpc)[a] |
| Apparent magnitude (V) | 10.5 |
| Characteristics | |
| Type | dSph/dE5 |
| Apparent size (V) | 13.2′ × 7.8′ |
| Notable features | satellite galaxy of M31 |
| Other designations | |
| PGC 2004, UGC 326, DDO 3, LEDA 2004, Caldwell 17 | |
The membership of NGC 147 in the Local Group was confirmed by Walter Baade in 1944 when he was able to resolve the galaxy into individual stars with the 100-inch (2.5 m) telescope at Mount Wilson near Los Angeles.