Pleiades
| Pleiades | |
|---|---|
A color-composite image of the Pleiades from the Digitized Sky Survey | |
| Observation data (J2000 epoch) | |
| Right ascension | 03h 47m 24s |
| Declination | +24° 07′ 00″ |
| Distance | 444 ly on average (136.2±1.2 pc) |
| Apparent magnitude (V) | 1.6 |
| Apparent dimensions (V) | 2° |
| Physical characteristics | |
| Mass | 800 M☉ |
| Radius | 20.34 light years |
| Estimated age | 75 to 150 million years |
| Other designations | Seven Sisters, M45, Cr 42, Mel 22 |
| Associations | |
| Constellation | Taurus |
The Pleiades (/ˈpliː.ədiːz, ˈpleɪ-, ˈplaɪ-/), also known as Seven Sisters and Messier 45 (M45), is an asterism of an open star cluster containing young B-type stars in the northwest of the constellation Taurus. At a distance of about 444 light-years, it is among the nearest star clusters to Earth and the nearest Messier object to Earth, being the most obvious star cluster to the naked eye in the night sky. It is also observed to house the reflection nebula NGC 1432, an HII region. Around 2330 BC it marked the vernal point. Due to the brightness of its stars, the Pleiades is viewable from most areas on Earth, even in locations with significant light pollution.
The cluster is dominated by hot blue luminous stars that have formed within the last 100 million years. Reflection nebulae around the brightest stars were once thought to be leftover material from their formation, but are now considered likely to be an unrelated dust cloud in the interstellar medium through which the stars are currently passing. This dust cloud is estimated to be moving at a speed of approximately 18 km/s relative to the stars in the cluster.
Computer simulations have shown that the Pleiades were probably formed from a compact configuration that once resembled the Orion Nebula. Astronomers estimate that the cluster will survive for approximately another 250 million years, after which the clustering will be lost due to gravitational interactions with the galactic neighborhood.
Together with the open star cluster of the Hyades, the Pleiades form the Golden Gate of the Ecliptic. The Pleiades have been said to "resemble a tiny dipper," and should not be confused with the "Little Dipper," or Ursa Minor.