The Pleiades, or Seven Sisters, is a young open cluster of hot blue stars in Taurus, the most famous star cluster in the sky and known to almost every culture.
At a glance
| type | open star cluster |
|---|---|
| distance from the Sun | 444 light-years (136 pc) |
| its light left it | 444 years ago |
| size in the piece | about 52 light-years acrossmodel |
Read off the piece’s own catalogue, the same values it draws with. Model marks a property of the piece’s galaxy model rather than a measurement.
About Pleiades (M45)
The Pleiades is a cluster of stars born together from the same cloud, young enough that its brightest members are still hot, blue-white stars of a type that burns out quickly. To the eye a small dipper-shaped knot of a handful of stars shows; a pair of binoculars reveals many more, and a telescope shows the whole family spread over an area of sky larger than the full Moon.
Its distance was the subject of a long dispute. The Hipparcos satellite placed the cluster noticeably closer than other methods did, which would have meant its stars were oddly faint for their type. Later measurements, including Gaia’s, settled the matter in favour of the larger distance, and the stars turned out to be ordinary after all.
Long-exposure photographs show the stars wrapped in blue haze. That dust is not left over from their birth: the cluster is passing through an unrelated cloud, and its starlight is scattered off the grains.
What you see in the piece
Its stars are among the hottest in the neighbourhood, so they show blue-white, and the faint blue glow of the Merope Nebula (NGC 1435) lies among them, lit only by the cluster’s own light.
Measured or modelled
The size drawn for the cluster is a modelled extent; like every open cluster it has no sharp edge and slowly thins into the surrounding stars.
Questions
How far away are the Pleiades?
The Pleiades are 444 light-years (136 pc) from the Sun, so the light you see left them 444 years ago.
Why is there blue nebula around the Pleiades?
The cluster is drifting through a cloud of interstellar dust that is not related to it. Fine grains scatter blue light more strongly than red, so the starlight they reflect glows blue.