The brightest feature in this photograph is the Pleiades, also known as Messier 45 (M45) or the Seven Sisters, a young open star cluster located in the constellation Taurus. At roughly 440 light-years from Earth, the cluster contains hundreds of stars, although a handful of luminous blue-white members dominate what we see with the naked eye and in photographs.
Among its best-known stars are Alcyone, the brightest member of the cluster, along with Atlas, Pleione, Electra, Maia, Merope, Taygeta, and Celaeno. Many of these are hot, luminous B-type stars, giving the Pleiades its distinctive cool blue-white appearance.
The cluster is relatively young by astronomical standards, at roughly 100 million years old. In longer-exposure astrophotography, faint blue reflection nebulosity can sometimes be seen surrounding several of its stars, particularly Merope. Here, the cluster appears as a compact concentration of blue-violet light suspended within the broader field of stars above the silhouetted treeline.
The Pleiades span roughly two degrees of the sky, or about four times the apparent width of the full Moon. Their small scale against the much wider field in this photograph emphasizes just how much of the night sky surrounds even one of our most recognizable stellar landmarks.
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