Messier 45
This bright open cluster of stars, more commonly called the Pleiades or Seven Sisters, is easy to see with the unaided eye.
Distance
445 light-years
Apparent Magnitude
1.6
constellation
Taurus
object type
Open Cluster
Commonly called the Pleiades or Seven Sisters, Messier 45 (M45) is an open star cluster. It contains over a thousand stars that are loosely bound by gravity, but a handful of its brightest members visually dominate the cluster.
One of these stars, Merope, is located just outside the frame of this image to the upper right. The colorful rays of light at the upper right, emanating from the star, are an optical phenomenon produced within the telescope. The nearly straight, blue-white wisps pointing toward the upper right are streams of large dust particles. As the cloud moves toward Merope, its smaller dust particles are slowed down by the star’s radiation pressure more than the larger particles are. The large dust particles continue moving toward the star while smaller particles are left behind, visible in the image's lower-left corner.
Observed since ancient times, the Pleiades have no known discoverer. However, Galileo Galilei, the Italian scientist best known for discovering the largest moons of Jupiter and championing a heliocentric model of the solar system, was the first to observe the Pleiades through a telescope. M45 is located roughly 445 light-years from Earth in the constellation Taurus, though this number is not universally agreed upon. It has an apparent magnitude of 1.6 and is easily spotted with the unaided eye from a relatively dark-sky site. The best time to observe the cluster is during December.
Anim.: STScI AVL; Images: Terence Dickinson (Pleiades w/ Jupiter, Saturn, Hyades); STScI Digitized Sky Survey; Chuck Vaughn (amateur astrophotographer, 85-min. exposure w/ 12.5" f/9 Ritchey-Chretien telescope); Hubble Heritage Team (NASA, STScI/AURA)
For more information about Hubble’s observations of M45, see:
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