The Pleiades

Located some 440 light years from Earth, in the constellation Taurus, the Pleiades is one of the most beautiful sights in the night sky: whether through the naked eye, an eyepiece or a camera sensor, this unmistakable celestial object never ceases to amaze!

The Pleiades is what astronomers call an “open cluster” or a group of stars formed from the same cloud of gas and dust: under the effect of gravity, these particles are pressed together pushing the temperature up to extreme levels. As the new stars take shape and increase in size, their own gravity becomes stronger, mutually bounding them together.

The cluster contains over three thousand stars (mostly hot B-type stars) although only a handful is visible to the naked eye as a consequence of increasing light pollution. Today, in fact, from most cities it is possible to recognise around 6 or 7 stars, thus the cluster is often referred to as “The Seven Sisters”.

The Pleiades has been known for centuries and there is no shortage of legends about it. According to the Greek mythology, the Pleiades were the seven daughters of the Titan god Atlas who rebelled against Zeus and was thus sentenced to hold up the heavens on his shoulders. Moved by compassion, however, Zeus allowed the seven daughters a place in the sky so they could stay close to their father.

In Japan, the cluster is known as Subaru and was chosen as the name of the 8.2-meter (320 inches) Subaru Telescope of the National Astronomical Observatory of Japan. The name Subaru was also chosen as the brand name of Subaru Automobiles, which has 6 stars in its logo.

The Pleiades is arguably the most famous star cluster in the sky, prominent and unmistakable to the naked eye, but who was the first astronomer to resolve the Pleiades through a telescope? Well, Galileo Galilei of course. The Italian astronomer was the first to discovered that the cluster contains way more stars than those visible to the unaided eye. He published his observations and a sketch of the Pleiades in his “Sidereus Nuncius” in 1610.

However, the nebulosity around the Pleaides was only discovered in 1859 by the German astronomer Ernst Tempel who described it as “a faint stain like a breath on a mirror”, when gazing at the Pleiades through his 4-inch (10cm) telescope. The nebulosity is not directly connected to the star cluster, but it rather seems that the latter is passing through a particularly dusty region, which reflects the light from the brighter stars.

Depending on the observer’s latitude, the Pleiades cluster is visible from October to April and it is best observed in November, when is up the whole night. As mentioned before, the Pleiades is clearly visible to the naked eye but have a look at it through a pair of binoculars or a telescope and I assure you your jaws will drop!