M45, the Pleiades

December 16, 2023

The Pleiades, M45, also called the Seven Sisters, is a very bright and distinct open star cluster in Taurus, surrounded by the reflection nebula NGC 1432 (most of that pale blue interstellar dust and cloudiness). The Seven Sisters are very hot blue stars about 444 lightyears away. Where I am in the northern hemisphere, around 43° latitude, the Pleiades rises in the night sky in October, peaks in January at almost 50° in the southern sky, before sinking below the horizon by the end of March—and then we don't see it in the night sky again until late autumn.

To the ancient Greeks, over 2,500 years ago, the rising of the Pleiades marked the start of shipping season, when sailing the Mediterranean was a bit less dangerous. Like a lot of ancient mariners, Ancient Greek sailors and navigators relied on astronavigation, using the stars to determine their precise position on the surface of the earth. An ancient Athenian ship could leave the Piraeus and sail directly out to sea, then head west, toward Syracuse, tracking the stars the whole way to determine their course. They would also be keeping track of the Pleiades' position in the sky each night, and use that to determine if they should pick up cargo and make the return trip or pick up some local coastal work through the summer and return to Athens in the fall.  

Imaging Notes: 71 x 5-minute sub-exposures stacked in PixInsight. ZWO ASI071MC color camera cooled to 0°C, Gain 0, Antlia V-Series Luminance/UV-IR Cut filter, William Optics RedCat 51 Apochromatic Refractor 250mm FL, f/4.9, Sky-Watcher EQ6-R Pro mount, ZWO ASIAir Plus astro controller.