According to Greek mythology, the Pleiades represents seven sisters of Atlas, who was busy holding the skies together and could not take care of them. Zeus turned them into stars, to protect them from Orion, the hunter chasing the girls. Similar stories exist in various cultures about the seven sisters and young males with a chasing habit. Only there are six stars visible to the naked eye in this beautiful star cluster, so one of the sisters is actually hiding. But there may be an explanation for all this. One of my colleagues, Ray Norris has recently proposed that the tale of seven sisters may be the oldest story in the world, possibly told around campfires in Africa 100.000 years ago. As the various tribes spread across the globe, they took their stories with them from the cradle of humankind.
But if we see only six, why seven? The Pleiades is a relatively nearby, young cluster, at a distance of 136 parsecs. As a result, the peculiar motion of individual stars in the cluster slightly altered their shape and general appearance. The tight pair of stars at the bottom of our image is Pleione and Atlas, and they cannot be separated by the naked eye today, but they were more apart 100.000 years ago. There is the seventh sister, hiding indeed!
We have been waiting for the opportunity to take this shot for a long-long time, as we had several months of cloudy weather. The processing of this image was not as straightforward as we thought it would be, and we are sure there is room for improvement. An earlier version of this image has been posted on the Vega Astronomical Society’s web pages. We have included here an additional layer where the stars had been subtracted using AI technology. This allowed us highlighting the nebulosity – interstellar dust clouds that scatter the light of the hot cluster stars – even further.
Technical data
M45, 150x60s
Hoogeveen, Netherlands
Saturday, 19 Dec. 2020
William Optics GT81, f/5.9
Flattener 6AIII 0.8x
ZWO ASI533MC-P, gain 101, -20 deg.
WO Uniguide 50/200 with ASI120MMmini
iOptron CEM40
Optolong L-pro
ASIair
Bortle~5
Moon 27%
ASTAP, StarNet++, Photoshop