The Pleiades

Every route to the Pleiades starts at Orion's Belt, because the Belt is the one line in the sky nobody mistakes. Take it north-west — up and to the right, from the northern hemisphere — and hold that direction.

21.8° along you reach Aldebaran, magnitude 0.87, unmistakably orange, sitting in the V-shaped face of Taurus. It looks like a member of that V and it is not: Aldebaran is 65 light-years away and the Hyades cluster behind it is 153. Two things in a line are not two things in a place.

Keep going on exactly the same line for another 13.7° and the arrow lands on a small knot of blue-white stars — close enough together that most people see it first as a smudge, then resolve it, then can never un-see it. This is M45, the Pleiades.

The bright core spans 1.8°, three and a half times the Moon's width, which is why binoculars are better than any telescope here — a telescope cannot fit it in. Alcyone is the brightest at magnitude 2.85. Behind the nine stars with names are over a thousand members, weighed by Gaia, all born together about 110 million years ago and still drifting as one group at 444 light-years.

Count them. This is the classic naked-eye test, and it is honest about your sky and your eyes at the same time. Under a suburban sky (Bortle 5) most people get five or six. Under a rural sky, eight or nine. The record claims run to fourteen. Try it before you look at the labels — and try it again after twenty minutes in the dark, because the answer changes.

The named ones: seven sisters — Alcyone, Electra, Maia, Merope, Taygeta, Celaeno and Asterope — with their parents Atlas and Pleione at the east end. Greek, Japanese (Subaru, and yes, that is the car badge), Māori, Lakota and Australian Aboriginal traditions all count sisters here, and several tell the same story of one who is lost or hiding. Pleione is a shell star that varies; the coincidence is at least interesting.

At declination +24° the Pleiades are visible from every inhabited place on Earth — from 66°N they barely set, from Tasmania they clear the northern horizon in summer. Watch where the azimuth ends up: this cluster was a calendar for half the world's cultures precisely because its first dawn appearance each year falls at a repeatable date.