The longitudes that had slipped

Hipparchus works on Rhodes. He has positions from earlier Greek observers, Timocharis and Aristyllus among them. He measures again. The longitudes have changed. The year, measured from the equinox, has slid against the lamps.

He does not yet have 26,000 years. He has a rate: about a degree in a century, in the figures that come down through Ptolemy. The still point is not still. North will later tell the same story with Thuban. Hipparchus tells it with a catalogue.

He also grades brightness in six steps, from the brightest to those just seen. That scale, adjusted, is still how a star’s apparent magnitude is spoken. The palimpsest recovery is 2022. It does not let us pretend we hold his book. We hold a method: compare, and do not assume the frame is eternal.