Topic

Bortle scale

The nine classes that measure how dark a sky is, what each one actually lets you see, and how to find the Bortle class of the place you observe from.

The Andromeda Galaxy Is a Naked-Eye Object, if You Know Where to Rest Your Gaze

At 2.5 million light-years, M31 is the most distant thing the unaided eye catches without strain. It spans three degrees, six full Moons laid end to end, climbs to 82 degrees above Paris, and the moonless window runs from 5 to 17 September. The exact star-hop, and what your own sky will let through.

La galaxie d'Andromède, M31, photographiée au téléobjectif : le disque incliné, le noyau brillant et ses deux galaxies compagnes.

The Bortle Scale: How Many Stars Does Your Sky Actually Let You See?

Between central Paris and the Millevaches plateau there is not «a few more stars». There is a factor of thirty. Here is what the satellite atlas built into SkyChart computes for twenty real locations, and what it cannot tell you.