Astra: Habits and Stars

Astra is a habit tracker with a real sky in it. Pick up to five habits. Mark all of them on the same day and Astra lights one star in the patch of sky above the place you first opened the app. Miss a day and nothing is taken back. The stars you have already lit stay lit. The stars are real ones. Positions, brightnesses and colours come from the Yale Bright Star Catalogue, and a star's colour on the map is worked out from its measured colour index. Tap any star for its surface temperature, its spectral class, and how its size compares to the Sun. Where the catalogue's distance is not reliable, Astra says nothing rather than printing a number that is wrong. Constellations arrive nearest first and smallest first, so the early ones finish in a couple of days and the later ones take a couple of weeks. Keep everything for two months and that is sixty-one stars and around twenty completed…