Backyard Moon
In one night the Moon moves west with the stars. Each night it slips back east about 13° and changes shape, and that slip is why it rises about 50 minutes later each day. Its light decides which hours suit faint targets, and Best tonight takes it into account when it ranks tonight’s targets.
How it is worked out
Section titled “How it is worked out”Both views work everything out in your browser, with formulas from Jean Meeus, Astronomical Algorithms. Positions are good to a small fraction of a degree. Moonrise times assume a flat horizon, and the skylines in the 3D view are made up. A spot you pick by hand gets a time zone guessed from its longitude.
The deep-sky targets are the ARIS catalog’s Messier, Caldwell and famous-target lists. The land outlines come from Natural Earth, and the 3D view is drawn with three.js.