SkyWindow

SkyWindow is a field almanac for astronomers and astrophotographers. It does not draw a planetarium. It times the night you are about to drive toward, then tells you if that night will open. TONIGHT Pick a date and a site. SkyWindow computes astronomical twilight, moonrise and moonset, lunar illumination, and the altitude of the Milky Way’s core (Sagittarius A*). A single verdict follows: • Open — true dark, a quiet moon, and the core above the haze • Narrow — a usable slice, but it will not last • Moonlit — landscapes, not dust lanes • Dark — astronomical night without a high core • Closed — no practical window Drag the hour strip to see the Sun, Moon, and core at any moment. A field note tells you when to be on site, and whether the moon or dawn will cut you short. OUTLOOK Fourteen nights at the same place. Scores come from darkness, moonlight, and how high the core climbs in a dark slot — so you can pick the weekend that actually pays. EXPOSURE Three intents: Milky Way, star trails, and moonlight. • NPF, 500, and 400 rules for tailless stars • Suggested ISO from aperture, shutter, and your Bortle class • Trail duration from Earth’s sidereal rate (15.04° per hour), with frame counts for 15° through a full turn Choose a body, set focal length and aperture, and switch on a tracking mount when you have one. SITES Save the lay-bys and ridge lines you actually use. Use the current location, search a town, or enter coordinates. Set Bortle class so the verdict and ISO know how bright the sky really is. OPTIONAL CLOUD COVER If you enable it, SkyWindow reads hourly cloud cover from Open-Meteo for the selected site. Leave it off and the almanac still works — all twilight, moon, and core times are computed on the device. RED LAMP A red-night mode for the field, so you can check the window without ruining your dark adaptation. Privacy: location is used on this phone to compute the sky. No account. No tracking. No ads. Written for people who already own a tripod.