Know what the numbers mean.

How each answer is made.

• Sunrise, sunset and golden hour

  The sun’s altitude is worked out for the date and the place and read every minute. Sunrise and sunset are the moments it crosses 0.833° below the horizon. Golden hour runs from 4° below to 6° above it, and blue hour from 6° below to 4° below. The method follows NOAA’s calculation notes.

  The daylight pages show a year of these moments in the clock time of the place’s zone. Clock changes come from your browser’s own zone tables and are marked apart from the sun’s motion.

• Window light and shadows

  A window gets direct sun when the sun clears the skyline you set and stands in front of the glass. A shadow’s length is the height of what casts it, over the tangent of the sun’s altitude.

• The moon

  The moon’s position and phase follow Meeus. The principal phases are given to the minute and checked against the U.S. Naval Observatory. The full-moon calendar is open data.

• The sunset forecast

  Cloud at each height over your place and toward the sunset, from MET Norway’s forecast (CC BY 4.0), read on Sol’s own server and judged as one of four words. A forecast says what is likely, not what will happen.

• Place, time and freshness

  Times follow the city you choose. A place found by name, and the time zone of one picked on a map, come from GeoNames (CC BY 4.0), read on Sol’s own server. Every page is rebuilt each night and works its numbers out again in your browser when it opens.

  The season pages give two conventions and name the local one first. The equinoxes and solstices are worked out to the minute by Meeus’s method and shown in the place’s clock. The calendar seasons are cited from the body that keeps them: the Bureau of Meteorology, the Met Office or the National Weather Service. No page suggests that a season’s first day says anything about the weather.

• Using Sol’s answers

  The geometry is right to about a minute. A forecast is one of four words. A computed sunrise does not promise that the sun will be visible from your street.

Your address, if you leave it.

The launch list keeps the address you type, when you typed it, the page you left it on and your language, for one email when the app ships. The beta list keeps the same and the answers you choose to give, for a TestFlight invitation. No page can read either list back.

An account adds a password and keeps what you save on it: sunset outings, city lists, rooms, teams and observations. Pages show it to you alone, and deleting the account deletes all of it.

There are no cookies. The privacy policy says what each of these keeps, who else receives anything, and for how long.