About CalendarCosmos
A printable calendar and a sky almanac on one site, for kitchens, offices, classrooms and back porches.
How the numbers are made
Moon phases, eclipses, seasons, sunrise, twilight and planet positions are computed with astronomy-engine by Don Cross, an open-source library built on the VSOP87 planetary theory and a lunar model derived from ELP. Tables of phases, seasons and eclipses are generated at build time; anything that depends on your location or today’s date is computed in your browser.
Our build script refuses to publish unless its output matches the US Naval Observatory Astronomical Applications API (moon phase times, 2026 equinox and solstice times, and the 2026 solar eclipse dates) to within 90 seconds.
Meteor shower peaks use the peak solar longitudes, activity periods and ZHRs from the International Meteor Organization’s Meteor Shower Calendar, converted to dates for each year.
US federal holidays follow 5 U.S.C. 6103, with observed days per Executive Order 11582 and the Office of Personnel Management. Easter uses the Gregorian computus; daylight saving time follows the Energy Policy Act of 2005 (US) and Directive 2000/84/EC (EU).
Full moon names are the traditional North American names as popularized by the Old Farmer’s Almanac. “Supermoon” marks full moons within 360,000 km of Earth.
Limits
Sunrise and sunset assume a sea-level, unobstructed horizon; mountains, tall buildings and unusual refraction can shift them by a few minutes. Eclipse visibility tables use 75 reference cities; use the local calculators for your exact location. The night sky planner’s written guide is generated by an AI model from the computed almanac and can make mistakes.
Spotted an error? Every table on the site comes from one of the sources above, so it can be traced and fixed.