Longer pieces on what the tools compute: where the dates come from, which standards apply, and how to work the same thing out for your own case.
Every tool on this site answers one question and stops there. These pages are for the rest: why the answer is what it is, which standard or piece of astronomy it rests on, and what it cannot tell you.
They are written to be useful on their own, and each one ends where a tool can take over.
Where the 5×5 grid with a free centre comes from, how to write squares people actually tick, and how to deal a different card to each player.
A screenshot of a countdown goes stale the next day. How the count works, what belongs on the image, and how to share a link that keeps counting on its own.
Day counts and anniversaries follow two ladders that never meet. How the days are counted, when 1,000 actually falls, and what the card should carry.
Chicagohenge falls 19-23 September 2026; Manhattanhenge returns 28 May and 14 July 2027. Where those dates come from, and how to compute your own street.