reading the catalogue…
Up right now
reading the catalogue…
Up right now
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What is drawn
Every position is worked out for the moment and the place you set, not looked up. The stars arrive from the catalogue at their year-2000 places and are carried forward by their own proper motion, then precessed, nutated and aberrated to the equinox of the date. The Sun, Moon and planets are summed from their series each time the clock moves. Nothing is cached and nothing is approximated as "close enough for a picture".
How far off it can be, measured against JPL DE440s over 1950 to 2100, worst case: stars 0.5″, the Sun 1.5″, the planets 4″, the Moon 27″. The Moon is the loosest because the tool carries only the main problem of ELP2000-82B; twenty-seven arcseconds is a fiftieth of the Moon's own width. The assertions are on a page of their own and run against the same files this page loads.
Typing a place name asks
geocoding-api.open-meteo.com to turn it into coordinates.
That is the only request this tool makes to anyone but this site, it
carries nothing but the words you typed, and it does not happen at all if
you enter coordinates or use here.
Where it comes from