Primer

Start here if you have not computed an eclipse before.

• How eclipses, occultations and transits are computed explains every event on the site as a body casting a shadow, with two cases set by who stands in it, the observer or another body, and pictures and animations of each.
• Worked example: a solar eclipse follows one prediction from the ephemeris to the second at which totality begins, in plain terms, and points into the research notes for the formulas. It ends with what changes for a lunar eclipse, an occultation and a transit.
• The glossary lists every term the site explains inline.