How Rare is the April 2024 Eclipse?

“Each square represents one of 8,000 solar eclipses from years 128 BCE to 2161 CE”—visualization method showing “regularities and confounding irregularities of solar eclipses in really beautiful way.”

For total solar eclipse like April 2024 to occur, “three independent motions of Moon and Earth must coincide almost perfectly.”

Moon must be between Sun and Earth—“happens on average every 29 days 12 hours 44 minutes and 2.9 seconds” (29.53059 days), period known as “synodic month.”

Moon’s orbit tilted relative to Earth’s orbital plane means shadow usually misses Earth unless Moon is “sufficiently close to Earth’s orbital plane” at nodes—cycle repeats “every 27 days 5 hours 5 minutes and 35.8 seconds” (27.21222 days), called “draconic month.”

Slow nodal precession means “one of two nodes line up between Earth and Sun on average every 173.310 days, little less than half a year—creates on average two Eclipse Seasons per year spaced a little less than 6 months apart.”

April 2024 eclipse is total while October 2023 eclipse is “annular where moon does not entirely block out sun.” Difference: “apparent size of moon has changed” due to elliptical orbit.

Moon’s elliptical orbit creates distance variation determining apparent size; takes “average of 27 days 13 hours 18 minutes and 33.2 seconds” (27.55455 days) “for moon to make round trip from closest point along its elliptical orbit and back”—called “anomalistic month.”

“After 223 synodic months or about 18.03 years our synodic, draconic and anomalistic months all come back into alignment producing very similar eclipse”—this 18-year period called “Saros.”

“Humans have known answer for at least 2,000 years”—ancient Babylonian tablet “shows record of solar eclipses from 347 to 258 BCE. Each column advances by exactly…223 synodic months.”

“April 2024 eclipse is part of Saros series 139. Next eclipse in this series will occur in April 2042”—series “will last around 1300 years starting in 1501 and ending in 2763.”

Saros length “does not line up well with rotation of earth equaling 6585.32 days—means consecutive eclipses in Saros series will not occur in same location on Earth.”

“Right now there are 40 different Saros Series in progress”—means eclipses occurring today belong to 40 distinct families, each with own evolution timeline.

“Looking further in time than 223 synodic months that make up Saros for stronger alignment…we’ll eventually land on 358 synodic months being very nearly equal to 388.5 draconic months and 383.67 anomalistic months”—called Inex cycle.

“From end of year 2024 to 2050 there will be 56 solar eclipses. 17 of these will be total solar eclipses, and of these only two will be visible in contiguous United States: one in 2044 and one in 2045.”

Austrian astronomer Theodor von Oppolzer published 1887 “Canon of Eclipses”—“incredible catalog of 8,000 solar eclipses…widely recognized as one of greatest computational Feats of its time.”