Why Easter is so late this year

By Nicholas Asheshov

Every afternoon this week, including Monday – which in Cuzco was the Day of Our Lord of Earthquakes – thunder has battered the steep sides of the Urubamba Valley.  This is very unusual.  Normally thunderstorms announce only the beginning of the rains in October and November.  Normally the rains end in Urubamba like clockwork between March 23 and the 28th.

Not this year and I consulted Kim Malville, professor of Astrophysics at the University of Colorado and a leading authority on ancient Andean astronomy, which I’ve always thought of as the Weather Channel for the Incas, Moches and the rest.  I wanted to know why Easter is so late this year and what effect this is having on our weather.

Here Kim, with whom I have traipsed into the rugged Vilcabamba looking for ancient solstice and other star markers, tells us how the Church which sadly, as we know, replaced the Incas, decides each year when Easter is to be, something I’d never understood.

Read carefully.

“Easter is the first Sunday after the first full moon after the Vernal Equinox – well, almost.  The Church has messed things up a bit by making it the first Sunday after the Paschal Full Moon, which is the ecclesiastical full moon, which may be two days off the real full moon because when they established tables of the full moon 1,700 years ago, in A.D. 325, they made a few accounting errors, which the Church cannot correct: you’ll have to check with your local Cardinal why not.

“But the Church fathers did not mess it up for 2011. There was a full moon on March 19, the day before the vernal equinox, so we have had to wait a full lunar month for the next full moon which was at the beginning of the week, on Monday April 18, and then another six days for Sunday April 24,” which, Kim adds, is his birthday.

April 24 is a very rare Easter Sunday.  I checked on the internet and it hits the 25th of the month about once a century: the last one was 1943 and the next one is in 2038.

Though Easter is so mobile, I’d always thought that the equinox, like the solstices, were fixed for the 20th or 21st of March and September.  The equinox is when the sun passes over the equator.  The solstice is when it reaches its furthest point north or south, 23.5 degrees: Antofagasta, for instance, is 23.4 degrees south, Lima is 12 degrees south and Cuzco 13 degrees.

However, Kim tells me that the equinox is itself “a pretty abstract concept” as it is the day the sun crosses the celestial equator,” which no one can actually see.

“On an island in the Pacific on the equator, with an utterly flat horizon, the sun will rise due east on the day of equinox. Elsewhere, either because of an elevated horizon such as at Urubamba or even Lima, or because of refraction, it will not rise due east.”

Kim adds that, “With so many llamas, condors, cats and dogs in the way it should make no difference to you.”

More to the point, the late Easter has no effect on the length of the rainy season.

“Your rains have nothing to do with the Church, the Paschal moon, surfing competitions at Punta Rocas, or anything astronomical.

“Because the Earth moves around the sun in an ellipse and travels faster when it is closest to the sun, the number of days between the two solstices and the equinox is not the same. The half day count between December and June solstice lands some 3-5 days after spring equinox (and before fall equinox), so that ancient people counting the days would celebrate equinox at a different date than on our wall calendar.”

Myself, I shall stick, as advised by Voltaire, to gardening.

Published April 22, 2011 by