March 2021
The Backyard Astronomer
by
Adam England

The Northern Equinox

Beginning, middle or end, depending on how you look at it

About 90% of Earth’s population lives in the Northern Hemisphere, so many of our astronomical traditions relate directly to how the sun, moon, and stars move across the northern night skies and northern weather patterns.

A prime example of this is the northern equinox, which we most commonly refer to as the spring or vernal equinox, although if one resides south of the equator, it’s more correctly the fall or autumnal equinox. On this day the center of the sun is directly perpendicular to the equator.

Derived from the Latin aequus (“equal”) and nox (“night”), March 20 and September 23 represent the two points in the year that most closely approximate equal times of day and night across the planet.

Ancient cultures did not recognize the exact angle of the sun relative to the center of the earth, but rather that the sun would rise and set directly east and west. The equinox also became a date for the beginning of many annual calendars and subsequent regional festivals.

The Persian and Indian calendars both begin on the day of or day immediately following the northern equinox, and are still used today in their respective countries. The Babylonians began their calendar on the first new moon following the March equinox, celebrating the return of the goddess Inanna from the underworld. The Jewish Passover and Christian Easter are both calculated based on the first full moon after the vernal equinox. 

The equinox is a perfect time to do home science projects. You can wake up with the sun and measure for yourself the exact hours of daylight. Find a local sundial (Sharlot Hall Museum!) or make one yourself, align it using a compass to magnetic north, and find what the solar time is at your home.

Last but not least, maybe we can bring back broom-balancing and pretend it’s real science!


If you would like to learn more about the sky, telescopes, or socialize with other amateur astronomers, visit us at prescottastronomyclub.org or Facebook @PrescottAstronomyClub to find the next star party, Star Talk, or event.

Adam England is the owner of Manzanita Financial and moonlights as an amateur astronomer, writer, and interplanetary conquest consultant. Follow his rants and exploits on Twitter @AZSalesman or at Facebook.com/insuredbyadam.