Encyclopedic Entry

equinox

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Encyclopedic Entry
Vocabulary

Encyclopedic Entry

Normally, the Earth is tilted either away from or toward the sun. This tilt is what gives us our seasons. When our side of the planet is tilted away from the sun, it's winter; when the Earth is tilted toward the sun, it's summer.

An equinox happens when the Earth isn't tilted at all. Twice a year, when equinoxes happen, the sun shines straight at the middle of the Earth, on the Equator. In the Northern Hemisphere, the vernal equinox takes place around March 21. The autumnal equinox takes place around September 22.

The word equinox comes from two Latin words meaning equal and night, which makes a lot of sense. During an equinox, the nights and days are almost equally long.

Many people are starting to use the terms March equinox and September equinox, instead of vernal, which means spring, and autumnal, which means autumn or fall. March and September are spring and fall in the Northern Hemisphere, but it's the opposite in the Southern Hemisphere. The Southern Hemisphere’s “spring” equinox takes place in September.

There are a lot of religious and cultural celebrations related to the equinox that are observed all over the world. The first day of the Baha'i and Iranian calendars falls on the March equinox every year. Vernal Equinox Day is a national holiday in Japan. The Jewish holiday of Rosh Hashanah is marked around the September equinox every year.

Photo: Harvest Moon over a bridge in Lisbon.

A harvest moon shines over Portugal.

Photograph by Miguel Claro, My Shot

Can You Hear Me Now?
Equinoxes disturb satellite communications. When the sun is directly behind a satellite in orbit, the sun's extreme radiation affects the communication beam between the satellite and the station on Earth.

Vocabulary

Term	Part of Speech	Definition
autumnal equinox	noun	autumn day, usually around September 22, when day and night are of generally equal length.
equinox	noun	period in which daylight and darkness are nearly equal. There are two equinoxes a year.
cultural belief	noun	faith or custom created and supported by a community's traditional behavior.
Earth	noun	our planet, the third from the Sun. The Earth is the only place in the known universe that supports life.
Equator	noun	imaginary line around the Earth running east-west, 0 degrees latitude.
Jewish	adjective	having to do with the religion or culture of people tracing their ancestry to the ancient Middle East and the spiritual leaders Abraham, Isaac, and Jacob.
Latin	noun	language of ancient Rome and the Roman Empire.
national holiday	noun	celebration or commemoration marked by citizens of a nation.
radiation	noun	energy, emitted as waves or particles, radiating outward from a source.
religious ceremony	noun	rituals performed surrounding spiritual or supernatural beliefs.
Rosh Hashanah	noun	Jewish holy day. Also called Jewish New Year.
satellite communication	noun	process of exchanging information using a device that orbits Earth.
season	noun	period of the year distinguished by special climatic conditions.
sun	noun	star at the center of our solar system.
tilt	verb	to lean or slant.
vernal equinox	noun	day, usually around March 21, when day and night are of generally equal length. Also called the spring equinox.