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What is an Equinox? - Definition & Types Video

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  • 0:00 What Is an Equinox?
  • 1:03 Types of Equinoxes
  • 1:31 Path of the Sun on the Equinox
  • 2:54 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

After completing this lesson, you will be able to explain what the equinox is, describe the types of equinox, and what is special about the path of the Sun through the sky on the equinox. A short quiz will follow.

What Is an Equinox?

It's common knowledge the days are longer than nights in summer, and that in winter, the days are shorter. However, this is not quite true during some parts of the year: during equinoxes. An equinox is a point in the year when daytime and nighttime are exactly the same length, 12 hours each. Equinoxes occur twice a year, usually on March 20 and Sept. 22, when the Earth is tilted neither toward nor away from the sun. The word is derived from Latin: 'equi,' which comes from aequus, meaning equal, and nox-', meaning night.

In actuality, day and night are not exactly the same length on the equinox, but they are very close. There are various reasons for this minor difference in duration. The way we define day and night uses the edge of the sun instead of the center as a point of measurement. Also, refraction allows people to see sunlight sooner than the sun actually rises above the horizon.

Types of Equinoxes

There are only two types of equinoxes. The March and September equinoxes each have their own names. In the Northern Hemisphere, the March equinox is called the vernal equinox, while in September, it is called the autumnal equinox. In the Southern Hemisphere, the names are the opposite because the seasons are switched. For example, autumn and the autumnal equinox occur in the Southern Hemisphere in March, when it is spring in the Northern Hemisphere.

Path of the Sun on the Equinox

When you get up each morning, take a look at where the sun is in the sky. It's probably somewhere in the East. Just before it goes dark outside, the sun is located westward. As many learned in primary school, the sun rises in the East and sets in the West. But it isn't quite that simple. If you're in the Northern Hemisphere, the sun will follow an arc that's a little off to the south during the day. It never goes directly overhead unless you live at the Equator. Whether it's nearly overhead or really far south depends on two things: your latitude and the time of year.

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