What is a solstice? What is an equinox? And what’s the difference between them? Let’s clear a few things up!
What Is an Equinox?
An equinox happens twice a year, marking the beginning of the spring and fall seasons. On an equinox, most places on Earth will receive roughly the same amount of day time as night time. In fact, the word equinox actually comes from two Latin terms that imply an equal length of day and night. Equi means “equal,” and nox means “night.” So the word literally translates to “equal night.”
From an astronomical perspective, an equinox is the instant of time when the plane of Earth’s equator passes through the center of the Sun. In other words, it is the moment at which the center of the Sun is directly above the equator.
Each year there is both a spring and autumn equinox. The spring equinox, otherwise known as the “vernal equinox,” occurs in March, either on March 20th, or the day before or after depending on the year. During the spring equinox, the sun moves northward over the equator, and the Northern Hemisphere begins to experience days that last longer than nights. This lasts until the autumn equinox.
During the autumn equinox, or “autumnal equinox,” the sun moves south over the equator, and this point tends to mark the onset of fall for the Northern Hemisphere. After this point, the nights become longer than the days. The autumnal equinox typically falls on or around September 22nd.
What Is a Solstice?
Like equinoxes, solstices occur twice a year. They are used to mark the points in time when the sun’s path is at its farthest point from the Equator. The Northern Hemisphere will typically experience the summer solstice on or around June 20th or 21st. The winter solstice occurs in late December between the 21st and 22nd.
Much like their names imply, the solstices are used to mark the transition from spring to summer and from autumn to winter, but these seasons will be experienced in opposite ways in the Northern and Southern hemispheres. This is because during the June solstice, the Northern half of the Earth is tilted toward the sun, and therefore the Northern Hemisphere will experience a long day while the Southern Hemisphere, which is farther from the sun, will experience a short day. Meanwhile, the opposite is the case for the December solstice.
During the June solstice, the sun is positioned directly above the Tropic of Cancer in the North. During the December solstice, it is above the Tropic of Capricorn in the Southern Hemisphere. This is why the Southern Hemisphere experiences their sunniest and warmest days during what is known in North America as winter.
Further reading: Summer Solstice Traditions
The Difference Between a Solstice and an Equinox
The term equinox is often used interchangeably with a solstice, but they are not at all the same phenomenon. What they do have in common, however, is serving as markers of the transition points between the seasons.
Essentially, the solstices mark the points at which the Earth is tilted toward the Sun at its most extreme angles, and the equinoxes mark the neutral transition points between these two extremes. This means that while they might seem like similar markers of the passing seasons, scientifically speaking, equinoxes and solstices are actually more very different.
Further reading: Why Do We have Seasons?
Equinox and Solstice Dates – 2021
2021 Equinoxes: March 20th and September 22nd
2021 Solstices: June 20th and December 21st
Did you like this post? If so, you might enjoy these other articles from the Sporcle Blog:
- What Is Midnight Sun?
- What Are the Dog Days of Summer?
- How Did the Seasons Get Their Names?
- Why Is the Flu Seasonal?