Equinoxes and Solstices are two different astronomical events. The equinox is a regular astronomical event that occurs twice a year. The Earth’s orbit causes it to move around the sun, which causes it to tilt on its axis.
This tilt causes our planet’s North and South Poles to face the sun at different times.
During the Northern Hemisphere winter and summer months (when days are shorter), the North Pole has pointed away from the sun, while during the spring and fall (when days are longer), the South Pole faces it directly.
Equinoxes and Solstices
Equinoxes and Solstices are two different terminologies. Below is a detailed discussion of these two astronomical events.
What are the Equinoxes?
The equinoxes are the days when day and night are equal. They occur twice a year, at the beginning of spring and fall.
Each year, the dates vary a bit because they’re based on astronomical phenomena (the Earth’s orbit around the sun) that aren’t precise down to the day, but they’ll always be between March 20th and September 23rd if you use a calendar without leap years.
The point is that while we think of March 21st as spring, it might be another day or two before that date passes into springtime in our area. So if you want to know when it’s truly spring in your neck of the woods, look up an almanac or reference book for your state or country instead of relying on just one date.
1. March equinox in the Northern Hemisphere
The March equinox occurs on March 20 or 21. The term “equinox” comes from Latin roots meaning “equal night.” Spring commences in the Northern Hemisphere when days and nights are roughly equal in length. It’s also known as the vernal (spring) equinox.
Vernal means related to spring, so this time of year is associated with new life, literally and figuratively.
The sun passes directly over Earth’s equator during an equinox, which means we don’t have a tilt toward any hemisphere or another at this point either; there’s no axis tilt during an equinox event.
2. September equinox in the Southern Hemisphere
The September equinox, also called the autumnal equinox, takes place on September 22nd. The equinox occurs when the sun crosses the celestial equator and marks the point where day and night are equal.
In the Southern Hemisphere—that is, anywhere south of Earth’s equator—the September equinox happens in spring. In contrast, it occurs in autumn in the Northern Hemisphere.
Understanding an equinox will help you understand why it occurs twice a year and at different times and how it relates to other astronomical events, like solstices.
An equinox is the time of year when the sun’s position on the Earth’s equator causes day and night to be approximately equal. As a result, the duration of a day is roughly 12 hours on both sides of an equinox, while the size of a night is also approximately 12 hours.
The four annual vernal (spring) and autumnal (fall) equinoxes occur at different times depending on your location in Earth’s northern or southern hemisphere. The actual dates vary, but they usually fall on March 20/21 and September 22/23 each year, with minor differences between them due to leap years.
What are the Solstices?
Solstice means “the sun must stand still.” It is derived from the Latin words sol for “sun” and sistere for “to stand still.” This is because the sun appears to stop moving north or south for three days.
During the winter solstices (December 21-22) and summer solstices (June 21-22), the Earth tilts toward or away from the sun. Solstices happen twice a year.
Therefore, people living on the sunny side experience longer days than those on the shaded side.
1. Summer solstice in the Northern Hemisphere
Summer solstice (also called Midsummer Day) is the day of the year with the most extended period of daylight, lasting around 12 and a half hours. It occurs on or around June 21st in the Northern Hemisphere, when the sun reaches its highest point in the sky.
On this day, it appears to be directly overhead at noon for points north of 23.5° N latitude—the same latitude as Cape Town, South Africa; Kangerlussuaq, Greenland; and Vladivostok, Russia (and slightly south of Seattle). These locations receive 24 hours of sunlight directly under our planet’s axis.
2. June solstice in the Southern Hemisphere
During the Northern Hemisphere’s summer solstice, the year’s longest day marks the start of summer. In contrast, in the Southern Hemisphere, it’s known as winter and marks the shortest day. Sun rises at the northernmost point on Earth during this time of year, directly over the Tropic of Cancer (23 degrees).
Regarding geographic location, all points north or south from that line have their longest days/nights in June. The sun’s path across our sky is perpendicular to this line, so if you’re standing on a beach somewhere in southern Alaska at midnight on June 21st while looking up into space at Polaris (the North Star), Polaris will be directly overhead.
The March equinox, or vernal equinox, marks spring’s arrival in the Northern Hemisphere, while the September equinox, or autumnal equinox, marks the start of fall in the Northern Hemisphere. In the Southern Hemisphere, the March equinox signifies the beginning of autumn, and the September equinox marks the start of spring.
Solstices occur twice a year, typically around June 21st for the summer solstice and December 21st for the winter solstice.
Equinoxes and solstices are both astronomical events that mark the changing of the seasons due to Earth’s tilt and rotation. Equinoxes occur when day and night are approximately equal in length, while solstices mark the longest or shortest day of the year. Together, they help define the four seasons we experience on Earth.
James Earl is an expert in equinox and dates. He has helped many people understand the importance of this event. James Earl is a published author and has given many lectures on the subject.