What is the Difference Between Equinox and Solstice

The main difference between equinox and solstice is that equinox is the time when the Sun crosses the plane of the Earth’s equator, while solstice is the time when the Sun’s path is farthest north or south from Earth’s equator.

Both equinox and solstice occur twice a year. They signal the changing of seasons on Earth. Equinoxes mark the beginning of fall and spring, while solstice occurs during summer and winter. Moreover, equinox results in equal lengths of day and night while result in changes in the length of the days and nights.

Key Areas Covered

1. What is Equinox 
     – Definition, Features
2. What is Solstice
     – Definition, Features
3. What is the Difference Between Equinox and Solstice
      – Comparison of Key Differences

Key Difference

Equinox, Solstice

What is Equinox

Equinox is the time when the Sun crosses the plane of the Earth’s equator, resulting in equal lengths of day and night.  At this time of the year, the Sun is nearest to the equatorial plane. In other words, the Sun sits directly above the equator. There are two equinoxes each year: spring equinox occurs in March, while autumnal equinox occurs in September. Therefore, this phenomenon occurs every six months. These mark the beginning of spring and fall. 

Figure 1: Equinox and Solstice

What Happens in an Equinox

Earth orbits the Sun on an axis that’s tilted 23.5 degrees. Twice a year, Earth’s tilt aligns with its orbit around the Sun so that Sun is directly above the equator. This casts a dividing line between the dark and light parts of Earth. We call this the terminator or twilight zone.

Furthermore, during an equinox, our planet gets more minutes of light than darkness. It’s also important to note that our planet is not the only planet to have equinoxes. In fact, every planet on the solar system experiences equinoxes.

What is Solstice

Solstice is the time when the Sun’s path is farthest north or south from Earth’s Equator. There are two solstices each year, happening during summer and winter. The summer solstice occurs when one of the poles of the Earth has its maximum tilt towards the Sun, while the winter solstice occurs when one of the poles of the Earth has its maximum tilt away from the Sun. Moreover, solstices result in changes in the length of the days and nights.

Figure 2: Winter Solstice

At the summer solstice, the Sun travels the longest path through the sky, so that day has the longest period of daylight. It is also the day the Sun reaches the highest point in the sky. At the winter solstice, the Sun travels the shortest path through the sky, so that day has the shortest period of daylight and longest night in the year.

Difference Between Equinox and Solstice

Definition

Equinox is the time when Sun’s path is nearest to the Earth’s equator while solstice is the time when the Sun’s path is farthest north or south from Earth’s equator.

Time

Equinoxes mark the beginning of spring and fall while solstices happen during summer and winter.

Length of Day

While equinoxes do not change the length of days and night, solstices result in changes in the length of day and night. Summer solstice has the longest day, while winter solstice has the shortest day.

Conclusion

During equinox, the Sun is nearest to the equatorial plane, which gives equal lengths of day and night. During solstices, the Sun is farthest from the equatorial plane, which results in long nights and days. Thus, this is the main difference between equinox and solstice.

Reference:

1. Wild, Sarah. “What Is an Equinox?” Space.com, 18 Aug. 2020, Available here.
2. “Winter Solstice.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 9 Feb. 2018, Available here.
3. “Summer Solstice.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 18 June 2020, Available here.

Image Courtesy:

1. “Orbital relations of the Solstice, Equinox & Intervening Seasons” By Colivine – Own work (CC0) via Commons Wikimedia
2. “Earth-lighting-winter-solstice EN” (CC BY-SA 2.0) via Commons Wikimedia