The one trait that has helped humans evolve through ages is the ability to learn and act accordingly. And recognizing patterns and utilizing the information for one’s gain is one of the most interesting parts of learning. From learning why ants move into a queue to utilizing patterns in technologies like machine learning, patterns are everywhere. The universe is full of them, and they affect our lives in several ways. There are so many more things.
And even though the change in seasons throughout the year is a gradual process, scientists (obviously) have figured out the points or, better say, the dates when seasons change. The change of seasons happens because of the tilt of Earth on its axis. Different parts of Earth receive less or more sunlight due to this change of angle. The terms ‘Solstice’ and ‘Equinox’ are related to the change of seasons on Earth, but people often get confused between the two.
Equinox vs Solstice
The main difference between equinox and Solstice is that the term ‘Equinox’ is related to the two moments of a year when the Sun is exactly above the equator. On the contrary, Solstice is referred to the two moments of the year when the position of the Sun is farthest (on either north or south) from the equator.
Equinox is the period when the length of day and night is of equal duration. The two types of Equinoxes are Vernacular Equinox and Autumnal Equinox; these two occur because of the Earth’s tilt. When there’s Autumnal Equinox in the Northern Hemisphere, the Southern Hemisphere experiences spring (Vernacular) Equinox and vice versa.
Solstice is the time when the duration of the day is either the longest or the shortest. The two types of Solstices are summer Solstice and winter Solstice. Due to Earth’s axial tilt, there’s a difference between seasons in Northern and Southern Hemisphere; during the winter Solstice in Southern Hemisphere, the Northern Hemisphere experiences summer.
Comparison Table Between Equinox and Solstice
| Parameters of comparison | Equinox | Solstice |
| Meaning | The time when the sun crosses the Earth’s equator to enter the Northern hemisphere | The time when the sun comes to the minimum or maximum descent |
| Occurrence | The two equinoxes happen around the 21st of March and about the 23rd of September. | The two solstices happen on June 21st or 22nd and December 21st or 22nd. |
| Position of the Sun | Precisely above the equator due to which the day and night are of equal length. | Farthest north or south from the equator due to which the day is either the shortest or the longest. |
| Condition | Subsolar point is the equator. | The subsolar point is 23.5 degrees North on the 22nd of June and 23.5 degrees South on the 22nd of December. |
| Significance | Derived from the Latin words ‘aequi’ and ‘noctium’, vernal equinox signifies the beginning of spring. | Derived from the Latin words ‘sol’ and ‘stitium’ meaning ‘stalled sun,’ Solstice marks the change of duration of day and night. |
What is an Equinox?
It’s a phenomenon when the plane of the equator of the Earth passes through the elliptical centre of the celestial axis. During this time, the Sun is directly visible above the equator or at either of the two points where the celestial equator and Sun’s pathway intersect. The equinoxes’ dates keep changing during the leap year cycle.
The two equinoxes are Vernacular equinox and Autumnal equinox.
The Vernal equinox (also known as northward equinox) that occurs about the 21st of March when the Sun moves north across the equator marks the beginning of the spring season in the Northern hemisphere. Astronomical coordinates such as celestial longitude and right ascension are measured from this equinox.
The Autumnal equinox that occurs about the 23rd of September as the Sun moves across the celestial equator to go south marks the beginning of the Autumn season. Autumnal equinoxes marked the beginning of the year in many Ancient Greek calendars.
These equinoxes are the only time when the edge between day and night is perpendicular to the Earth’s equator. This event caused both the hemispheres to light up equally. From a cultural point of view, these equinoxes mark the beginning of seasons, and many conventional harvest festivals are celebrated on these dates.
What is a Solstice?
A Solstice occurs when the Sun is either at the most northernly or southernly extent concerning the celestial equator. The Solstice denotes the pausal of the Sun’s movement in its path, at the extreme north or south, before reversing its direction.
The two types of solstices are June Solstice and December Solstice.
June Solstice, better known as Summer Solstice in the Northern Hemisphere, is the period when the location of the Sun is directly over the Tropic of Cancer. This day is the longest day of the year (21st of June). The situation is the exact opposite in the Southern Hemisphere.
December Solstice, also known as Winter Solstice in the Northern Hemisphere, occurs about, 22nd of December when the location of the Sun is above the Tropic of Capricorn from the celestial equator. The day is the shortest of the year, and night is the longest.
The time of Solstices is not easy to determine, unlike equinoxes, as the declination in the speed of the Sun is less than 30 seconds before and after a few days of the Solstice. Many cultures celebrate Summer and Winter Solstice, and equinoxes, and the midpoints between those events.
Main Differences Between Equinox and Solstice
- Equinox is the time of the year when the length of day and night is equal due to Earth being the nearest to the Sun. On the other hand, Solstice is the time of the year when the length of day or night is the longest due to the Sun being farthest from the celestial equator.
- Vernal and Autumnal equinoxes indicate the start of the seasons like spring and autumn (fall), respectively. In contrast, June and December Solstice marks the beginning of summer and winter, respectively.
- Equinoxes occur in March and September, and Solstices, on the other hand, occur in June and December.
- Solstices signify the change in length of day and night, but Equinoxes do not.
- Equinoxes result in an equal amount of light and darkness received across the Northern Hemisphere.
Conclusion
Equinox and Solstice are two opposite phenomena. As the Earth travels around the Sun, seasons change and the length of days and nights; these two phenomena manifest the beginning of different seasons in the Northern Hemisphere.
References
- http://solar-center.stanford.edu/AO/Sun-Track-Model.pdf
- https://mis.kp.ac.rw/admin/admin_panel/kp_lms/files/digital/CoreBooks/Core%20Books%20in%20Geography/E167%20-%20E265_%20%20Physical%20Geography%20I%20&%20II_%20%20Introduction%20to%20Physical%20Geography%20038.pdf