ROCHESTER, N.Y. (WROC) — March 20th, marks the first day of astronomical spring for us this year. It began at approximately 5:37 AM this morning, and the forecast could not have been more perfect.
Spring Equinox History
The earth rotates on its axis and orbits around the sun. At the start of spring, or vernal equinox, the earth is tilted neither towards or away from the sun, and the sun is located directly over the equator. This is why we have roughly equal parts day and night around this time.
However, the actual day we receive 12 hours of day and night doesn’t always occur on the equinox due to how the earth’s atmosphere refracts, or bends sunlight. In fact, the day we received equal parts day and night was back on the 17th, a whole three days before this event. The refraction of the sun’s light ultimately causes the upper edge of the sun to be visible above the horizon for a few minutes even after it physically sets.
“The day we received equal parts day and night was back on the 17th, a whole three days before this event.”
The term equinox comes from the latin word “aequalis” meaning equal, and “nox” meaning night. The term “vernal” means “fresh and new” like how spring feels after a long winter.
Even though the length of our day and night become nearly equal around this time, the time it takes for the sun to rise and set is not compared to other times throughout the year.
Did you know it’s around the spring and autumn equinoxes that our sunsets and sunrises occur the fastest? Meaning, it takes much less time for the sun to set below or rise above the horizon during twilight than during the solstices. Why?
It’s all based on the changing angle of the sun moving across our sky throughout the year.
The sun rises due east and sets due west on the equinoxes, which means it’s rising and falling at the steepest possible angle in the sky. It’s this steep angle that causes the sun to set and rise much quicker than during the solstices. Your latitude ultimately determines the duration of the sunset, and it’s because of this that the sun sets the fastest near the equator, and the slowest near the poles.
Since the sun sits much higher in the sky near the equator at solar noon than at the poles, the equator gets the most direct sunlight year round. With a much lower sun angle at the poles, the path it takes for the sun to set is much more parallel to the horizon, so it stays closer to the horizon longer as it sets. This is why the sunset is much more “abrupt” the closer you are to the equator, while the amount of twilight in somewhere like Alaska lasts much longer (because of the slower sunset).
Did you know not everyone experiences such drastic temperature changes between seasons year round?
Since the center of the earth gets the most direct and constant sunlight year round, the change in daylight is drastically different than at the poles. For example, in Quito, Equador which the closest city to the equator gets roughly 12 hours of day and night year round. Barrow, Alaska, located just north of the Arctic Circle sees 67 days of straight night, and over 80 days of straight daylight.
This results in very different seasonal experiences throughout the globe. The closer you are to the equator, the less change in daylight and therefore seasons you see. This results in very little temperature changes throughout the year at the equator since the amount of sunlight reaching this part of the earth stays fairly consistent even with the change in tilt. This is why the equator stays fairly hot throughout the year, while Western New York State for example, located around 43° north of the equator is much more affected by the earth’s tilt, and therefore has more pronounced seasonal and temperature changes.
~Meteorologist Christine Gregory