It’s finally here! The Vernal (Spring) Equinox kicks off the season where days continue getting longer and temperatures continue getting warmer. The equinox occurs at 5:58pm EDT and that’s the precise minute the sun is directly over earth’s equator.
The reason for the season
The reason we have “seasons” on earth is all because of the tilt of Earth’s axis. Instead of the north and south pole pointing directly up and down respectively, they tilt at a 23.5° angle. Due to this, as the earth revolves around the sun, the direct sunlight will strike in different places. During the equinoxes (spring and fall), the rays of the sun are directed exactly at the equator.
Nothing is Equal…Or is it
The term “equinox” translates to “equal night.” A common misconception of the equinoxes is that there are equal amounts of time during the day and night. While both day and night are very close to each other on the equinoxes, there will always be a few minutes of extra daylight. This is due to how we define “sunrise” and “sunset.” Sunrise and sunset are defined and recorded using the top of the sun’s “disk.” Sunrise begins when the top of the disk rises above the horizon and sunset is finished when the top of the disk lowers below the horizon. The diameter of the sun’s disk relative to us causes daylight all around the world to be a few minutes more. Therefore on the equinoxes, the 12 hour sunlight day will be accompanied by a few extra minutes.
Now, depending on latitude, you may experience a day that is equal in the time of day and night. As the earth tilts towards or away from the sun, the daylight time will get longer or shorter respectively. Therefore, twice a year, there will be a day that has exactly (or almost exactly) a 12 hour day and night. The location’s latitude will determine when you get that phenomenon. Lexington’s equal day and night occurs around March 17th and September 26th. The Equator and the poles never get to experience this phenomenon.
Another reason why the equinoxes don’t bring equal amounts of day and night time is due to the refraction of light. The earth’s atmosphere bends light in a way that even after the sun’s disk has lowered below the horizon, the top of the disk is still visible (assuming flat terrain). Likewise, the atmosphere’s refraction of the sunlight could make the sun’s disk visible in the morning before it has actually appeared above the horizon. This small discrepancy also adds a few more minutes to the daylight time.
A Super Astronomical Double-Header
The spring equinox will occur just under four hours before the Super Worm Moon. These two astronomical events haven’t happened together since the year 2000 and won’t again until 2030. More information on the Super Worm Moon can be found here: The Last Supermoon of 2019