Spring equinox 2024: In Greece the day is longer than night – What astronomers say

On Wednesday, March 20th, we have officially, but not equal day and night. On the day is longer than night. The “entered” on 20 March 2024 marks the beginning of this spring in Greece and in the northern hemisphere in general. However, the astronomical term “same” often leads to the misunderstanding that this day marks the same day and night duration. In particular, in Greece the day is longer than night. The equal duration occurred a few days earlier, on March 17. As Professor Emeritus of the Department of Physics of the ATH, Charalambos Varvoglis points out, if we look for the hours of sunrise and sunset of this day we will see with surprise that, for example, the sunrise in Greek Attica is at 6:28 and the west at 18:37. “What kind of equinox is this, which day is 18 minutes longer than night? The answer is simple: during the equinox we would indeed have equal durations of day and night, if the Sun were a sign (geometry) and if the Earth had no atmosphere (refraction)”, he explains. The refraction of sunlight in the Earth’s atmosphere Specifically, as the Sun is a disc and not a bright point, sunrise and west do not occur momentarily. Varvoglis explains that the time between the sunrise of the Sun’s lip and the east of its center is very easy to find for places located in the equator, where the Sun rises and sets vertically on the horizon, and corresponds to a first minute. However, in the middle latitudes, such as Greece (it is about 40 degrees latitude) this time is longer and equals about 1.5 minutes. As there is another difference in the west, only because of this phenomenon during the equinox the day in Greece would last 12 hours and 3 minutes and the night 11 hours and 57 minutes, so the difference would be 6 minutes. Regarding the phenomenon of refractive sunlight in the Earth’s atmosphere, Mr Varvoglis observes that the Earth’s atmosphere refractives the rays of the Sun, so that at sunrise it seems to be higher than where it really is. So due to refraction during the equinox, the day would be 12 minutes longer than night. As the two phenomena of geometry and refraction are added, Mr Varvoglis concludes, the difference of 18 minutes arises. Dr. Tina Nanchu, a scientific associate of the Department of Physics of the CRP, suggests during the spring equinox, “to carry out the historical experiment of the mathematics of antiquity Eratosthenes and with a ruler or a rod and our minds to calculate the circumference of the Earth.” It is an experiment of the 3rd century BC in which Eratosthenes managed to calculate the circumference of the Earth in a geometric manner. The method is applied to this day for educational reasons and equinoxes and solstices are ideal dates for its realization.