Astronomy begins on Monday, March 20 at 10:24 p.m springthis is when the equinox occurs – the National Meteorological Service wrote on its website, drawing attention to the fact that the textbooks date the event to March 21, but it can also fall on March 20 or 21.
They added: the date of the equinox “slips” because an Earth year is not an exact integer multiple of the Earth day, to be exact 365 days, 5 hours, 48 minutes, 46 seconds. This is the reason why the leap day had to be introduced, as the difference is almost 24 hours in four years, they noted.
It was pointed out: in addition, the Earth’s orbital parameters – its eccentricity, the location of the vernal point, the precession of the rotation axis – are also not constant, but these only cause very small deviations, the date of the vernal equinox during the 400-year period of the Gregorian calendar is only one changes two hours.
They added: the last time the vernal equinox fell on March 21 was in 2011, and it will happen for the first time on March 19 in 2048.
The meteorological service also wrote that at the equinox, despite the name, day and night are not of equal length.
As it was written, one of the reasons for this is that due to atmospheric refraction (light refraction), celestial bodies appear a little higher above the horizon than their true location, this very small difference on the horizon is the largest, half a degree.
This means that the Sun appears on the horizon at sunrise a few minutes earlier than it actually does. In the same way, at sunset, it seems to rest that much later. This phenomenon increases the length of days by a few minutes, they wrote.
The other reason is that on the day of the equinox, the geometric center of the Sun is above the horizon until 12 o’clock, but the Sun has an extension, i.e. a circle shines on us, i.e. it is visible even when its center is not yet arose, and radiated even when its center had already settled down, they wrote.
They added: for this reason, there is no day-night equality at the equinox, in fact, because of this, there is never exactly a day-night equality, but on March 16 and 17, the length of day and night is almost equal.
MTI
