Last year, Astronomical Spring (vernal equinox) began on March 20th.
In 2023, the spring equinox will occur on March 21st.
But what is it? What happens on this day and why does this period attract so much attention?
So, let's start in order!
On the day of the vernal equinox, the Sun, moving along the ecliptic (the trajectory of its apparent annual movement in the celestial sphere), passes from the southern hemisphere of the celestial sphere to the northern one. As a result, an astronomical spring will come in the Northern Hemisphere of the Earth.
On the entire planet, with the exception of the polar regions, the duration of daylight and night becomes almost the same.
Also, during the equinoxes, the Sun during its annual cycle crosses the celestial equator - the circle of the celestial sphere, the plane of which coincides with the plane of the earth's equator.
!!! This event takes place twice a year: in March and September (there are no clear dates, they can shift by one to three days).
The points of intersection of the celestial equator with the ecliptic are called the equinoxes.
At the vernal equinox, the Sun moves from the southern to the northern hemisphere of the celestial sphere, and at the autumn equinox, from the northern to the southern.
In the Northern Hemisphere, the March equinox is called the spring equinox, and the September equinox is called the autumn equinox (in the Southern hemisphere, vice versa).
These days the Sun equally illuminates both hemispheres of the planet, being approximately 12 hours above and below the horizon.
In astronomy, the vernal equinox is used to determine the astronomical coordinates of stars and other space objects in the equatorial coordinate system, when the celestial equator is taken as the reference point.
From the point of the vernal equinox, right ascensions are counted (the angular distance from it to the great circle of the celestial sphere passing through the poles of the world and the observed luminary) along the celestial equator, longitudes along the ecliptic.
The concept of right ascension was known as early as the 2nd century BC. e., when the ancient Greek astronomer Hipparchus determined the location of the stars in equatorial coordinates, so for 2 thousand years it shifted 20 degrees west from the constellation Aries to the constellation Pisces.
