This year, the autumnal equinox will occur on September 23 at 09:50 am Bulgarian time, Pencho Markishki, a physicist at the Institute of Astronomy with NAO at the Bulgarian Academy of Sciences and at the Department of Astronomy at Sofia University "St. Kliment Ohridski" told BTA. Kliment Ohridski".
He pointed out that the late start date of autumn, not on September 22, as is customary, is impressive. The reason for this is that we are in the previous year of leap year 2024, explained Markishki.
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"The average length of a tropical (sunny) year is 365 days, 5 hours, 48 minutes and 45 seconds, but for convenience the calendar system must work with an integer of days a year – 365. Therefore, from this and the previous two non-leap years, residues of nearly 6 hours have accumulated, due to which logically the beginning of the annual seasons is delayed by about 18 hours. Reporting the leap date of February 29 next year will compensate for the accumulated residues and in 2024 the astronomical autumn will occur on September 22 at 15:43 – nearly 18 hours earlier, "he said.
The physicist recalled that the equinoxes occur when the Sun crosses the celestial equator, passing, for example, from the southern to the northern celestial hemisphere on the date of the vernal equinox - around March 20, which is the beginning of astronomical spring for the Northern Hemisphere of the Earth. In September, the opposite happens – the Sun returns from the northern to the southern starry sky on the date of the autumnal equinox, which marks the beginning of autumn for our hemisphere.