Die Tagundnachtgleichen

Jason Harris

Viele Menschen kennen die Tagundnachtgleichen im Frühjahr und im Herbst als Kalenderdaten, die den Beginn des Frühlings bzw. des Herbstes auf der nördlichen Halbkugel markieren. Wussten Sie, dass die Tagundnachtgleichen auch Positionen im Himmel sind?

The Celestial Equator and the Ecliptic are two Great Circles on the Celestial Sphere, set at an angle of 23.5 degrees. The two points where they intersect are called the Equinoxes. The Vernal Equinox has coordinates RA=0.0 hours, Dec=0.0 degrees. The Autumnal Equinox has coordinates RA=12.0 hours, Dec=0.0 degrees.

The Equinoxes are important for marking the seasons. Because they are on the Ecliptic, the Sun passes through each equinox every year. When the Sun passes through the Vernal Equinox (usually on March 21st), it crosses the Celestial Equator from South to North, signifying the end of Winter for the Northern hemisphere. Similarly, when the Sun passes through the Autumnal Equinox (usually on September 21st), it crosses the Celestial Equator from North to South, signifying the end of Winter for the Southern hemisphere.