The March equinox occurs on March 20th at 5:24 p.m. EDT. The Sun will then shine directly over the equator, being positioned on the celestial equator—the imaginary line in the sky directly over the Earth’s equator. This is the first day of Spring (the vernal equinox) in the Northern Hemisphere and the first day of Fall or Autumn (the autumnal equinox) in the Southern Hemisphere. After crossing over the celestial equator, the Sun heads north toward the summer solstice which occurs on June 21st at 10:58 a.m. EDT., the first day of Summer. At that point, our Daytime Star stops its northward movement, appearing to stand still, then begins to drop south again in the sky on its way to the autumnal equinox. This marks the first day of Fall in the Northern Hemisphere and occurs on September 23rd at 2:50 a.m. EDT this year.
Perhaps you have had an opportunity see a picture of the amazing “analemma loop”—an image showing the position of the Sun in the sky at the same time of every clear day throughout the year. (There are many of these available to look at online.) It shows the Sun’s longer path across the sky in Summer, resulting in longer days and shorter nights, while its shorter path in Winter brings shorter days and longer nights. This helps explain why despite colder temperatures and fewer clear nights, Winter is the favorite season of most stargazers. Earlier darkness and longer nights for viewing. (And also the sky’s brightest stars and constellations visible at this time of the year—just think “Orion” to see what is meant!).
— James Mullaney
Former assistant editor at Sky & Telescope magazine & author of 10 books on stargazing. His latest, Celebrating the Universe!, is available from HayHouse.com.