Astronomy Picture of the Day . ... The Vernal Equinox occurs March 20, marking the first day of Spring for the Northern Hemisphere. It also marks a favorable celestial situation for potentially viewing all the objects in 18th century French astronomer Charles Messier's catalog in one glorious dusk to dawn observing run. This year a bright full moon will interfere with dark skies near the actual equinox, so good nights near new moon for weekend marathoners are March 11/12 and April 1/2. ...