Happy Equinox Everyone!
Long ago astronomers imagined a great dome over the Earth’s sky and called it the celestial sphere. They imagined the celestial equator as being in the middle of the north and south poles and right above the Earth’s equator. During the March equinox, when we have twelve hours of daylight and twelve hours of darkness, “the sun crosses the celestial equator, to enter the sky’s Northern Hemisphere. No matter where you are on Earth (except the North and South Poles), you have a due east and due west point on your horizon. That point marks the intersection of your horizon with the celestial equator, the imaginary line above the true equator of the Earth. And that’s why the sun rises due east and sets due west, for all of us, at the equinox. The equinox sun is on the celestial equator. No matter where you are on Earth, the celestial equator crosses your horizon at due east or due west.”
Reprinted from EarthSky, written by Bruce McClure: http://earthsky.org/tonight/equinox-sun-rises-due-east-and-sets-due-west