Spring officially returns to Utah and all of the northern hemisphere on Tuesday, March 20 at 6:07 p.m. MDT. Known as the vernal or March equinox, the arrival of spring here in the northern hemisphere marks that moment when the Sun slides northward through the celestial equator.
The celestial equator is an imaginary line in space above the Earth's equator.
As NASA Solar System Ambassador Patrick Wiggins explains it, "One way to think of the equinox is that day when the periods of darkness and light are nearly, but not exactly equal and the Sun rises due east and sets due west."
The next such event, known as the autumnal or September equinox, will occur when the Sun passes southward through the celestial equator next September, marking the start of fall in the northern hemisphere.
Similarly, there are two times a year when the Sun is furthest from the sky's equator. One is at the start of our summer, when it's furthest north, and the other is at the start of our winter, when it's furthest south. These events are known as the June and December solstices.
Wiggins adds that while Utahns and others who reside in the northern hemisphere mark this month's equinox as the start of the longer, warmer days of spring, those in the southern hemisphere, where the seasons are reversed, see this event as the start of the shorter, cooler days of autumn."
For further astronomical information log onto Wiggins' Solar System Ambassador website at http://utahastro.info.