By Andrew Hill
Spring officially returned to Utah and the northern hemisphere on Tuesday night, March 20, 2007.
The first day of spring, also known as the vernal equinox, is marked by the moment that the sun passes directly over the celestial equator, an imaginary line in the sky directly above the Earth''s equator.
'So that means on the first day of spring, the noon sun will be directly over the equator,' said Clark Christensen, a BYU associate professor who specializes in meteorology. 'After the first day of spring, the noon-day sun will be overhead someplace on the Earth that''s north of the equator.'
The vernal equinox is one of only two days of the year when this phenomenon occurs. The other is the autumnal equinox.
'It''s just a time that no matter where you are in the earth, the daytime and the nighttime are equally divided,' said Joseph Moody, a BYU professor and astronomer.
The reason for this phenomenon is due to the tilt of the Earth''s axis. The angle of the Earth''s tilt measures about 23 degrees and faces the same direction throughout the year. As the earth passes through it''s orbit, different parts of the earth lean more directly toward the sun. This causes changes in the seasons and in the length of days.
'When a part of the earth is tilted toward the sun, you get more direct, concentrated sunlight, and you get summer,' Moody said.
NASA Solar System Ambassador to Utah, Patrick Wiggins, said in a news release that this is also a day that, at the equator, the sun rises directly east and sets directly west.
Although the advent of spring indicates warmer weather, Provo will receive rain for the next few days and possibly snow.
'We''ll still see some more cold weather,' Christensen said. 'We''ll get some more snow-we always do after the first day of spring,' Christensen said.