How to Identify When Vernal Equinox Occurs

Vernal equinox is identified as a day, but in truth, it is a moment: the precise instant when the middle of the sun crosses past the celestial equator. If you stood on the equator at that moment, the sun would appear to stand at its highest point in the sky. For those who don't live in northern Brazil, central Africa or Indonesia, however, it may be a bit trickier to identify when vernal equinox occurs.

Instructions

1. Determine the exact moment of vernal equinox. The quickest way to do this is to check an almanac which has plenty of information on astronomical phenomenon.

2. Remember that times given for the vernal equinox are given in Universal Time (also called Universal Time Coordinated), not local time. Universal Time is essentially Greenwich Time minus daylight savings time (if applicable). If you want to know when vernal equinox occurs in your time zone, simply add or subtract from Greenwich Time plus 1 additional hour, since daylight savings time is usually in effect when the equinox rolls around.

3. Note that vernal equinox occurs when the center of the sun passes over the celestial equator. Because the sun is a sphere and not a single point, it takes over a day for the entire sun to pass over the equator.

4. Identify the point when the sun's declination equals 0. Declination is a measure of the sun's angular distance north or south of the equator. When it equals 0, the vernal equinox occurs. You can identify it by using the following basic mathematical formula: d = 23.45 * sin [360/365 * (284 + N)]. Where d equals declination and N equals the number of days since New Year. (January 1 = 1 day.) More complex mathematical formulas can be used with a greater amount of accuracy.

5. Count the hours of daylight and compare them with the hours of night. The equinox takes place on the day which almost perfectly balances day and night. This has considerable significance in Wicca and other religions which place value on the equinox: The notion of balance moving towards light symbolizes the rebirth of spring and the hopefulness of that season.

6. Observe that the vernal equinox falls about 6 hours later each ensuing year. This is one of the reasons why we have leap year every 4 years. The extra day "resets" the time of the equinox and allows the calendar year to more accurately reflect the seasons.

Tips & Warnings

• If you prefer to cut to the chase, the 2008 vernal equinox will occur on March 20 at exactly 1:48 a.m., Eastern Daylight Time.