How to Calculate the Vernal Equinox

In the northern hemisphere, the vernal equinox marks the exact date and time when the sun crosses over the Earth's equator, and spring arrives. In the southern hemisphere it's called the autumnal equinox. Calculating precisely when the vernal equinox will arrive takes some work.

Difficulty: Moderate

Instructions

1. Check your calendar for a date near March 20 and 21. This is the time when night and day last about the same length of time because the sun is as close to the equator as it can be. The date of the vernal equinox is floating earlier and earlier. Every 100 years or so it moves up a day.

2. Compute the vernal equinox using the universal time. This is the time that scientists use to compute astronomy events. When you want to convert the universal time to Eastern standard time, you subtract five hours.

3. Compute the vernal equinox using vernal equinox computing software. This software uses complex formulas relating to the stars and sun to determine times within an hour that will reveal the exact point of the vernal equinox each year.

4. View a vernal equinox graph. The vernal equinox graph is a graph created by scientists that shows the positions of Earth compared to the sun. The vernal equinox happened on the 21.4 day in March in 1960 and has slowly moving up from that date ever since. It will reach the 20.0 day at some point near the year 2040.

Resources

• Find software to calculate the vernal equinox at Mathematica Scientific Astronomer Software.
• View a vernal equinox graph at Astrology Stations.