How is the spring equinox defined?
Planetary alignment observed since ancient times
At the equinox, which happens twice a year, the earth is balanced on its axis and the length of day and night are roughly equal. If you are looking due East in the morning, or West at night, you are being blinded by the sun. From the observer's viewpoint on Earth, the sun is in the middle of its course between north and south that it follows every year. According to Wikipedia, "At an equinox, the Sun is at one of two opposite points on the celestial sphere where the celestial equator (i.e. declination 0) and ecliptic intersect." For those of us who are not Wikipedia, or astronomers, the Spring Equinox means that we are exactly halfway to the beginning of summer, or half a year from fall.
Notes and Special Information
Special note: Although the equinox has been steadily observed for thousands of years, we place no warranty on future equinoxes. Tomorrow on YouTube, Bill Nye debates an Equinox Denier