The March equinox is celebrated by people all over the world, and around this time of year there are the major spring festivals of Passover and Easter, with the latter occurring on the first Sunday after the first full Moon following the vernal equinox. Other festivities across the globe includes Japan’s Cherry Blossom festival (Hanami), the Hindu festival of Holi celebrated in India and Nepal, and Thailand’s Songkran Festival
This year, the Spring Equinox falls on Sunday, March 20th, a day which marks the end of winter and start of spring in the Northern Hemisphere, and in the Southern Hemisphere the time when summer turns to autumn. But, what exactly is happening in the celestial heavens to make this astronomical event occur. In a nutshell, it is caused by the tilt of the Earth on its axis as it orbits the Sun.
Each equinox or solstice marks a change in the Earth’s seasons, which in turn is a result of our planet’s 23.4 degrees tilt towards the celestial pole, which either points towards or away from the Sun as we our complete our annual 365-day orbit. Obviously, as one hemisphere points towards the Sun (summer) it will become warmer as it receive more of our sun’s rays, while the other hemisphere will be experiencing its winter time, together with longer shadows and colder temperatures.
At the time of the equinoxes, however, the Earth’s rotational axis is neither tilted towards or away from the Sun, given us equal day and night. In fact, if the Earth had no tilt at all, then we would experience things very differently on our planet, and as Jim Todd, an astronomer at the Oregon Museum of Science and Industry (OMSI), explains:
“In the winter, when we are tilted away from the Sun, the rays pass through the atmosphere at a greater slant, bringing lower temperatures. If the Earth rotated on an axis perpendicular to the plane of the Earth’s orbit around the Sun, there would be no variation in day lengths or temperatures throughout the year, and we would not have seasons.”
During the vernal equinox, the amount of day and night hours will be roughly equal at 12 hours each, after which in the north we will receive progressively more daylight than dark until the Summer Solstice when the Sun reaches its high point of around 16.5 hours of light, depending on your location. After that, the ratio begins to reverse once more as we head towards the Autumnal Equinox on September 22nd, and by the time we reach the Winter Solstice we will receive around 16.5 hours of nighttime, instead.