With spring season set to officially begin this weekend, astronomers are preparing for a celestial event as well where the rays from the Sun start crossing over the equator from the Earth's southern hemisphere to its northern hemisphere.

This event is called an equinox and it is known to occur twice a year. The first one is known as the vernal equinox, which falls on March 20 or March 21, and the other one is known as the autumnal equinox, which falls on Sept. 22 or Sept. 23.

The upcoming vernal equinox this weekend marks the passing of the Sun from the Earth's southern region into its northern one, during which its rays are expected to shine directly over the planet's equator. This creates a phenomenon in which both hemispheres receive the same amount of light from the sun.

For people living in countries located in the northern hemisphere, such the United States, they will see the Sun rise earlier than during winter and it will set a little later in the day as well. Plants will begin to sprout from the ground, while the winds start to become softer again.

As the changing of the season ushers in warmer and gentler weathers for residents in the northern hemisphere, it also signifies the transition to autumn season for countries south of the equator.

An Earlier Start For Spring

According to the research group organization EarthSky, 2016's vernal equinox is set to make its earliest start since 1896. This is because the tropical year, which is determined by measuring the number of consecutive March equinoxes, does not include an even number of days. It only has 365.242 days.

Meanwhile, the calendar that many people use has 365 days during common years and 366 days during leap years.

In 2012, the March equinox also had a relatively early start, but this year's spring is expected to begin at a much earlier date.

At the turn of the century, the March equinox was pushed approximately three-quarters early because 2000 was considered to be a leap year.

It is set to be pushed to an earlier time again at the start of the 22nd century because 2100 is expected to be suppressed as a leap year. This is based on Pope Gregory XIII's revision of the Julian calendar, in which he stated that years ending in "00" should only be given leap years if they can be divided evenly by 400.

Photo: NASA Goddard Space Flight Center | Flickr