Here’s what to know about the first day of spring.

How is the first day of spring determined?

The first day of spring, or the vernal equinox, is determined by where the Earth is in its orbit around the sun. On this day, the Earth’s axis is not tilted toward or away from the sun, causing roughly an equal amount of sunlight and dark hours at all latitudes, the National Weather Service explains.

This year’s first day of spring in the Northern Hemisphere occurs precisely at 5:01 a.m. EST on March 20, according to NASA. The date and time of the equinox varies slightly from year to year.

The Earth is not tilted toward or away from the sun on the first day of fall as well, also called the autumnal equinox. On both equinoxes, the sun is exactly above the equator.

Once the Earth hits its vernal equinox, the Northern Hemisphere moves into spring and the Southern Hemisphere moves into fall.

The Earth sits at 23.5° on its axis, which is also what causes the seasons, the National Weather Service explains. When the Earth tilts toward the sun, the hemisphere closest to the sun gets more light hours during the day and vice versa. The longer the daylight lasts, the warmer the weather gets, but it’s on a lag due to the time it takes the ground and water to heat up.

How is the vernal equinox celebrated?

The start of spring is celebrated in a variety of ways around the world. Here are a few examples:

In Japan, the vernal equinox, or Shunbun no Hi, is a public holiday to show appreciation for nature and welcome the start of cherry blossom season. The country also recognizes a seven-day period around the equinox called Higan, during which people pay respects to their ancestors, the Ministry of Foreign Affairs of Japan says on its website.

In Mexico, one of the traditions is to visit the Pyramid of the Sun in Teotihuacán, according to the Smithsonian Science Education Center.

Holi, the annual Hindu festival of colors, is another example of a celebration of spring, but it occurs on the last full moon in the Hindu month of Falgun, rather than being tied to the equinox. This year, Holi was held on March 13-14.

Nowruz, meaning “new day,” is a new year and spring equinox celebration in Iran and other countries in Central Asia and elsewhere. Dating back to the Persian empire, “it is an ancient celebration of life, rebirth, and the triumph of light over darkness,” the United Nations says.

Can you really balance an egg on the vernal equinox?

The myth that you can balance an egg on the vernal equinox is not rooted in science. According to the Astronomical Society of the Pacific, the equinox has nothing to do with getting an egg to stand on its own.

The good news is you can balance an egg any time of the year.

What’s the difference between an equinox and a solstice?

The equinoxes occur when the sun is right above the equator, making day and night equally long. The solstices occur on the longest and shortest day of the year, respectively.

In the Northern Hemisphere, the summer solstice is when the North Pole tilts toward the sun and the winter solstice is when the South Pole tilts toward the sun.