Even though last weekend’s snow storm may not exactly seem like a herald of spring, nothing can stop the season from arriving astronomically speaking.

The vernal equinox arrives at 11:33 a.m. Sunday. For the first time since September, the sun is entering the northern half of the celestial sphere. From now until late June the sun will climb higher in the sky until the days reach their maximum length.

According to Krishna Mukherjee, assistant professor in the department of physics and engineering at Slippery Rock University, the word vernal originates from Latin meaning spring, and equinox means equal night. On this day, the Northern Hemisphere is transitioning from tipping away from the sun to towards it.

A planet’s axial tilt makes the vernal and autumnal equinox special. On those two days, the length of day and night are equal. Without a tilt, the day and night would be equal length throughout the year and we would have one season, according to Mukherjee.

The sun starts to climb higher after the winter solstice and this continues until summer solstice when the noon time sun reaches its maximum height.

However, Mukherjee said, during the equinox, the noon time height of the sun above the horizon is equal to ninety degrees minus your latitude. For a visitor to the North Pole, this would mean observing the sun skirting the horizon throughout the entire day on vernal equinox. Dawn and dusk merge.

According to Mukherjee, on the first day of spring and fall, the sun rises precisely in the east and sets in the west.

“This is noticeable if you are driving along an east-west road, the rising sun hits your eye if you are driving east in the early morning,” he said.

Lee Hendricks, a meteorologist with the Pittsburgh office of the National Weather Service, said of the vernal equinox: “It’s just really showing when the sun is more high in the sky in the Northern Hemisphere.

“It’s the gradual lifting of the sun into the sky in the Northern Hemisphere,” he said. “That’s really the official time when spring arrives meteorologically speaking.”

The equinox really has no effect on the weather. Temperature highs and lows for this time of year, Hendricks said, are 51 and 31 degrees.

While there is a gradual warming trend this month, Hendricks warned there can also be snowstorms as well, citing the winter blast of March 1993.

That’s the scientific reason behind noting the vernal equinox.

Other cultures see a more spiritual aspect to the sun’s course across the sky.

For instance, the vernal equinox is used to determine the date of Easter every year.

According to the editors at the Old Farmer’s Almanac, this year Easter will be observed on Sunday, April 17. (Eastern Orthodox Easter will take place Sunday, April 24.)

Easter this year is just one day after April’s full moon (April 16), which is the first full moon to occur after the vernal equinox and is therefore known in the Christian calendar as the “Paschal Full Moon“ and it determines the date of Easter.

Easter is a “movable feast” and does not have a fixed date. However, it is always on a Sunday between March 22 and April 25.

Over a 500-year period (from 1600 to 2099 AD), it just so happens that Easter will have most often been celebrated on either March 31 or April 16.

Many Eastern Orthodox churches follow the Julian calendar rather than the Gregorian. In this case, the observance of Easter can occur between April 4 and May 8, according to the Old Farmer’s Almanac.

Mike Dittman, a professor of English at Butler Count Community College and an amateur folklorist, said that for many cultures, the arrival of the new season was the renewal of life itself, the triumph of light over darkness.

“Every culture has some sort of story around the vernal equinox,” he said.

The ancient Egyptians, Greeks and Mayans celebrated the resurrections of their gods during the spring equinox.

One holdover from an ancient Chinese myth, said Dittman, was the belief that you could stand an egg on its end only during the vernal equinox, when day and night are equal in length.

“That’s just a myth. You can stand an egg on its end any day of the year,” he said. “The belief comes from China originally. The legend is a Chinese princess swallowed an egg on that day and later gave birth to a magical sort of guy.

“Eggs play a big role in the Chinese celebration of the coming of spring,” he said.

In ancient times, people performed rituals during the equinox to cleanse old energy in themselves and in their homes.

Dittman said the Japanese have a holiday celebrating the coming of spring called Shunbun no Hi, a public holiday dedicated to sprucing things up after winter ends.

“People go out and clean their dead relatives’ gravestones,” said Dittman.

Though it is presently considered a secular holiday, Shunbun no Hi has its origins in Shinto tradition.

Some pagan religions celebrate the equinox with a ritual called Ostara, which involves observing agricultural changes. The ritual venerates the Anglo-Saxon goddess Eostre, also known throughout history as Astarte and Ishtar, who is associated with flowers and springtime. Her name gives us the modern word “Easter.”

The Persian new year, Nowruz, is still celebrated on the spring equinox. Nowruz has been celebrated in Iran and the Persian diaspora for more than 3,000 years. Its roots are as a feast day in Zoroastrianism, a religion practiced in ancient Persia that viewed the arrival of spring as a victory over darkness.

“In Central Asia, Nowruz is huge. It’s like New Year’s Eve and St. Patrick’s Day and Christmas and the Fourth of July all rolled into one,” said Dittman. “They have this tradition where they jump over huge bonfires. That’s part of the celebration of the coming spring. There’s special foods. It’s a two-week celebration.”

According to Mukherjee, without any calendar the ancient people needed markers to observe the occurrence of spring equinox.

“This was essential for religious and agricultural purposes. They built archaeological sites where on the first day of spring the sun would strike a particular rock or spot,” she said.

For example, on the vernal equinox, she said, the sun rises above the main tower of the largest Buddhist temple Angkor Wat in Cambodia. In Mexico, the Mayan archaeological site of Chichen Itza, people can witness the play of light and shadow along the steps of the pyramid of Kukulkan creating a giant snake. It signifies the descent of the feathered serpent god “Kukulkan” on spring equinox.

In Peru, the Incas carved a stone at Machu Picchu, that casts no shadow when the sun is at high noon on the first day of spring.

“Closer to home, we have structures in the Chaco Canyon in New Mexico, where the sun shines through certain opening on vernal equinox,” she said. adding in some cultures, the new year begins with spring, like Nowruz celebrated by Iranians.“