The first day of spring arrived Tuesday with the 2012 vernal equinox, heralding the end of a winter that, for most of us, wasn't. The United States experienced the warmest winter of the 21st century so far and the fourth-warmest winter in 117 years of record keeping, according to the National Oceanic and Atmospheric Administration.

New Mexico was the only state with temperatures below its long-term 20th century average this winter. Most others were well above, with typically snow-capped locales like Grand Rapids, Mich., Grand Forks, N.D., and Green Bay, Wis., boasting their second-warmest winters ever.

As the vernal equinox arrived on Tuesday, the first day of spring proved to be equally mild with temperatures in the upper 60s and 70s across much of the U.S. East Coast.

The vernal or spring equinox marks the point in space and time when the sun moves across the celestial equator, an invisible circle projected into the sky above the Earth's equator. In the Northern Hemisphere, the days grow longer and the nights shorter. In the Southern Hemisphere, the same equinox marks the beginning of longer nights and shorter days and heralds the beginning of autumn.

In theory, the equinox should mark the time when day and night are equal, when both share 12 hours apiece. However, in practice that happens days earlier due to atmospheric effects. The date of the equinox varies each year from March 19 to 21 depending on location and corrections due to a discord between the Gregorian calendar (logging 365 days a year) and the actual duration of the Earth's orbit around the sun (which takes approximately 365.25 days to complete).

The occasion is celebrated in a myriad of ways across the globe. Press Start to have a look.

Kabul, Afghanistan
Afghans gather to celebrate Afghan New Year (Nawroz) in Kabul March 20, 2012. Afghanistan uses the Persian calendar which runs from the vernal equinox. The calendar takes as its start date the time when the Prophet Mohammad moved from Mecca to Medina in 621 AD. The current Persian year is 1391. REUTERS/Omar Sobhani
Valencia, Spain
Effigies burn during the finale of the Fallas festival, which welcomes spring and honors Saint Joseph's Day. Fallas are giant elaborate sculptures and effigies made of wood and plastic that are burned at the end of a week-long spectacle of processions, fireworks, music and dancing. REUTERS/Heino Kalis
Malta
A visitor meditates after the sunrise at the megalithic Mnajdra Temple during the vernal equinox, which marks the first day of spring, outside Valletta March 20, 2012. The temple, which is covered by a protective tent, is listed as a UNESCO World Heritage site and is believed to date back to around 3600 B.C. REUTERS/Darrin Zammit Lupi
Mexico City, Mexico
A woman dances during a carnival as part of the spring equinox at Paseo de la Reforma Avenue in Mexico City. REUTERS/Edgard Garrido
Washington DC, USA
People paddle a boat on the Tidal Basin during the first bloom of the cherry blossoms in Washington. This year marks the 100th anniversary of the gift from Japan to the United States that started with a planting ceremony between then U.S. First lady Helen Herron Taft and Viscountess Chinda, wife of the Japanese ambassador. REUTERS/Gary Cameron
Tehran, Iran
People do their New Year shopping near a bazaar in northern Tehran March 20, 2010. Iranians celebrated their New Year on Saturday. The Iranian New Year Day marks the first day of spring and is celebrated on the day of the astronomical vernal equinox, which usually falls between March 20 to March 22. Reuters
Beijing, China
Actors in traditional costumes perform with axes and shields during a ceremony adapted from an ancient Qing Dynasty tradition where emperors offered prayers to the sun, at the Temple of the Sun in Ritan Park, central Beijing March 20, 2011. According to organizers, the ceremony is held on Chunfen, also known as the vernal equinox, which falls on March 21 this year according to the Chinese lunar calendar. Reuters
Mexico Mexico