When you purchase through links on our site, we may earn an affiliate commission. Spring is the season during which the natural world revives and reinvigorates after the colder winter months. During spring, dormant plants begin to grow again, new seedlings sprout out refresca the ground and hibernating animals awake. What most people call spring relies on the astronomical definition of the word.

Defined by the angle of Earth’s tilt toward the sun, astronomical spring relies on equinoxes and solstices to define it. Spring is generally considered the period between the spring equinox and the summer solstice. Equinoxes are days during the year when day and night are almost equal. There are two equinoxes each calendar year, one in the spring and one in the fall. The spring, or vernal, equinox occurs around March 20 in the Northern Hemisphere and around Sept. Earth’s axis is not pointed toward or away from the sun.

In the Northern Hemisphere, the North Pole is tipped at its greatest angle toward the sun during the summer solstice, which occurs around June 21. In the Southern Hemisphere, around December 21, it is the South Pole’s turn to be nearer. A illustration of the Earth’s position during four seasons. As such, in the Northern Hemisphere, astronomical spring runs from March 21 to June 21, while in the Southern Hemisphere it encompasses Sept. 21, though the dates may shift slightly from year to year. The air may lose its winter chill before the middle of March or September, though.

Weather forecasters define meteorological spring as a three-month period based on rising temperatures. In the hemisphere that is tilted closer to the sun, temperatures become warmer. Warmer temperatures means the ground, which may have frozen over the winter months, grows softer and more yielding to plants. Spring is often marked by increased rainfall, which helps to water the infant seeds taking root in the ground.

Animals that spent the winter in hibernation come out of their dens, while those that traveled to warmer regions return. Many animals give birth in the spring. Winter coats are shed by those that sported them, and some animals may change coloration to blend in with their new surroundings. The rising rainfall of spring may bring with it an increase in flooding as melting snow overwhelms rivers. Spring may also boast storms, as warm air from the equator combines with still-cool air farther north or south. Tornadoes are common during the spring in the United States as air of different temperatures combine. The world’s deadliest tornado occurred April 26, 1989, in Bangladesh.