Spring has come in the Northern Hemisphere, amid snow still tightly gripping many part of the region.

Spring equinox, or the yearly celestial alignment happening between Earth and sun, announced this shift in seasons and the arrival of spring. The phenomenon took place in March 20, Monday, at 6:28 a.m. Eastern time.

The Equinox Explained

Twice every year, Earth gets to a point in its annual trip around the sun when its Northern and Southern hemispheres obtain the same dose of daylight, called equinox or “equal night” in Latin. The Northern Hemisphere’s spring equinox also heralds the start of fall in the Southern Hemisphere.

Its autumnal equinox, on the other hand, takes place in September and signals the arrival of spring south of the equator.

Daylight is nearly always unequally distributed across Earth due to the way the planet orbits the sun. One of the Northern and Southern hemispheres is receiving daylight longer during a 24-hour period.

"During two special times twice a year, the tilt is actually perpendicular to the sun, which means that Earth is equally illuminated in the Northern and Southern hemispheres," explained C. Alex Young of Heliophysics Science at NASA’s Goddard Space Flight Center to Live Science.

How Satellites Improved Our Views

It remains unclear at what exact point ancient civilizations were first made aware of this occurrence. Humans, however, have been erecting structures for thousands of years in order to observe the sun and sky’s changing positions relative to the seasons.

Spacecraft today, though, offer planetary views that capture light distribution across the planet's surface and can very well see the effect of an equinox, Young added.

Satellites established in space offer long-range perspectives of the planet, including the extent of cloud cover, water bodies, and landmasses. During equinoxes, for instance, both hemispheres are lit up equally.

Other Rare Occurrences

It’s not just the annual equinoxes that can take one’s breath away. This year, a rare solar alignment is anticipated: a total solar eclipse seen across the entire country on Aug. 21. It will be the first of its kind in almost four decades.

The total solar eclipse will move across the United States for around 90 minutes, offering scientists the chance to study complex sun-Earth connection because of the eclipse’s long path over land.

“The path of the total eclipse crosses the U.S. from coast to coast, so scientists will be able to take ground-based observations over a period of more than an hour to complement the wealth of data provided by NASA satellites,” NASA said in a statement.

In a total solar eclipse, the moon blocks out the sun’s brightness, revealing the corona or the faint solar atmosphere.

The space agency continues to observe the sun even without anticipated eclipses. Its Heliophysics System Observatory (HSO), comprising 23 spacecraft and 20 missions, take care of this mission.

In 2018, it expects a more intimate look at the sun via Solar Probe Plus, an unmanned space probe flying closer to the sun than any other man-made object. It will explore why the corona is way hotter than its surface, and what leads the sun to give off different high-energy particles that can pose risks to astronauts and space vehicles.

Going back to springtime, U.S. forecasters are predicting balmy weather for much of the season, but not before winter keeps striking in sections of the Northeast and the Midwest, reported CS Monitor.

The flowers may already be pretty, but you may also want to delay breaking out the picnic basket if you are one of the 50 million Americans battling seasonal allergies.

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