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The vernal (or spring) equinox occurs just after 7 a.m. EDT on Wednesday, March 20. If you live in the United States or other places in earth’s Northern Hemisphere, spring began for you at that time.
The Latin word equinox means “equal night.” On the day of an equinox, daytime and nighttime are almost the exact same length. This will happen again on the autumnal equinox in exactly one half year.
This constantly changing variation in the length of daytime is actually caused by the same thing that gives us changing seasons: the tilt in the earth’s axis.
The earth spins on an axis that has an angle which is 23.5 degrees different from the angle of the path the earth makes around the sun.
Night and day are caused by the rotation of the earth on its axis. Sometimes your part of the earth is facing the sun (day), and sometimes your part is facing away (night). One rotation takes about twenty-four hours.
Meanwhile, the earth is traveling around the sun in a path called an orbit. One full orbit takes one full year.
If the angle of the earth’s orbit and the angle of the earth’s equator were the same, the sun’s rays would hit all of the places of the earth the same way all year long. In addition, every place on earth would have one never-ending season with temperatures that got colder as you moved further from the equator.
However, our orbit and our equator don’t line up. The earth is tilted on its axis. For half a year’s time, the bottom half (Southern Hemisphere) of the earth gets more sun than the top half (Northern Hemisphere). During the next six months, the top half gets more. The vernal equinox begins six months of longer and warmer days for the Northern Hemisphere.
Learn more about the seasons of the year from NASA.
Image description: A full-scale model of the James Webb Space Telescope was displayed at South by Southwest in Austin, Texas.
Photo by Chris Gunn, NASA.
Image description: The Hubble telescope sees a ‘Space Invader.’
In this photo, the image of a spiral galaxy at upper left has been stretched and mirrored into a shape similar to that of a simulated alien from the classic 1970s computer game “Space Invaders!” A second, less distorted image of the same galaxy appears to the left of the large, bright elliptical galaxy.
Photo from NASA/ESA
Image description: A scientist from the Minerals Management Service surveys the German U-boat U-701 off the coast of North Carolina as part of the Battle of the Atlantic Expedition.
The expedition was the first part of a larger multi-year project to research and document a number of historically significant shipwrecks tragically lost during WWII.
The project is dedicated to raising awareness of the war that was fought so close to the American coastline and to preserving our nation’s maritime history.
Photo from the National Ocean and Atmospheric Administration