To those in the Northern Hemisphere, enjoy the beginning of milder weather and say hello to early sunsets and late sunrises. The September equinox is a time that welcomes Earthlings to a new season. Solstices are commonly referred to as the longest (summer solstice) or shortest (winter solstice) day of the year. Solstices are when the Sun appears to reach the lowest or highest point in the sky all year they mark the beginning of summer or winter. Astronomical seasons are marked by the equinoxes and solstices that each happen twice a year. Meteorologists group the seasons into time periods that line up with the weather and monthly calendar: December through February is winter, March through May is spring, June through August is summer, and September through November is fall. Credit: NASA/Space PlaceĪstronomical seasons are defined by the Earth’s journey around the Sun, while meteorological seasons are guided by annual temperature cycles. “In the Southern Hemisphere, sunlight is less direct (winter), which means that the ground is not heated as easily.” A visual aid to better understand how the Earth’s tilted axis causes the different seasons throughout the year in the Northern and Southern Hemispheres. “On the June solstice (summer) in the Northern Hemisphere, sunlight is more direct, so it warms the ground more efficiently,” said Mitzi Adams an Assistant Manager in the Heliophysics and Planetary Science Branch at Marshall. As Earth orbits around the Sun, the angle of sunlight that the Northern and Southern Hemispheres receive is different. Seasons are caused by Earth’s tilted axis which always points in the same direction. The opposite is true in the Southern Hemisphere where the days begin to last longer. Following the autumnal equinox, the Sun gradually continues to rise later and set earlier in the Northern Hemisphere – making the days shorter and the nightfall longer. (Image not to scale) Credits: NASA/GSFC/Genna Dubersteinĭuring an equinox the Sun shines directly over the equator resulting in nearly equal amounts of day and night throughout the world – except for the North and South Pole where the Sun approximately straddles the horizon for the entire day, according to Alphonse Sterling, an astrophysicist at NASA’s Marshall Space Flight Center in Huntsville, Alabama. During the equinoxes, both hemispheres receive nearly equal amounts of daylight. An illustration of the March (spring) and September (fall or autumn) equinoxes. This year’s autumnal equinox (for the Northern Hemisphere) or spring equinox (for the Southern Hemisphere) occurs on Sept. A number of harvest festivals are marked around this time, including S outh East Asia's Mid-Autumn Festival.Complemented by cooler temperatures and falling leaves, the September equinox marks the beginning of the fall season for the Northern Hemisphere. Times of sunset and sunrise vary depending on the location of an observer – longitude and latitude – so the dates when day and night are closest together in length depend on location.Ĭultures across the world celebrate the September equinox in a number of different ways and is linked to ancient myth and superstition. Secondly, Earth's atmosphere refracts sunlight and as a result, an observer sees daylight before the first glimpse of the sun's disk above the horizon. At that instant, the disk's centre is still below the horizon. This definition is inaccurate, however.įirstly, sunrise occurs when the top of the sun's disk rises above the eastern horizon. This is derived from the oldest understanding of an equinox, which suggests it is the day when daytime and night are of equal duration. Or from a broader perspective, it is one of the two days of the year when the Northern and. The term equinox comes from the Latin aequus, meaning equal, and nox, meaning night. The Autumnal Equinox that came and went, marking the beginning of Fall for those of us in the Northern Hemisphere, marks the halfway point of the Sun as it travels, inching daily, back and forth through our sky. This means that day length is the same - 12 hours - at all points on the Earth's surface on these days, with the exception of each pole, where it will be about to change from permanent light to dark, or vice versa. The Mid-Autumn Festival, a southeast Asian harvest festival, is marked around the time of the equinox ChinaFotoPress/Getty
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