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Ancient CulturesĪncient cultures didn’t have clocks to calculate minutes of daytime and nighttime, but they could measure the sun’s position geometrically. The reverse is true in the Southern Hemisphere where the September equinox signals the first day of spring. In the Northern Hemisphere, the September equinox marks the first day of fall. The equinox marks the point of the year where this transition occurs, and on the equinox the part of Earth closest to the sun is the equator, rather than places north or south. Then, as the Earth continues to move around the sun at its fixed angle, the North Pole is tilted slightly away from the sun. For half the year, the North Pole is tilted slightly toward the sun, bringing longer days to the Northern Hemisphere, while the South Pole is tilted slightly away from the sun, bringing fewer hours of sunlight to the Southern Hemisphere. On the equinox, day and night are of nearly equal length across the planet.Īs the Earth orbits the sun, it is tilted at a fixed angle. NASA.Equinox comes from the Latin words “aequi,” which means equal, and “nox,” or night.

Marshall Space Flight Center Meteoroid Environment Office.

Search this blog Search for: Search Archives Today, we celebrate the equinox as an astronomical event caused by Earth’s tilt on its axis and its motion in orbit around the Sun.Įnjoy the new season – whichever side of the globe you’re on! Additionally, earlier civilizations built the first observatories, like Stonehenge in Wiltshire, England, and the Intihuatana stone in Machu Picchu, Peru, to follow the Sun’s annual progress. They knew that the Sun’s path across the sky, length of daylight, and location of sunrise and sunset all shifted in a regular way throughout the year. The people of ancient cultures used the sky as a clock and calendar. We will also feel cooler days with chillier winds, and dry, falling leaves. In the Northern hemisphere, the September equinox marks the start of a period bringing us later sunrises and earlier sunsets. But on these special days – the spring and fall equinoxes – the Sun shines almost equally on the Northern and Southern hemispheres. That’s because Earth’s axis is tilted with respect to the Sun-Earth plane.

The rest of the year, the Sun shines unevenly over the Northern and Southern Hemispheres. This only happens twice in Earth’s year-long trip around the Sun. Spring twilight at the North Pole begins a few weeks before the vernal, or spring, equinox in March, when the Sun rises above the horizon again. Credit: NASA/JPL-CaltechĪlong with marking the beginning of astronomical fall, the Sun will be exactly above Earth’s equator, moving from north to south, making day and night nearly equal in length – about 12 hours – throughout the world.Īt the North Pole, over the upcoming days, the Sun will sink below the horizon for a kind of twilight from now until sometime in October when it will be completely dark, according to NASA solar scientist Mitzi Adams. During the equinoxes, both hemispheres receive equal amounts of daylight. An illustration of the March (spring) and September (fall or autumn) equinoxes. 1, however, the September (or fall) equinox gives us the green light to welcome the astronomical fall season in the Northern Hemisphere (and astronomical spring season in the Southern Hemisphere). In meteorology, the fall season begins on Sept.