September 2019 – March 2020
Autumnal Equinox is today!
The autumnal (fall) equinox is the first day of the fall season.
As the earth travels around the Sun in it orbit, the north to south position of the sun changes over the course of the year due to the changing orientation of the earth’s tilted rotation axes. The dates of zero tilt of the earth’s equator correspond to the spring equinox and the autumn equinox.
Equinoxes occur when the axis of rotation of the earth (i.e. the line from the north to south poles) is exactly parallel to the direction of motion of the earth around the sun. This happens on just two days of the year, the spring and autumn equinoxes. This means that day length is exactly the same (12 hours) at all points on the earth’s surface on these days (except right at each pole, where it will be about to change from permanent light to dark, or vice versa).
Seasons are opposite on either side of the equator, so the equinox in September is known as the autumnal (fall) equinox in the northern hemisphere, and is considered the first day of fall. At the same moment in time in the southern hemisphere, it is known as the vernal (spring) equinox, and marks the first day of spring.
Science: Earth and Space
Have You Ever Wondered…?
- What is the vernal equinox?
- Is the vernal equinox on the same day in the northern and southern hemispheres?
- Can you really balance an egg on end during the vernal equinox?
As Earth revolves around the Sun, there are two moments each year when the Sun is exactly above the equator. These moments — called equinoxes — occur around March 20 or 21 and September 22 or 23. Equinoxliterally means “equal night,” since the length of day and night is nearly equal in all parts of the world during the equinoxes.
The March equinox marks when the Northern Hemisphere starts to tilttoward the sun, which means longer, sunnier days. In the Northern Hemisphere, the March equinox is called the vernal equinox, because it signals the beginning of spring (vernal means fresh or new like the spring). The September equinox is called the autumnal equinox, because it marks the first day of fall (autumn).
When the Northern Hemisphere starts to tilt toward the sun in spring, the Southern Hemisphere starts to tilt away from the sun, signaling the start of fall. Thus, in the Southern Hemisphere, the March equinox is called the autumnal equinox, and the September equinox is called the vernalequinox.
People have celebrated the vernal equinox for centuries. For ancient cultures, the vernal equinox signaled that their food supplies would soon return. Early Egyptians even built the Great Sphinx so that it points directly toward the rising Sun on the day of the vernal equinox. In Christianity, the vernal equinox is significant, because Easter always falls on the first Sunday after the first full moon after the vernal equinox.
If you keep your eyes and ears open around the time of the vernal equinox, you’re likely to hear or see people talking about a magical phenomenonthat only occurs on that day. According to legend, the special astronomicalproperties of the vernal equinox make it possible to balance eggs on end.
So is there any truth to this popular legend? Nope! It’s actually possible to balance eggs on end on any day of the year. It just takes a lot of patienceand determination. There’s nothing magical about the vernal equinox that makes it any easier to balance an egg on end.
You might be wondering how such an interesting and widespread legend got started. No one knows for sure, but some believe the Chinese may have started the practice of balancing eggs on end during the vernal equinox. Given that day and night are balanced at the time of the vernal equinox, it’s possible that the Chinese chose a balanced egg as a symbolicrepresentation of this astronomical phenomenon.