photo credit: PermanentTraveller
Because of the nature of the cosmos, there are celestial events that are remarkable because of how much different from the norm they happen to be. Full moons are often fascinating and many legends have come to be associated with the phenomenon. Even rare is the blue moon, an extra full moon that happens once every three years or so, and it is infrequent enough to have led someone to coin the saying “once in a blue moon”. Also fascinating are eclipses, where one celestial object moves into the shadow of the other. Whether they are a solar eclipse, where the moon is between the Earth and the sun, or a lunar eclipse, where the Earth is between the sun and the moon, eclipses are transfixing and rare. An occurrence that happens twice a year is the equinox, where the sun is positioned directly over the Earth’s equator, causing the day and night to be precisely the same length.
Everything in the universe is moving in some level. On a minute level, atoms move around quickly or slowly, depending on the object’s state of matter, the temperature of the object, and other such variables. A movement that we are very familiar with is the revolution of the planets around the sun, as well as the rotation of the planets and the sun around their respective axes. The time it takes for Earth to revolve around the sun is known as a year, while the time it takes for the Earth to make a complete rotation on its axis is referred to as a day. When the Earth has completed its journey around the sun once, it has rotated on its axis about 365 times; hence, the reason why a year is known as 365 days long. Because of this phenomenon, the Earth is never in a fixed position relative to the sun: both objects are always moving in some fashion. This rotation and revolution explains many concepts that may boggle children and adults alike, such as the reason why seasons exist, the concept of night and day, and so on. It also explains the phenomenon of the autumnal equinox.
This year’s autumnal equinox will occur on September 22 at 11:44 AM EDT, or Eastern Daylight Time, which encompasses the East Coast of the United States during the summer. The time will also mark the beginning of autumn in the Northern Hemisphere, the event from which the autumnal equinox derives its name. At this point in time, the sun will appear to be directly above the Earth’s equator, but the definition of what this means and its implications are a bit more complex. Three astronomy terms are used in the textbook definition of the autumnal equinox: celestial sphere, celestial equator, and ecliptic.
The celestial sphere is an imaginary rotating sphere that shares the Earth’s center and the Earth’s axis, rotating with the Earth as it goes about its normal movement. The purpose of the celestial sphere is to serve as an aide to visualizing the rest of space from our perspective, because one could perceive the rest of space as being points on the celestial sphere. As it moves around the Earth, the stars move in such a way that allow us to see different stars at different times of the year, which is most notable stargazers attempt to find constellations.
Conceptually similar is the celestial equator, which is similar to the Earth’s equator in that it is situated around the widest point of the Earth, but differs in that it is the projection of this imaginary line into space. When a celestial object, such as the sun, is located near the celestial equator, it is visible throughout the whole world, although the revolution of the Earth only allows each part of the world to see it briefly due to the cycle of night and day. Because of the way that the Earth tilts on its axis, the celestial equator is actually at a 23.5 degree angle from the vertical.
The final term is the ecliptic, which is the perceived route that the sun takes throughout the sky during the year. As we all know, the sun does not actually revolve: we are revolving around it. But because of our vantage point from the Earth, it seems to revolve around us in a path that is more or less flat: that is, without the incline that the celestial equator has. Putting the terms together, the autumnal equinox is the moment when the ecliptic intersects the celestial equator on the celestial sphere, meaning that the sun is equidistant from the two poles. Because of the sun’s orientation relative to the Earth, night and day will be roughly the same length in some parts of the world. In the Northern Hemisphere, this marks the passage of summer to autumn.
Although the mysterious workings of the cosmos are rather fascinating, so are the ways that humans throughout history have interpreted these events. One of the most prominent testaments to the interest of mankind in the patterns of the cosmos is Stonehenge, which was reputedly created to allow the ancient inhabitants of Britain to mark events like the autumnal equinox. Ancient Irish structures were created in such a way to let sunlight illuminate certain writings within the structure only when the equinox was occurring: these writings were early astronomical symbols. Astrologers throughout history know the autumnal equinox as the time when the sun enters the Libra sign. The equinox, and other such celestial phenomena, was diligently recorded by the Mayans, whose elaborate temples sometimes contained extensive methods to determine when things like the equinox were occurring. Temple inscriptions also contained important dates and directions that hinged upon the movements on the cosmos, such as the beginning of harvest or the need for a religious ceremony.
Some cultures continue to have celebrations that are either a result of the autumnal equinox or at least associated with it. In Japan, some celebrate the three days before each equinox and the three days after as part of a ritual that includes repentance for sin and prayers for enlightenment in the next life. It is said that the reason for the festivals is the temperate weather that comes during the time of the equinox, the best climate in which to reflect and meditate on the meaning of life. A rumor that persists even today in many parts of the world is that the equinox marks the time when one can actually balance an egg on its end. The explanation often ties back to the perceived balance during the equinox, that day and night are equal, but there is no scientific proof that the passage of seasons has anything at all to do with the ability to balance an egg on one end.
Whether you recognize the autumnal equinox as a time to balance eggs on their end, reflect on the meaning of life, or just an indicator that summer is on its way out, it is always interesting to learn about the intricate coincidences that the cosmos create. For centuries before us, people have been fascinated by the autumnal equinox, and although science has spoiled much of the mystique of the autumnal equinox, it is nonetheless a very special occurrence.
