The Fall or Autumnal equinox in the Northern Hemisphere (U.S, Canada) occurs every year on September 22, 23 or 24. In 2015, the Fall Equinox or the first day of Fall/Autumn will occur on Wednesday, September 23. With its sparkling colors and bright days, Fall is a favorite season for most people.
But how do these seasons change? Each solstice and equinox is an astronomical event caused by the Earth’s rotation on its axis and its ceaseless revolution (orbit) around the sun.
Seasons (summer, fall, winter and spring) are defined according to the position of the sun in relation to the winter and summer solstices. According to astronomers, the sun rises along the horizon in the Northern and Southern hemispheres in June and December respectively, regardless of your location on earth.
Astronomers use solstice points to define the start of winter and summer seasons. For instance, June marks the start of winter solstice in the Southern Hemisphere while it marks the start of summer solstice in the Northern Hemisphere.
Equinoxes and Seasons
The equinoxes fall almost halfway between the winter and summer solstices. This is the reason why fall and spring are defined in terms of equinoxes. However, the Earth’s orbit is not really circular but elliptical because it tilts on its axis by 23.5 degrees. As a result, the fall and spring equinoxes do not fall exactly halfway between the summer and winter solstices.
This means that during the two equinoxes (March and September), the sun shines directly on the equator because the Earth’s tilt and orbit is perpendicular to the sun. On other days of the year, either the Northern or the Southern hemisphere tilts more towards the sun.
Day and night have almost the same length (12hours) during the equinox. This is why it is known as equinox, a Latin word meaning “equal night”. In reality, equinoxes don’t have precisely 12 hours of daylight.
Fall is the perfect time to enjoy the cool temperatures and watch the colorful leaves fall. However, these leaves can damage your roof and lead to costly roof replacements or repairs. That’s why you should install rain gutter guards before the end of Fall.