An autumnal equinox or the equal duration of day and night will be experienced on September 22.
According to the astronomical diary of the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA), the autumnal equinox will be observed at 9:31 pm.
“The equinoxes are the only times when the solar terminator (the “edge” between night and day) is perpendicular to the equator,” the PAGASA explained.
“On an equinox, day and night are of approximately equal duration all over the planet. They are not exactly equal, however, due to the angular size of the sun and atmospheric refraction,” it added.
The National Aeronautics and Space Administration (NASA) stated that there are two equinoxes in a year, the other one is the spring equinox during the month of March.
“Hence, thereafter, Philippine nights will be longer as the sun moves below the celestial equator towards the southern hemisphere,” PAGASA added.