State astronomers said night will be as long as the day during the equinox, after which nights will grow longer in September as the Sun approaches the celestial equator.
"Philippine nights will be longer as the Sun approaches the celestial equator. Autumnal equinox will occur on September 22 when day and night will have equal time length on Earth," PAGASA administrator Nathaniel Servando said.
Science site EarthSky.org said the 2012 September equinox will occur at 2:49 p.m. universal time (10:49 p.m. in Manila).
After Saturday, it said "(t)he shorter days are bringing cooler weather," adding "a chill is in the air."
EarthSky.org noted each equinox and solstice is an astronomical event caused by Earth’s tilt on its axis and orbit around the sun.
Since Earth does not orbit upright but is instead tilted on its axis by 23.5 degrees, its northern and southern hemispheres may not receive the Sun's light and warmth equally - at least for most of the year, it said.
"We have an equinox twice a year – spring and fall – when the tilt of the Earth’s axis and Earth’s orbit around the sun combine in such a way that the axis is inclined neither away from nor toward the sun," it said. — LBG, GMA News
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