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The fall equinox, also known as the autumnal equinox, is when astronomical fall arrives. This year, it will occur at 8:44 a.m. EDT on Sept. 22, according to the Naval Observatory.
The solstices, together with the equinoxes, are connected with the seasons. In some languages they are considered to start or separate the seasons; in others they are considered to be centre points (in England , in the Northern Hemisphere, for example, the period around the northern solstice is known as midsummer).
Systematically observing the sunrise, people discovered that it occurs between two extreme locations at the horizon and eventually noted the midpoint between the two. Later it was realized that this happens on a day when the duration of the day and the night are practically equal and the word "equinox" comes from Latin aequus, meaning "equal", and nox, meaning "night".
The two equinoxes, known as the vernal equinox and the autumnal equinox, occur on or near March 20 and September 22 each year. On the day of an equinox, the center of the visible Sun appears to be directly above the equator, and the durations of day and night are approximately equal all over the planet. Compare solstice. escape velocity
Astronomical fall starts on the autumnal equinox, between Sept. 21 and Sept. 23, and ends on the winter solstice, between Dec. 20 and Dec. 22.
So, the two equinoxes are in the spring and fall, while the two solstices occur during summer and winter. The Earth’s constantly changing position, relative to the sun, is why our seasons come ...
The first day of each month is shown in black, and the solstices and equinoxes are shown in green. It can be seen that the equinoxes occur approximately at altitude φ = 90° − 51.5° = 38.5°, and the solstices occur approximately at altitudes φ ± ε where ε is the axial tilt of the Earth, 23.4°.
Why full moons in the night sky are worth viewing, how they got their names and other interesting lunar facts.