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Autumn starts tomorrow > just look at the sun September 22, 2007

Posted by grhomeboy in Nature, Science.
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Autumn is nearly upon us. According to astronomer Ioannis Fakas, the season officially begins tomorrow at 1.51pm with the autumn equinox.

The Director of the Fakas Institute explained that autumn will last until December 22, after which winter will begin.

According to online encyclopaedia Wikipedia, an equinox is the event when the Sun can be observed to be directly above the Earth’s equator.

This usually takes place around March 20 and September 22 each year. On these dates, night and day are nearly of the same length and the Sun crosses the celestial equator.

In a wider sense, the equinoxes are the two days each year when the centre of the Sun spends an equal amount of time above and below the horizon at every location on Earth. The word equinox derives from the Latin words aequus (equal) and nox (night).

In theory, the day is longer than the night. Commonly the day is defined as the period that sunlight reaches the ground in the absence of local obstacles.

For several reasons the day lasts about 14 minutes longer than the night at the equator, and longer still at sites toward the poles. The real equality of day and night only happens at places far enough from the equator to have at least a seasonal difference in day-length of seven minutes and occurs a few days towards the winter side of each equinox.

Although the word ‘equinox’ implies equal length of day and night, this simply isn’t true. For most locations on earth, there are two distinct identifiable days per year when the length of day and night are closest to being equal.

Those days are commonly referred to as the ‘equiluxes’ to distinguish them from the equinoxes. Equinoxes are points in time, but equiluxes are days. By convention, equiluxes are the days where sunrise and sunset are closest to being exactly 12 hours apart.

This way, you can refer to a single date as being the equilux, when, in reality, it spans sunset on one day to sunset the next, or sunrise on one to sunrise the next.

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