Automn epualnox confussion

Kava · September 24, 2008, 2:19am

I have a question about the first day of Fall… Now Fall is suppose to officaly begin at 10:44 am, or 11:44 am eastern time. Now Fall is suppose to be 12 hours of day, and 12 hours of night, so why would it begin at 10:44, and I looked in the papper monday, and sunset, and sunrise was diffrent. So what is the deal?

Lucidity_Master · September 25, 2008, 3:59am

Here is an article from Wikipedia that should help clear up the confusion.

The word equinox derives from the Latin words aequus (equal) and nox (night). In reality, the day is longer than the night at an equinox. Commonly, the day is defined as the period that sunlight reaches the ground in the absence of local obstacles. From Earth, the Sun appears as a disc and not a single point of light; so, when the centre of the Sun is below the horizon, the upper edge is visible. Furthermore, the atmosphere refracts light; so, even when the upper limb of the Sun is below the horizon, its rays reach over the horizon to the ground. In sunrise/sunset tables, the assumed semidiameter (apparent radius) of the sun is 16 minutes of arc and the atmospheric refraction is assumed to be 34 minutes of arc. Their combination means that when the upper limb of Sun is on the visible horizon its centre is 50 minutes of arc below the geometric horizon, which is the intersection with the celestial sphere of a horizontal plane through the eye of the observer. These effects together make the day 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 daylength of 7 minutes, and occurs a few days towards the winter side of each equinox.

Basically due to things like the refraction of sunlight through the atmosphere the sun rays appear earlier than the actual rising of the sun. Also due to the differences between the equator and very northern/southern places the length of day at these extremes is slightly different.