The astronomy picture of the day for September 23 illustrates the autumnal equinox which occurs today at 3:09 UT. The Moon is full and is called Harvest Moon, which means that the narrow angle to the ecliptic causes the moon to rise 30 minutes later each day rather than 50 minutes, creating the illusion that the Moon remains at its full phase for several nights. The equinox, which is the point where the ecliptic intersects the celestial equator, marks the first day of fall and occurs when the angle between the Earth's axis and the sun is perpendicular. The equinox results in 12 hours of daylight and 12 hours of night and a shorter time of darkness between sunset and moonrise which allowed farmers to gain a few more hours of work since they could see their crops in the moonlight. The Harvest Moon appears orange to us because it rises at the horizon and it is here that the atmosphere is its thickets which causes more blue light to be scattered resulting in red light passing through our eyes.
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