The long days of summer have passed and as we move into autumn months the hours of daylight are fewer while the hours of darkness increase. In the third week of September the sun is above the horizon just as long as it is below the horizon. This event occurs on the Autumnal Equinox, the day the sun crosses the celestial equator going from North to South.
The path of the sun, called the ecliptic, is tilted to the celestial equator by 23½ degrees. This tilt is the reason we have seasons’ It causes the sun spend more time over the horizon in the summer and less in the winter. Because the moon also follows the ecliptic around the sky, how this tilted line intersects the local horizon in the mid-northern latitudes leads to other interesting phenomena, the Harvest Moon and the Hunter’s Moon.
The Harvest moon is the full moon that occurs closest to the date of the Autumnal Equinox, and the Hunter’s moon is the next full moon of the year. During September and October the path of the ecliptic is tilted to the Eastern horizon at a shallow angle, so for a few nights around the full moon, the moon peeks over the horizon at nearly the same time the sun sets. The change in time of moonrise from one night to the next is only about 30 minutes, noticeably less that the 50 minute average change. During those evenings the sky remains bright into the late evening while farmers gather in their crops or hunters track their prey.
The moon is visible near the horizon during dusk for several days. While the moon is low in the sky moonlight passes through a thick layer of Earth’s atmosphere. The atmosphere scatters out blue colors making the moon appear amber. Glare reducing twilight allows your eyes to out more detail, and the moon’s position just above distant landscapes makes the moon seem larger – “the moon illusion”. If you think the moon is larger, compare it to your outstretched fingertip as it rises and again later in the night when it is higher in the sky.