The first quarter moon Saturday night helps us celebrate the autumnal equinox, which is officially at 7:49 a.m. in Tucson on Saturday.
If you look at the moon around 7:30 Saturday night, you will see it sitting just above Sagittarius the Archer, which actually looks more like a teapot. The moon will be sitting above the lid of the teapot with the spout to the west and the handle to the east. It will take low-power binoculars to best appreciate Sagittarius due to the bright moon.
The autumnal equinox is the official start of autumn. At the exact time of the equinox, the sun crosses the celestial equator from the northern part of the sky to the southern part of the sky. "Equinox" means "equal night" - the hours of day and night are equal.
An astute reader, Bob L., pointed out that the hours of day and night are close but not exactly equal at the time of the spring equinox around March 21 or at the time of the autumnal equinox.
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For Tucson's latitude of about 32 degrees north, the times of equal daylight (from sunrise to sunset) and night (from sunset to sunrise) are five to six days prior to March 21 and five to six days after Sept. 21. Even so, there is somewhat more daylight than night, because the atmosphere acts as a giant lens and bends the sun's light up above the horizon a few minutes before sunrise and a few minutes after sunset.
Around the times of the vernal and autumnal equinox, the sun rises due east and sets due west. Check that out on Sunday when the sun rises at 6:13 a.m. and sets at 6:18 p.m.
Moon Watch
The moon is a waxing (growing larger) crescent that reaches first quarter on Saturday.
Contact Tim Hunter at skyspy@azstarnet.com