New York — Oct. 1: Almost full, the big, fat, waxing gibbous moon is in Pisces, very near the Vernal Equinox, where the sun is stationed on the first day of spring. Above the horizon at sundown, the moon fills the earth and sky with light until dawn. Mercury is at inferior conjunction today, passing from left to right between sun and Earth. This takes the planet into the morning sky.
Oct. 2: Today's full moon is the harvest moon, the name given to the full moon occurring closest to the date when autumn begins. When the full moon is near the vernal equinox and the moon is rising, the lunar orbit is inclined to the horizon by the minimum angle, which tends to minimize the daily retardation (or lag) in the time of moonrise. This gives the appearance of a full or nearly full moon in the sky all night long for several successive nights. The advantage of the bright early evening moonlight to aid in ''bringing in the crops'' gives it the name ''harvest'' moon.
Oct. 2: Mars, drifing easterly through the stars very rapidly, passes Antares , in Scorpius, moving to its east (left) on successive nights. The planet is above Antares, in the constellation Ophiucus, moving toward Sagittarius.
Oct. 6: The gibbous moon is now waning, rising about 8 p.m. Tonight, the Pleiades (Seven Sisters) appears as a fuzzy patch of dim stars to the right and above the moon while Aldebaran, the glinting red eye of Taurus, the Bull (located in the V-shaped cluster known as the Hyades), is below the moon to the left.
Oct. 8: The perigee moon (nearest earth) enters Gemini, where you will see it tonight from moonrise (before midnight) on.
Oct. 9: Still in Gemini, the moon is at last quarter, passing below the ''twin'' stars Pollux (the brighter) and Castor, above and to the left of the moon. After midnight on Sunday night, the slightly crescent moon rises in line with and below Pollux and Castor.
Oct 10: Mercury resumes its easterly motion through the stars, after passing between Earth and sun.
Oct. 12-13: The shrinking crescent moon is still visible in the dawn sky of both mornings. The star below and to the moon's left early Tuesday morning is Regulus, in Leo. The moon passes above Regulus on the evening of the 12th, while both are below the horizon, and the star is closer to the moon, above and to its right, on the morning of the 13th.
Oct. 16: The new moon is in Virgo, near Spica.
Oct. 17: Mercury is at the greatest distance to the right of the sun (greatest westerly elongation), placing it in the best position for viewing as a morning star. The inclination of Mercury's orbit favors this elongation, but the planet's distance from the sun does not. However, there is a fair chance of seeing it low in the east after dawn, if the eastern sky is very clear, for a week or so.
Oct. 18: The young crescent moon is in conjunction with Jupiter, but barely 39 hours after new moon. There is a chance of seeing them before they set, low in the east during twilight, but it will require exceptionally clear skies. Saturn is in conjunction with the sun and becomes a morning star as the sun moves from right to left past it. The planet should be far enough from the sun to be seen in the morning sky by mid-November.
Oct. 19: The young crescent moon of the new cycle should be visible tonight after sundown. The reddish star below to its left as they set is Antares in Scorpius.
Oct. 21: Mars is below the crescent moon tonight. Since the moon sets before midnight, it will not interfere with viewing the Orionid meteors. This shower, producing up to 25 meteors an hour, reaches maximum about 1 p.m. on the 21st, so viewing may be equally good after midnight on Wednesday and Thursday night.
Oct. 23: Apogee moon (farthest from Earth) is in Sagittarius.
Oct. 24: The moon is at first quarter phase tonight.
Oct. 29: The waxing gibbous moon moves into line with the eastern edge of the Square of Pegasus. Two stars above the moon are Alpheratz (upper) and Algenib, in Pegasus. Diphda, below the moon, is in Cetus, the Whale. Mercury, in Virgo, is in conjunction with Spica but the two morning stars rise too late in the twilight to be seen.
Oct. 31: (Communities that use daylight time return to standard time this morning, setting clocks back by one hour.) Aries is in the home of the moon tonight. Above the horizon at sundown, the moon sets with Aries before dawn. Not much about Aries suggests the ''Ram'' for which it is named, but two of its stars are easy to recognize. Look above the moon for Hamal and Sheratan, two second-magnitude stars (among the ''second rank'' in stellar brightness was the origin for this description). Sheratan is the fainter, to the right.