Saturn's ring system visible in September

You can look forward to two occultations in September.

At evening twilight on Sept. 12, the waxing gibbous moon occults Neptune. Starting about 8:42 p.m., the ice giant disappears behind the moon, and reappears about 9:47 p.m. Neptune is at magnitude 7.2, so you will need binoculars to observe this fairly rare event, in the constellation Capricorn.

A week later, on the night of the 19th, the moon moves through the Pleiades, Messier Object 45. Of the nine named stars of the Seven Sisters (up to 14 can be seen with the naked eye) only Electra, Celaeno, Maia and Alcyone will be hidden by the moon. This should be a beautiful sight, beginning at about 9 p.m. and ending at midnight. M45 is also known as the Maia Nebula, and is actually a cluster of 500 stars, 12 light-years in diameter.

At the beginning of September, around 8:15 p.m., the moon, Mercury, Mars and Venus hover right above the western horizon. By month's end at this time, only Venus will be visible, outshining all but the moon at magnitude -3.8.

Jupiter remains in Sagittarius, quite conspicuous in the south at magnitude -2.4. The planet is right above Nunki, the second brightest star in the constellation. Nunki is the one of the stars that make up the bowl of the ''Little Milk Dipper.'' This is an asterism, or a pattern of stars seen in the sky that is not an official constellation.

Saturn rises in the last half of the month about 6:30 a.m. in the constellation Leo, about 40 minutes before sunrise. By month's end, the ringed planet will rise about an hour earlier. This might be the last month before winter to get a good look at the ring system. The system will appear to ''close up'' from our perspective on Earth, and will not be as open until about next May.

Uranus is at opposition on Sept. 13, in the constellation Aquarius. It is visible without binoculars under a dark, clear sky. Two days before or after this date, place the star Phi Aquarii (find a star chart on the Web or at the library) at the right edge of the field of 7 x 50 binoculars. Uranus will appear as a gray-green dot right in the center of the field.

Sept. 22 marks the autumnal equinox, once again bringing an end to summer.