The heavens of early September offer a double-double deal.

In the hours before dawn Wednesday, gaze to the eastern sky. There you will find the planets Venus and Saturn in a cosmic conjunction seen below the stars Castor and Pollux in the Gemini constellation.

Castor and Pollux ascend the east-northeastern sky after 3 a.m., and Venus and Saturn rise about 3:45 a.m. in the same location. By 5 a.m., the planets are high enough to be found easily above the eastern horizon.

Dancing cheek to cheek, Venus and Saturn waltz across the east until the sunrise washes them out. Venus, the brightest of the two planets, is at negative fourth magnitude (very bright), while Saturn remains steady at zero magnitude (bright enough to see from urban areas.) By Thursday, the planets hobnob in close proximity, but they soon go their separate ways and move farther apart with each passing morning.

Not one to miss the merriment, the waning, crescent moon is found directly above Saturn and Venus on Sept. 8. (Saturn is higher than Venus.) On the following morning, Sept. 9, the moon appears to nudge Castor, Pollux and Saturn. Then the moon sashays between Saturn and Venus on the morning of Sept. 10.

The fleet Mercury speeds into the morning skies early in September. On the morning of Sept. 9, the planet provides its best show of the year. Look to the east before sunrise, and you'll see bright Mercury about 18 degrees above the horizon.

Neither Mars nor Jupiter can be seen this month. Jupiter returns in late October, and Mars comes back in November.

Finally for the fine folks in the Northern Hemisphere, the autumnal equinox arrives at 12:30 p.m. Eastern time Sept. 22, according to the U.S. Naval Observatory here. This is the precise astronomical moment when the sun appears to cross the equator into the Southern Hemisphere. Don't worry; the sun will return next spring.

Down-to-Earth Events

* Wednesday -- Ross Irwin, of the Smithsonian's Center for Earth and Planetary Studies, discusses the "Soviet TKS Spacecraft: Versatile Building Blocks for the First Modular Space Stations." Meet at Milestones of Flight (Gallery 100) at the National Air and Space Museum on the Mall, noon. Information, 202-357-2700; www.nasm.si.edu.

* Sunday -- Open house at the University of Maryland's observatory, College Park. Scan the heavens through a telescope, weather permitting, after the talk. 9 p.m. Information, 301-405-6555; www.astro.umd.edu/openhouse.

* Sept. 10 -- In a lecture, Robert Ehrlich, a physics professor at George Mason University, explains why neutrinos may be more fleet than imagined. His talk, "Seven Reasons That Neutrinos May Be Faster-Than-Light Tachyons," is hosted by the Philosophical Society of Washington, at the John Wesley Powell Auditorium, Cosmos Club, 2170 Florida Ave. NW. 8:15 p.m. www.philsoc.org.

* Sept. 11 -- The National Capital Astronomers will hold its regular meeting at the University of Maryland's observatory, College Park. 7:30 p.m. capitalastronomers.org.

* Sept. 12 -- Steven J. Dick, NASA's chief historian, will review the "American 19th Century Transit of Venus Expeditions" with the Northern Virginia Astronomy Club. The meeting will be at Enterprise Hall, Room 80, George Mason University, Fairfax. 7 p.m. Information and parking instructions, www.novac.com.

* Sept. 13 -- "The Stars Tonight" at the Arlington Planetarium, 1426 N. Quincy St., adjacent to Washington-Lee High School. 7:30 p.m. Tickets are $1.50 for children and seniors and $2.50 for adults. Information, 703-228-6070.

* Sept. 18 -- Enjoy the heavens from inside the Capital Beltway at "Exploring the Sky," presented by the National Capital Astronomers and the National Park Service, at Rock Creek Park, near the Nature Center, in the field south of Military and Glover roads NW. 8 p.m. 202-895-6070. capitalastronomers.org.

* Sept. 18 -- See the stars from a dark-sky location with astronomer Sean O'Brien of the National Air and Space Museum at Sky Meadows State Park, near Paris, in Fauquier County. 7:15 p.m. to 11 p.m. $4 parking fee. Information, 540-592-3556. www.dcr.state.va.us/parks/skymeado.htm.

* Sept. 20 -- Open house at the University of Maryland's observatory, College Park. After the talk, view the night sky through a telescope, weather permitting. 9 p.m. Information, 301-405-6555; www.astro.umd.edu/openhouse.

* Sept. 22 -- Forget pennies from heaven; huge rocks sometimes strike Earth. Find out what happens in the lecture "When the Sky Falls" at the Montgomery College Planetarium, Takoma Park. Parking available in the faculty lot. 7 p.m. Information, 301-650-1463; www.mc.cc.md.us/departments/planet.

Blaine Friedlander can be reached at bfriedlander@earthlink.net.