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Giant Jupiter Cozies to Earth

By Lewis McCool �2010

In History

Sept. 1, 1979 – U.S. probe Pioneer 11 flies by Saturn. Launched in 1973, the craft discovered new rings, new moons and details of Saturn’s magnetic field.

Sept. 8, 1960 – President Eisenhower dedicates Marshall Space Flight Center in Huntsville, Ala. Wernher Von Braun was its first director. The center developed the nation’s most powerful rocket, the Saturn V.

Sept. 8, 1966 – The original Star Trek series premieres with “The Man Trap” episode.

Sept. 14, 1915 – Birth date of San Francisco’s “sidewalk astronomer,” John Dobson, inventor of the popular and inexpensive Dobsonian mount for telescopes.

Sept. 23, 1846 – German astronomer Johann Galle detects and identifies the planet Neptune, using calculations by French astronomer Urbain Jean Joseph Leverrier.

Sept. 24, 1930 – Birth date of one of the nation’s most experienced astronauts, John Young. He flew two Gemini missions, went to the moon twice and commanded two space shuttle missions, including the program’s inaugural flight.

MOON PHASES

Last quarter: Sept. 1, 11:22 a.m.

New: Sept. 8, 4:30 a.m.

First quarter: Sept. 14, 11:50 p.m.

Full: Sept. 23, 3:17 a.m. (Harvest Moon)

Now is the time to take a good look at our neighborhood's giant. Jupiter is ideally positioned for viewing in September. It reaches opposition on the 21st, the point in its orbit when it is about as close to Earth as it gets, only 370 million miles away.

Jupiter has a diameter 11 times that of Earth and its volume could contain more than 1,300 Earths. Near opposition it shines at magnitude minus 2.9, making it the third brightest celestial object in the night sky after our moon and Venus.

Named for the ruler of Roman gods, Jupiter can be found in Pisces, rising around sunset, highest in the sky around midnight and setting around sunrise. Look for the full moon just 6 degrees to the north on the 23rd.

Its disk can be seen in binoculars, its Galilean moons in a small telescope. Those four large moons were first seen by Galileo in 1670 through the newly invented spyglass. Even a cheap department store scope will give a better view than he had, though I don't recommend you buy one. Watching the moons shift positions from hour to hour, is fascinating and a simple lesson in celestial mechanics, one appreciated by Galileo, if not the Catholic Church of the day. A good, modest scope also will reveal Jupiter's cloud bands and the "Giant Red Spot."

Fall begins on Sept. 22 with the autumnal equinox at 9:09 p.m. MDT. With late summer and early fall nights still relatively warm you can spend enough time outside to detect the Jupiter's rotation as well as its moons' shifts.

Uranus is in Pisces too, hiding practically in the shadow of Jupiter. In a rather unusual planetary alignment, it reaches opposition just hours after Jupiter. Small and nearly five times farther away than from us than Jupiter, at magnitude 5.7 it is barely visible to the naked eye on a good night.

The two planets are only a degree apart for several nights. A modest scope will reveal Uranus' tiny greenish disk just above (north) of Jupiter. Uranus was, in fact, the first planet discovered with a telescope (by British astronomer William Herschel in 1781).

Now past inferior conjunction, speedy Mercury is visible in the predawn sky and reaches its greatest western elongation (18 degrees from the sun) on Sept. 19. This is the best viewing opportunity of the year for the elusive innermost planet. Have a look low in the east before dawn beginning around midmonth. It brightens to magnitude minus 1 late in the month but drops toward the horizon after the 19th.

Venus continues as the "evening star," shining at magnitude minus 4.5 near the southwestern horizon after sunset. A crescent moon will hover nearby on the 10th and 11th.

Early in the month, you might be able to pick out a much fainter Mars to the right of Mars near the star Spica. Binoculars will help find them in twilight.

Saturn will be even more difficult to spot a little more than 20 degrees to the right of Venus during the first week of September. It will soon be lost in the sun's glare.

One of my favorite deep-space objects is readily visible this time of year: our neighboring galaxy Andromeda (Messier 31). It rises in the northeast before sunset and is highest in the night sky around 3 a.m. early in September and two hours early by month's end. It's is easy to spot in binoculars and is a beautiful image in a scope using a wide-angle eyepiece.