Fall Planet Roundup

Observer's Notebook for November, 2000

by John Rummel

November is a good month to focus on planets. Both Jupiter and Saturn reach opposition this month, and Venus continues its climb in the western skies as the brilliant evening star.

"Opposition" is an astronomer's way of saying that the earth has caught up to an outer planet as both orbit the sun. Jupiter and Saturn still appear relatively close in the sky, fresh from their 20-year conjunction this past May (part of that "grand conjunction" that you may have read about). Earth overtakes and passes both in a 9 day period in late November. In practical terms, opposition means that each planet is at its closest approach to earth for the year, and thus at its brightest and largest apparent size for observing. Because they're opposite from the sun in the sky, they're also up all night long.

Observing Jupiter and Saturn through small telescopes is the amateur astronomer's delight. Both objects are easy for observers of limited experience - plenty of visible detail and lots of "gee-whiz" appeal. They also carry considerable merit for deeper study, and will reward the patient observer through many hours at the eyepiece. The full moon passes by Saturn and Jupiter on November 11 and 12. On the evening of the 12th, all four of Jupiter's Galilean moons are visible, but in a somewhat unusual configuration as Callisto appears to pass directly above Jupiter's north pole. Watch the moons over a period of hours or nights, and note the changes in position. If you're lucky, you will catch the occasional shadow transiting the face of the planet, or watch one of the moons disappear behind Jupiter.

Saturn, with its largest moon Titan visible in a small telescope, presents a beautiful view of the rings near their maximum tilt, displaying Saturn's southern hemisphere prominently. NASA's Cassini spacecraft, currently en route to a 2004 rendezvous with Saturn, will swing pass Jupiter next month, at a distance of about 7 million miles. Using a gravity assist maneuver, Cassini will gain a little speed and adjust its course to finalize the Saturn approach trajectory. NASA's Galileo spacecraft is currently exploring the Jovian system, and this will mark the first time that two separate robotic missions have explored a planet simultaneously. We'll try to provide you with an update and some links in next month's Madison Skies.

Visible in the southwest anytime after the sun goes down, Venus shines at a dazzling magnitude -4.0, and only gets brighter as the month wears on as it gets closer to earth. Just as the Earth is catching up to Jupiter and Saturn in their orbits, the speedy Venus is overtaking Earth. As Venus gets closer, it passes between the earth and the sun, and it goes through a crescent phase, something only Mercury and Venus can do. Twice every hundred years or so, Venus actually crosses the disk of the sun in an event known as a transit. Observers of our generation are lucky and will get two chances to observe this rare and wonderful phenomenon, in 2004 and again in 2012. These represent the first Venus transits since 1882 and the last chances to observe one until 2117.

On November 29, the four day old crescent moon just two degrees above Venus, making for a memorable sunset experience.

  Looking southeast at 6 am on November 16, 2000. Image produced by Starry Night Pro.

The other two naked eye planets also make appearances this month, but you'll have to get up early in the morning to see them. Mars is high enough above the eastern horizon by about 4 am and shines at an unimpressive magnitude 1.5. Mars will rise a little earlier each day and as it slowly returns to evening skies by early May of next year. Mercury is visible just before sunrise between November 10th and 20th. You can orient yourself to the eastern sky this way: Mars will be highest and dimmest. First magnitude Spica will be in the middle, and brighter Mercury will be lowest to the horizon, just ahead of the sun's morning glow. The best observing times are between 5:30 and 6:00 am.

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