Observer's Notebook for October 1999

by John Rummel

October brings ever shorter days and cooler evenings as fall firmly takes over where summer leaves off. As October opens, Mars is continuing its eastward journey, growing ever dimmer after a spectacular spring and summer. On October 1st Mars is more than 126 million miles away but still fairly bright at 1st magnitude. Having departed Scorpius, Mars starts the month low in the south in the constellation Ophiuchus, and by the 11th, has moved into Sagittarius. Watched with binoculars throughout the month, Mars will march past several bright star clusters. On Friday the 15th, Mars is just 6 degrees below the moon. Directly in between the two solar system objects are two breathtaking deep sky wonders, M20 or the Trifid Nebula, and M8 the Lagoon Nebula. Both are visible as hazy patches in binoculars. On the 27th and 28th, it passes just a degree from the brilliant globular cluster M22. A small telescope is needed to see M22 as anything more than a fuzzy dot. Through a medium sized telescope, it is a brilliant conglomerate of nearly a million stars.

Mars is not the real story of October, though. As the month opens, Jupiter and Saturn return with a vengeance to our evening skies. By October 1st, both planets are well up in the eastern sky by 9:30 pm, and after daylight savings time ends, even the kids will have plenty of time to gaze at these giants before bedtime. If Jupiter seems a bit brighter this year, it is. About every 13 months, Earth in its orbit "catches up" with Jupiter and passes it in an event called opposition (so-called because at that time Jupiter is opposite the sun in our sky). Because Jupiter's orbit is slightly elongated, once every twelve years its opposition date happens at the same time that the planet is physically as close to us (and the sun) as it can be. This is that "12th year," so Jupiter is just a little bit bigger and brighter this year than usual.

Jupiter reaches opposition on October 23, and on that night, will shine at a magnitude of nearly -2.9. Of the naked eye planets, only Venus is routinely brighter than this (almost unbelievably, Mars will shine brighter than this during its opposition in August of 2003). There is no better time to observe Jupiter through a telescope than this month. Nights of steady skies will reveal a stunning array of features on the cloud tops and the continual dance of the four Galilean satellites.

Saturn, not nearly as bright as Jupiter, will sit just below and to the left of its brilliant partner in the early evening skies. Saturn will reach opposition next month, and will be the subject of next month's article.

Also on the 23rd, the nearly full moon will appear just to the right of Jupiter, with Saturn and the Pleiades to its left. This same lineup, minus the moon, will still dominate the following weekend. So if you're out trick or treating with the kids, take a few minutes for some sidewalk astronomy, and point out some of the wonders of the night sky. The kids will be wowed by your firm grasp of celestial goings-on.

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