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Jupiter is a favorite target of backyard astronomers and October sees the giant planet begin its return to prime time. By mid-month, Jupiter is rising about 11 p.m. and each night sees it rise four minutes earlier. Time to dust off that small telescope and take a look at the king of planets. It will be easy enough to spot, being the brightest object in the eastern sky among the stars ofGemini.
Aside from the moon, there is nothing in the sky that offers more detail through a telescope than Jupiter. The rapidly spinning planet presents a constantly changing face full of colorful swirls, ovals and bands. Its two most prominent bands, called the north and south equatorial belts stand out in dark contrast to the lighter pastels of the disk. The bands are noted for displaying an infinite variety of notches, bumps and festoons. Jupiters most famous feature, the Great Red Spot, rotates into view every 10 hours and is easy to see for about 50 minutes of each rotation. Its not really red, more of a pale orange-tan these days, but still a large unmistakable oval depression in the south equatorialbelt.
One of the more interesting phenomena associated with observing Jupiter is the transits of its four largest moons. Called the Galilean moons after their discoverer, Galileo, the moons are aligned in their orbit around Jupiter in such a way as to pass directly in front of the planet from time to time. The moons are quite difficult to see as they transit across the planets disk, overwhelmed by the brightness of the planet, but their shadows are quite a different story. They present inky black dots that are easy, and fun, to observe. This month there are a number of double shadow transits events where the shadows of two moons can be seen crossing the disk at the same time. Unfortunately, we will miss out on the rare triple shadow transit that occurs on Oct. 12. That event will conclude just before Jupiter rises from our location, but the several double shadow transits are quite special in their ownright.
Type phenomena of Jupiters moons into your search engine and youll find a number of sites that will help you calculate the times of shadow transits. The popular magazines, Astronomy, and Sky & Telescope both have charts or tables predicting the start and end times of the events eachmonth.
Mark your calendars: Oct. 12 is Astronomy Day in Sierra Vista! Ever since 1973, amateur astronomers have been setting aside a day each spring to share their enthusiasm and their telescopes with the public. The theme of the day is bringing astronomy to the people. In 2010, the organizations that promote Astronomy Day celebrations decided to extend the practice by adding a fallevent.
This year, you are invited to visit the Patterson Observatory on the campus of the University of Arizona, Sierra Vista, on Saturday Oct. 12 to celebrate Astronomy Day with the Huachuca Astronomy Club(HAC). The event is free and open to all ages. There will be two sessions. The observatory will open from 1 p.m. until about 4 p.m. for an afternoon of solar observing. HAC members will help you safely observe the sun through properly filtered telescopes. Youll be able to see sunspots, solar prominences, and all sorts of surface features on ourstar.
The observatory will open again at 7 p.m. for an evening viewing session featuring views through the 20-inch research grade telescope as well as a battery of smaller scopes. Oct. 12 is also International Observe the Moon Night, an event designed to encourage people to take notice of our nearest neighbor, and in keeping with that effort, the moon will be a featured object. The moon viewed through a large telescope is quite an incredible experience, especially if its not something youve done before. Of course, youll be treated to views of many other celestial wonders, too, and be guided around the sky by some very knowledgeable astronomers. One caveat: the event is weather dependent. Cloudy skies may forcecancellation.
Next month, I hope to have some good news to share about Comet ISON. Astronomers all over the world are closely watching this new visitor to the inner solar system and by next column we should have a pretty good idea of how it willperform.
TED FORTEis a member of the Huachuca Astronomy Club and a contributing editor for Sky & Telescope magazine. He can be reached attedforte511@gmail.com.
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BACKYARD ASTRONOMER: Jupiter rising and Astronomy Day
