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un-check the "Show all asteroids" box, and then tell Guide to show (say) only the first 30000 numbered objects. This can cause Guide's asteroid display to be much faster. 18: ECLIPSES, OCCULTATIONS, TRANSITS One of the most powerful features in Guide is the ability to make charts showing the paths on the earth cast during events where one celestial object blocks out (part or all) of a second object. This includes events such as solar eclipses, lunar occultations of stars and planets, occultations of stars by planets and asteroids, transits of Mercury and Venus in front of the Sun, and the (extremely rare) cases where one planet occults another. In this chapter, all events of this sort will be called "eclipses", to evade the phrase "eclipses, occultations, and transits". To show such charts, there are a few steps you have to do first. You need to set Guide's date and time to sometime not too long before the actual conjunction or eclipse. (For an example, there have been numerous solar eclipses. By setting the date and time, you tell Guide in which event you are interested.) Some events of this sort are listed in Guide's "Tables" menu (see page 50). If you just want to look at solar eclipses, you can simply set the date/time near that of the eclipse, then hit the ':' key. But if you want to look at, say, an occultation of Antares by the Moon, you need to right-click on the Moon, then on OK; then right-click on Antares, and then click on OK. By doing this, you're telling Guide: "I'm interested in seeing when _this_ object occults/transits/eclipses _that_ object." Once you have done this, the "Find Conjunction" and "Show Eclipse" options in the Extras menu will no longer be grayed out. Click on "Find Conjunction", and Guide will pause briefly while finding the nearest (or next) conjunction of those two objects. (From Guide's point of view, "conjunction" means "closest apparent approach of the objects to each other"). It will reset the time and show you the conjunction of those objects. If one of the objects is the moon, Guide is bright enough to realize that conjunctions occur at roughly 27-day intervals; you can click on "Find Conjunction" repeatedly to show subsequent conjunctions. Alternatively (or in addition), you can click on "Show Eclipse". Guide will clear the screen and switch from drawing charts of stars to drawing charts of the earth; you'll get a world map, and the path of the event in question will be shown. (Depending on your computer speed, this may take a few seconds; it is a very math- intensive task!) The eclipse path will usually be in light gray, shading to blue in
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