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points on the horizon, plus the zenith (point directly overhead) and nadir (point directly below you). Click on one of these ten buttons, and Guide will center the chart on that point. The "Satellite" option will prompt you to enter the name of an artificial satellite. Do so, and Guide will recenter on that satellite. (See page 32 for some important warnings about which satellites Guide knows about and how accurate its information is.) You can find a planet (or the Sun or Moon or other natural satellite) with the "Planet" option. This gives a list of all planets and their satellites. Click on one, and Guide will recenter on it. Incidentally, there is an extremely useful shortcut: hitting, for example, Ctrl-0 recenters on the Sun; Ctrl-1, on Mercury; Ctrl-2, on Venus; and so on, up to Ctrl-9, on Pluto. Use Ctrl-- (Control-Minus) to recenter on the Moon. One "goes to" planets so often that having them a keystroke away can be really helpful. (Ctrl-3 will "recenter on the earth". Unless you've set Guide to show you the universe from a different planet -- an option discussed on page 34 -- that means it will show you the nadir, the point directly underneath you.) By default, Guide will show the names of the planets and satellites in red, yellow, or green. Red indicates the object is below the horizon; yellow, less than ten degrees above the horizon; green, more than ten degrees above the horizon. This color coding (also used for lists of comets, asteroids, and constellations) is very helpful in giving you an immediate idea of what is currently visible. The next option lets you center Guide on a given planetary feature (usually, a lunar crater; but features are also available on other planets.) To use it, you must first center Guide on the planet in question, and zoom in until that planet shows a disk. Then use the "Planet Feature" option, and Guide will list planetary features currently in view. Select one, and Guide will center on that feature. Three comments are important. First, a feature on the far side of that object won't be listed. Second, if you zoom in so far that only part of the planet is shown, only those features in the view will be listed. So you can, for example, zoom in on Tycho and get a list of lunar features in the Tycho area. For details on how to display these features in Guide, see page 23. Third, the coloring scheme is slightly different: here, red means the object is on the "night" side of the planet; yellow, within ten degrees of the terminator; green, in full sunlight. In the "Comet" option Guide will list the comets that are currently visible according to the limits set in the Data Shown dialog (p. 20). Click on one of them, and Guide will recenter on it.
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