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Systems of latitude and longitude are also defined for other planets. The center of the visible side of the moon (as seen from Earth) is defined to be at latitude 0, longitude 0. If you select "Luna" as your home planet, and set those values, the Earth will be shown very near the zenith. (It wanders a bit around that point, due to librations, as described on page 15.) The next item, "Alt 100 meters", tells you that your point of view is 100 meters above sea level. Once again, you need usually be only approximately correct here. Clicking on the "Use geocentric position" causes Guide to ignore the lat/lon/altitude values; instead, your viewpoint will be from the center of the earth (or whatever home planet you have selected). The final four options only have meaning if your "home planet" is Earth and the "geocentric" option is not selected (i.e., you are observing from the surface of the earth). Set the "Include refraction" button, and refracted altitudes will be shown in the legend and when right-clicking on objects, whenever the altitude is above the horizon. In general, including refraction doesn't make a very large difference (about an arcminute or so), except for locations very close to the horizon. The temperature, humidity and pressure data are used to compute the amount of refraction. All three values are used in computing the limiting visual magnitude in Quick Info (see page 15). 8b: Inversion Menu The Inversion Dialog is used to adapt Guide's charts to the view seen through your telescope. It can be reached by clicking on the compass symbol in the legend, or through the Display menu. It shows these options: * Chart uninverted Chart inverted Mirror image E/W Mirror image N/S Rotation 0.0 * RA/dec (north at top) Alt/az (zenith up) Ecliptic north up Galactic north up The first four radio buttons let you flip the chart top to bottom, left to right, or both. "Chart uninverted" says that the chart is oriented as you would see it without a telescope. In your telescope, however, you might see something different. Many telescopes use mirrors, so you might see a
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