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3: WHAT GUIDE IS SHOWING YOU The first time you start Guide, a large area of the sky appears. It shows roughly what you would see looking at the Big Dipper with the unaided eye. The stars are of different sizes, corresponding to how bright they appear to be from Earth. There are also some lines which the sky does not show, and a block of text. For example, a set of green lines connect the stars of the Big Dipper. These "constellation lines" join together the major stars within a constellation. They have no real astronomical significance, but help you to remember where stars and constellations are. The constellations are separated by orange lines, known as constellation boundaries. The entire sky was officially subdivided into 88 constellations in 1930. The borders are like those of the Western United States; they run the equivalent of east-west and north-south. They provide a further frame of reference. Each constellation has a three-letter label shown in light blue somewhere within the constellation bounds. For the Big Dipper it is "UMa": "Ursa Major" or "The Great Bear". (The Great Bear is usually shown with the Dipper serving as its tail. Seeing the rest of the Bear, or of most constellation figures, requires some imagination.) Many of the stars have Greek letters attached to them. This shows the most common way of naming the brighter stars: letter plus constellation name. Thus, the star at the end of the tail of the Great Bear can be called Eta Ursae Majoris. (The added "is" is a Latin version of "belongs to.") These letters are called Bayer letters, after the astronomer who first assigned them. Usually, but not always, they are in order of brightness within a constellation, i.e., Alpha is brighter than Beta which is brighter than Gamma. In Guide, there is a fairly general way to adjust the display of any of these objects when they appear on-screen. If, for example, you found the constellation lines to be objectionable and wanted to get rid of them, or change their color, you would click on one of them with the right mouse button. You will immediately get a short bit of information about the object you clicked on (which can help in "what in the world is _this_?" situations.) But the dialog box with that information will also have a "Display" button; clicking on this will give you a chance to turn that class of objects on or off, or change its color, and (sometimes) adjust magnitude limits and labelling. Also, there is a legend at the lower left corner of the chart, showing the position of the cursor, the constellation you're in, the sizes of stars for different magnitudes, and some other data. As you move the cursor, the position readout will be updated. Clicking on most of the items in the legend will allow you some sort of control over Guide. For example, click on the constellation
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