Traced in dot and dash lines on the accompanying star map are a series of ellipses. From the points where these ellipses come nearest to the edge of the map, arrows project radially to the names of the months which are printed around the map. Each ellipse marks the extent of the heavens visible at nine o'clock p.m. of the first day of that month toward which its arrow points. To avoid confusion, the best plan is to cut in a piece of stiff paper an oval opening of the exact size of one of the ellipses, and to place this over the map, so as to expose to view only that portion of the map which represents the visible heavens at the time of the observation. The map should be held with the arrow pointing toward the South, then contrary to custom in geographical maps the East will lie on the left-hand side and the West on the right-hand side. This is due to the fact that the heavens are viewed looking upward, whereas the map is viewed looking downward. In locating stars and constellations it is best to hold the map overhead, when the actual points of the compass and those marked on the map will bear the true relation to each other. Now, suppose the night be the first of December and the hour nine p.m.; cover up the entire map except that included within the ellipse whose arrow points to December. Then when the map is held overhead with the arrow pointing south it will be possible to pick out the stars visible at that hour and date. As time passes the ellipse must be slowly moved eastward around the Pole Star as a center at the rate of nearly 15 degrees per hour, so that two hours later, that is at 11 p.m., the visible heavens would correspond with that portion enclosed by the ellipse marked for the first of January. Owing to the fact that this eastward movement is not exactly 15 degrees per hour, the ellipse for the second day of December will

Directions For Using The Star Map 299

Copyright, 1904, by Munn & Co.