Page:The story of the comets.djvu/221

XI. When a new comet has been discovered and its elements have been ascertained, it is usual for some astronomer, specially interested in the particular comet, to provide a table of predicted places for the comet many days or weeks in advance. Such a table is called an "ephemeris" and will enable other astronomers to know where to look for the new body, and, finding it, to obtain observations



which will be available for improving the accuracy of the elements first circulated.

The significance of the various sections of a cone which constitute the different forms of orbit affected by comets is well and tersely stated by Howe in the following extract:—"Suppose that a small body is at a very great distance from the Sun, and both bodies are motionless. The body will begin to fall toward the Sun, its path being