1. A method of automatically tracking and photographing a celestial object which moves relative to a photographic apparatus due to diurnal motion so that a celestial object image, which is formed on an imaging surface of an image sensor via a photographing optical system, becomes stationary relative to a predetermined imaging area of said imaging surface of said image sensor during a tracking and photographing operation, said method comprising: performing a preliminary photographing operation at a predetermined preliminary-photographing exposure time with said photographic apparatus directed toward said celestial object and with a celestial-body auto tracking action suspended to obtain a preliminary image before automatically tracking and photographing said celestial object; calculating a moving direction and a moving speed of the celestial object image from said preliminary image that is obtained by said preliminary photographing operation; and automatically tracking and photographing said celestial object based on said moving direction and said moving speed of the celestial object image.