Using J-Track's Sighting Capability

We recommend our J-Pass applet for complete sighting predictions

J-Track presents sighting data by displaying a spacecraft visibility circle which includes the requested location and the time for which the circle is valid. Sighting data is computed only for the current spacecraft. To select a spacecraft, click on it (its image). To request a visibility circle press and hold the (left) mouse button. The time of a displayed visibility circle is displayed in the lower left corner of the tracking system display.

In this example, the user has requested sighting data for Cairo, Egypt - notice the mouse location. The tracking system computes the orbit of the current vehicle until it crossed the meridian (longitude) of Cairo sufficiently close so that it could be seen from Cairo. Then J-Track displayed that visibility circle and time. The ground track through the circle is also displayed. By placing the mouse at points along the ground track (and pressing and holding), the user can see new visibility circles and determine the earliest and latest visibility times (earliest and latest circles which include the observation point - Cairo in this case) and the time of the highest elevation (closest point on the ground track). By examining the map, the direction from the observation point to the vehicle can also be determined. Remember, the vehicle is always on the ground track and always at the center of the circle at the time shown.

Visibility circles are based on a 20 degree elevation angle.

The tracking system only looks ahead 100 orbits.