| The brightness of a spacecraft is influenced by
several factors, including its size, orientation, reflectivity of its
surfaces, distance from the observer, and the angle between the sun,
spacecraft and observer. The size and reflectivity determine the "intrinsic"
brightness, and this is either estimated from observations or from a
knowledge of the size and type of coverings used in the construction. The
distance, and sun-satellite-observer angle can all be calculated from the
orbit. This leaves just the orientation or attitude, which is usually
unknown, and often varying rapidly (e.g. a tumbling rocket body). For this
reason, our magnitude estimates should only be treated as a rough guide, and
the actual brightness you see could be considerably more or less than this. |