(See description below)
Comet C/2002 T7
Discovered by the the Lincoln Near Earth Asteroid Research (LINEAR) project in October of 2002, comet C/2002 T7 made its closest approach to the Sun April 23, 2004. In this gorgeous telescopic view recorded before dawn April 21, 2004, the clearly active comet has developed an extensive, complex tail extending over 2 degrees in a direction away from the Sun, and a pronounced anti-tail or anomalous tail.
When a comet's tail appears to be pointing toward the Sun, this is called an anti-tail or anomalous tail. In reality, the tail only appears to be pointing toward the Sun. To get an anti-tail, the comet must produce large ("heavy") dust particles. If this happens, these particles are left along the comet's orbit instead of being pushed away from the Sun and the comet's orbit by light pressure. Often dusty comets will produce particules of different sizes creating a fan-shaped appearance. The smallest dust will be pushed directly away from the Sun (like the gas tail) and the largest will be left in the comet's orbit. When a comet is close to the Sun, the angle of this fan can be 90 degrees or larger. If the Earth-comet-Sun geometry is correct, the dust in the comet's orbit will appear to point toward the Sun. [Try this...make a right (90 degree) angle with your thumb and index finger. Your index finger is the main tail and your thumb is the dust left in the comet's orbit. Point your finger and thumb directly away from you (keeping the angle 90 degrees). Your finger seems to be going in exactly the opposite direct from the thumb. This is what causes an anti-tail.]