By December, 1985, the long-anticipated brightening of Halley's comet was well under way, and early that month a faint tail was detected as it approached the sun. This picture was taken by the UK Schmidt Telescope in the middle of the month in blue light, and has been enhanced to emphasised the tail. The background stars appear as streaks as the telescope followed its motion for the 25 minute exposure, somewhere on the border between Pegasus and Pisces.

The diffuse coma appears large here because of the action of sunlight on gases evaporated from the icy nucleus produces a blue halo. The faint tail is made mostly of tiny dust grains shining by reflected sunlight. Both tails became much more obvious and differentiated after perihelion passage (after its closest approach to the sun), and photographs of this period are elsewhere in this series.