Turn off the daylight and horizon displays. Use the
"Planet" Palette to center on Comet Halley and lock on
Comet Halley. Use the "Settings" button to set Orientation
to Equatorial. Use the "Zoom" button to zoom in until the
field of view is 40º. Set the date to December 1, 2061. Set
the time step to 1 day. Step ahead until you pass the time
that the tail of Comet Halley seems to be the longest. Then
step back and forth in time until you find the date that the
tail is longest. Use the Angular Separation Tool to find the
angular length of the tail of Comet Halley. Set the cursor
on the nucleus of Comet Halley and find the distance of
the comet from the Earth. Step forward in time and see
how the distance of the comet changes with time. Find the
date on which Comet Halley will be closest to the Earth
and its distance on that date. Try to explain why Comet
Halley isn't closest to the Earth on the date its tail is longest.
