As a bright November Moon lit up the night sky last week,
Gil Esquerdo spotted this lovely Moon
halo overhead at
the Whipple Observatory on Mt. Hopkins, Arizona.
In the foreground, the structure and individual
component mirrors of Whipple's
10 meter gamma-ray
telescope actually block direct light from the
lunar disk, emphasizing the halo in
this dramatic view.
The halo was caused by ice crystals in the thin
high clouds above the observatory - crystals that are
hexagonal in shape
and produce the characteristic ring of
light with a 22 degree radius.
In fact, the ice crystal shapes are much like the
flat, hexagonal mirrors of the
specialized telescope in
Used together the mirrors can collect brief flashes of
optical light caused by high-energy
gamma-rays impacting Earth's atmosphere.