Have you ever seen a halo around the Sun?
This fairly common sight occurs when high thin clouds containing millions of tiny
ice crystals cover much of the sky.
Each
ice crystal acts like a
miniature lens.
Because
most
of the crystals have a similar elongated
hexagonal
shape, light entering one crystal face and exiting
through the opposing face refracts 22
degrees,
which corresponds to the radius of the Sun halo.
A similar Moon halo
may be visible during the night.
Pictured above, a nearly complete
sun halo was photographed high above the ancient
Bayon temple in
Angkor,
Cambodia.
Exactly how
ice-crystals form in clouds remains under
investigation.
Most galaxies have a single nucleus — does this galaxy have four?
The strange answer leads
astronomers
to conclude that the nucleus of the surrounding galaxy is not even visible in
this image.
The central
cloverleaf is rather light emitted from a background
quasar.
The gravitational field of the visible foreground
galaxy
breaks light
from this distant
quasar
into four distinct images.
The quasar must be
properly aligned behind the center of a massive galaxy for a
mirage like this to be evident.
The general effect is known as
gravitational lensing, and this specific case is known as the
Einstein Cross.
Stranger still, the images of the
Einstein Cross vary in relative brightness,
enhanced occasionally by the additional
gravitational microlensing
effect of specific stars in the foreground galaxy.