[11] The gegenschein visible in the dark
skies over the VLT in Paranal, Chile
(credit: ESO/Y. Beletsky).[12] The Moon photographed in
broad daylight.[13] The majesty of the Aurora Borealis
from Norway.[10] The Moon illusion – seen against
familiar objects, the Moon appears
larger than when alone in the sky.at altitudes of 20,000 feet. There are rare clouds which occur much
higher than this in a very thin layer located in the atmospheric layer
known as the mesosphere at altitudes between 47 and 53 miles. At
this height, these clouds are able to reflect sunlight when the Sun
is below the horizon while "normal" tropospheric clouds remain in
darkness. Sometimes seen in the summer months from latitudes
50–70 degrees north and south of the equator, these clouds can put
on quite spectacular displays glowing with a beautiful electric blue
light. As they shine at night they are known as noctilucent, or “night
shining”, clouds, often abbreviated to NLCs.Moon Illusion
Most people over-emphasize the apparent size of the Moon in the
sky, and in many paintings, artists often incorrectly show the Moon
the size of a dinner plate. In reality the Moon’s size is quite small
and its disc can easily be hidden behind your little finger held up at
arm's length. However, when the Moon's low down and close to the
horizon, it registers as being much larger than it does when it’s high
up, an effect first noted in ancient times. Ptolemy, the last of the
great Greek astronomers (AD 120–180) had an explanation for it. He
pointed out that when the Moon is low, it is seen across “filled space”1011Astronomer Book