Skywatch
Skywatch is a programme designed to monitor
the background brightness of the night sky.
A simple understanding of why a star is visible
to an observer is that the star is brighter
than the background it is observed against.
An observer can see this on any night when
there is a bright moon, many of the starsin
the vicinty of the moon cannot be seen, however
as the moon apparently moves away those stars
become visible.
The moon is not the only object in the sky
which contributes to the night sky brightness,
our Galaxy itself is very bright, just look
into the Milky Way, and there also is the
Magellanic Clouds. The combined brightness
of the multitude of stars in a galaxy can
hide other objects in the line of sight.
An insidious form of night sky brightness
is found in our very homes, in our streets
and in our cities. This is "artificial
light". It has been a pursuit of society
to provide artificial light to illuminate
our activities of the night, however because
light is an electomagnetic wave , then light
will behave like a wave. Two principal behaviours
of light: , the abilitity to radiate from
a point source and the ability to reflect
from a surface create a situation here all
light sources contribute to producing upward
radiating light. This happens when the light
is directly radiated upwards and when the
light is reflected from the ground, after
being radiated downwards. Once the light
is moving upwards it will then be reflected
and refracted from all manner of particles,
dust, molecules. This process is known as
scattering, and this scattered light then
behaves like the ancient light from other
galaxies and other stars, it contibutes to
the brightness of the night sky.
As the number of light sources which are
permitted to "spill" light increases
so to does the night sky background become
brighter, over a number of years this brightness
can and does become obvious. If for a moment
you pretend that you were a citizen of the
early colony of Sydney, imagine how many
stars you would see on a moonless night.
Now go outside and look at the night sky,
how many stars can you see? Imagine the night
sky in 100 years?
For a person with an interest in astronomy
this may be a serious concern - do you want
to observe the night sky from your home?