Explanation:
Fix your camera to a tripod, lock the shutter open,
and you can make an image
of
star trails -
graceful concentric arcs traced by
the stars as planet Earth rotates on its axis.
Of course, the length of the
star trails
will depend on the exposure time.
While exposures lasting just
five minutes produce
a significant arc, in about 12 hours
a given star would trace out
half a circle.
But in any long exposure, the background glow from
light-polluted
skies can build up to wash out
the trails.
Still, astronomer Josch Hambsch produced
this
stunning composite of star trails around the South
Celestial Pole
with an effective "all night" exposure time of
almost 11 hours.
To do it, he combined 128 consecutive five minute long
digital exposures recorded in very dark night skies
above Namibia.
In his final image, the background glow on the right is due
in part to the faint,
arcing Milky Way.
