City of the stars
[21] A magnified composite showing 24 hours of star rotation around the north celestial
pole. The brightest ring in the shot is caused by Polaris, the "North Star". Note how many
fainter stars there are between Polaris and the pole.
[22] An inexpensive way of taking a flat field is to cover the end of the imaging
telescope with a taut white cloth and take a photo with the telescope pointing at an
evenly lit patch of sky. It’s important that the camera and telescope stay in the same
configuration between imaging and taking the flat.2122Known as exoplanets, the count of discoveries increases daily thanks
mainly due to a spacecraft called Kepler which monitors a region of sky
roughly 12° in diameter in the constellation of Cygnus, the Swan. Here it
looks at the light of 150,000 stars looking for tiny dips in output caused
by planets passing across the star’s disc. For a terrestrial sized planet,
the dip would typically be around 100 parts per million of the star's light.
When three such transits have been seen and confirmed, then the object
is certified as a valid exoplanet. At the time of writing there are in excess of
700 certified exoplanets known and thousands waiting for verification.
Of course, the holy grail of planet hunting would be to locate a world
much like our own which exists at a distance from its parent star (the
Goldilocks Zone) where water can be liquid on its surface. At the time
of writing numerous “Super Earth” candidates have been put forward:
planets larger than Earth but located within or close to the habitable zone,
such as Kepler 22b. As our techniques and equipment improves, no doubt
we will discover planets similar to Earth but the question as to whether
they will harbour life still remains unanswered. Probability and the history
of discovery would tend to suggest that the finding of extraterrestrial life in
some form is very likely.Paint Shop Pro or the freeware GIMP is useful for tweaking the final
image but for the best results a program that can perform what’s
commonly known as a DDP or Digital Darkroom Process on the image
will be the best place to start.
Amongst some of the commercial applications that can do this are
Maxim DL, AstroArt and ImagesPlus. The powerful, yet sometimes
daunting freeware IRIS package is also well worth considering. The DDP
is basically used to stretch the image data but designed to bring out the
fainter detail without causing the brighter detail to appear over-exposed.
If all this seems like too much hard work from the description given,
don’t worry, you wouldn’t be the first to think that. If this is how you feel then
start out by taking some basic images of bright subjects and progress from
there. Remember no one’s judging your efforts and the experience should
be an enjoyable one. Your first astrophoto taken through a telescope will
give you a thrill, irrespective of its appearance.
More advanced imaging can be carried out by using mono cooled CCD
cameras and using filters. Of particular interest are narrowband filters
which restrict the light coming into the camera to specific wavelength
bands. Examples of astronomical narrowband filters are those which
centre on the H-alpha, OIII, H-beta and SII. Imaging through these filters
allows you to concentrate on the light given off by specific atoms in the
target object. As such, the information that is captured can show precisely
where these atoms are concentrated. An additional bonus for using
certain types of narrowband filter is that many are tuned to regions of the
spectrum which are not emitted by streetlights. As an example, imaging
with H-alpha light in badly light-polluted skies can produce great results.
Planets Around Other Stars
Our Solar System is not unique in the Universe and advanced techniques
to micro-analyse stars are revealing the existence of other worlds, referred
to as exoplanets, in orbit around distant suns. An area currently the realm
for professional or advanced amateurs, it’s an amazing journey of the mind
to imagine these alien worlds of all shapes and sizes scattered throughout
our Galaxy and no doubt the Universe.