What You Need to Be A Successful Deep Sky
Knowledge and Desire
Attics and garages
around the world are full of unused telescopes. This is the unfortunate
fate of the majority of instruments sold. Yet there are so many interesting
observing projects that I couldn't begin to list them here. There is something
for everyone in the night sky, it's just a matter of finding out which
things are for you.
The primary motivations of the deep sky observer typically
fall into two categories. We'll call the first wonder. Deep
sky objects are anything but flashy in the eyepiece. They typically aren't
colorful, don't move, and most are so subtle that they are challenging
to see at all. If it is flashy and colorful you desire, the planetarium
gift shop has plenty of pictures for you. Seeing a deep sky object for
yourself is like attending a sporting event versus seeing it on TV. There
is a connection with the universe we inhabit that cannot be made through
a photograph. The photons that enter your telescope from M31 traveled over
2 million years just to be recorded by your eye. An entire galaxy's worth
of light, an incredibly vast area full of stars and gas and dust and planets,
and it's all there waiting just for you. There is incredible beauty in
the night sky, but it isn't the kind you find in photographs. It's the
kind of beauty that is apparent only to those who understand the grandeur
they behold. People are born, they mate, raise their children and they
die. What a shame it is that more don't take the time to open their eyes
and have a look around them while they are here. Observing is about taking the
time to look; and the beauty lies in knowing what it is you are seeing.
We'll call the second the hunt.
There are billions of people who inhabit this planet. How many of those
can find M31 all by themselves? How many can even identify Andromeda, its
constellation in the sky? Hunting down deep sky objects isn't easy. It
requires knowledge and skill that most people don't posses. Finding anything
in the sky is something to take pride in, whether it be the Great Nebula
in Orion with binoculars or the Twin
Quasar in a 20-inch Dob.
Knowing the Sky
The deep sky observer
should know the constellations and brightest stars. These are your guideposts.
You should also be aware of where north, south, east, and west are and
how the sky moves over the course of a day or year.
The Dark Period
The moon is the
natural enemy of the deep sky observer because it lights up an otherwise
dark sky, rendering many objects invisible in the sky glow. You must learn
the motion and phases of the moon in order to avoid its light. You must
also be aware of the length of twilight at your location at the current
time of year. There are calendars, handbooks, and software available that
can tell you when it will be truly dark.
Recognizing and Predicting Good Observing
Not all dark skies
are alike. We observe through an often turbulent and cloudy atmosphere.
The two important factors are seeing and transparency.
Seeing describes how steady the atmosphere
is. As light passes through air of differing temperatures it can be refracted,
acting like a large lens. The effect is to bend the path of the light to
and fro, causing the stars to appear to twinkle, distort, swell, and even
dance about. Poor seeing has the effect of blurring and dimming your view,
making faint objects and intricate detail more difficult to see. To quantify
the seeing astronomers often use Seeing
Transparency describes how much light is
passing through the atmosphere. The journey of light through the atmosphere
can be a perilous one; clouds and dust may keep some or all of it from
ever reaching your scope. The transparency of the atmosphere is a very
complicated subject, but it is clear that moisture plays a significant
role. Even if the sky appears cloudless, there can still be a uniform haze
that may keep you from seeing all that you might otherwise.
The Proper Time and Place
Take the sun.
When it is high in the sky it is bright and can give you quite a sunburn.
Yet when it is setting it is much dimmer and redder. This is the result
of the amount of atmosphere the sunlight passes through. When an object
is low in the sky, near the horizon, it passes through many times more
air than when it is directly overhead. Astronomers quantify this with the
unit. The amount of air light must travel though from directly overhead
is termed an airmass of one. As you observe an object lower in the sky
the airmass increases until at about 30o
above the horizon you are looking through twice as much air as you would
overhead, or two airmass. At this point the effects of the earth's
atmosphere on your observation is doubled.
For this reason, in general it is best
to observe an object when it is at its highest point in the sky, whenever
possible. At the very least it should be more than 30o
above the horizon.
Deep sky observers
count on their eyes to see faint detail. In order for your eyes to perform
at their best they must be completely dark adapted. It takes time for this
adaption to take place--at least 30 minutes. You must shield your eyes
from any light for this amount of time if you expect to see faint objects.
Using a red flashlight to read your charts can help, but even a red light
can do harm. If you observe in the presence of lights you may need to drape
a dark cloth over your head at the eyepiece. Another useful item is an
eye patch, available at any pharmacy. Keep the eye patch over your observing
eye while reading your charts or in the presence of any lights. I highly
recommend a pair of AstroGoggles as well. These goggles will shield your
eyes from most of the light which causes them to react, allowing you to
even go into a lighted room yet preserve much of your night vision.
Knowing What to Look For
I can't emphasize
this point enough. You will be much more successful if you have a good
idea what the object will look like ahead of time. Knowing how large it
will appear in the eyepiece and how bright it will be are the two keys
to success. Much of this comes via experience, which is why you should
start with the brighter, easy objects first and work your way down to those
Find out the true field of view of your
eyepieces. One simple way to do this is to find a star near declination
zero and time how long it takes to drift across the field of view (with
the drive off if you have one). Your field of view in arc seconds will
be the time in seconds times 15. Divide this by 60 to get the field of
view in arc minutes.
Knowing What You Are Looking At
You will become
bored with deep sky observing quickly if you don't take the time to learn
about what you are seeing. Visit your local college bookstore and look
for an Astronomy 101 textbook. These texts are written for freshman astronomy
courses, use no math, and are appropriate for anyone interested in astronomy.
I recommend a subscription to Sky & Telescope magazine as well.
next --> Skill and
1. A Dark Observing
2. Knowledge and Desire
3. Skill and Patience
4. Good Finder Charts
5. The Choice of