RASC Calgary Centre - Starhopping
by: John Mirtle
Page last updated: November 7, 2001
It's a clear, moonless night and you are about to look at your first deep sky object with your new telescope!
An exciting moment, your first serious attempt at amateur astronomy.
"Where is the Sombrero Galaxy?"
At about this point, people new to the hobby begin to realize that the universe is a really big place. The telescope
shows only a small part of the sky, leading to no end of frustration finding things. At star parties, the novice is
often amazed at how experienced observers seem to pull faint fuzzy after faint fuzzy out of an almost blank part of
the sky. The truth is, no observer is born knowing where M104 is! Finding deep sky objects is an acquired skill, as
are many other aspects of this hobby. This means practice!
There are two main ways of getting around the sky - setting circles and star hopping. Setting circles assume
familiarity with polar aligning and the celestial co-ordinate system, and will be dealt with in another article. Star
hopping helps to develop familiarity with the sky and constellations, it works with both binoculars and telescopes. With
dobsonians, star hopping is the only way to get around. The first step with becoming adept at star hopping is often
the hardest. Turn off the TV and go outside! With most modern TV's hitting the "power" button on the remote will
accomplish this.
With telescopes, becoming familiar with your finder is an important first step. There are two things to figure out -
the field of view and image orientation. Most straight-thru finders give a simple inverted image. Up is down, but left
is left and right is right. Right angle finders are more convenient for many 'scopes, but are more difficult to use as
up is down and right is left! Star patterns are much more difficult to match with charts. Practice using the finder
and main scope in the daytime to become comfortable moving from point "A" to point "B". Amici prism finders are more
user friendly as they provide "correct" images. Up is up, left is left. Star patterns on charts match what you see in
the finder.
Knowing how much sky your finder shows is also important. Many finders have the field of view stamped on them, measured
in degrees. If unknown, you can get a good idea by looking through the finder and comparing to a set of charts. What
many observers find helpful initially is a simple template, cut out of cardboard. On your star charts, measure how big
your finder's field of view is in centimetres and cut a hole in a piece if cardboard to that size. By placing the
template over the charts you will see what is visible is your finder. This will make right angle finders a little
easier to use. Don't forget to align the finder to the main scope! Get a rough alignment in the daytime and fine tune
the alignment under the stars.
Star hopping is not difficult to learn, in fact most people find it intuitive. It is much like driving across Canada
with a road map. To get from Calgary to Salmon Arm you could use the latitude and longitude co-ordinates and get there
that way. This is the idea behind setting circles. You could also "hop" from town to town, the route you would pick
from a map. The most direct route would be from Calgary to Banff, Field, Golden, Revelstoke and finally Salmon Arm.
The same idea applies to star hopping. Instead of using towns and cities to mark the way from point "A" to point "B",
chains of stars or asterisms are used to mark the way.
Start off by selecting an object to observe, making sure it is above the horizon and locate the object on your charts.
Next, look for the nearest naked eye star on the chart and locate that star in the sky. If the star is overhead and
you are using binoculars, you may wish to wait an hour or two until the object is in a more comfortable part of the
sky. Look at your charts (with a red flashlight!) and locate the deep sky object and the bright star. Look between
the two, and try to pick out any chains of stars or asterisms that link the two together. These may take the form of
triangles or rectangles. Try to pick something that will be obvious in the finder. This is where the template can
come in handy. On the chart you can see how many finder fields you must move from the bright star to the next
identifiable star pattern. The rest is easy! Continue from one star pattern to the next until you get to what you
are after. The better your charts, the easier this will be. The Uranometria shows stars down to 9th magnitude. With
this, star hopping is easy as it shows as many stars as most finders do. With practice tracking down a 15th magnitude
galaxy is no more difficult than any of the Messier objects. (Try it!)
Once you have the field of view you are after in your telescopes' eyepiece, this doesn't mean that you are going to
see your faint fuzzy! First, check the size of the object. If it's size is 2 or 3 arc seconds, you won't see anything
with binoculars or at low power. You will need several hundred power to see a planetary this small. Conversely, if it's
size is measured in degrees, (such as the Small Sagittarius star cloud M24) you will need very low power or binoculars
to see it. Don't forget that your finder is a small telescope - it will give fine views of the largest deep sky objects.
Next, check the magnitude. A 20th magnitude galaxy will not be visible with a 10cm scope! The sky is a very important
factor here. High cirrus cloud can block out 12th magnitude galaxies even from a 17 1/2" scope. If the sky is clear
and relative humidity is low, even a small scope can give stunning views. For fainter objects try using averted vision.
This is an observing technique that takes a little while to master as it involves looking
AWAY from the object
you are trying to see. Photo receptors in the eye are more sensitive around the edge of the retina, meaning that
peripheral vision is more sensitive than direct vision. For really faint fuzzies you are more likely to observe the
object by looking away from it slightly. Rocking the 'scope slightly may also help in detection. (or you could tap
your head...) Don't be afraid to try other magnifications as well, as some objects may be easier to spot at higher
power. If at first you don't succeed, try again another night. Deep sky observing is another acquired skill that
takes place far away from televisions. The more you do it, the better you will be. Sketching is a tremendous aid in
observing. It forces you to take more time observing an object. You will develop observing skills at a faster pace
than if you were to just have a quick 30 second peek.
If you are new to the hobby, forget your setting circles for now and get into star hopping! There is no better way
to learn the sky. With a little practice, you too can impress others by pulling faint fuzzy after faint fuzzy out of
an almost blank piece of sky!
(Printed in the Calgary Starseeker, many years ago)
Back