Observing - Basics of Astronomy 2

A hand at arm’s length, a star chart, and the ability to remember simple shapes and lines puts you right on target.

The key ingredient in finding objects that are either barely visible or invisible (hiding) to the naked eye is to use brighter (bigger)  objects for reference points. For example:”Go about two thirds of the way past Walmart toward McDonalds and take a right at the phone booth; go down to the end and turn left. Go about fifty feet and you’ll see the a six foot tall pink flamingo wearing sunglasses; that’s the place!”

 1 - Learn Angular Size & Distance relative to the outstretched hand.

Angular Size & Distance is the length, width, and/or diameter of a celestial object as seen against the sky.  

The ANGULAR size of the tip of a pinky finger is is 1(one) degree.

The ANGULAR size of the tips your ring, middle, and index fingers together is 5 degrees.

The ANGULAR size of your fist from pinky to thumb inclusive is is about 10 degrees.

The ANGULAR size of your hand stretched out from pinky tip to thumb tip is 20 degrees.

2 - Transpose angular sizes and distances of objects from charts and lists

A  telescope with an eyepiece that yields 35X magnification has approximately a 2 degree field of view; a 8 X binocular or typical telescope finder scope has approximately an 8 degree field of view. The greater the magnification, the narrower the field of view; and as power increases, the concentration of light diminishes as it is visually spread over a larger area. 

It is important at this point for you to understand why most astronomical viewing is done at low powers - well below the capability of the telescope. The more you magnify an image, the broader it’s light is distributed over the view through the eyepiece; and the smaller that field of actual view becomes.  Limit use of higher powers only to reveal small details and small objects.

The angular size of the moon is 1/2 degree, so you can easily cover it with your pinky finger extended to arm’s length.  Many objects in the night sky have much larger angular size than the moon. A few galaxies in our local group and even more nebulae in the Milky Way galaxy are larger than (1) one degree.

The Great Andromeda Galaxy - M31 is  three degrees long and one degree wide - much larger than the full moon.

The Hercules Globular Cluster - M13 is 1/4 degree or 15 minutes in diameter - half the angular size of the full moon at .

When I point out objects,  I use degrees and describe geometric shapes or imaginary lines which point to the object. I point out a star and say “go west 10 degrees and then 3 degrees south”, or “”those 3 stars for a right triangle; imagine a line between the two southernmost stars and look at a point 1/3 of the way along that line from the east.”

If you don’t have someone to point things out, just remember what you see on your chart and then identify (within a few degrees) nearby stars. Considering the wide field of 7 X to 10 X binoculars and finder scopes, finding many objects invisible to the naked eye quickly gets easier.  For dim objects, use the lowest magnification eyepiece in your telescope.

Demonstrations of described methods are just one part of our public astronomical observation program. Join the fun.