BASIC OBSERVING TIPS AND TECHNIQUES

 

 

TIPS ON ALIGNMENT:

 EQUATORIAL-MOUNT TELESCOPE ON POLARIS

The first thing that you are going to do in order to align your telescope will be to find Polaris.  The only place from which you could observe without having to go through this procedure is at either the North Pole or South Pole because all stars there move parallel to the horizon, neither rising nor setting.

For everyone else, the stars rise in the East, reach a maximum elevation, and set in the West.  Their motion is a great circular path, the view of the complete circle cut off by the horizon.  They are moving parallel with the Earth’s equator due to the Earth’s eastward rotation;  remember that it is Earth, not the starry sphere, that is actually moving.  Stellar motion is very slow, and many generations must pass before any naked-eye changes are noted.

In the Northern Hemisphere, we are fortunate to have a bright star that reveals Celestial North—Polaris.  In the Southern Hemisphere, there is no bright star near the South Celestial Pole that may be used for alignment.  From the Southern Hemisphere, alignment is done by moving about five times the long axis of the Southern Cross (constellation) southward toward a blank space in the sky.

Throughout the night, all of the stars in the heavens seem to be rotating around the Poles.  If we align our telescope with the proper Pole for our hemisphere, this polar axis (which is a metallic shaft located on the tripod mount that must be aligned with Polaris) will turn parallel with our own rotation, and any star can be followed across the sky with one constant and smooth westward motion.  This is much easier than using an alt-azimuth mount such as a camera tripod.  With these mounts, you must constantly use the motion controls both upward and westward as the star rises in its circular arc.

After finding Polaris (Northern Hemisphere only), turn your tripod so that the polar axis of the telescope is facing north.  Turn the telescope tube so that it is parallel with the polar axis shaft.  See diagram below.  On the side of most mounts, you will find a set of angles for you to match your latitude for tilting the polar axis toward Polaris.  If you don’t know your latitude, you can find it at:  http://www.heavens-above.com/countries.asp .

If you have properly tilted your polar axis, and have turned it northward, Polaris should be in the field of view of your finder ‘scope.  You may need to turn the mount left or right a bit in order to get it aligned to “True North,” and tilt the polar axis a little to get Polaris centered as a match for your latitude.  Polaris is not exactly at the celestial pole, but this alignment will be good enough for your clock drive to automatically follow objects for several minutes without any correction.  If you are planning to do long-exposure astrophotography, you will have to use much more precise alignment than just sighting on Polaris.  This is advanced amateur astronomy.  You will still be able to take astrophotos up to ten minutes duration with just this alignment. 

 

Description: Description: Description: http://eaaa.net/basic_observing_tips_and_techniq_files/image002.jpg 


 

BALANCING THE GERMAN EQUATORIAL MOUNT

Like the fork equatorial mount, the German equatorial must be aligned on Polaris, as shown in the diagram at left.  However, the German equatorial must be properly balanced for good tracking.  This procedure is necessary  to perform well on all new telescopes.

To balance the telescope, you will need to shift the tube back and forth until it is properly balanced, and the counterweight must be shifted up and down the declination axis to balance the weight of the tube.

To balance the tube, turn the telescope until the tube is parallel with the horizon, and the declination axis is parallel.  The tube will be horizontal to the ground, and the declination axis will also be horizontal to the ground, since it moves independently of the tube and polar axis.

 If the tube is balanced, it will not move when you release all of the locks on the ‘scope motions.  If the back shifts downwards, then loosen the straps that hold the tube in the cradle, and shift the tube forward slightly.  Check again, and continue in this manner until the tube stays horizontal on its own.

If the counterweight moves downwards, shift it up the declination axis column toward the tube until it balances the weight of the tube and both remain horizontal. 

Once properly balanced, the German Equatorial Mount will track smoothly westward with only a tiny bit of adjustment with the motion controls located on the polar axis.  This is especially important if you are using a clock drive mechanism.  The unbalanced telescope will not track improperly, but you risk burning out the clock drive due to the stress of the torque on the gears and motor.

If properly polar aligned, the declination slow-motion control should not need adjustment unless you change your view to a different object. 

 

Description: Description: Description: http://eaaa.net/basic_observing_tips_and_techniq_files/image004.jpg


 

USING THE ERECT IMAGE EYEPIECE

This is a high quality achromatic eyepiece with a built-in roof prism for erect images. Achromatic lenses have a flatter field of view without noticeable curvature at the edges, and with less color distortion.
This erect image is fine for terrestrial viewing, as well as astronomy. It will give you erect right-left correct images, instead of images that are upside down and backwards.
It requires about 2" in-focus (moving it toward the telescope tube), compared to a regular 10.5 mm eyepiece which may be positioned farther from the telescope tube. This means that it may not work with some Newtonians, several of which do not have the option of positioning an eyepiece that close to the tube. It should work well with all Schmidt-Cassegrains and Refractors, because they have a wider focusing range. For refractors, it should be used without the star diagonal in place in order to get the erect image.
This eyepiece generally fits a standard 1.25" barrel.
To find out what magnification you will get from an eyepiece, divide your main objective's focal length (printed on the telescope tube or listed under specs) by the eyepiece focal length--in this case, 10.5 mm.
So, for a 700 mm focal length refractor such as a typical 60 mm department store telescope, this eyepiece will yield about 67 power (67x) [700 / 10.5 = 67]. This is an excellent medium power eyepiece for observing the entire disc of the Moon, as it almost fills the entire field of view of the eyepiece. As many NASA and other maps of the Moon are erect-image oriented, this makes identifying Lunar features much easier than with ordinary inverted-image astronomical eyepieces.



ALIGNING THE FINDER 'SCOPE


If your telescope has a finder 'scope attached, first find an object at least a quarter mile away that stands out, such as a radio tower, water tower, tall building, or tall tree.  After you have chosen an object to sight on, use your lowest power eyepiece to center the top of the chosen object (or a particular distinctive feature, such as a satellite dish) in the eyepiece of the telescope. 
Lock the telescope in place, and look through your finder ‘scope.  Use the setting screws on the finder ‘scope (that hold it to the telescope tube) to move the finder ‘scope until its cross-hairs align with the top of the object at the center of the field of view in your eyepiece.
Now, switch to your high-power eyepiece.  And again, recenter the chosen object.  Go back to the finder ‘scope and make minor adjustments to recenter the object at high power. 
Now, your finder ‘scope should be aligned well enough for you to find distant planets, stars, and other celestial objects, even with high magnification.
It is important to choose an object on the ground for this alignment because celestial bodies are constantly in motion as the Earth rotates, and trying to align on them would keep you constantly going back and forth to compensate for the continuous motion.

 



TIPS ON OBSERVING FAINT OBJECTS

For the novice astronomer, keeping the sun (with proper solar filter) or moon in the telescope can be a challenge.  Eventually, however, everyone works up to common objects such as the Orion Nebula or the Beehive Cluster.  Those can easily be seen through binoculars as well as through a telescope.  If however, you want to see Deep Sky Objects, you will need to learn a couple of the basic tricks of faint object observation.  But first, a little explanation….

The light-gathering portion of the eye includes both rods and cones.  There are more rods than cones, and most of them are situated outside of the central hub of densely packed cones.  The cones give us color vision, but are not particularly sensitive to light.  The rods, however, are not sensitive to color, but they are sensitive in low-light to faint objects. 

Cones have been tested and charted at different wavelength receptivity.  Some cones are more receptive to red light, some blue, and some green.  The majority of these reside in the macula.  Macular degeneration results in the eye’s dependence on peripheral vision since the macula (center) is no longer functioning.  

Rods are more than one thousand times more light-receptive than are the cones.  Under optimal conditions, it is believed that rods can detect individual photons of light.  It takes a while for the rods to reach maximum efficiency in the dark, however.  This is why stage hands and actors might close their eyes onstage before the lights are shut off between acts.  Closing the eyes several moments before the lights are shut off give the rods a chance to “charge up” so that when the lights go off, you can see how to exit the stage without tripping over scenery, or set up props for the next act.  Full dark adaptation generally occurs after about thirty minutes of darkness. 

Rods pick up more short wavelengths than do cones, and although less responsible for object resolution, the rods are better motion sensors as well as dark adapted, faint object resolution.  Since the rods are located toward the outer edges of the retina, they provide your peripheral vision.  If you look through a telescope eyepiece directly at a faint object, your eye may not be able to gather enough light to allow you to see the object either clearly, or possibly, at all.  If you allow your eyes to relax and stare just off-center, your peripheral vision will pick up the object and you can then concentrate on seeing the object more clearly without looking directly at it.  This is generally referred to as “Averted Vision.”

Rod sensitivity peaks in the blue wavelengths, and they do not pick up red very well.  It is this reaction that allows you to use a red beam flashlight to see your log book or find objects in your sky charts without spoiling your dark adaptation.  With a red-filtered flashlight, you can see clearly.  The rods do not pick up much of that wavelength, so they don’t have to recharge when the light goes out.  This is why it is much easier to photograph any red nebula, such as the Horsehead, than it is to see it visually. 

Red-Filtered Light is the only acceptable light for use at an observing session.  White light ruins everyone’s dark adaptation.  This is one of the reasons you park away from the observing site, and enter the parking area with the lights off (if possible…some newer cars do not allow this), and disconnect the dome light so that it doesn’t shine out every time a door or hatch is opened.   

To turn your regular flashlight that came without filters into a suitable red light,  you can get a piece of red cellophane and make a filter to fit behind the glass.  This will work just as well as commercial filters.


[ Home ]


Page design by Draco Productions.
dracoproductions@hotmail.com
All rights reserved on this and all other pages produced by Draco Productions.