Published: December 19, 2008 12:10 am      

Telescopes have been around four centuries

First steps with a telescope

Telescopes go back 400 years. In the first two centuries, most of the major types of telescopes were developed.

The first telescopes used simple lenses; before 1700, some of these telescopes grew to be many feet long, attached to high poles in an effort to achieve high power and clear images.

Then Isaac Newton invented the mirror scope that was free from false colors, the big problem with the simple lens telescopes.

Now all large observatory telescopes are mirror or reflector telescopes. A few decades later, the achromatic objective was developed, with a crown front lens and a flint back lens cemented to the crown; this arrangement eliminated most of the false colors seen in lens telescope images.

Achromatic objectives are used in most binoculars, all spotting scopes and lens telescopes.

In the 1800s, telescopes began to be built with gears and a motor attached to one axis so the telescope could turn to match the Earth’s rotation.

This attachment to the telescope mount is called a clock drive. By using this device, a telescope can be aimed at a star, planet or our moon without the need to continually adjust the telescope’s aim (as the Earth turns).

Telescopes do two basic things — collect light and magnify. Every optical telescope acts as a light bucket, collecting more light than your eye can. The amount of light collected depends on the area of the front lens or mirror (positioned at the bottom of the tube). So a telescope with a fat tube (wide lens or mirror) will have brighter images and can discern more detail.

The magnification or power of a telescope tells you how much closer sky objects appear through the telescope.

How much a telescope magnifies depends on how far the image is from the front lens or mirror and the focusing distance of the eyepiece (what your eye looks through).

The Earth’s atmosphere in most areas limits the magnification to several hundred. If you magnify more, no more detail is seen, but the atmospheric distortions become more obvious.

There are two very essential things to know about your telescope.

Does it use a large lens or large mirror? Second, what is the width of the main lens or mirror? (Some of the more expensive telescopes have both a large front lens and large back mirror.

These telescopes are called compound telescopes.) The width of the main lens or mirror determines how far you can see well with your telescope.

Small telescopes work well with the moon, planets and sights seen by eye. But for crisp views of the fainter planets, distant star clusters and galaxies, you need a telescope with a lens or mirror at least five or more inches across.

Beginners with their first telescope are often confused as where they place their eye. A majority of new telescopes are 60 or 80 mm wide lens telescopes.

These telescopes are just like a spyglass where you look through the back end of the tube.

There is usually a right angle eyepiece holder attached to make viewing objects high in the sky comfortable.

At the end of this diagonal, the eyepieces are inserted. The eyepiece with the wide lens is lower power while the eyepiece with the small lens is higher power.

A standard reflecting telescope has its eyepiece holder near the top of the tube. You look at right angles to the object that the telescope is viewing.

Different eyepieces give you an array of magnifications.

As soon as you get your telescope assembled, take it outside on a nice day and align the finder scope with the main scope.

Aim the main telescope on some distant pole, hill top or antenna. Use a low power eyepiece. Turn the focusing knob until the object is seen clearly. Then adjust your finder scope so its’ crosshairs are on the object seen in the main scope.

At night, start with the moon or a bright planet so you can get some confidence in your ability to aim your telescope.

Space prevents me from any more recommendations. But if you desire more information or pointers about your telescope, just send me an email at rdoyle@frostburg.edu .

Even better, put your telescope in your car trunk and see me after our Sunday Planetarium shows; I will be glad to look at your scope and offer my suggestions (free) for any difficulties you may be having.

Last shows, shortest day

Today we have our last December planetarium programs at 4 p.m. and 7 p.m. In “Ancient Skies of the Holy Lands,” we view the night skies seen by Abraham (nearly 4,000 years ago), that of Moses (about 3,200 years ago), the skies seen by Jesus in first century and the skies of Muhammad in the seventh century.

In this program, we will adjust the skies for different locations; Caanan or Judea (for Abraham and Jesus), Mount Sinai (for Moses) and Mecca (for Muhammad).

The planetarium is in Tawes 302, just off the front lobby. Call (301) 687-4270 for directions or call (301) 687-7799 to request a free planetarium bookmark with small map by leaving your name and mailing address.

Our January program, “Polar Skies” will resume on Jan. 11 with 4 p.m. and 7 p.m. presentations.

Winter officially began this morning at 7:04 a.m. when the sun’s direct rays reached farthest south close to the Prime Meridian (longitude 0) at the Tropic of Capricorn (latitude 23.5 south) to the west of Namibia and south of Ghana (Africa).

In this area, the sun rose this morning about 7:35 a.m. and will set about 4:55 p.m., giving us 9 hours and 20 minutes of sunlight, the shortest duration of the year.

Bob Doyle invites any questions or comments from readers; you can either leave a message on his voice mail at (301) 687-7799 or use email (rdoyle@frostburg.edu).