Rome Star Gazers

One of the challenges and frustrations for observers is locating a faint object in the telescope.  The typical telescope field of view is less than one degree.  When looking for a specific object through a telescope, one needs to be able to use reference stars to locate the object.  This is easy if there are many prominent reference stars to guide you.  When you are looking in an area where there are few landmarks (skymarks), then the hunting is very difficult.

A finder scope is a small telescope or spotter, which you attach to and align with the telescope.  It has a relative wide field of view and provides the observer with a much easier way to narrow down the area where the object is located.  Once the object is approximately in the field of view of the telescope, the observer can pinpoint it through the telescope.

There are several types of finder scopes and I will discuss them in the next article.

No Comments »

If you have ever looked at the moon through your telescope on a crystal clear night, you have noticed that it takes a while before your eyes readjust to the dark.   The moon is so bright, especially when observed through a telescope, that your eyes lose there dark vision very quickly.

If you look at the full moon through a telescope, you may even have a dark spot in your vision for 20 minutes or so, not to mention losing your dark vision.

The moon filter does two things for the observer.  First, the moon filter blocks a lot of the light from the moon preventing the observer from losing much of their dark vision.   It also gives the observer a better view of the moon.  You can actually see features on the moon with the filter that you can not make out without the filter.

Of all the filters that you can buy for your telescope, the moon filter is probably the least expensive.  So, if you enjoy viewing the moon, you should seriously consider spending the few dollars necessary to add a moon filter to your equipment box.

No Comments »

When stargazers talk about field of view, in effect they are talking about how large an area they can see in the night sky through their instrument.  Generally speaking, greater the magnification of your telescope, the smaller the field of view you will have.

You can calculate the Field of View that your telescope will have if you know the “Apparent Field” of your eyepiece and the magnification that your telescope will have using the eyepiece.  You take the “Apparent Field” and divide it by the magnification.

It is useful and important to use a magnification and corresponding field of view that is appropriate for the object you are going to observe.  For example, you may want to look at the Seven Sisters in Taurus, the Bull.  Remember that this star cluster is quite large.  It would not be useful to have your telescope on a magnification that left the field of view smaller than the Seven Sisters.  It would be like trying to look at an elephant through a straw.  You could only see a part of it at time.  The beauty of an object like the Seven Sisters is the whole cluster within the background field in which it resides.

On the other hand, it would not be helpful to be looking at the Ring Nebula in Lyra using a low power large field of view.  In a case like this, you could not see the object at all; it would be too small.

Therefore, when deciding on which eyepiece to use in your telescope, keep in mind the magnification and field of view you will need to have a good image of the object you want to observe.

No Comments »

If you are a car enthusiast, the term light bucket will refer to a headlight or tail light assembly.  However, if you are interested in and read about astronomy or telescopes, you have no doubt have come across the term, light bucket, as well.  This is what stargazers call a reflecting telescope that has a large diameter mirror.  Usually the telescope has a Dobson type mount with a simple tube or truss frame assembly.  The idea is that the cost of the telescope is primarily spent on optics and not on the tube assembly or stand.

A Light Bucket!

The term Light bucket comes from the notion that the telescope collects so much light that it is acts like a bucket.  The amount of light that a telescope collects is determined by the diameter of the mirror.  A 4” telescope has a surface area of 12.56 in2.  A 6” mirror has a surface area of 28.27 in2 or 125 percent more surface area than the 4” mirror.  If we go up to a 12” mirror, it has a surface area of 113.09 in2 or 800 percent more surface area or light gathering ability than a 4” mirror.  The reason stargazers want more light gathering ability is, they want to see very dim objects: nebulas, open clusters, globular clusters, and galaxies (deep sky objects).

No Comments »

Collimation refers to the proper alignment of the optical elements of a telescope.  By this, we mean that the mirror, diagonal mirror, and eyepiece are all in the proper position to maximize the light gathering and focus ability of the optical elements.

In the lower picture, the light has been collimated.

This website: http://www.astro-tom.com/telescopes/collimation.htm gives you a good example of a telescope image before proper alignment and after alignment.  It is critical to make sure the telescope is properly set up.  Each time you move the telescope from one location, it slightly moves the optical elements.  This means the alignment is slightly disturbed.  If you go to many star parties and do not collimate your scope between parties, your telescope will be performing well below its capability.

It is well worth the effort to learn how to properly care for your telescope and adjust its elements.  It will provide you with images that will please and touch your soul.

No Comments »

Of course, this question is based on a generalization but a useful one in any case.  Everything else being equal, a reflecting telescope uses a mirror to collect and focus the starlight to the eyepiece while a refracting telescope uses a lens.

The logistics for making a 4” mirror are much different from making a 4” lens.   First, the material that the lens must be made from is much more precise than the mirror.  One must look through the lens so there can not be any occlusions or concentration gradients within the lens.  Since we are simple looking at an image reflected from the surface of the mirror, the purity of the material is not as much a consideration.

Secondly, when making a lens, one must shape and grind and polish two surfaces.  Additionally, these two surfaces must be in proper orientation to each other for an image to be clear.  When making a mirror, one grinds and polishes only one surface.  Finally, when placing the lens in the telescope, one can only support the lens from the sides.  A mirror can be supported from its entire back.  This advantage is clearly more obvious when the telescope becomes quite large.

Everything else being the same, refracting telescopes cost more than reflecting telescopes because a lens costs more to fabricate than a mirror.

No Comments »

Telescope Corner: I have a pair of binoculars and they have a “60×15” on them.  What do the numbers mean?

First, let me congratulate you on a fine pair of binoculars.  The two numbers on binoculars tell you the aperture and magnification.  The first number tells you how much light your pair of binoculars collect.  It is a measure of the diameter of the objective in millimeters.  I say, “Congratulations,” because your binoculars are as large as many department store telescopes.  They are very good for stargazing but you might find them a bit heavy for the average observer, especially during a long observing session.

The second number, “15,” is the magnification of the binoculars.  Unlike most telescopes, most binoculars have only one magnification (I know that you can get some binoculars that have a zoom feature).  For binocular observing, 15 power (magnification) is plenty.  Remember you are going to be holding these in your free hands.  Any more magnification than that and they will simply show too much vibration from your shaking hands and arms – especially later in your observing session.

Much is written about binocular stargazing and you can see quite a bit using them.  In fact, I spent most of my first year stargazing as an adult using a pair of 60 x 12s and found more than half of the 110 Messier Objects easily.  Naturally, the more you look, the more you want to see, and the larger the instrument you want and “need” to have.  Aperture Fever can really take hold of a typical stargazer.  That is, if a 2” scope is good, a 4” is better.  Once you have a 4” telescope, you must have an 8” scope.  Well, from an 8” the next step is a 10” or 12” behemoth.  The fact that the price of large scopes seems to be dropping, does not help this matter either.  It seems that I can get a 12” Dobson for what I remember an 8” scope would cost just a couple years ago.  Oh well… these are some of the trials and tribulations of stargazing.

After all of my rambling, if you have a good pair of binoculars, your stargazing will be much easier.  You can see quite a bit through binoculars, they are extremely easy to carry with you.  You can start observing almost immediately, no set-up time involved.  It does not take a special car to carry them as it does for some larger scopes.  A pair of binoculars may weigh a couple pounds where a large scope may weigh over 100 lbs.  Binoculars are great but they will soon lead you down the path of “aperture fever,” so beware!

No Comments »

Telescope Corner: What are the parts of a telescope?

A simplified answer would be an eyepiece, tube, and primary mirror (reflecting telescope) or objective lens (refracting telescope).  For a detailed diagram and explanation for the parts of a telescope go to the following website: http://www.universetoday.com/guide-to-space/telescopes/telescope-parts/

The way a telescope works is, light from the celestial object enters the end of the telescope and passes through the objective in a refracting telescope or it bounces off the primary mirror in a reflecting telescope.  The light then strikes the diagonal mirror before passing through the eyepiece on its way into your eye.  The other part of a telescope is the mount or tripod which holds the telescope steady.  In some ways, this is one of the more important parts of a telescope.  You can see anything if the telescope is unsteady or vibrating.

No Comments »

The answer is simple; some things are big and some things are small so sometimes we need low power and sometimes we need high power.  I would suggest that most people assume that a telescope is primarily designed to magnify objects that are viewed through them.  To a degree, this is true.  However, it can be argued that the most important feature of a telescope is not magnification but rather light gathering ability.  Many of the objects in the night sky are plenty large, they are just extremely faint.  Many of the nebulae are very difficult to see with the unaided eye but with proper light gathering ability of the telescope and filters, the nebulae become quite visible.  The North American Nebula, in Cygnus the Swan, is just such a nebula.  I have a hard time seeing it, even though I know exactly where to look, with the naked eye.  It is certainly large enough to see with the naked eye, it is just very faint.  Using a large aperture telescope, at very low power, is ideal for viewing it.

This is most easily demonstrated by the fact that of the 110 Messier objects, most can be seen nicely through a simple pair of binoculars.  Usually, a pair of binoculars has a magnification (power) of only 7X.  The value of using binoculars in astronomy, instead of magnification, is the amount of light gathering that they put into the observer’s eyes.  You are able to see fainter objects by looking through the binoculars.

Now, to be fair, if you are interest in planetary observing and similar viewing, magnification becomes very important as well.  The planets are already bright enough to see.  It is the finer details that we wish to observe, and that takes magnification.

In conclusion, it takes both; magnification and light gathering ability to make a telescope useful.  Since the amount of magnification changes depending on what you are observing, you will need to change the magnification of your telescope by changing the eyepieces.  On another note, it is also possible to change the light gathering ability of your telescope by using a shield over part of the lens or mirror to “stop it down.”  This is often done if the object is exceedingly bright, such as the Moon.  Perhaps we will talk more about this later.

No Comments »

Determining the magnification of a telescope is not difficult although it does take a little division.  Every telescope has a focal length that is prominently written on the side of the telescope.  The common department store refracting telescopes have a focal length of 1,200 millimeters (mms).  Some of your Newtonian reflectors have similar focal lengths.  When we say that the focal length of a telescope is 1,200 mms, we are saying that the primary lens or mirror of the telescope has that focal length.  Often this lens or mirror is referred to as the “objective.”

When you buy at telescope you also get some eyepieces that go along with the telescope.  These eyepieces attach to the end or side of the telescope and they are what you look through to see celestial objects.  Each of these eyepieces have a specific focal length engraved on them as well.

To determine the magnification or power of your telescope, take the focal length of the objective and divide it by the focal length of the eyepiece.  Say the telescope objective focal length is 1,200 mms and you use a 12 mm eyepiece.  You take 1,200 mms and divide by 12 mms.  This gives you a 100 X magnification.  Say you change the eyepiece to a 24 mm eyepiece.  By doing so, you change the magnification or power of the telescope from 100 X to 50 X (1,200 mms / 24 mms).    Now you change to a 6 mm eyepiece.  The magnification then becomes (1,200 mms/ 6 mms = 200 X), twice as powerful!

No Comments »