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What you should know before buying a telescope for Christmas

ROCKWALL (December 11, 2013) If you are a parent interested in purchasing a telescope for your child as a Christmas present, the Golden Rule is: DO NOT BUY A TELESCOPE AT A DEPARTMENT STORE OR BIG BOX STORE.

If you are busy and/or don’t like to read very much, then you just have to read the next paragraph to know all you need to avoid buying a useless telescope as a Christmas gift:

Follow the Golden Rule above and DO NOT buy it at a local big box department store, because you will only buy a cheaply made, unfocus-able, unsteady, non-pointing bucket of trouble. DO buy about a 4”-6” reflecting telescope on a simple, stable, non-electronic mount.

The BEST telescope for a young beginner is by far the STARBLAST. You can buy a new one for less than $200 with free shipping. Go here to order one: tinyurl.com/qa8e72h (To avoid overt advertising, I made the URL tiny to hide the manufacturer, but it’s good equipment that you cannot find at any big box store.)

Tied for BEST telescope you can possibly buy this season is a new introduction that will not only satisfy your family desire for a telescope, but also contribute to a worthy cause. This year, Astronomers Without Borders has introduced “The One Sky Telescope.”

Shown here is the telescope itself – a very easy to use and easier to store rig that features a 5-inch, f/5 mirror, with a truss tube that collapses to 14.5 inches in seconds and a total weight of just 14 pounds.

.http://store.astronomerswithoutborders.org/index.php?main_page=product_info&cPath=5&products_id=4&zenid=17e30b4c8132991b0ce17634bea5ffc8

Once you have the scope, go to the internet and download star charts for your location from for free here fourmilab.ch/yoursky/ (just click “set for a local city” and scroll down to Dallas…close enough). Wait until the time when there is little or no Moon in the sky, go outside at night and compare the star chart to the sky by holding it up as described and move the telescope to the object you want to see. Congratulations! You have just conquered amateur astronomy.

More Telescope Information: Way More than You Need to Know

When you buy a telescope, remember that it’s really a system of two parts – the mount and the telescope (optical tube – OT). The most important and unfortunately overlooked aspect of the telescope system is the mount, for it determines how the optics are applied against your search of the night sky. Even some “experienced” amateurs forget this point as illustrated in the very writing of this article…the person who asked me to write this actually wrote about optical tubes first.

Mounts come in several varieties ranging from your arms holding a pair of binoculars to a fully computerized, remotely operated system. Forget that last part if you are just getting into this hobby. Before we look closely at the mount, consider that the mount itself determines what your optical tube can be used to see or even what you can eventually image with a camera. Telescope mounts come in the following varieties from least complex to most complex.

• Handheld – For binoculars or other viewing system
• Alt-Azimuth
• Dobsonian (named after John Dobson)
• Equatorial Mount
• Fork Mount

For our purposes, both the fork mount and equatorial mounts sit atop a simple tripod system that comes with the mount itself as an integral part. The big differences in these mounts are in whether they track the sky automatically, how they move, and how they align.

The simplest type of mount is your pair of arms. Believe it or not, if you learn how to read a simple star chart (covered in another section of this exciting series) and learn how to “aim” your body using your shoulders, the human body makes a very good telescope pointing and aiming system. My favorite beginner star chart that always “gets you in the ballpark” is produced by Fourmilab and can be downloaded for free here fourmilab.ch/yoursky/.

The Alt-azimuth Big Box Disappointment Mount

The next simplest type of mount is the kind usually found by those who violate the Golden Rule of telescope purchase (see above) when they buy a scope at their local big box retailer that offers 600X Magnificent Magnification to enable viewing slimy green space aliens on Mars. Yes, this is the alt-azimuth telescope mount. BEWARE. This mount has two perpendicular axes of motion, vertical (altitude) and horizontal (azimuth). Standard camera tripods have alt-azimuth mounts. These mounts are usually mated to the optical tube, badly aligned, shaky and make tracking the sky almost impossible at all but the lowest magnification.

Now we’re going to see another type of Alt-azimuth mount, that really makes life easy for the new observer. One of my personal favorites is the Dobsonian or “Dob” mounted telescope. The Dobsonian telescope takes its name from the astronomer/philosopher John Dobson, who introduced the concept of inexpensive, large aperture telescopes to astronomy and founded the San Francisco Sidewalk Astronomers. Amateur astronomers at the time were so amazed that a telescope built from simple, inexpensive materials performed so well that they could hardly believe their eyes. As home-built Dobsonians started showing up at star parties and people saw what Donsonians could do, the Dobsonian revolution swept the world.

This is the scope recommended in the beginning of the article. The Dob is a system unto itself but for this discussion just consider that when you set up your telescope, you move the base and then set the optical tube into the base and just point it at the target you are interested in viewing. Several years ago, only the most advanced models of these scopes would find and track an object with a computer assist, but nowadays there are several versions that align simply and accurately with only a few alignment star inputs into a user friendly box. I personally have owned two “Dobs” one a ten-inch and my current “light bucket” is a 16-inch telescope. The one big important thing about any Dob is having an accurately aligned finder scope system. My suggestion is that the newcomer should buy a 4-inch to 6-inch Dob (that was a recommendation) but whatever kind of Dob you purchase, please spend an extra $30 on some sort of Zero magnification, Reflex finder. My two favorite zero mag finders are the TELRAD and the Rigel QuickFinder. I currently operate both of these finders on my telescopes.

The Equatorial mount. The equatorial mount has two perpendicular axes, but they are called right ascension (R.A. or polar) and declination (Dec). When the RA axis is aligned parallel with the Earth’s rotational axis, objects can be easily “tracked” as they drift across the sky (due to Earth’s rotation) by turning just one of the slow-motion controls (R.A.) instead of two, as is required with an alt-azimuth mount. A motor drive can be coupled to the R.A. axis for automatic sky tracking. Sounds complicated and sort of is complicated because in order to have any chance of an accurate alignment, one must accurately align the polar axis of the mount to what we call “Polar North”. In the United States this is pretty simple as long as you have a polar finder scope in the mount, know what time it is, and have a way to identify the astronomical or “Sidereal” time. I don’t recommend purchasing an equatorial mount on your first go unless you’re in for the long haul.

Several commercial manufacturers, namely Meade and Celestron, have made fork mounts popular. With most fork mounts comes a computerized capability right in your hands. Using a thing called a hand paddle, which is really a mini-computer processor with memory and everything, you simply tell the telescope where you are, what time it is and point it at a couple objects in the sky and you have an alignment. Several years ago, Meade added a simple function that allows you to enter your zip code, as the location can’t be easier than that. The downside to all this automation is that when you press “Go-To” an object, if the telescope doesn’t put the object in your eyepiece or finder scope, the mount is really not very user friendly in terms of searching the sky for the object. However, there are some simple fixes to better enable this search process. On my 10-inch Meade LX200 I removed the little finder scope so I could have a second imaging telescope and added a TELRAD zero-mag finder. One of the most appealing aspects of a fork-mounted telescope is its ability to accurately track objects in the sky. You might find that you like to take pictures of the night sky and this kind of mount will allow you to do just that for several seconds at a time. Unfortunately, when the mount is sitting “flat” as depicted in fig. 4, any images of longer duration than maybe 30-seconds will result in a thing called “star-trailing” that is most pronounced at the edges of the image. But wait, there’s a solution to this problem. You can make your alt-az fork mounted telescope into an equatorially based fork mount by placing it on a thing astronomers call a “wedge”. In fig. 5 you can see what my Meade used to look like in my observatory before I dismounted it in favor of a German equatorial mount.

Meade and Celestron both manufacture wedges but they are unsteady and cheaply made in my opinion. So by the time you decide you need a wedge to support what may become your new “addiction” to astrophotography, you may want to consider a high-end wedge such as a Milburn or Mitty product. The robust wedge in fig. 5 is an aerospace grade aluminum Milburn wedge.

Considering what kind of Telescope Optical “tube” to buy:

If you are not going to follow the advice to purchase one of the two recommended “first” telescope sets for your children or self, then you should consider the mount first and the type of telescope (the thing you look through) second. For amateur astronomy, consider that there are generally three popular types of telescopes, refractors – made popular by Galileo (lens up front similar to a magnifying glass), reflectors – invented by Sir Isaac Newton and still used today (single mirror that bounces light up to a diagonal mirror that lands the image onto your eye), finally there are combination, compound, or Catadioptric telescopes. You cannot say that one is better than the others, it all depends on your observing needs, where you observe and what you want to do in the future.

Here goes a little explanation.

Refractor telescope. Did you notice earlier that I didn’t write that Galileo invented this kind of scope? That’s because it was really invented by a Danish optician, Hans Lippershey. According to NASA’s Jet Propulsion Lab (JPL) for which I serve as a Solar System Ambassador, Lippershey’s two little children were playing with lenses in his shop when one of the children looked at a weather vane on a nearby church through two lenses held together. The object became larger and clearer. The rest of the story is that Lippershey then put a tube in between the two lenses, thereby inventing one of the first telescopes. This early model only magnified an image by 3 or 4 times..Lippershey applied for a patent in 1608 for his new invention.

The dark side of the story continues; in July of 1609, Galileo heard that Lippershey was on his way to Venice to sell his invention “that made distant objects seem near.” Galileo needed money, and the Venetians were offering Lippershey a high price for his device. In 24 hours, Galileo had a telescope made and sent word of “his invention” to a monk in a high office of the government. For this, Galileo received a raise in salary from 520 to 1000 florins per year.

These telescopes are either really inexpensive (avoid) or can be moderately to extremely expensive. I have had all three types and as long as you know what you’re getting, it’s fine. The simple cheap refractor will be Achromatic and you will see purple around the bright stars. You can eliminate this with a simple “Fringe-Killer” purple filter. As long as you know this and it’s ok, this is a fine scope. Next is the APOchromatic telescope. These are either ED (with two lenses) or fully APO with three or more lenses to correct the colors. The three or more lens scopes are very expensive. Currently, my stable of telescopes includes a five-inch apochromatic refractor and a three-inch quadruple lens widefield refractor. Both instruments cost thousands of dollars without mounts or additional hardware.

Reflector Telescope: In 1668 Isaac Newton, an English mathematician, built a reflector telescope that used a metal mirror to gather and focus light rays. Objects like planets and asteroids are so far away that all of the light rays coming from them reach the Earth as parallel rays. In the reflector telescope, one or more curved reflector mirrors focus those parallel lights rays to a single point. All modern research telescopes and large amateur ones are of the reflector type. The Dobson mounted telescope is actually a simple reflecting telescope. Today, amateurs refer to these telescopes as “Light Buckets” because large apertures (we refer to mirror or lens size as aperture) can be bought for relatively small amounts of money. Also, the reflector creates no unwanted color fringing. So why doesn’t everyone want as big a reflector as possible? With size comes a challenge such as images not being as sharp or crisp as in a refractor. Also, in a place like the DFW metroplex with all our light pollution, you cannot appreciate the large aperture because you are collecting an equivalent amount of light pollution and dim, deep-sky objects are not visible. With these telescopes, we must constantly assure that the mirrors remain in alignment or “collimation”.

Catadioptric Telescope: Also known as a “Cat”, this is a telescope that uses a combination of mirrors and lenses to increase the effective focal length of the telescope while allowing it to be folded into a more convenient and compact size. The use of a full-aperture correcting lens in these scopes virtually eliminates spherical aberration, chromatic aberration, and coma. The simple Cassegrain telescope was first developed by Laurent Cassegrain in 1672. In 1944, Russian optician and astronomer, Dmitri Maksutov invented a catadioptric telescope, the Maksutov telescope. A few years later, John Gregory, an employee of the technology company Perkin-Elmer, published the first designs for the Maksutov-Cassegrain in a 1957 issue of Sky & Telescope magazine for the use of other amateur astronomers. The commercial creation of the Maksutov-Cassegrain was to be reserved for Perkin-Elmer.

The most popular advanced telescope is the 10-11 inch SCT. I own a 10-inch Meade SCT and it’s a lovely telescope. Unfortunately, if you get into science or imaging there are several undesirable characteristics such as mirror flop, star-stretching and collimation challenges.

In summary, don’t buy your kids a telescope from a big box or department store. DO buy something like I described in the first couple of paragraphs and spend some time to be in the moment with your children and help them discover the night sky. You’ll be amazed at your experience for there is something about how people react while exploring the heavens. In these conditions, young and old alike seem to open up and communicate with honesty and clarity that they find difficult in the daylight hours.

Clear skies to you and yours – andremember that the best telescope system is the one that you can use and enjoy the most.

Our Universe Today is a column written by Blue Ribbon News special contributor, Max Corneau, aka AstroDad, of Rockwall. Images provided by Max Corneau.

Max retired from the U.S. Army in 2009 as a Lieutenant Colonel, Senior Space Operations Officer and Master Aviator.  He amassed over 3,200 hours as a pilot of Special Electronic Mission Airplanes.  Since 2004 he has been a NASA/JPL Solar System Ambassador, is a Master of Astronomical Outreach through the Astronomcial League and built his own astronomical observatory. His amazing images can be seen at AstroDad.com.

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