Sunday, July 10, 2016

Against Fatuous Advice to Beginning Astronomers

Last night, the Austin Astronomical Society sponsored an “Out of the Box Clinic” for new astronomers with unused or under-used instruments.  The event was held at our Canyon of Eagles “Eagle Eye” Observatory near Lake Buchanan, about 80 miles northwest of Austin. (I did not attend.) Following that, today the club president issued an email to make further recommendations based on the interactions between newbies and sages. He was wrong on every point.

"1) A decent finder is crucial: Some of your scopes had no finder.  Others had the old fashioned tube finders that are very hard to calibrate with their three thumbscrews.  I recommend you pick up an inexpensive Red Dot Finder for your beginner scopes.  We can help you install it or swap it with your tube finder."

A.   I started as a kid with the old-fashioned tube with crosshairs and six screws: three front and three back.  It was easy to use and the crosshairs were a reliable reference for moving the telescope up-down-left-right when I lost the object under higher magnification. (See #3.) I now have a new, modern telescope with a Red Dot Finder. It is a pain in the neck, literally. I usually sit on the ground to look through it.

B.   Nothing is ever where the dots may (or may not) line up. Do this for yourself: Use your index fingers pointing upward about a foot apart, and not lined up with your eye. Now, sight some object in the room and move your head back and forth until both fingertips line up with it. You are off-center. You are not lined up. But you think you are.  With the little red dots and the little bright stars, it happens all the time.

C.   The best thing for me is to put some bright star in the telescope center and then align the viewer to it, using the two insufficient screws to set it. I say insufficient because two points make a line, but three are needed to fix a plane and the viewing field is planar

D.   You will need their help installing a new finder because you will have to drill holes in your telescope, mount screws washers and nuts – and not drop anything down the tube to damage the mirror or lens.


"2) Calibrating the view in your scope to the view in your finder is a necessary first step.  With some of you, we spent time trying to dial it in during the daylight hours so you'd be prepared when the sun went down.  For those of you without finders, you experienced a lot more challenges getting your tubes pointed at the objects you want to see."

A.            Turn Left at Orion.  The sages with their huge Dobsonian “light buckets” often do not have finder scopes at all. They know the sky and “star hop” to find what they want to see.
B.            Because my Red Dot Finder is so useless, I often sight up along the tube to locate an object.  You get close then make small moves. That was the advice that Ellie Arroway’s dad gave her with the ham radio, and which she followed as an astronomer: small moves.  (See Contact by Carl Sagan.)
C.            The sages should have been pretty good at teaching this because it is what they do with their own Dobsonians. (See A above.)

"3) Get a low-magnification eyepiece.  For beginner scopes, nothing beats a good 40mm Plossl-type eyepiece.  Most of you showed up with a 24mm or a 20mm eyepiece as your lowest magnification eyepiece.  There's nothing wrong with those magnifications.  However, you will find it easier to bring your target into view with a low-magnification eyepiece.  Once your target is identified, then you can swap to your higher-power eyepiece(s) for viewing."

A.            Now you tell me. (And what is a "Plössl"? Note the umlaut-o: "Play-sell.")
B.            I bought a beginner telescope, a Celestron 130-EX refractor. It came with a 20mm ocular and a 10mm ocular.  Then I bought a box of eyepieces for beginners. The biggest is 32 mm.  But, you know what, my first telescopes were not much different. I never had a big eyepiece. I learned with the little ones – not the littlest; admittedly, the largest of them; and the middle one. The laws optics are against high magnification on a little telescope.
C.            Speaking of the laws of optics, the diameter of the ocular is only one factor in the equation of magnification.  M = f/d. The Magnification is the focal length of the telescope, divided by the diameter of the ocular lens. So, a small telescope with a 24mm eyepiece will have lower magnification than a larger (longer) one. Lower magnification is easier to work with when hunting objects – especially without a finder scope. But that is not just a function of the ocular.
D.            Moreover, the other factor is the light-gathering area of the main lens or main mirror, the “aperture.” A 10-inch mirror gathers four times as much light as a five-inch mirror: area increases by squares.  So, a beginner with a 3-inch telescope will gather 40% more light than a beginner with a 2-1/2 inch instrument. 
E.             That’s nice to know… but if you did not buy a 3-inch telescope but got the smaller one, then the point is moot. The reason for the “Out of the Box Clinic” is supposed to be to help you get the most from your instrument, not make you wish that you worked at Mount Palomar.
F.             And once you have your object in the low-power field of view, moving to higher power is also another thing to be learned. If you are off center by little bit, when you drop that higher power eyepiece in the viewer, you may well have to start over finding the object.  There is no way around it. It is not like flipping TV channels with the remote.
G.            Finally, the AAS should have had eyepieces at the ready. These things are pretty standard and come in only a few diameters. That would have been more productive than telling people what they should have done.

"4) Several of you asked about choices for your next, "better" scope.  We have some suggestions on an FAQ page on austinastro.org.  http://austinastro.org/index.php/f-a-q/#bestscope"

A.            Buy the most telescope you can afford. It is like any other tool. Any mechanic, craft worker, or technician will tell you the same thing. None of the advice I saw actually explains that when you buy a telescope, you are getting three things: a telescope, a mount, and a tripod. 
B.            Every instrument I have seen for consumers is a collection of junk because compromises are made for the production of each component.  But it does not need to be that way. 
C.            For the AAS magazine, Sidereal Times, I interviewed a member who is a mechanical engineer. He broke the problem down and bought the best telescope, the best mount, and the best tripod that he could afford, each from a different source.

PREVIOUSLY ON NECESSARY FACTS


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