Don Shedrick

Jan, 2001

January DAS Focus

COMPUTERS IN ASTRONOMY by Don Shedrick

With Christmas behind us, I hope Santa was good to you and brought you the telescope of your dreams. If you were not nice enough to warrant this reward from Santa, you may want to now take it upon yourself to purchase some new equipment. The Catskills Astronomy Club has prepared a very good guide to purchasing telescopes in the price range from under $100 up to about $1500. It is a very frank discussion on what is currently on the market and the advantages and disadvantages of the various choices. It is on the Internet at:

http://www.geocities.com/catskills_astronomy_club/telescopes.pdf

If you were luck enough to receive a new telescope, you will want to make sure it is performing optimally. A good starting point is with the article on the web by the well known amateur astronomer and author Dick Suiter titled "Top Ten Ways of Improving Newtonian Telescope Optics" at: http://home.digitalexp.com/~suiterhr/TM/TM.htm

One of the tips in this article is to "star test" the telescope optics. Dick wrote a whole book on this subject, and he gives some good info on his top ten tips site. In addition, some good articles on the subject are available on the web, along with the closely related subject of collimation. A star test is a very sensitive way to test both the quality of your telescope optics and the accuracy of the alignment of the optical components (primarily related to Newtonian reflectors). Collimating a telescope is lining up its optical components (lenses, mirrors, prisms, eyepieces) in their proper positions. This should be accurately done, or else the image quality will suffer. Many new telescopes come with quite poor optical alignment, or collimation, and some relatively simple adjustments can make a significant performance improvement.

A "Star Test Primer" by amateur Thomas Back is on the web at: http://voltaire.csun.edu/tmb/tmb4.html

Mel Bartels has a web site giving clear collimination instructions using a simple sight tube collimator at: http://www.efn.org/~mbartels/tm/collimat.html

Be sure to check out his Java script program to calculate optimum diagonal size and offset at:

http://www.efn.org/~mbartels/diagonal/diagonal.html

as well as the other links on his site.

Nils Olof Carlin provides a very detailed discussion of the collimation of a Newtonian telescope, as well as some info on star tests, in his article "FAQ about Collimating a Newtonian Telescope" at: http://zebu.uoregon.edu/~mbartels/kolli/kolli.html

French amateur Thierry Legault, known for his beautiful CCD images on the web, has put together a very good explanation of collimation and star testing, as well as other topics related to optical performance at: http://perso.club-internet.fr/legault/collim.html

An interesting feature of his web site is photos of planets showing how their image would deteriorate with increasing misalignment of the telescope optics.

For the ambitious, there is a software program called Aberrator written by Cor Berrevoets from Ritthem, The Netherlands. This program calculates star test patterns as they would appear in a telescope with parameters as input by the user. Varying degrees of various aberrations can be input so the user can study the subtle differences in the star test pattern that they cause. In addition, the deterioration of images of planets and double stars due to varying aberrations can be observed, and the effects can be animated. This is a very interesting tool for the more advanced user. It is available on the web at: http://aberrator.astronomy.net/

where a program manual is available.

For our Cool Web Site of the Month, we will have a lesson in star and constellation pronunciation. Do you have trouble with some of the foreign sounding star and constellation names rolling off your tongue like a pro? Well, you need not be ashamed to open your mouth any more at meetings or star parties. Go to http://www.earthsky.com/Features/Skywatching/pronounce.html

and click on any star or constellation name once for a phonetic spelling, and click again and have a listen to the correct pronunciation, as well as a brief bit of info on the object!