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The CONSTELLATION is the official publication of the Bucks-Mont Astronomical Association, Inc, a 501(c)3 non-profit organization incorporated in the Commonwealth of Pennsylvania and exists for the exchange of ideas, news, information and publicity among the BMAA membership, as well as the amateur astronomy community at large. The views expressed are not necessarily those of BMAA, but of the contributors and are edited to fit within the format and confines of the publication. Unsolicited articles relevant to astronomy are welcomed and may be submitted to the Editor.

Reprints of articles, or complete issues of the CONSTELLATION, are available by contacting the Editor at the address listed below, and portions may be reproduced without permission, provided explicit acknowledgement is made and a copy of that publication is sent to the Editor. The contents of this publication, and its format (published hard copy or electronic) are copyright © 2000 BMAA, Inc.

At the November meeting, the club had a membership quorum and elected the officers for the year 2001 as follows:

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Last month we talked about starting at the beginning, with the old stand-bys, the Messier objects. Abbreviated 'M___', these number up to 110. Yeah, I know I said I only accept the first 103, but wiser heads prevailed and convinced me to include notes on all 110 currently accepted objects.

Some background info on this extraordinary individual seems appropriate.

Charles Messier was a Frenchman, employed as a clerk-assistant to Nicholas DeLisle, the titular 'Astronomer of the Navy.' His observing was limited, at first, to scanning the stars as a semi official duty. Born June 26th, 1730, the 10th of 12 children in Badonviller in Lorraine. He left his home to seek a career in Paris at the age of 21.

Messier's neat handwriting and drafting abilities led DeLisle to offer employment to the young country boy. His original tasks at DeLisle's observatory in the Hotel de Cluny involved copying maps and transcribing documents. He later was assigned to keeping the observatory's records, more in keeping with his interest in the heavens. After being moved up to a full clerking position, he was given observing time, and became 'fanatical' about comets.

Of prime interest at the time was the predicted return of Halley's comet. Edmund Halley had been the first to announce that comets traveled in closed orbits, and predicted the return of this comet as he suspected that it was the same one seen at intervals over the years. His prediction of a 76 year orbit, so easily calculated today, was revolutionary at the time. The world had just gotten around to accepting a sun-centered solar system after all.

Anyhow, credit for the comet recovery on Christmas night, 1758 is given to Palitzch. He visually spotted a fuzzy glow at the limit of naked eye vision while returning from a neighborhood party. News of the discovery and confirmation did not reach Paris for months.

Meanwhile, dear old Messier had been searching an area of the sky assigned by DeLisle from his own calculations. He found a faint glow on Jan. 21st, 1759 which later proved to be the comet. In Messier's own words, 'I would have discovered the comet two months earlier, when the comet was further from the sun, if the area assigned me had not been so limited'. Apparently, DeLisle was a bit of weenie, his arrogance in believing in his own calculations and limiting the search to only those specific areas of the sky loosing him the acclaim which comet discoveries invoked at the time.

Messier also did daylight observations of sunspots, along with meteorological work. He was finally elected to the Paris Royal Academy of Science after many ballots. It seems they were reluctant to give this distinction to a mere observer.

Messier was called the "Ferret of comets". At the time, he was in competition, albeit friendly, with a fellow Frenchman named Pierre Mechain. Between them they owned cometary discovery at the time. Many of Messier's objects were actually discovered by Mechain, and the information was freely exchanged between them.

I have heard and read that Messier composed his list of objects as they were a mere annoyance to a comet hunter. His list supposedly helped him avoid mistaking the objects for comets. I think this is horse hockey. In light of his lifelong commitment to observing and the diligence he paid to his duties, I think they were just as attractive to him as they are to us. His drawings of the locations of these objects are true works of art. Being hand drawn in the most intricate detail, they immediately impress the viewer with his pride and ability.

Admittedly, his own words tell us he started the list to identify the objects as permanent fixtures and not comets. But he continued to add to his original 45 objects for the rest of his life. He lived to the ripe old age of 87, although he had gone into a sort of retirement two years earlier.

Among his achievements in cometary discoveries, either independently or shared, are 16 unequivocal finds. Some lists claim up to 27, and some 36, though these are clouded by who actually was the first and deserved the credit.

The M objects are of the following types.... not known at the time of Messier who described his objects as cometary or some such similar title.... Gaseous or diffuse nebula 7 Galactic clusters 27 Globular clusters 29 Planetary nebula 4 Galaxies 33 Supernova remnant 1 Asterisms 2

I know this doesn't add up to 110. I'm not sure why.

William Herschel, perhaps the most famous observer of all time, listed the thousands of objects he located with his 24 and 48 inch telescopes. Out of respect for Messier, he did not give his own listings to M objects. The NGC of Dreyer does give their designation for M objects.

This is getting to be a long article. More in the future.

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If the wavefront is advanced or retarded for part of the diameter of the primary a situation like Figure two will result. Here the knife cuts all of the rays from one part of the objective while others are only partly dimmed. In the last issue of CONSTELLATION we considered what happens when different temperature air masses disturbed the wavefront. However, if the knife-edge is carefully placed at the best focus (by trial and error) the careful observer may be able to detect those aberrations of the wavefront that are the result of defects of the optical system. On most nights these will be hard to see, but are easily detected when the atmosphere settles.

We started this exploration of knife-edge testing with a look at disturbances introduced by the atmosphere. This was the right place to start in that tube problems can often be controlled, while the defects of the optical system are harder to do something about. Also, the disturbances from the atmosphere are often much greater than those of the optical system! Nevertheless, such testing will open the observer to greater understanding of optical performance. Return to the use of the knife-edge on a frequent basis as you will find some changes over time. Some of the observations as to the knife-edge will vary with tilt of the telescope, temperature, tension from objective support, etc.

This examination of the optical system is not quantitative. However, it is very sensitive to changes in the wavefront, and can demonstrate very small defects in the system.

Figure three shows the appearance of a Maksutov-Cassegrain that yields excellent images, yet I have seen this shadow pattern under the knife-edge test at focus on a semi-regular basis. I suspect it comes from distortion of the corrector as a result of the weight of the secondary. Figure four shows a knife edge pattern observed in a 17.5in Coulter "light bucket". This mirror is grossly undercorrected. For comparison Figure five represents what is seen in an overcorrected system.

Such testing is useful for figuring optical components, and is one of the best methods for Cassegrain and other compound systems. Used to this end the test is a null test for spherical aberration. Testing your telescope under the stars will lead to valuable insights into optical performance. Almost as much fun can be had with Cor Berrevots freeware ABERRATOR at: http://home.wxs.nl/~erkma000/aberrator.htm.

In an upcoming issue we will explore the Ronchi test for really quick evaluation of optical performance. This is no more difficult to build than the knife edge tester. You will need another plastic 35 mm film can, the hole punch, and a piece of Ronchi grating- available form Williman-Bell for less than four dollars. Eight or more test eyepieces can be made from a single 2 in x 2in 133 line grating. Handle the grating like any optical surface- with care, and keep in mind it is much more susceptible to scratching than glass.