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The Webfooted Astronomer - June 1999


Minutes: Telescope Makers, Astronomical League

by Leslie Irizarry

The May Seattle Astronomical Society Meeting (SAS) was held on May 19, 1999, at 7:30 p.m. at the University of Washington Physics/Astronomy Building.

Judy Schroeder announced that Saturday is Astronomy Day at Pacific Science Center. Solar scopes are needed.

Ed Barnes indicated that a street map will be provided and that Seattle Center provides us with parking tickets. Those with solar equipment can set up near the fountain. Please arrive between 8:30 and 9 a.m.

Steve Schonberger: Please contact him if you are missing your Webfooted Astronomer.

Karl Schroeder: There is a star party at a school Friday night. Please notify him if you wish to participate.

Judy Schroeder: This Saturday is the Greenlake and Paramount Park Star Parties.

Telescope Makers
Peter Hirtle of the SASís Telescope Makers Special Interest Group (SIG), was the first speaker. At Telescope Makers people get started grinding mirrors, beginning with a six-inch blank. Typical mirrors are F7 to F8.

Using a 12-inch diamond saw (masonry/concrete saw) and a rotating spindle (1200 rpm), a curve is cut into the blank. You start with a sphere. It is later ground using a tile and plaster tool (costing approximately $1), grit, and water. You begin with a 120 grit, which is the largest that is used, and progresses to smaller grits. There are six grits in all, ending with three micrometer grit size. You spend 45 minutes to one hour with each grit size. The total mirror grinding time is about 10 hours, not including clean-up.

Polishing pads are used for the initial polish. After the polishing pads, the final polishing is done with pitch lap. Glass is used for figuring. Mirrors can be coated at Peter Hirtleís. Then the mirror must be tested with a Fucault tester. It takes a lot of practice, but itís possible to get a mirror figured to ľ-wave, which is pretty good optical quality.

At Peterís place, you can grind up to an 8-inch mirror. His son ground his first mirror at age 5! Peter then hollowed out a bowling ball and put his sonĎs mirror into it. Peter demonstrated the "Bowling Ball" telescope.

The benefit of grinding your own mirror is that you can develop optical systems that are not available commercially. If you have specific requirements, you can create superior mirrors to those available commercially. It is best if you have a mentor, which is what the Telescope Makers SIG is all about.

Astronomical League
Loren Busch presented information about the Astronomical League (AL) in his role as the Astronomical League Coordinating Representative (ALCOR) for the SAS.

The Astronomical League is a non-profit organization that has existed for many years. In the Pacific Northwest, there are 27 different member organizations. Any group or members at large can affiliate with the AL. Any affiliate group or individual has voting privileges.

Members of the Astronomical League receive many benefits, including The Reflector, its quarterly publication. The AL also offers observing awards and books at a discount.

It costs the SAS $3 per member each year to be a part of the Astronomical League. The chairman of the Northwest Region of the Astronomical League (NWRAL) is Gene Dietzen.

The Table Mountain Star Party began as a AL function. Concern about the perpetuation of the Table Mountain Star Party after the officers changed resulted in the formation of the Table Mountain Star Party Association.

There are many Astronomical League observing clubs, including: Messier, Binocular Messier, Deep Sky Binocular, Southern Skies Binocular, Meteor, Planetary Observing, Universe Sampler, Lunar, Urban, and so forth. The Astronomical League Web site ( provides good links to other Web sites, including Marswatch, which has images from amateurs and some professionals.

AstroCon 99 is this yearís annual convention for the AL. This year it will be held in Cheney, Washington, on July 13-17. It will feature such speakers as Story Musgrave, Jack Horkheimer, Bill Nye, Louis Freedman, and more. There will be vendors, new products from Celestron, fellow astronomers, and more.

Why does the club spend its money every year? "If we donít hang together, we shall all hang separately," Loren concluded.

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