Volume 28 Number 6 March 1999 http://physics.weber.edu/oas/oas.html


THE MARCH MEETING

The regular meeting of The Ogden Astronomical Society will be held this Thursday March 11, 1999 at 7:30 p.m. in the Ott Planetarium on the Weber State University campus.

This month will be another in the series of "Show and Tell" events although several OAS members have already asked to be spotlighted. Jim Seargeant has a demonstration on collimation for SCT telescopes. Dale Hooper has infrared photographs of galaxies and the Prez has a presentation on galaxies.

Everyone is encouraged to bring their projects and equipment to discuss or display.

THE PRESIDENTS PARSEC

Greetings Earthlings; The Prez has been busy this month. Along with looking for land to build a house on and doing my taxes, I've been putting the finishing touches on my mirror grinding machine.

Steve Dodds and I finished it early Feb. I got it home and did some alterations and it now has the capacity to grind a 32 inch blank! I get weak in the knees when I think about optics in that size. What I am

looking for now is an optical test flat to test the mirrors with. Anyone reading this with any information on where to buy one please contact me. They are proving difficult to come by.

Speaking of aperture. Some of you know "Meter Mike", the guy that literally spends his life going from one star party to another dragging his 40 inch scope with him. Well this guy is a real aperture junkie who has no concept of increments. He is currently in Arkansas building a 70 INCH f/3.8 transportable telescope. This man has no shame. He claims it will be done in time for the Aug star party at Elizabeth Ridge this summer. So if you want to see some planetary nebula....in another galaxy... this would be a good opportunity.

Last fall at Cathedral Gorge I viewed M-42 thru Mike's 40 inch. I almost blacked out the view was so incredible. With ordinary puny scopes, like my 16 inch, you look "at" M-42, with a 40 inch scope you look "into" M-42. As a added bonus you see it in color!

Aperture fever is contagious. There is no cure only temporary "fixes." Be forewarned before you ever look in the eyepiece of a LARGE scope.

March is the month for the Messier Marathon the weekend of 19 and 20. We still need to decide on a location. Antelope Island or a farm in West Haven, Hooper, or the Morgan area could work. Contact me with your suggestions.

The Prez

nitesite@lgcy.com

APRIL 18, 1999, ALDEBARAN GRAZE

The graze path for the next Aldebaran occultation will be passing just a few kilometers south of Willard, UT on 18 April at about 8:40 p.m. MDT.

This will be the last crescent-Moon dark-limb graze at night in the U.S.A.; you will have to wait 14 years for the next one.

Hansen Planetarium is considering organizing an expedition for observing, timing and recording this event but first needs to know if there is sufficient interest to proceed.

If you think you might be interested in participating, please contact Patrick Wiggins at the planetarium at p.wiggins@m.cc.utah.edu or 801.531-4952.

Additional information about the graze can be obtained from the International Occultation Timing Association's web site at:

http://www.sky.net/~robinson/iotandx.htm.

Carpe Noctem!

Patrick

Patrick Wiggins

Hansen Planetarium Education Department

email: p.wiggins@m.cc.utah.edu

voice: 801.531-4952, fax: 801.531-4948



MINUTES

OGDEN ASTRONOMICAL SOCIETY

February 11, 1999

President Ron Vanderhule called the regular meeting of the Ogden Astronomical Society to order at 7:30 p.m. in the Ott Planetarium.

Business included:

the open letter in the Star Diagonal to amateur astronomers from Timothy Ferris,

the mirror making group will meet on an upcoming Saturday,

the next meeting will be a group participation, and

the Antelope Island and Monte Cristo star parties are scheduled and posted in this month's Star Diagonal.

Dr. Sohl requested OAS member assistance at a school star party set for Thursday February 18 at Mountain View Elementary school. Directions to the school were given.

As described in the newsletter, a vote to reconsider the January vote to join The Astronomical League was entertained. Considerable discussion was made. At the end, the motion to sustain or rescind the previous vote was taken. Results were 24 to rescind and 3 to sustain the vote. The Ogden Astronomical Society will not join the AL. Members may become a Member-At-Large if they choose.

Discussion moved to telescopes for sale and other new equipment. Elgie Mills suggested an Astronomy Workshop to be held at WSU. Discussion to follow at a later date. Dr. Sohl described the difficulties the university is having getting the observatory project moving. New technical difficulties have arisen.

The meeting moved to the main subject. The newest planetarium show was presented and a video taped program followed. Both of these presentations featured the planet Mars.

Following these programs, the meeting adjourned to informal discussion at 9:30 p.m.

Bob Tillotson, Secretary

Jim Seargeants's - Images

M79

Sd3-99_jim_image.jpg (50405 bytes) Sd3-99_jim_graphic.jpg (43851 bytes)

This is an image of M79, or NGC 1904, an extremely compressed globular cluster in the constellation Lepus. This magnitude 8.0 cluster is about 20° south of Orion's Great Nebula.

This image was taken by three of Adam Johnston's astronomy students, Melanie Romano, Nathan Smith, and Jason Engle, on 24 Feb - one of our few clear nights. They used my 12" Meade and SBIG ST-7 and AO-7 for this image. Working at f/6.3, the ST-7's imaging chip sees this 8.25 x 12.37 arc min area of the sky, which works well for as tight a cluster as M79. The Meade sports fairly long lens hood to keep dew and light from the front corrector plate, so the breeze that kicked up occasionally pushed the telescope around quite a bit and ruined several of our attempts at long exposures, even with the AO-7 trying it's best to keep the image steady. We used the 2x2 binning option on the ST-7 to keep the exposure time down to 60 sec and just kept trying until the stars showed up round. If we had used the full resolution of the ST-7 with no binning, a 4 minute exposure would have been required and the breeze never would have let us get away with that.

Post processing included subtracting a dark frame, removing hot and cold pixels, contrast and range adjustment, and 5 iterations through the Lucy-Richardson sharpening algorithm. The resulting stars measure in the 2.2 - 2.6 arc sec range, which isn't that bad considering the only fair seeing conditions.

A cluster like M79, which lies in a region fairly well populated with foreground stars, is a good object for the AO-7. It uses the tracking chip on the ST-7 - shown here as the smaller square just above the larger rectangle of the imaging chip - to detect movement in the image as the exposure progresses. If the guide star move from it's initial position, the AO-7's diagonal mirror tips and tilts to move it back. This rate at which this process cycles depends upon how bright a star can be seen by the guide chip - and the faster the cycle the sharper the image. We were able to locate the mag 11 star in the upper left of the guide chip for a reasonably fast tracking exposure of .3 sec.

Jim


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