The Star Party at McDonald Obsevatory


	Davis Mountains, Texas, Friday, January 13: Having driven all the way from the Canadian border to the Mexican one to escape winter, why would Linda and I be shivering in the sub-freezing night high in the Davis Mountains of West Texas? The reason is we were at a Star Party.
No, a Star Party is not where the revelers beat each other with sticks until they see stars. It is when a bunch of folks that are interested in astronomy get together at an observatory and look at some things they could not see otherwise. Like Saturn's rings or the nebula in Orion's sword.
This was at the McDonald Observatory, a world-class research observatory in the Davis Mountains of West Texas, which is in the area with the darkest skies in the lower 48 states. It has dark skies because it is the emptiest, most desolate area we have seen. Between El Paso and South Texas there are around 800 miles of driving, and apart from a few tiny towns, it is empty. Big Bend National park is to the south, with no farming or even much grazing anywhere around. Empty. Dark skies. Lousy for most things, but GREAT for an observatory.
The McDonald Observatory is part of the University of Texas. It has 3 huge telescopes, and many smaller ones. The first telescope built there has an 82 inch mirror and was completed in 1939. A few times a year, they do fit a viewing eyepiece on this baby, and have a special star party for the real keeners in the area.
The second big telescope built there has a 107 inch mirror and was completed in 1968. We toured this one during the day, and saw inside the dome and watched it being positioned for azimuth and elevation. It is used for spectroscopy rather than visual observation, as are all the major telescopes here. The thing is huge, and yet moves smoothly and with great precision
The third telescope is a radical design, put into service in 1999, with a huge segmented mirror of 10 meters by 11 meters, consisting of 91 small spherical mirrors (as opposed to the usual single parabolic). These segments are precisely positioned by computer to work as one large mirror. The huge mirror is at a fixed elevation of 55 degrees, but can rotate to any azimuth. This allows the telescope to view 70% of the sky with a power equivalent to a 9.2 meter single parabolic mirror. It and its twin in South Africa are the number 3 and 4 telescopes in the world. (Numbers 1 and 2 are the twin 10 meter Keck telescopes in Hawaii.)

This telescope collects the reflected light from the mirror high above using correction mirrors (due to the spherical sections of the primary mirror), and fiber optics to pipe the light under the whole telescope, where the spectroscopic instruments live. We were able to view the mirror and watched the upper mechanism being positioned in preparation for the night's work. (This was still in the daytime.) The reason for the radical design is they would have had to spend at least 5 times as much to build a conventional 9.2 meter telescope.
For the Star Party, we started with an inside lecture at dusk, learning to use a "planisphere," then moved outside to locate stars and constellations as they came out.
Then when it got dark (and COLD), we were treated to five telescopes set up by five staff members to reveal different targets. The largest telescope was a 22 inch reflector trained on the Orion nebula. Another one provided our first view of Saturn's rings. Also, we had stunning views of the moon, Mars and the Seven Sisters.
	The ride home after the Star party, was 70 miles down the mountain on a winding road with no traffic and no light whatsoever except for 1 small town for the first 40 miles. We were home and warm again by 11. What an experience. Next time, we will time our visit for one of the rare times the public can use the 82 inch telescope. Click on Saturn to see all the pictures from the Observatory.