McDonald Observatory

February 23, 2019

Space – The Final Frontier

Amphitheater (left), Small Domed Telescopes (center), Frank N. Bash Visitors Center (right)

The visitor center had a small but interesting museum. You’ll learn a little bit about spectroscopy and why it’s so important in astronomy. You’ll also be introduced to some astronomers and learn how they use spectroscopy in their research.

One display contained several “old” astronomy tools, such as a sextant (used for celestial navigation at sea), a celestial globe (designed for classroom instruction and solving spherical geometry problems), and a micrometer (for precise measurement of star positions)

Tools of astronomy

We also paid for a tour of two of the three largest telescopes. Our guide took us to the main floor of the Harlan J. Smith Telescope. She showed us how they moved the telescope into position and how the floor can be moved up or down to permit the telescope to be serviced or to swap out instruments. We did not get to see the domes open during the tour as the wind was still ripping through the mountains and gusting up to 50 miles an hour. It was actually nice to be inside the dome where we could hear the wind but not feel it.

That night we attended their Star Party. It was cold and windy but we bundled up as best we could. We may fail in our search for warmer weather but always succeed in finding interesting things to do. It was a clear, dark night. The path to the amphitheater was lined with red lights so we could adjust our vision to the darkness. The speaker talked about Greek and Roman myths and pointed out the constellations related to them. He said one constellation was supposed to represent a beautiful woman. He joked that he had been on this mountain so long that if there had been a beautiful woman in the stars he would certainly have noticed by now. After the program we could look through eight or so telescopes at different stars, nebulas, star clusters, and galaxies. To my untrained eye they all looked pretty much the same. Still it was a fascinating program.

The 10-meter Hobby-Eberly Telescope (HET) is one of the largest telescopes in the world.

 Hobby-Eberly Telescope (HET)

Its primary mirror is composed of 91 identical hexagonal segments. The mirror is nestled in a 60-ton welded-steel structure. This structure can be lifted by 16 air bearings and smoothly rotated by two drive wheels. We watched an operator do this and it was quite impressive. Because the earth rotates most telescopes have to move to follow a celestial object. In the case of this telescope, a tracker is used to follow an object’s reflection on the mirror while the telescope remains stationary. The collected light travels through fiber optic cables to various spectrographs. Amateur astronomers may still peer through a telescope but professional astronomers today do most of their work sitting at a computer console.

HET Mirror

Since it went operational in 1996 HET has discovered huge black holes, massive supernovae explosions, and new planetary systems.

Many folks know the universe is expanding. But scientists had expected that the rate of expansion would decrease due to the universe’s gravitational pull. Instead they discovered that it was expanding at an accelerating rate, speeding up instead of slowing down. The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is designed to measure how the expansion of the universe has changed. The plan is to collect data on a million galaxies, some as far as 10 billion light years away, and to create a detailed three-dimensional map of the universe. One goal is to begin to illuminate the nature of dark energy. Dark energy is a phrase that astronomers and physicists use to represent the unknown. In this case it’s that unknown thing that’s causing the expansion of the universe to accelerate.

Two other telescopes on the mountain are the 82-inch Otto Struve Telescope built in the 1930s and the 107-inch Harlan J. Smith Telescope built in the late 1960s.

Harlan J. Smith Telescope (left) and Otto Struve Telescope (right)

There’s an interesting story behind the Otto Struve Telescope. In 1926 William Johnson McDonald died and left most of his estate to the University of Texas to establish an astronomical observatory. There was just one small problem. The University of Texas didn’t have an astronomy program. So it had to create one and hire professors who might know something about observatories.

The newest telescope is the 82-foot diameter radio telescope operated by the National Radio Astronomy Observatory.

Radio Telescope

Another little known fact is that the astronauts who landed on the moon left behind special mirrors. These mirrors are used by the McDonald Laser Ranging Station which is jointly operated with NASA. Precisely timed laser pulses are fired at the moon and over a dozen satellites orbiting the Earth to measure things like continental drift and Earth’s rotation rate and position in space.


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