By Emily Levesque, University of Washington
A new advance in telescope building has taken on the challenge posed by our planet’s own atmosphere. The best telescope sites on the planet—places like Mauna Kea in Hawaii and the Andean foothills in Chile—are located on high, dry mountaintops where, thanks to the quirks of weather and airflow, our Earth’s atmosphere is unusually stable. Even so, any observatory on the Earth has to contend with the effects of atmospheric turbulence.
Our Atmosphere Gets in the Way
The little ripples and eddies of our atmosphere—an effect you’ve seen if you’ve ever looked through the shimmery heat waves rising off of a hot road in the summertime—can wreak havoc on a telescope’s image quality, blurring the stars that astronomers are trying to observe.
Today one solution is a technique known as adaptive optics. An adaptive optics system combines a computerized system of magnets—placed behind shaved-thin telescope mirrors to deform the reflective surface—and a bright yellow laser fired into the sky. The laser will excite sodium atoms in Earth’s upper atmosphere, making them glow and producing what appears to the telescope as a fake star.
By comparing the fake star’s appearance to the theoretical perfect image that one would expect from the laser, an adaptive optics system can measure atmospheric distortions of light in real-time and use the magnets to adjust the mirror’s shape accordingly, canceling out the slight deformations in the image and producing beautifully sharp images.
The best adaptive optics systems in use today can create sharper images than the Hubble Space Telescope.
This article comes directly from content in the video series Great Heroes and Discoveries of Astronomy. Watch it now, on Wondrium.
Roger Angel’s Mirror Lab
Presently, the University of Arizona hosts one of the world’s premier mirror labs, founded by Roger Angel back in 1980. Angel used an improvised backyard kiln to fuse two custard cups together, an early proof of concept demonstrating that a honeycomb pattern could be used to quickly cast large and relatively light telescope mirrors.
Today, the lab features an enormous round furnace, designed to reach more than 2100° Fahrenheit and rotate nearly five times per minute. This setup can cast mirrors up to 8.4 meters in diameter, or more than 330 inches.
The spinning is key: by rotating the furnace, the molten glass inside naturally settles into a perfect parabola shape, a process known as spin-casting. This dramatically decreases the amount of glass needed in the original casting, along with the years of grinding required to produce the parabolic shape that used to take others so many years to achieve with telescope mirror blanks.
The Never-ending Quest for Telescope Building
The quest for larger and larger telescopes still continues. The twin Keck telescopes in Hawaii, the Hobby-Eberly Telescope in Texas, and the Gran Telescopio Canarias in the Canary Islands are all 10 meters or larger, the biggest optical telescopes operating today. All of the largest telescopes take advantage of segmented mirrors, combining smaller carefully-shaped segments of glass to serve the same optical function as a single large mirror.
Plans are also underway to build even larger telescopes. The Arizona mirror lab is currently churning out a set of seven, 8.4-meter mirrors that will ultimately be combined into a single telescope in Chile, the Giant Magellan Telescope, with a diameter of 24.5 meters, or just under 1000 inches. The Giant Magellan telescope is one of the several enormous telescope projects planned for the 2020s, at observatories known as the Extremely Large Telescopes, or ELTs.
Advantages of the Advances in Telescope Building
With the ELTs, astronomers will be capable of setting new observational distance records. We’ll be able to focus on and study individual stars in galaxies hundreds of millions of light-years away, probe the detailed chemistry and physics of galaxies and supernovae that we’re barely able to glimpse with current telescopes, and push at the outer edges of the observable universe, capturing light that has been traveling from distant galaxies to Earth since the earliest epochs after the Big Bang.
There are many other advances in telescope building—from using other wavelengths in the electromagnetic spectrum to putting telescopes into space—but the progression from Hans Lippershey’s tiny refracting telescopes of the early 1600s to the Keck telescopes of today, and the Extremely Large Telescopes of tomorrow, makes for a fascinating evolution .
Common Questions about the Exciting Tech Developments in Telescope Building
The atmosphere, with its temperature, can potentially downgrade the quality of the image a telescope provides. The little ripples and eddies of our atmosphere can wreak havoc on a telescope’s image quality, blurring the stars that astronomers are trying to observe. That’s why telescope building mostly happens on high ground where the atmosphere is comparatively stable.
Roger Angel used an improvised backyard kiln to fuse two custard cups together, an early proof of concept demonstrating that a honeycomb pattern could be used to quickly cast large and relatively light telescope mirrors. His finding dramatically decreased the amount of glass needed in the original casting, along with the years of grinding required to produce the parabolic shape.
The twin Keck telescopes in Hawaii, the Hobby-Eberly Telescope in Texas, and the Gran Telescopio Canarias in the Canary Islands are all 10 meters or larger, the biggest optical telescopes operating today.
