How Things Work: Telescopes

Sometimes, the most distant objects are the most interesting to study. Telescopes allow scientists to discover and analyze star clusters, planets, and galaxies beyond what the naked eye can see.

A telescope magnifies an image by collecting incoming light and bringing it into focus using a mirror or lens. The telescope’s eyepiece then spreads this light across the viewer’s retina, thus enlarging the image.

There are two types of telescopes: refractor telescopes and reflector telescopes. Refractor telescopes use a lens to bring light into focus, and reflector telescopes use mirrors.

Reflector telescopes are powerful enough to magnify deep-sky objects such as galaxies and nebulae. Refractor telescopes, on the other hand, can only be used to study stars and planets.

Some of the world’s larger telescopes are equipped with computerized instruments that enhance the viewer’s ability to analyze the structure of space objects.

The South Africa Large Telescope (SALT), built in 2005, is equipped with an optical corrector assembly that helps detect objects in distant space. SALT is the largest optical telescope in the southern hemisphere. Carnegie Mellon University is one of many institutions that funded its construction.

Carnegie Mellon physics professor Richard Griffiths said, “Basically, we build bigger and bigger telescopes all the time because we want to see fainter and fainter things.”

Griffiths said that SALT is currently under commission but in the process of being tested. Once it is in use, its primary purpose will be to take photos of objects in space and analyze light emitted by these objects using spectroscopy.

To take photos of objects in space, the telescope is equipped with the SALTICAM, a camera that also measures the intensity and absorption of light.

“This telescope does, in fact, have the capability to measure polarization,” Griffiths said.

SALT contains a number of subsystems as well. In particular, the telescope structure is capable of positioning and reporting the direction of the telescope direction within five arc-seconds, or 5/3600 of a degree.

The primary mirror of the telescope further focuses light collected from the surrounding environment. The mirror, comprised of 91 smaller, interchangeable mirrors that are hexagonally shaped, can be tilted forward and backward using special controls.

Astronomers in Australia use a similarly designed microscope called the Anglo-Australian telescope. The telescope allows astronomers to view the center of the Milky Way galaxy and a collection of smaller galaxies called the Magellanic Clouds.

The telescope, 3.9 meters in diameter, uses charge coupled devices (CCDs), which convert light into digital signals to produce images of distant objects. These images are then stored onto a computer.

The Anglo-Australian telescope is equipped with spectrographs, or instruments that divide incoming light into spectrums of color. Scientists study these spectra to learn about the chemical composition and temperature of distant objects.

Scientists also use infrared devices to detect objects that do not emit visible light, such as objects that are very cold or hidden by dust clouds. Different telescopes detect different frequencies of electromagnetic radiation. A radio telescope, for instance, detects radio signals.

The Arecibo radio telescope, which is part of the National Astronomy and Ionosphere Center Arecibo Observatory in Puerto Rico, is equipped with a radio mirror 1000 feet in diameter and 167 feet deep. This giant dish, coupled with a series of antennas and radio receivers, enables the telescope to detect weak radio signals emitted by galaxies millions of years ago.

The Arecibo observatory is also home to a number of different research projects, including atmospheric science and radar astronomy.

In fact, researchers recently used the Arecibo telescope, managed by Cornell University, to detect radio emissions from the Crab Nebula pulsar, which is a star that emits radio waves. According to a Cornell press release, the Crab Nebula pulsar is smaller than a soccer ball. Yet, this pulsar emits extremely strong radio waves in short time intervals — about four-tenths of a nanosecond.

This type of radio emission has never been seen before, and researchers suspect that it may be due to a third magnetic pole that is separate from the usual north and south poles.

As writer Timothy Ferris stated in his book The Big Shebang, “We live in a changing universe, and few things are changing faster than our conception of it.”