By Robert Hazen, Ph.D., George Mason University
Data collection is a key part of science, and, of course, astronomers’ principal tool is the telescope. Many astronomers refer to the present age as the golden age of astronomy because, for the first time, we now have satellite observatories and telescopes in space that can measure all the different wavelengths.
The Telescope
The key part of science, and of course astronomers’ principal tool, is the telescope. Telescopes, in the most general sense, are devices that collect photons from space. We have all seen many photographs of remote observatories in Chile, in Hawaii, and so forth.
The science of astronomy has gone hand-in-hand with the development of new telescopes: new kinds of telescopes and improved larger instruments.
Different instruments allow the astronomers to study different wavelengths. There are telescopes in space that can measure all the different wavelengths: x-rays, gamma rays, radio waves, and so forth. Optical telescopes are the most familiar, and they use a combination of lenses, or mirrors, to concentrate and magnify light from different objects.
This is a transcript from the video series The Joy of Science. Watch it now, on Wondrium.
Galileo Galilei
Galileo Galilei was the first person to use a telescope trained on the heavens in 1609. He used that telescope to discover the craters of the Moon, the moons of Jupiter, the rings of Saturn, and so on.
His telescopes used lenses — a combination of lenses through which light was bent. However, as one makes lenses larger and larger, the glass gets very heavy, and there comes a limit beyond which a lens cannot get larger.
Learn more about works of Kepler and Galileo.
Astronomy and Observatories
The challenge with the size of lenses led to the using of mirrors. Curved mirrors began being used to focus the light, because a mirror can be very thin and still be reflective. The largest telescopes use mirrors of this type, which, sometimes are more than 25 feet in diameter.
There’s a new technology that allows one to make these mirrors on a giant rotating wheel. As it spins, it causes the glass to form a beautiful curved surface, a perfect mirror-curved surface. There are also new multiple-mirror telescopes that have lots of cheap, small mirrors that are all precisely aligned by computers.
The best astronomical observatories for visible light are constructed at very high elevation that’s far from the light pollution of cities, and far above most of the atmosphere. There are many such observatories. The Keck Observatory in Hawaii, for example, has one of the largest telescopes. There’s also a wonderful cluster of telescopes in the high mountains of Chile.
Radio Telescopes
There are telescopes in place today that measure all the wavelengths of electromagnetic radiation. The atmosphere is largely transparent to radio waves, so radio telescopes can be based on the ground — and that’s a good thing because radio waves are so long that one needs a very large dish to collect them.
There are two strategies here. One of them is to have one huge dish; for example the Arecibo Observatory, in Puerto Rico, has one dish that fills an entire valley. The other option is to have lots of smaller dishes that form an array; for example, the Very Large Array of radio-telescopes in Socorro, New Mexico.
Extending this idea to the extreme, there have been various times when radio telescopes around the world have been linked to photograph one object, and in this case you have a 4,000-mile or more baseline, which gives very high resolution to the outer reaches of the universe.
Microwave Radiation
As we go to other forms of radiation and other wavelengths, we have to have other strategies. Short-wavelength microwave radiation can be studied from ground-based telescopes, but there’s a great deal of interference, especially from communication, so here it’s best to go into space.
The Cosmic Background Explorer, NASA’s COBE satellite, was a satellite-based microwave observatory, and there’s several new microwave observatories that are on the books.
Infrared Observatories
There is also the option of having infrared observatories. These reveal warm objects in the heavens, things like dust clouds, young stars, and even planets. Any object that’s relatively cool emits infrared radiation.
The problem here is that the atmosphere is just chock-full of infrared radiation, so the satellite has to be above the atmosphere.
Indeed the satellite itself, the detector itself, emits infrared radiation. The detector, therefore, has to be cooled down to liquid-nitrogen temperature or colder. This means one has to carry the coolant along with the spacecraft, and all of these infrared satellites have a short lifetime.
The infrared astronomical satellite, IRAS, was launched in 1983, and it operated for about nine months before it died.
Learn more about the Hubble.
X-Ray Telescopes
X-rays are also absorbed by the atmosphere, and x-ray telescopes are really interesting. This is so because x-rays are highly energetic, and x-ray telescopes reveal some of the most energetic events in the universe.
The first x-ray satellite was the Roentgen satellite launched by NASA in 1990, and it studied the brightest x-ray sources in space.
Thus, one undoubtedly gets the sense that this is an incredibly exciting time in astronomy and we are living in the golden age of astronomical observations. Never before in history has the pace of discovery been so rapid, or the instruments been so sophisticated. This indeed is an incredible time to be an astronomer.
Common Questions about the Golden Age of Astronomy
In astronomy, the use of curved mirrors began to focus the light. It was so because a mirror can be very thin and still be reflective. The largest telescopes use mirrors of this type, which sometimes are more than 25 feet in diameter.
The best astronomical observatories for visible light are constructed at very high elevation that’s far from the light pollution of cities, and far above most of the atmosphere.
The atmosphere is largely transparent to radio waves. This is why the radio telescopes can be based on the ground.
