Telescopes

People have been gazing at the stars for as long as there have been people. The Babylonians and other ancient civilizations had sophisticated observatories from which they plotted the movements of the stars and planets.

However, just looking at the stars and planets with the naked eye will never tell you much about them–they’re only points of light.

The telescope changed that.

Most historians believe the telescope was invented in 1608 in Holland by Hans Lippershey. He created what is called a “refractor,” in which a lens collects light rays from distant objects and brings them together to form an image.

The Italian scientist Galileo Galilei was the first person to use the telescope to seriously study the heavens. Though his telescopes were limited to magnifications under 30 times, he discovered mountains on the moon, the four bright satellites of the planet Jupiter, the phases of the planet Venus, spots on the sun and the myriad stars of the Milky Way. On January 28, 1613, he even observed the planet Neptune, though he thought it was a star; Neptune wasn’t officially discovered for another 230 years.

All of this got him in trouble with the religious authorities, because it led him to put forward the idea that the Earth was not the centre of the solar system. He was forced to recant his heretical views and was kept under house arrest the rest of his life.

However, what he had discovered set off a long and continuing effort to build ever-better and more powerful telescopes.

Early refractors had two problems: chromatic aberration (false colour in the image) and spherical aberration (blurred images). To avoid those problems, telescope builders used very thin lenses–but that meant their telescopes had to be very, very long. In fact, some as long as 60 metres were built before Sir Isaac Newton demonstrated a better idea in 1668. Called a “reflector,” his telescope collected light with a concave mirror instead of a lens, avoiding chromatic aberration.

Over the next couple of centuries a way was found to avoid aberration in refractors, too, eliminating absurdly long focal lengths. Meanwhile, reflectors suffered from the fact the material used to make mirrors, called speculum metal, was hard to work with, didn’t really reflect all that well, and tarnished easily.

Some extremely large and powerful instruments of both kinds were constructed, however. The largest speculum-metal reflector of all had a mirror 1.8 metres in diameter and was installed by the Third Earl of Rosse at Birr Castle in Ireland in 1845. With it, Lord Rosse discovered the spiral nature of galaxies, even though it was so huge it had to be mounted between thick stone walls and could therefore only view a narrow band of the sky.

Refractors, meantime, reached their pinnacle in 1879 with the construction of one at Yerkes, near Chicago, that had a lens just over a metre in diameter. It’s still the largest refractor in existence, because the reflector permanently became the telescope of choice for major observatories with the development of silver-on-glass mirrors. The first large reflector after that was the 1.5-metre telescope at Mt. Wilson in California, built in 1908.

Eleven years later one 2.5 metres in diameter was built at the same observatory, and in 1948 the famous Mt. Palomar 5.1-metre giant was installed, the largest in the world until the Soviets constructed a six-metre reflector in 1976.

These huge optical telescopes taught us much of what we know about the universe–but they all suffer from a common problem: they’re all located on Earth, and the trouble with Earth is, it has an atmosphere.

Now, sure, we’re all grateful for that. The human race would have had a tough time reaching its current level of civilization if it hadn’t been able to breathe. There wouldn’t even have been anyone around to pen the immortal lyrics to “Twinkle, Twinkle Little Star.”

But from an astronomer’s point of view, that would have been just as well. Not that they’re opposed to breathing; it’s twinkling they don’t like. Twinkling, caused by the turbulent atmosphere, means there’s a limit to how sharp an image of a celestial object you can obtain from the ground, no matter how powerful your telescope is.

That’s led scientists at Johns Hopkins University to develop a “detwinkler,” which uses sensors to determine where and how starlight is distorted and then, with a high-speed computer, reshapes a flexible mirror to correct the distortion.

Another solution, undreamed of by Galileo, is to get outside the atmosphere altogether: and that’s why astronomers so eagerly anticipated the launch of the Hubble Space Telescope by the U.S. space shuttle last spring.

Boasting a 2.4-metre mirror that is the most perfect ever made (so smooth that if it were the size of the Gulf of Mexico, there would be no waves in it more than a millimetre high), the Hubble is the first large telescope ever to view the heavens from 370 miles overhead, free from Earth’s troublesome atmosphere.

Despite its well-documented problems, caused by an embarrassing error in the placement of the main mirror, the Hubble Space Telescope has already revealed details that could never be observed from Earth, such as a giant storm on the planet Saturn; and once it gets some high-tech “spectacles” to correct its blurred vision, sometime in the next couple of years, the 13-metre-long, 11-tonne instrument will almost certainly uncover even more astronomical surprises–as will the new ground-based telescopes that take advantage of “detwinklers” and other technological advances.

The technology has changed since Galileo, but the goal of telescope makers remains the same: to see things in the night sky no one else as ever seen. Or, to put it another way, “to go where no one has gone before.”

At least for now, telescopes are the closest things to starships we have.

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