COSMIC TIME MACHINES

The World’s Observatories

Modern astronomers use a wide variety of observatories to explore the universe. They range from research-grade university telescopes, eight-meter-wide professional instruments on remote mountaintops, and multi-dish radio arrays to space-based observatories and planet probes. There are more than 11,000 professional astronomers in the world today studying objects as close as the Moon and as far away as the first ripples of radiation detectable after the Big Bang. In addition, there are (by some estimates) more than half a million amateur observers watching the sky with binoculars, small backyard-type instruments, and even some amateur radio astronomy dishes. No matter what their size or where they’re located, these cosmic time machines extend our vision across time, space, and the electromagnetic spectrum.

History of the Telescope

Our first astronomical instruments were our eyes. From the earliest sky-gazing activities in antiquity through the invention of the telescope in the 1600s, people simply had to observe objects in the universe without magnification. In 1608, the first instruments that could magnify a person’s view were created. The invention of the telescope is often credited to Dutch opticians Hans Lippershey, Zacharias Janssen, and Jacob Metius. These telescopes were likely originally used as spyglasses aboard ships or by generals during a battle, but it wasn’t long before someone thought to look at the sky with these newfangled inventions. The news of these instruments reached astronomer Galileo Galilei, who promptly built his own instrument in 1609.

The first telescope was simply a lens through which light would pass into an eyepiece. Later on, astronomers began to build telescopes with metal mirrors at one end, inspired by a design by Isaac Newton. Newton’s design was so useful that it is still used today in telescopes called Newtonian reflectors. The primary purpose of all these optical telescopes is and always has been to gather as much light from dim, distant objects as possible.

Over the next few centuries, people worked to improve the telescope, replacing metal mirrors with larger (and heavier) ground and polished glass ones. With the advent of electricity and automation, people began using motors to guide their telescopes through long observations. Today’s modern optical (visible-light) telescopes are computer-guided creations that can be steered quickly to view an object or event occurring in the sky. Among the better known are:

• Mauna Kea in Hawaii, including the twin Keck telescopes, the Subaru Telescope, and the Gemini North telescope
• The European Southern Observatory in Chile
• The Australian Astronomical Observatory in Coonabarabran
• Palomar Mountain Observatory, Mount Wilson, and Lick Observatory in California
• The Kitt Peak National Observatory in Arizona

In addition, radio astronomers use dishes and antennas to detect the radio emissions reaching Earth from distant objects. Most, but not all, radio telescopes are arranged in arrays such as the Very Large Array (VLA) in Socorro, New Mexico, and the Atacama Large Millimeter Array (ALMA) in Chile. Radio arrays are also being built in Australia and South Africa, including the Square Kilometer Array (SKA) and the Murchison Wide-Field Array (MWA).

Multi-Wavelength Instruments

There are hundreds of observatories spread across every continent on Earth and orbiting our planet. Most ground-based facilities are limited to detecting visible light or radio emissions coming from objects in the sky, while space-based instruments cover a wider range of emissions. Since the late nineteenth century, astronomers have been attaching instruments to ground-based telescopes, including cameras (which record light) and spectrographs (which break incoming light into its component wavelengths). In the past few decades, some facilities here on Earth have been designed and optimized for infrared observations. Infrared (IR) is absorbed by our atmosphere, so these observatories are generally located at high altitude in very dry climates. This allows them to detect near- and mid-infrared light. The twin Gemini telescopes at Mauna Kea in Hawaii and Cerro Pachón in Chile, as well as the Very Large Telescope in Chile, are good examples of such IR-enabled observatories.

Space-Based Observatories

Earth’s atmosphere is the bane of astronomical observing. Motions in our atmosphere cause stars to appear to twinkle and images of planets to waver. Our blanket of air, which protects us by absorbing infrared, ultraviolet, x-rays, and gamma rays, also makes it very difficult to spot cosmic sources of these emissions. On top of that, all astronomers often have to deal with clouds, which block their view, and light pollution, which washes out the view of dim and distant objects. Some of these problems can be mitigated by locating observatories at high altitude and away from light sources, but an even better solution has been around for decades. Beginning in the 1960s, astronomers began placing observatories in space, which gives constant access to distant objects not always visible from Earth, or radiating in wavelengths of light not always detectable from the ground.

Flying Observatories

Balloons and high-flying aircraft also act as observatories. The first balloon-borne astronomy facilities were lofted to high altitude beginning in 1957. Astronomy instruments have been carried up into the atmosphere, giving astronomers x-ray, microwave, gamma-ray, and infrared access to the cosmos. Flying observatories include the Kuiper Airborne Observatory (KAO), which was used until it was decommissioned in 1995, and the Stratospheric Observatory for Infrared Astronomy (SOFIA), which flies in a modified Boeing 747 and began its mission in 2010.