Throughout almost all of human history, astronomy has been done with the unaided eye. Only over the last 400 years have telescopes allowed us to magnify our sense of sight. Sky-watchers during Galileo’s time were treated to stunning, star-filled nights afforded by naturally dark skies. Without the intrusion of artificial light, they enjoyed a night sky that most people in today’s world can only imagine.

However, Galileo and his contemporaries were limited to observing only the light they could detect with their eyes. Now, technology allows us to view the whole range of the electromagnetic spectrum—from radio to gamma waves—and carry out observations both day and night.

Observing at Night

Amateur astronomers can use their naked eyes, binoculars, or a telescope to view the night sky. This is best done from a dark location. With the naked eye on a dark night away from city lights, one can view about 3000 stars. Galileo’s telescope allowed astronomers of his day to view, in his words, “an almost inconceivable number” of stars beyond what the unaided eye could see. In his book Siderius Nuncius, Galileo said he saw about five hundred stars in Orion, whereas previously only a handful were known. Modern backyard telescopes now unveil stars that are hundreds of times fainter than what can be seen with the naked eye.

But today, we no longer use just our eyes to see through telescopes. Film and now digital cameras replace the human eye and allow us to see far more celestial sights. Larger mirrors on mountaintop telescopes collect much more light than is possible with backyard telescopes, enabling astronomers to see stars that are one-billionth the brightness you could see with the naked eye.

And while technology allows us to build larger and larger telescopes, the number of places we can use them has shrunk due to light pollution from streetlights, billboards and other artificial sources. For example, the venerable 100-inch Hooker telescope outside of Los Angeles, as well as the 200-inch Hale telescope outside of San Diego, have to contend with the encroaching light pollution of their respective, neighboring cities.

By making smart choices about lighting, we can reduce our impact on the night sky and the environment, and save energy, too. Light pollution is generally the result of bad lighting design, which allows artificial light to scatter and shine up into the sky instead of downward. One of the earliest efforts to control light pollution was in Flagstaff, Arizona, half a century ago, to protect the view from Lowell Observatory. Flagstaff has since tightened its lighting regulations, and in 2001 it was declared the first International Dark Sky City.

GLOBE at Night is a worldwide campaign to record the light pollution where you are by observing the stars in the night sky. This year’s citizen science project will take place March 16-28, 2009.

...and in the Day

Some types of astronomy—namely solar, radio and space astronomy—can be done during the day. The nearest and most frequently studied star is the Sun. Even Galileo engaged in solar astronomy, using sunspots to observe the Sun’s rotation. But never look at the Sun—with or without a telescope—without special protective equipment.

Visible light is only one, small part of the electromagnetic spectrum, which includes all types of radiation found in space. Radio waves represent another portion. Karl Guthe Jansky, an engineer with Bell Telephone Laboratories, discovered the first identified astronomical radio source in the early 1930s. He was investigating static that interfered with short wave transatlantic voice transmissions. Jansky compared his observations with optical astronomical maps and concluded that the radiation was coming from our Milky Way galaxy and was strongest in the direction of the center of the galaxy.

Subsequent advances identified other sources of radio emission, including stars and galaxies, as well as the more exotic radio galaxies, pulsars, quasars and masers. Radio astronomy is conducted with either a single telescope or multiple, linked telescopes that use a technique called interferometry. These telescopes can be linked across a continent (such as the Very Long Baseline Array, with telescopes across North America), or even across several continents (the European Very Long Baseline Interferometry Network, with telescopes in Europe, China, South Africa, and Puerto Rico).

Yet another type of telescope that can be used day and night is a space telescope. These telescopes are located high above the Earth, outside of the atmosphere, where the celestial heavens are always black. Space telescopes collect radiation from more of the spectrum than telescopes on Earth can. Electromagnetic radiation is always traveling toward Earth, but much of it is blocked by our atmosphere. This includes most ultraviolet, most infrared, and almost all X-ray waves.

One of the most famous space telescopes is the Hubble Space Telescope, located about 360 miles above the Earth. Others include Chandra, Spitzer, Fermi and SOHO, the Solar and Heliospheric Observatory. These telescopes are opening new windows of discovery for astronomers across the world.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

360-degree panoramic picture of the Milky Way as seen from Death Valley. Credit: Dan Duriscoe, National Park Service.

Artificial light pollution around the world as viewed from space. This data was compiled from October 1994 to March 1995. Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio.

Electromagnetic radiation is always traveling toward Earth, but much of it is blocked by our atmosphere. This includes most ultraviolet, most infrared, and almost all X-ray waves.

The Hubble Space Telescope is located 360 miles above the Earth. It sees in ultraviolet, visible, and near infrared wavelengths.

The Chandra X-Ray Observatory is located in an elliptical orbit that takes it to an altitude of approximately 86,500 miles above Earth—more than a third of the distance to the Moon.

Spitzer detects the infrared energy, or heat, radiated by objects in space. Most of this infrared radiation is blocked by the Earth's atmosphere and cannot be observed from the ground. Spitzer was launched into an Earth-trailing solar orbit.