Artist's depiction of a telescope in orbit around Earth. (Credit: RHESSI)

We have always built bridges to the sky. Our earliest ancestors were skywatchers, making careful observations of the Sun and Moon, making drawings and paintings and keeping count of changes on sticks and tablets. These cosmic connections later were immortalized in stone, through ancient observatories like Stonehenge, the pyramids, Macchu Picchu, and Chichen Itza.

By the 17th century, new tools were being used to reach the sky -- telescopes were invented and discovered new worlds and a new Universe. The types of telescopes and their instruments changed over the years, as we built bigger observatories on remote mountains.

Great Balls of Fire -- NOT! Astronomers studying the Sun discovered that it is composed of gases, not fire, and first discovered the gas helium in the Sun's spectrum.

Today, our bridges reach much further.

Robotic missions have flown past, orbited and landed on worlds, making new discoveries. Great observatories in space are studying the solar system and Universe at a variety of wavelengths. Our connections to the sky have grown, giving us a better understanding of the cosmos, and of ourselves.

Many civilizations observed the rising and setting positions of the Sun as a celestial marker -- a calendar. These changing positions could be used to prepare for annual floods, times for planting and harvesting and migrating to avoid inclement temperatures. We have evidence of this in the buildings and recordings of these civilizations. Stonehenge in England, a variety of kivas in the American southwest, and Aztec and Mayan pyramids in Mexico and Central America bear testimony to the importance of the changing Sun's position throughout the year -- astronomers have noted windows, doors, posts, and the actual building itself aligned to match the sunrise for important dates during the year.

Ancient peoples did not all rely solely on the Sun; many also kept track of the changing Moon -- leading to our use of the month. The appearance of certain stars in the sky were also used as a clock and calendar; for instance, the "dog" star Sirius was visible just before sunrise in August in ancient Egyptian times, possibly leading to the "dog days of summer." Particular stars overhead could be used as a clock as the night went by.

Solar telescopes orbiting the Sun, such as STEREO, are studying it in a variety of wavelengths. Image credit: STEREO.

Some of these people also kept special, even sacred observations of the planets. The planet Venus was held particularly sacred to the Mayans. Babylonian astrologers kept careful records of changing positions of objects in the sky.

In the western Middle Ages, observatories were set up with instruments to measure the position of the stars and planets in the sky, but without the benefit of any magnification.

By the seventeenth century, the first telescopes were used to observe celestial objects, and the incredible new discoveries revolutionized our understanding of the Universe, and even the process of science.

Telescope designs improved, and larger telescopes were built, along with special buildings to house them -- observatories. New tools were invented. In the 19th century, astronomers began to examine the spectra of the Sun and other stars, and used the first photometers to measure the brightness of objects in the sky.

By the 20th century, astronomers built telescopes to study wavelengths other than visible light, beginning with radio telescopes.

Today, modern tools study the light -- and the reflected light -- we see from the Sun, Moon, planets, comets, and stars. We use radio telescopes to study radio waves, space-borne gamma ray telescopes to observe gamma rays, and other telescopes to study everything in-between.