Technology in Astronomy Astronomy is the oldest science. Humans have always looked up at the night sky and wondered about what they saw. In ancient times, celestial objects seemed to hold great power over civilizations. People not only studied the sky to track the Sun and Moon for planting seasons, but they also worshipped the Sun, Moon, and stars. The Anasazi, who They observed celestial movements and recorded them very lived in the southwest, drew a carefully on bones, stones, parchment, and the walls of caves bright star in 1054. and dwellings. How do you think ancient sky watchers were This was the affected by not having modern technology to explore space? earliest record of a star that exploded Early Tools of Astronomy as a supernova. Sky watchers built huge stone structures aligned (lined up) with the Sun, Moon, and planets. When people began to depend on agriculture, they needed to know the exact course of the seasons to help them decide when to plant and when to harvest. Ancient Europeans, Egyptians, Celts, and Mayans built huge stone structures not only for their religion, but also as tombs for royalty and tools to study the sky. They aligned these structures to the seasonal risings and settings of the Sun, Moon, planets, and some bright stars. Native Americans constructed stone circles for similar purposes. Stonehenge (England) Pyramids (Egypt) Pyramid (Yucatan) aligned with Sun’s position aligned with certain stars aligned with planet Venus Used in the 16th century before telescopes, a quadrant was a giant curved wall that also marked angles in the sky. In this image, Dutch astronomer Tycho Brahe Developed about 400 A.D., the catalogued positions of astrolabe marked the angle from stars and motions of the horizon to a celestial object. By planets. His was the most 1650, it was used widely in accurate data at the time. Europe. 1 Technology in Astronomy Make Your Own Astrolabe To find the angle of an object in the sky, you need the following: • Plastic protractor with a hole on straight edge • Large plastic drinking straw • String or heavy thread • Weight, such as a washer or heavy paper clips • Tape Tie the string with a weight through the hole in the protractor. Tape the straw along the straight edge. To find the angle of an object in the sky, hold the astrolabe with one hand in front of your eye. Slowly pivot the astrolabe upward until you see the object through the straw. Allow the weight to hang freely. Press the string against the astrolabe to keep it in that position. Subtract the angle you read from 90 degrees. That is the angle from the horizon. In this example, the angle or altitude above the horizon is 20 degrees. The Telescope Changes Everything Prior to the 17th century, all observations were made with the naked eye. Humans could see only the Sun, Moon, stars, and five planets (Mercury, Venus, Mars, Saturn, and Jupiter) in the sky. The universe was very small to ancient observers. In 1609, a Dutch lens maker named Hans Lippershey invented a telescope to observe ships among other things. Telescopes gather light from distant objects and magnify them. In 1610, Italian astronomer Galileo Galilei improved the telescope and turned it toward the sky. What he Galileo (in grey) shows discovered forever changed our view of the universe. telescope to church officials. Since then, we have found other planets and moons in our solar system and galaxies beyond our own, among many other things. Do not confuse “astronomy” with the term “astrology.” Astronomy is the science that studies objects and events in our universe. Astronomers noted how the Sun moved through 13 constellations called the zodiac constellations. Astrology, however, is not a science. It is a false belief that the positions of objects along the zodiac have power over people’s lives. Based on the zodiac, astrologers try to make predictions or “horoscopes” about the events in one’s life. 2 Technology in Astronomy Types of Telescopes A refracting telescope uses lenses to bend, gather, and focus light. Galileo's refractor magnified the image much more than the human eye could see (20 power). Never before seen individual stars in the Milky Way, craters on the Moon, and moons orbiting Jupiter came into view. Although inventors soon made bigger diameter refractors (up to 40 inches in diameter) that showed bigger images, the large lenses sagged and distorted the images. In 1671, Isaac Newton used mirrors instead of lenses to gather light, and thereby created the first reflecting telescope. He used a small lens, called an eyepiece, to focus the light that entered the open end of a tube and reflected off a mirror at the opposite end, bounced off a secondary mirror, and went out an eyepiece. In reflecting telescopes, the mirrors can be supported underneath, while lenses in refracting telescopes can only be supported around the edge. This lets them sag and distort the light passing through them. Therefore, the mirrors in reflecting telescopes can be made as large as you want. Their images are clear and not distorted. Because Newtonian telescopes have eyepieces on their sides, large ones are hard to manage. A more streamline reflector, called a Cassegrain, also uses two mirrors, but the light is sent out the middle of the bottom of the telescope. These are commonly used in research observatories around the world. They can be made quite compact for home use. To make telescopes even more precise and easier to use, companies now make electronic “smart” telescopes with computerized programs that allow you to find objects using a small handheld control panel. The telescope automatically moves to the right position for your viewing. 3 Technology in Astronomy Visit a local astronomy club’s public observing night called a “star party,” where you can see the Moon, planets, nebulas, and distant galaxies. Many club members are eager for you to look through their scopes and to explain to you what you are seeing. Also, visit planetariums located in your area. Planetariums project a starry sky and show onto a dome. Which would you like to visit: an astronomy club star party or planetarium show? Why? Observing the Sky in Visible and Invisible Wavelengths Telescopes designed to see the sky in visible wavelengths of light are continually being improved. People built larger telescopes, along with special buildings to house them, called observatories. In the 19th century, a new tool, called a spectroscope, was invented. It attached to the telescope to analyze the light coming from the Sun and other stars. A spectroscope produces a spectrum when it separates light into its individual wavelengths. A prism is one way to separate the colors. We can discover the composition of many objects in the universe—including distant stars—simply by analyzing the visible light these objects emit. Scientists compare the unique colors (spectrum) given off by burning known elements to the colors given off by a star. This is spectroscopy, the study of the electromagnetic spectrum to determine an object’s composition. Today, of course, the information needed to analyze light coming through telescopes is stored on computers. Burning elements in order to get this information is a thing of the past. The entire spectrum of electromagnetic radiation emitted by any object is made up of wavelengths of visible and invisible light. 4 Technology in Astronomy By the 20th century, astronomers had built telescopes to study wavelengths other than visible light, beginning with radio waves coming from planets, comets, giant clouds of gas and dust, pulsars, and black holes among other things. Radio telescopes use huge bowl-shaped antennas called dishes to gather radio waves. These dishes can be linked to form one gigantic telescope, such as New Mexico’s Very Large Array (VLA). Look at the image of a galaxy (bottom left) taken by a telescope in visible wavelengths. Can you see a jet of light emitted on the right side? Now compare that to a radio image of that same galaxy taken by the VLA. The jet of light is coming from the center of the galaxy. Scientists think it could be powered by a black hole. What do you think? Orbiting Observatories Scientists realized images from land-based observatory telescopes are limited because of disturbances in our atmosphere. An orbiting telescope would see an image unaffected by the air’s shimmering fluctuations and this would open up a study of wavelengths that the atmosphere absorbed. Examples are NASA’s four great observatories in space: • Hubble Space Telescope (HST): In 1990, the Hubble Space Telescope, a giant reflector, was launched into Earth’s orbit; it is still taking spectacular images of the cosmos in visible, infrared, and ultraviolet wavelengths. Among other things, the HST has discovered that the universe is expanding faster and faster every day; it has found planets beyond our solar system; it has discovered the presence of black holes in the centers of many galaxies. 5 Technology in Astronomy • Chandra X-Ray Observatory: This observatory has studied violent processes in the Universe, including gamma-ray bursts, black holes, quasars, and supernova explosions (1991–present). • Spitzer Space Telescope: This telescope has gathered infrared waves from dense gas and dust that block our view of star formation, from the centers of galaxies, and from new planetary systems (2003–present). • The Compton Gamma Ray Observatory (CGRO): Deployed from a space shuttle in 1991, the CGRO recorded bursts of gamma radiation, perhaps when extremely distant neutron stars merge into black holes. Such a burst of gamma radiation emits more energy in a few seconds than the sun will emit in 10 billion years (1991–2000).