Six Messengers From Outer Space
BY AWAKE! CORRESPONDENT IN JAPAN
MESSENGERS from outer space are constantly arriving. They carry with them amazing information about the vast universe around us. These messengers, six in all, travel at the speed of light, 186,000 miles per second [300,000 km/sec]. One of them is visible, but the others are all invisible to the human eye. What are they?
The Electromagnetic Spectrum
It has been known for more than 300 years that when light passes through a prism, it emerges in the seven major colors of the rainbow. This shows that ordinary light contains all the seven colors of the rainbow in the order of red, orange, yellow, green, blue, indigo, and violet.
Light is considered to be a flow of massless particles called photons, which also have the properties of waves. The distance from the crest of one wave to the crest of another is called a wavelength and is measured by a unit called an angstrom, abbreviated Å. It is equal to 39 ten-billionths of an inch [one ten-billionth m]. Visible light measures between 4,000 and 7,000 angstroms, and light of different wavelengths appears as different colors.—See illustration, page 15.
Photons, however, may have other wavelengths as well. The streams of photons, called electromagnetic radiation, are given different names depending on their wavelengths. Below 4,000 angstroms, as wavelengths become shorter than those of visible light, electromagnetic waves progressively appear as ultraviolet (UV) radiation, X rays, and gamma rays. When longer than 7,000 angstroms, the waves are no longer visible but are in the infrared to radio part of the electromagnetic spectrum. And there we have the “six messengers” from outer space. They carry a wealth of information about celestial bodies. Let us now see how they are being tapped for valuable information.
Visible Light—The First Messenger
From the time Galileo turned his telescope toward the sky in 1610 until 1950, astronomers primarily used optical telescopes to study the universe. They were acquainted with just the visible portion of the electromagnetic spectrum. Some celestial objects could only be seen very faintly in optical telescopes, and astronomers recorded the images on photographic film to study them. Now, electronic detectors known as charge-coupled devices, which are 10 to 70 times more sensitive than photographic film, are becoming much more common. The visible messenger provides information on star density, temperature, and chemical elements as well as distance.
To capture light, ever larger telescopes are being built. Since 1976 the largest reflecting telescope in the world has been the 236-inch telescope at the Zelenchukskaya Astrophysical Observatory in the Caucasus, Russia. In April 1992, however, the new Kecka reflecting optical telescope was completed on Mauna Kea in Hawaii. Instead of one single mirror, the Keck telescope has a combination of 36 hexagonal mirror segments. The segments have a combined diameter of 33 feet [10 m].
There is a second Keck telescope under construction adjacent to the original, now called Keck I, and the two telescopes may be able to function as an optical interferometer. This involves linking up the two 33-foot [10 m] telescopes by computer, resulting in a possible resolving power that would equal a single mirror 280 feet [85 m] in diameter. “Resolving power,” or “resolution,” refers to the ability to distinguish details.
The Tokyo National Astronomical Observatory has under construction a 27.2-foot [8.3 m] optical/infrared telescope, Subaru (the Japanese name for the Pleiades star cluster), on Mauna Kea. It will have a thin mirror supported by 261 actuators that will adjust the shape of the mirror once every second in order to compensate for any deformation of the mirror surface. Construction of other huge telescopes is under way, so we are sure to learn more from messenger number one—visible light.
Radio Waves—The Second Messenger
Radio wave emission from the Milky Way was first discovered in 1931, but it was not until the 1950’s that radio astronomers began working with optical astronomers. With the discovery of radio emissions from space, what could not be seen by optical telescopes became observable. Observing radio waves made it possible to see the center of our galaxy.
The wavelength of radio waves is greater than that of visible light, and large antennae are therefore needed to pick up the signal. For use in radio astronomy, antennae 300 feet [90 m] or more in diameter have been constructed. Since resolution is poor even in instruments of that size, astronomers link up radio telescopes in arrays by computer with a technique called radio interferometry. The greater the distance between the telescopes, the better the definition.
One such linkup includes the Nobeyama Radio Observatory’s 148-foot [45 m] antenna in Japan; the 330-foot [100 m] antenna in Bonn, Germany; and a 122-foot [37 m] telescope in the United States. This type of linkup is called very long baseline interferometry (VLBI), and it results in resolution of one thousandth of an arc second, or the capability to distinguish a six-foot-[1.8 m] square structure on the moon.b Such VLBI is limited by the diameter of the earth.
The Nobeyama Radio Observatory is going one step further in capturing this messenger by placing a 33-foot [10 m] radio antenna in space. It is to be launched from Japan in 1996 and will be linked to radio telescopes in Japan, Europe, the United States, and Australia, creating a baseline of 18,750 miles [30,000 km]. In other words, this linkup will be like one giant telescope three times as large as the earth itself! It will have resolving power of 0.0004 arc second, which means that it will be able to distinguish a 28-inch [70 cm] object on the moon. Called the VLBI Space Observatory Programme, or VSOP for short, it will be used to map and study galactic nuclei and quasars, where supermassive black holes are thought to be bedded. As the second messenger from the universe, radio waves are performing spectacularly and will continue to provide information about their sources.
X Rays—The Third Messenger
The first X-ray observations were made in 1949. Since X rays cannot penetrate the earth’s atmosphere, astronomers had to wait for the development of rockets and artificial satellites to get information from this messenger. X rays are generated at extremely high temperatures and thus provide information on hot stellar atmospheres, supernova remnants, galaxy clusters, quasars, and theoretical black holes.—See Awake!, March 22, 1992, pages 5-9.
In June 1990 the Roentgen satellite was launched and succeeded in mapping the entire X-ray universe. Information recorded indicated four million X-ray sources distributed over the whole sky. However, there is an unknown background glow between these sources. It could be coming from clusters of quasars, which are believed to be the energetic cores of galaxies near what some astronomers call the “edge of the visible universe.” In due time, we can look forward to reaping more information from the X-ray messenger.
Infrared Radiation —The Fourth Messenger
The first infrared observations were made in the 1920’s. Since water vapor absorbs infrared radiation, for best results orbiting satellites are used to investigate this messenger. In 1983 the Infrared Astronomical Satellite (IRAS) was used to map the entire infrared sky and discovered 245,389 infrared sources. About 9 percent (22,000) of the objects are apparently distant galaxies.
Optical telescopes cannot see through all the regions of gas and dust in space. Nevertheless, this fourth messenger makes it possible to “see” farther through the dust and is of particular value in observing the center of our galaxy. Scientists plan to orbit an infrared telescope called Space Infrared Telescope Facility, which is 1,000 times more sensitive than IRAS.
Ultraviolet Radiation—The Fifth Messenger
The first astronomical observation of ultraviolet (UV) radiation was made in 1968. The ozone layer prevents most of this radiation from reaching the earth’s surface. The Hubble Space Telescope, launched in April 1990, is equipped to observe both visible and ultraviolet radiations and will target 30 quasars out to a distance of ten billion light-years.c In other words, observing the ultraviolet messenger makes it possible to see what the universe was like some ten billion years ago. It is hoped that this messenger will reveal many mysteries of the universe.
Gamma Rays—The Sixth Messenger
Gamma rays are high-energy radiation with extremely short wavelengths. Fortunately, the atmosphere prevents most of these harmful rays from reaching the earth’s surface. This messenger is associated with violent events in the universe. On April 5, 1991, the National Aeronautics and Space Administration launched the Gamma Ray Observatory into space. It will observe events surrounding quasars, supernovas, pulsars, theoretical black holes, and other distant objects.
With the advent of the space age, astronomers are now able to observe the entire electromagnetic spectrum, from radio waves to gamma rays. Truly, it is a golden age for astronomers. When we ‘raise our eyes high up,’ we are now able to “see”—with the help of the six messengers from stellar sources—the stupendous wisdom of the Creator of them all. (Isaiah 40:26; Psalm 8:3, 4) As astronomers keep decoding the information carried along by these messengers, we will continue to feel just as Job did more than 3,000 years ago: “Look! These are the fringes of his ways, and what a whisper of a matter has been heard of him!”—Job 26:14.
a Named after a wealthy donor, W. M. Keck.
b The resolution of the human eye is one arc minute. The resolution of one thousandth of an arc second is 60,000 times greater than that of the eye.
c One light-year equals 5,880,000,000,000 miles [9,460,000,000,000 km].
[Chart on page 15]
(For fully formatted text, see publication)
0.1Å Gamma rays
1Å X rays
4000-7000Å Visible light
[Picture on page 15]
With the VSOP space radio telescope, it will be possible to distinguish a 28-inch [70 cm] object on the moon
VSOP: Courtesy of Nobeyama Radio Observatory, Japan
[Picture on page 15]
A drawing of the optical/infrared telescope Subaru, now under construction
Subaru: Courtesy of National Astronomical Observatory, Japan