What Our Eyes
Images of the heavens shown on these pages were not painted by artists. These images are real objects that were photographed by several organizations across the globe. One reason that these images are so dramatic is that these images are recorded in different kinds of light. Modern telescopes can see formations in the Universe that our human eyes cannot see. What we do see is called "visible" light. Visible light is, however, only a tiny sliver of a much bigger picture, called the "electromagnetic spectrum".
Light waves are a kind of electromagnetic radiation. We identify various bands of radiation by wavelengths. For example, visible light covers the electromagnetic band of 700 to 400 nanometers, while cell phones send and receive radio messages in the centimeter-wavelength band. The entire range of radiation wavelengths is called the "electromagnetic spectrum". The entire electromagnetic spectrum is a range of wavelengths from tens of kilometers, very, very long, to billionths of billionths of a meter, very, very short. Wavelengths that are longer than "red light" and shorter than "violet light" are beyond what our eyes can see.
We often hear talk about "infrared" and "ultraviolet" light, neither of which humans can see; i.e. "invisible light". Infrared radiation has longer wavelengths than visible light and infrared is perceived as heat by humans. Some species of insects and reptiles have infrared "vision". When one feels warmth from a fire, one is "sensing" infrared radiation from a fire.
Ultraviolet light has shorter wavelengths than visible light. Although ultraviolet light is not visible to humans, we can see the effects of ultraviolet radiation, for example sunburn or the glowing (florescence) of florescent light. As the wavelength of ultraviolet light (UV) shortens, UV light causes changes in living cells; short-wavelength UV is, therefore, called "ionizing radiation". Ionizing radiation forces an oxygen molecule (O2) to accept one more atom of oxygen to make one highly unstable molecule of ozone (O3).
The longest wavelengths of electromagnetic radiation are in the neighborhood of 20 kilometers (15 kiloHertz, or 15,000 cycles per second). Military submarines use these very long wavelength radio waves for communicating across oceans from under the sea.
At wavelengths in the ultraviolet band that are shorter than 124 nanometers (10−9 meters), we enter the realm of ionizing radiation. Ionization means that an atom has been forcibly stripped of one or more electrons. The ionization of atoms in living tissue causes alteration and damage to cell DNA, which means that ultraviolet radiation and all shorter wavelengths of radiation are hazardous to the health of all living creatures.
Ionizing radiation includes most wavelengths of ultraviolet light, x-rays, gamma rays, and cosmic rays.
Forttunately, 100 percent of all radiation at wavelengths shorter than the near-ultraviolet are absorbed by Earth's atmosphere. The nitrogen, oxygen, trace gasses, and perhaps all industrial polutants, including ozone, in Earth's atmosphere absorb incoming high-energy, ionizing radiation; life-threatening radiation is blocked by our atmosphere from reaching the surface of the Earth. Absorption of this "energetic" radiation warms the Earth and reduces the range of surface temperatures between night and day.
All wavelengths of electromagnetic radiation that are
than almost-visible ultraviolet radiation, about 120 nanometers, are described as "ionizing"
Ionizing radiation is produced by atomic processes, rather than molecular processes. In other words, the interaction of +protons, 0neutrons, +positrons, and in some cases −electrons produces ionizing radiation. Exposure to ionizing radiation can change a chemical element into another element, which in turn stealthily changes the chemical behavior of molecules, ergo illness.
Ionizing radiation means that ultraviolet radiation, as well as all shorter wavelengths
, can damage DNA and affect living cells by breaking the weak chemical bonds of which much living tissue is made. All radiation having wavelengths longer
than ultraviolet light are described as "non-ionizing"
radiation, which means that exposure to long-wavelength radiation is not hazardous
to your health, unless a person is prone to doing unreasonable things; for example, looking directly into bright sunlight for long periods of time, which will more than likely do considerable damage to one's eyes.  Another example of being unreasonable would be a person irresponsibly puting their hand into a blazing fire. When reasonable behavior is the norm, long-wavelength radiation is not hazardous to one's health.
We should also mention at this point that cell phones, microwave ovens, radio and television broadcasting, automobile remote controls, computers, and radar systems operate at wavelengths quite a bit longer than visible light and, therefore, should not be hazardous to our health if used sensibly. For example, an "infinitely long-wavelength", i.e. non-ionizing, otherwise known as direct current (DC), can terminate a person's life by electrocution just as decisively as can ionizing radiation from the decay of uranium terminate a person's life by severely damaging a person's DNA. Ionizing radiation is invisible, silent, and can do damage at a distance. One only has to be in the proximity of the source of ionizing radiation to suffer illness or death.
Although we normally think of radiation as being bad, a hypothesis is beginning to emerge that suggests that small micro-doses of ionizing radiation may actually help our immune systems to work well; the process is referred to as hormesis
, which could also be the mediating force behind mutations that drive the process of "survival of the fittest"
. If these ideas seem to be completely crazy, then consider that cancerous-tumor irradiation with radioactive cobalt 60 (Co60)
is a common therapeutic procedure.
Ultraviolet light is used to detect counterfeit paper money, artwork forgeries, and fake credit cards. Disco dancers are familiar with so-called "black light", which is a mixture of purple light and ultraviolet light. Although invisible, the ultraviolet light changes our view; things look different when illuminated by ultraviolet light. Unlike humans, mosquitoes can see ultraviolet light. Mosquito zappers attract mosquitoes with ultraviolet light. As the mosquitoes fly to the source of the light, they are electrocuted by high-voltage electricity. "Sanitary lamps", which emit ultraviolet light, have been used in public rest rooms to kill bacteria.
Compare these whole-body images "happiness" and "depression": Infrared photography reveals activity in living organisms. Yellow indicates the hottest temperature and light blue indicates the coldest temperature.
Infrared light is used by remote control devices to communicate a user's choice to the television receiver or music player. Soldiers and rescue workers use infrared goggles to see in the dark. Rattle snakes find their prey at night by "seeing" in the dark; in addition to a pair of eyes that see "visible" light, rattle snakes also have a pair of "eyes" that sense infrared radiation, which is also known as "heat".
A Magnetic Storm on Our Sun: The loop of hot gasses extending beyond the Sun's surface reveals a magnetic storm. Our Son, as well as all of the stars in the Universe, are quite violent places. Surface features of the Sun are constantly changing and several types of activities eject intense fields of radiation across much of the electromagnetic spectrum.
Slightly more than half of the total energy from the Sun that arrives at the Earth is infrared energy. Much of that infrared energy does not penetrate our atmosphere, but rather, is absorbed by the atmosphere, producing heat; heating of the atmosphere by absorbing incoming radiation is called the "greenhouse" effect. In addition to radio waves, infrared waves, and visible light waves, our Sun also bombards our Earth with ionizing ultraviolet rays, x-rays, and gamma-rays. These ionizing wavelengths are also absorbed by Earth's atomosphere and contribute to Earth's warmth. Long-wavelength radio waves and visual-light waves, however, do not heat the Earth's atmosphere, because the atmosphere does not absorb them.
The amount of the Sun's radiation that heats the Earth periodically varies . Our Sun periodically experiences several phenomena that vary the intensity of heat-producing radiation: magnetic storms, sunspot activity, and volcanic-like ejections of highly energetic particles in the form of x-rays and gamma-rays, which all affect Earth's atmosphere.
Expanding Our View: infrared, plus visible, plus ultraviolet together are still only a sliver of the entire "spectrum" of electromagnetic waves that exist. Physicists tell us that light travels in waves that have both magnetic and electrical characteristics; therefore, we use the terms "electromagnetic waves", or "electromagnetic radiation". In everyday language, the terms are equivalent.
Most of us are familiar with ocean waves; if you watch waves, you observe different distances between moving waves. The distance between the peaks is called a "wavelength". Electromagnetic radiation is also measured in wavelengths. Light is one kind of electromagnetic radiation, along with waves of other kinds of radiation: i.e.radio waves, microwaves, infra-red light, ultraviolet light, x-rays, gamma rays, and cosmic rays.
Wavelengths: Radio waves have the longest wavelengths, measured in meters to thousands of meters (103). Broadcast AM radio and ship navigation aids continue to operate at these low frequencies, i.e. long wavelengths, despite the increased use of much higher frequencies nowadays. Over-the-air television and FM radio are transmitted at meter (101) wavelengths. Microwaves, used by radar ovens and for cell-phone communications, are measured in centimeters (10−2) and millimeters (10−3), while infrared waves are measured in micrometers (10−6). Visible light and near-ultraviolet waves are measured in nanometers (10−9). Ionizing ultraviolet rays and x-rays are measured in picometers (10−12. Beyond x-rays, gamma rays and cosmic rays are microscopically short. Gamma rays and cosmic rays are usually associated with atomic-level nuclear processes and are decidedly destructive of living tissue. Because of the destructiveness of gamma and cosmic radiation, astronauts and the electronic components used in spacecraft must be shielded from these highly penetrating and destructive forms of radiation.
High-intensity waves at a variety of wavelengths from many cosmic and solar-system sources continually bombard the Earth's atmosphere and sometimes interfere with radio and television broadcasting, interrupt some types of telephone service, and create grand auroral light displays
, usually in high-latitude skies.
Unusually intense bombardment of Earth's atmosphere by oxotic solar emissions may have a connection to global warming. Future research and rigorous evaluation of available data may eventually clarify the cuases and cure for global warming.
"Io" [ah-i_oh] is one of the four large moons of the very large planet Jupiter that were discovered by Italian astronomer Galileo in 1610. Through Galileo's simple telescope, Io was merely a smudged point of light. Nowadays, however, space-vehicle cmaeras record much fine detail.
Io is slightly larger than Earth's Moon. Earth is about three times the diameter of its Moon, while Jupitor is 33 times larger in diameter than Io.
A highly abundant chemical element on Io is yellow-colored sulphur (chemical symbol = "S"). On both Io and Earth, volcanoes spew out noxious sulphur dioxide (SO2). Sulphur dioxide is used on Earth to preserve the color and freshness of dried apricots and in the sulphite form [SO3], as a preservative for some wines. Bubbling SO2 through water produces the very strong acid, sulphuric acid (H2SO4), that is used in automobile batteries.
The surface of Io is illuminated by light from the Sun. In sunlight, Io's surface appears in an array of colors, depending on the temperature of the surface sulphur: from black (the hottest) to bright orange to yellow to white (the coldest). The range of colors visible in this photograph of Io indicates that the surface temperature of Io varies across a wide range of temperatures.
Saturn: is famous for its rings, but Saturn also has 62 moons (53 are named), the largest number of moons of any planet in our Solar System. Although Galileo in 1610 was the first person to perceive structures beyond the planet, Christiaan Huygens in 1655 was the first person to suggest that Saturn was surrounded by "a ring". In 1675, Giovanni Domenico Cassini determined that Saturn's ring was composed of multiple, smaller rings with gaps between them. As recently as 1980, Saturn's outermost E-Ring was first observed and photographed by both Pioneer and Voyager spacecraft.
The bright ring of light at the southern pole of Saturn is an aurora. Discovering a fleeting aurora on Saturn was a "lucky break"; fortunately, the space-based Hubble Telescope in 2004 was aimed at the right place at the right time. Credits: NASA, ESA, J. Clarke (Boston University), and Z. Levay (STScI)
Saturn completes an orbit around the Sun in 30 earthly years. Saturn, like the Earth, is slightly tilted on its rotation axis; consequently, Saturn's rings seem to briefly disappear as the planet biannually crosses the plane of the Sun's orbit, called the ecliptic. Earth crossing the ecliptic is called the summer or winter solstice.
, the outermost ring of Saturn, is unique. Rather than being composed of rocks and other solid debris, as are the other rings of Saturn, the E-Ring is a misty blend of sodium chloride crystals (NaCl, table salt)
, silicates (SiOX; i.e. sand and quartz)
, ammonia (NH3)
, and water vapor (H2O)
all mixed with a little mineral dust from Saturn's moon, Enceladus
. Interestingly, these chemicals are among the basic building blocks of bio-chemistry.
was discovered by NASA's Pioneer 11
spacecraft as Pioneer passed by the ringed planet (6 April 1973)
M16, the Eagle Nebula, in the near infrared: Compare this infrared image with the image of the same area in visible light. Near-infrared photography penetrates dust clouds to reveal objects behind the clouds of dust. What we see with our eyes is only a narrow view of the universe. A variety of modern celestial and terestrial instruments is helping us to gain more and more knowledge of our Universe (VLT/ISAAC/McCaughrean & Andersen/AIP/ESO)
How Do We Know?
One may wonder why stars have different colors in visible light. Most stars, called "Main Sequence"
stars, change color
over their lifetimes. Studying the colors of the rainbow that are present in the light of a star can reveal much information, for example: age, size, gravity at the surface, surface temperature, and expected lifetime of the star, as well as telling us whether the star is moving toward us on Earth or moving away from us. Chemical elements in a star can be identified by plotting the dark lines and bright lines that appear in starlight.
That is a lot of information derived from the visible color of an object! When viewed in non-visible electromagnetic wavelengths, e.g. ultraviolet-rays and x-rays, even more information is gathered about an object.
A Philosophical Perspective
From Hubble and other space-based telescopic images, scientists observe that the early Universe was less ordered and more chaotic than our present-day Universe. Galactic formations of 10-billion years ago seem to be more strange and exotic than are much younger galaxies, which is the reverse of normal physics; i.e., the ancient Universe moved from chaos toward order, while in normal physics, order moves toward chaos. We could suppose that the Universe has been moving from an extreme state of chaos to an extreme state of orderliness.
Is Creation a Hologram?: At times, extreme speculation by responsible scientists leads to bizarre ideas. One recent extreme idea is that our everyday human experience is a hologram. To explore this kind of speculative hpothesis, one has to be somewhat familiar with black holes, gravity, the behavior of light and other electromagnetic phenomenon, heavy-duty mathematics, and whatever else modern science can conjure. The very fact that human beings can contemplate such notions challenges the intellectual boundaries of the human brain, perhaps to a point that humankind is not yet ready to approach. If exploring the fundamentals of existence seems otherworldly, realize that our smart phones, the Internet, and gene-focused medical treatment all work because we continually learn more and more about the most basic of natural processes. Nature does have much to teach us.
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