All electromagnetic radiation is light. Visible light is the only part of the
spectrum you can see. For all your life, your eyes have relied on this narrow
band of EM radiation to gather information about your world. Thought our Sun's
visible light appears white, it is really the combined light of the individual
rainbow colors with wavelengths ranging from violet at 380 nanometers to red at
700 nanometers.
Before Isaac Newton's famed experiment in 1665, people thought that a prism
somehow colored the Sun's white light as it bent and spread a sunbeam. Newton
disproved this idea by using two prisms. To show that white light is made up of
the bands of colored light, Newton used second prism to show that the bands of
colored light combine to make white light again. Visible light contains
important scientific clues that reveal hidden properties of objects throughout
the Universe. Minute gaps in energy at specific visible wavelengths can identify
the physical conditions and composition of stellar and interstellar matter.
Human eyes aren't nearly sensitive enough to detect these faint peaks, but
scientific instruments can. Scientists can learn the composition of an
atmosphere by considering how atmospheric particles scatter visible light.
Earth’s atmosphere, for example, generally looks blue because it contains
particles of nitrogen an oxygen which are just the right size to scatter energy
with the wavelength of blue light. When the Sun is low in the sky, however,
light travels through more of the atmosphere and more blue light is scattered
out of the beam of sunlight before it reaches your eyes. Only the longer red and
yellow wavelengths are able to pass through, often creating breathtaking
sunsets. When scientists look at the sky, they don't just see blue, they see
clues about the chemical composition of our atmosphere.
However, visible light reveals more than just composition. As objects grow
hotter, they radiate energy with a shorter wavelength, changing color before our
eyes. Watch a flame shift from yellow to blue as it is adjusted to burn hotter.
In the same way, the color of stellar objects tell scientists much about their
temperature. Our Sun produces more yellow light than any other color because of
its surface temperature. If the Sun's surface were cooler, say 3,000 degrees
Celsius, it would look reddish, like the stars Antares and Betelgeuse. If the
Sun were hotter, say 12,000 degrees Celsius, it would look blue like the star
Rigel.
Like all parts of the electromagnetic spectrum, visible light data can also help
scientists study changes on Earth such as assessing damage from a volcanic
eruption. This NASA EO-1 image combines both visible and infrared data to
distinguish between snow and volcanic ash and to see vegetation more clearly.
Since 1972, images from NASA's Landsat satellite have combined visible and
infrared data to allow scientists to study changes in cities, neighborhoods,
forests, and farms over time.
Visible light images taken by NASA's Mars lander have shown us what it would
look like to stand on another planet. They have expanded our minds, our
imagination, and our understanding.
NASA instruments can do more than passively sense radiation, they can also
actively send out electromagnetic waves to map topography. The Mars Orbiter
Laser Altimeter sends a laser pulse to the surface of the planet and sensors
measure the amount of time it takes for this laser signal to return.
Документальный фильм "Tour of the EMS 05 - Visible Light Waves"
