Some Definitions

cataracts: A cataract is a cloud or film that can form over a person's eye. It is a very thin film that grows inside the eyeball. The presence of a cataract can degrade the quality of someone's vision by blocking light as it enters the eye. Cataracts can be removed with surgery.
centigrade or Celsius: This is a term which describes temperature, much in the same way Fahrenheit scale. In this scheme, called the Celsius scale, water freezes at 0 degrees C and boils at 100 C. The coldest temperature possible is -273 C.
corona: The outer atmosphere of the Sun.
degrees: The temperatures listed in this document are in degrees Kelvin. If you live in the United States or England, for example, you may be more familiar with degrees Fahrenheit. If you are from almost anywhere else in the world, you are probably more familiar with degrees centigrade.
element: A substance that consists only of one type of atom and constitutes most of what exists in the world.
Fahrenheit: In this scheme, water freezes at 32 degrees F and boils at 212 F. The coldest temperature is -459.4 F.
gases: A gas is a fairly low concentration of atoms or molecules in a relatively large volume of space. When atoms or molecules are spread apart relative to each other, one may describe this condition as a gas.
Kelvin: In this scheme, water freezes at 273 degrees K, and boils at 373 K. The coldest temperature possible is 0 K, also known as absolute zero.
light speed: Light travels at 300 million meters per second, which is almost 700 million miles per hour! That's fast! In fact, it is the ultimate speed limit of the universe.
ozone: Ozone is a molecule existing in the atmosphere which shields us from harmful ultraviolet (UV) radiation from the Sun.
periodic table: A periodic table is a chart listing all of the known elements of the universe.
red giant: A red giant is a huge, reddish star, many times larger than the Sun is across.
solar flare: A solar flare is a violent emission of energy and particles from the surface of the Sun. Once this energy reaches the Earth it can disrupt radio communications on the Earth!
SPF: Sun Protection Factor, a number which indicates how much longer you can stay out under the Sun before getting a certain amount of damage. Always use sunscreen of SPF 15 or higher if you are going to be outside for more than a few minutes.
star: Most of the objects you see in the night sky are stars, and they come in many different varieties. Stars usually emit light (like the Sun), but this is not true for all stars. Some are as small as the Earth and others are bigger than the Earth's orbit around the Sun.
Even though you cannot see the stars during the daytime, they are still present. The intense light coming from the Sun simply overwhelms the dim light coming from the star.
twinkle: Have you ever noticed the stars flickering or "twinkling" at night? In most cases it it not really the star changing in brightness, but wind in the Earth's atmosphere distorting the light from the star before it reaches your eye.
ultraviolet light: Ultraviolet (UV) light refers to particular colors of light which are so blue that most cannot be seen by the human eye. UV light from the Sun reacts highly with many chemicals in the atmosphere and controls many aspects of climate and weather. UV light also reacts with human skin to cause suntans and sunburns, which can lead to skin cancer.
UV: Ultraviolet. See ultraviolet light.
white dwarf: A white dwarf is a very small, dense, whitish star.

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-Revised 26 January 1996 by webmaster@hao.ucar.edu.

Copyright 1995, NCAR. - Approved by Dick White -