Glossary

• Atmosphere - a layer of gas held around a planet by gravity.

• Aurora - electrical particles (mainly electrons and protons) flow from the sun to the Earth (the solar wind). They are guided by the Earth's magnetic field to two oval-shaped regions around the north and south poles (actually the magnetic poles, which are a little different from the geographic poles). There they bombard the upper layers of the Earth's atmosphere and cause the oxygen and nitrogen atoms and molecules to emit light, which is the light of the aurora.

• Chromosphere - from the Greek chromos, color. The layer just above the photosphere (see below); it is seen during a solar eclipse, and appears as spikes of light that are a pinkish color.

• Corona - from the Latin for crown. The sun's very hot, upper atmosphere; it appears as a ghostly white halo during a solar eclipse.

• Electromagnetic spectrum - the complete range of radiation given off by the sun, and includes heat, light, x-rays, radio waves and other kinds of energy.

• Ionosphere - the region of the Earth's atmosphere which is electrically charged; between 50 km and 600 km above the surface of the Earth.

• Light Year - a scientific way of measuring huge distances, it is the distance that light travels in one year; light travels at 186,300 miles per second, or 6 trillion miles per year. Our nearest star (other than the sun) is Alpha Centuri, which is 4.2 light years away.

• Milky Way - our galaxy; contains over 200 billion stars.

• Nuclear Fusion - the process in which hydrogen atoms are combined or fused into helium atoms. The sun changes 600 million tons of hydrogen into 596 tons of helium every second, and loses 4 million tons of mass that has been converted into light and heat energy.

• Photosphere - from the Greek photos, light. The lowest layer of the sun's atmosphere, it is the layer we see in visible light.

• Prominences - huge eruptions of glowing gas from the sun, they can extend from 20,000 miles above the surface to over 300,000 miles; a huge arch of gas in the sun's lower corona.

• Solar flares - spectacular, forceful eruptions that burst forth from sunspots; waves of intense heat, light and radiation. It takes about two days for solar wind particles associated with solar flares to reach Earth's atmosphere.

• Solar Maximum - the peak of the 11-year solar activity cycle. The last one occurred in 1989-90, and the next one is expected in 2000-01. It is a time in which we are more vulnerable to "space weather."

• Solar system - the sun and everything that moves around it, including the planets, comets and asteroids.

• Solar wind - a high-speed flow of low-density electrical particles, mainly electrons and protons, emitted by the sun in all directions into space. The speed of the solar wind varies from about 200 to 1000 miles per second, so takes between one and five days to reach the Earth.

• Spectroscope - an optical instrument used by scientists to analyze what elements are present on the sun; it can also be used to detect motion and the speed of motion of gaseous objects.

• Spectrum - the rainbow of colors of light that make up the white light of the sun. The spectrum may be seen by passing the sun's light through a prism.

• Sun - our star; the central and largest body in our solar system; the essential energy source for life on Earth.

• Sunspots - a cool, dark spot on the sun's surface, that is created by regions of very strong magnetic field near the sun's surface. The magnetic field restrains circulation of hot gases from lower, hotter levels in the sun to the surface.

Back | Next | Table of Contents