הבנת הנקרא

The Earth and other planets of the solar system are each enclosed in a thin shell of gas called an atmosphere. Only the Earth’s atmosphere will be discussed within this article.

The atmosphere clings tightly to the Earth by the attraction of gravity. If the Earth is compared to an orange, the atmosphere can be considered the skin of the orange. The air composing the atmosphere moves freely — sometimes violently. The Earth’s atmosphere consists mainly of nitrogen, oxygen, argon, water vapor, carbon dioxide and small amounts of other gasses and solid and liquid particles.

The atmosphere serves to moderate the extremes of heat and cold on the Earth. During the day, as the heat of the sun penetrates the air and warms the Earth, the atmosphere traps this heat, so that it escapes more slowly into space, making the night warmer than it would be without this effect. The atmosphere also protects the Earth’s inhabitants to some extent from meteor particles, cosmic rays, radiation from the sun and stars, atmospheric dust, and other hazards.

The atmosphere is in constant motion due to the Earth’s rotation and changes in temperature and pressure. The sometimes violent changes that take place in the atmosphere are experienced on Earth as weather, wind, ocean currents, lightning, and rainbows. Large masses of air moving above the Earth’s surface can cause changes in weather and produce winds with speeds of over 100 miles per hour (160 kilometers per hour). Vital exchanges of matter and energy occur between the atmosphere and the oceans, which are vast reservoirs of the heat, moisture and carbon dioxide needed by the atmosphere. The atmosphere, in turn, supplies ocean surfaces with the energy of motion that produces ocean currents.

The sun’s rays that stream down to the Earth appear as white light. However, white light is composed of light waves of all the colors of the spectrum, each color having a different wavelength. As it passes through the atmosphere, sunlight is reflected and refracted by the air molecules and by dust particles and molecules of water vapor. This scattering process is called diffusion. The short blue light waves are more widely scattered and rescattered than are the long red waves. Because of this, the sky appears blue. Outer space is black because there is no atmosphere to scatter the light waves.

Adapted from "Atmosphere", Britannica Kids, Encyclopædia Britannica. 8 Aug. 2020. kids.britannica.com/students/article/atmosphere/273000