Earth's atmosphere is essential to life. This ocean of fluids and suspended particles surrounds Earth and protects it from the hazards of outer space. It insulates the inhabitants of Earth from the extreme temperatures of space and stops all but the largest meteoroids from reaching the surface. Furthermore, it filters out most radiation dangerous to life. Without the atmosphere, life would not be possible on Earth. The atmosphere contains the oxygen we breathe. It also has enough pressure so that water remains liquid at moderate temperatures.
Yet the same atmosphere that makes life possible hinders our understanding of Earth's place in the universe. Virtually our only means for investigating distant stars, nebulae, and galaxies is to collect and analyze the electromagnetic radiation these objects emit into space. But most of this radiation is absorbed or distorted by the atmosphere before it can reach a ground-based telescope. Only visible light, some radio waves, and limited amounts of infrared and ultraviolet light survive the passage from space to the ground. That limited amount of radiation has given astronomers enough information to estimate the general shape and size of the universe and categorize its basic components, but there is much left to learn. It is essential to study the entire spectrum rather than just limited
regions of it. Relying on the radiation that
reaches Earth's surface is like listening to a
piano recital with only a few of the piano's
The following activities use demonstrations to show how the components of Earth's atmosphere filter or distort electromagnetic radiation. Since we cannot produce all of the different wavelengths of electromagnetic radiation in a classroom, the light from a slide or filmstrip projector in a darkened room will represent the complete electro-magnetic spectrum. A projection screen represents Earth's surface and objects placed between the projector and the screen represent the effects of Earth's atmosphere. With the exception of a take-home project, all the demonstrations can be conducted in a single class period. Place the projector in the back of the classroom and aim it towards the screen at the front. Try to get the room as dark as possible before doing the demonstrations.