This tutorial explains some of the techniques developed by astronomers to determine the distances of objects we see in the sky. Links to additional information are embedded in the text. Full description.

This guide provides a brief introduction to the hydrologic cycle and related concepts. Users can choose from a set of links to pages which explain the distribution of water among the oceans, land, and atmosphere, and the mechanisms by which water is moved between its various sinks and sources. Full description.

This document provides a basic explanation of the process by which ozone in the stratosphere is destroyed by human-made gases (particularly chlorofluorocarbons) that have been released into the atmosphere. Additional material describes the research being conducted in Antarctica by the National Oceanic and Atmospheric Administration's (NOAA) Earth System Research Laboratory. Full description.

This basic explanation of the greenhouse effect is accompanied by a diagram. Full description.

At this site, users can read a basic explanation of the greenhouse effect, which is accompanied by a diagram illustrtating the concept. Links to additional information and to related topics are included. Full description.

Materials presented here are intended to help the learner understand the complex interactions between the oceans and the atmosphere that affect global weather and climate events. Users may learn how data from the TOPEX/Poseidon and Jason-1 satellites provide monitoring of oceanic conditions that may produce El-Nino/La Nina events, and help track the Pacific Decadal Oscillation (PDO), a long-term oceanic ... Full description.

This brief description of the rock cycle is for younger students. They will learn about the processes by which the three types of rocks can be changed into one another. Full description.

This collection of images features spacecraft and instruments used for high-energy research, typically studies of X-rays and Gamma rays. The collection includes pictures of early astronomy rockets and instruments, an archive of videos, and a large selection of images of vehicles and instruments from more recent missions. Some of the more recent missions also include lightcurve, spectral, and/or image ... Full description.

Visitors to this site will learn about NASA's manned and unmanned explorations of the Moon and Mars. Topics include the history of the Apollo program, robotic missions to Mars, and future visions for space exploration. The document "Vision for Space Eploration," which describes a timeline and major realignment of NASA's resources and efforts for manned and unmanned missions to the Moon and elsewhere, ... Full description.

This page presents information about the four principle types of volcanoes found on Earth. Diagrams showing the internal structure of each type and photographs of well-known examples are provided. Full description.