The Earth, like other planets, is explored by spacecraft. Earth orbiting spacecraft observe phenomena that are large and global in scale. Using a variety of sensors, satellites may record data that would require tens of thousands of ground-based measurements. Much has been learned about our planet from the vantage point of space that we could not see from the ground.
Below are some of the earliest satellites used to study the Earth from space.
The Laser Geodynamics Satellite (Lageos) orbits the Earth to aid in accurate measurement of the distances between points on the Earth's surface. Lageos was launched May 4, 1976 and placed in a very stable circular orbit of 5,900 kilometers (3,700 miles) altitude. It was joined in 1992 by Lageos II.
Lageos satellites are passive satellites that carry no electronic equipment or moving parts. The spherical satellite takes on a golf-ball appearance due to the "retrocollectors", three-dimensional prisms that reflect light back to the source regardless of the angle of the light received by the satellite.
Magsat was a sun-synchronous satellite designed to measure the Earth's magnetic field. It flew from 1979 to 1980, and acquired accurate data on the direction and strength of the field.
This 1/2 scale model on display in Exploring the Planets was used to test the optical properties of the spacecraft.
From Applied Physics Laboratory.
The SEASAT satellite was launched into a polar orbit in 1978, and was designed to test the capabilities of radar for determining wave height, the amount of water vapor in the atmosphere, and the roughness of the ocean surface.
Although the satellite lasted only four months, it provided details in radar images that were useful in ocean as well as land studies.
Artist's concept courtesy of NASA
The Landsat series of spacecraft are designed to look at the surface of the Earth in different parts of the visible and near-infrared spectrum. Sensors aboard these satellites have been observing Earth since 1972, aiding in crop forecasting and environmental monitoring.
This is a 1/4 scale model of the first Landsat spacecraft (Landsat 1) on display in Exploring the Planets.
From General Electric Company Space Division.
To learn more about Landsat and the monitoring of Earth from Space go to the Looking at Earth gallery website.