Forty-two years ago today, the United States launched the first satellite in what would become a continuous program that keeps an eye on Earth from space to this day.

The Landsat 1 satellite, a joint project of NASA and the U.S. Geological Survey, flew into orbit on July 23, 1972, from Vandenberg Air Force Base in California. The mission: to study and monitor the approximately 30 percent of the Earth's surface that is covered by land.

Landsat 1 carried a camera system and a multispectral scanner. The camera was designed to be the primary observation instrument, according to NASA, but scientists soon discovered that the scanner was sending back far better data. [Earth from Space: Landsat's Legacy]

Landsat soon proved its worth — and even became an explorer of sorts. In 1976, scientists combing through Landsat images found a tiny scrap of land never seen before. It was an island that no human had ever discovered, sitting along the northeastern coast of Labrador.

Landsat 7 image taken on Aug. 7, 2002, of the far northern portion of Labrador, revealing Landsat Island.
Landsat 7 image taken on Aug. 7, 2002, of the far northern portion of Labrador, revealing Landsat Island.
Credit: NASA

At only 82 feet (25 meters) wide by 148 feet (45 m) long, this island seemed too little to write home about. But it jutted out farther east into the sea than any other land in the area, extending Canada's border by 26 square miles (68 square kilometers). To verify the island's existence, Canadian Hydrographic Service hydrologist Frank Hall took a helicopter to the island. The aircraft couldn't land, so Hall was attached to a harness and lowered down.

"As he was lowered out of the helicopter, a polar bear took a swat at him," Canadian politician Scott Reid would later recount in Parliament. "The bear was on the highest point on the island and it was hard for him to see because it was white. Hall yanked at the cable and got himself hauled up."

This death-defying experience prompted Hall to recommend naming the island "Polar Island," but the spit of land was named for its discoverer, instead: Landsat. Today, Landsat Island remains home to nothing but polar bears.

Landsat 1 was decommissioned in January 1978. By that time, it had a partner in orbit: Landsat 2, which launched in January 1975 and sent back Earth observations until 1982. The Landsat program is now the longest-running, continuous observation of Earth's land ever. The eighth satellite in the series, Landsat 8, launched on Feb. 11, 2013.

Today, Landsat data is used to study everything from glaciers to rainforests. Images from the satellites have revealed mountain ranges in Antarctica and previously unmapped volcanoes. Instrumentation has improved, too: Landsat 8 carries instruments that can capture the Earth's surface down to a resolution of 49 feet (15 m).

Landsat also occasionally snaps photos of other objects in orbit, such as old Russian satellites or spent rockets. In February, Landsat 8 even snapped a photo of its older sibling, the decommissioned Landsat 5, which flew under it while both were over Brazil.

Editor's Note: If you have an amazing Earth or general science photo you'd like to share for a possible story or image gallery, please contact managing editor Jeanna Bryner at

Follow Stephanie Pappas on Twitter and Google+. Follow us @livescienceFacebook & Google+. Original article on Live Science.