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Landsat at 40: Images from the longest-running eye in the sky

Landsat has been watching Earth from space for four decades. As the next-generation LDCM satellite prepares to launch, we look at what Landsat has shown us so far.

An artist's rendition of the next Landsat satellite, the Landsat Data Continuity Mission (LDCM) that will launch in February 2013.

The first Landsat satellite went into orbit 40 years ago today, and during the past four decades, a series of seven different "birds" have trained a watchful eye on Earth from just about the most wicked vantage point around.

The program's youngest eye in the sky, Landsat 7, has been flying since 1999 and will be joined next year by the next-generation Landsat Data Continuity Mission satellite, or LDCM. The LDCM features up-to-date thermal infrared sensors and land-imaging equipment that will make it a full-blown orbiting observatory.

The Earth observation program was created at the urging of Interior Secretary Stewart Udall during the Johnson administration -- Udall had seen a photo from space of pollution spewing from power plants in his home state of Arizona and saw the potential for learning about our own planet that seeing it from a distance held.

The ERTS-1 satellite was launched July 23, 1972, and sent back images of Earth that exceeded all expectations, according to NASA's official history.

Over the decades, the Landsat program has survived funding debacles, a failed attempt at commercializing the program, and satellites asked to operate much longer than they were originally designed for. Since 2008, the U.S. Geological Survey has made all of the images it's captured from Landsat available for free on the internet and there's now over three million images in the program archives.

The scheduled launch of LDCM in February promises to take Earth observation to yet another level. In the meantime, with the assistance of some helpful folks at NASA, we put together a gallery of some of the most remarkable and revelatory images captured by Landsat in 40 years of operation.