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"There aren't many U.S. government programs \u2014 even space programs \u2014 like Landsat. Since the 1970s, the project's satellites have continuously imaged the surface of the Earth, providing the longest-running archive of Earth observation photography. You've almost certain seen pictures from the Landsat program: They're used extensively in Google Maps.\nIt's very important the government maintains that long-running archive, so there's usually more than one Landsat satellite in space at any one time. In fact, right now, there are three. There's Landsat 8, the youngest and spiffiest addition to the program. (It just celebrated its first anniversary of operation, on Tuesday.) Then there's Landsat 7, which launched in 1999 and still functions despite some technical issues. \nThere's no Landsat 6. It failed to reach orbit in 1993.\nThere is, however, Landsat 5. Landsat 5 retired only last year after spending 29 operating years in space. It launched in 1984. It was the first satellite to photograph the aftermath of both the Chernobyl accident and the 2004 Indian Ocean tsunami. It is the longest-lasting Earth-observing satellite ever. Landsat 5 is a beast.\nIt is, however, retired. Last June, after Landsat 8 came online, scientists moved Landsat 5 to a graveyard orbit. It will linger there until 2034, losing and losing altitude until it crashes into Earth's atmosphere.\nSo: Three satellites in space. Landsat 5 will orbit for another 20 years. It's on a graveyard orbit \u2014 it's closer to Earth. Landsat 8 is in an operational orbit. It's farther from Earth.\nEarlier this week, Landsat 8 passed over Landsat 5. The two satellites were much closer to each other than either of them were to Earth, yet \u2014 as you'll see \u2014 they're still a blip against their home planet. But thanks to Mike Gartley, a research scientist at the Rochester Institute of Technology, they're blips we can see. Here is Landsat 5 as seen by Landsat 8:the Landsat 5 satellite is seen as a streak of pixels (dark or light depending on the spectral band).\nImage: NASA RIT/USGS\n\nDepending on which color sensor Landsat 8 uses, Landsat 5 appears either white or black. With the \"coastal\" band, which picks up deep blues, the satellite appears black. It appears the same in the green band:Landsat 5 in Landsat 8 band 3, green band\nImage: NASA RIT/USGS\n\nIn the panchromatic band \u2014 which picks up all the colors to form a contrast-heavy black and white image \u2014 it appears white:Landsat 5 in Landsat 8 band 8, panchromatic band\nImage: NASA RIT/USGS\n\nDitto the cirrus band:Landsat 5 in Landsat 8 band 9, cirrus band.\nImage: NASA RIT/USGS\n\nRemember: These are all the same image. They just look different depending on which color that Landsat 8 is sensing. And it's funny to think that a device that looks something like this . . .An artist's rendition of Landsat 5.\nImage:  NASA\n\n. . .appears, even to another satellite, nothing more than a visual whoosh."^^<http://www.w3.org/2001/XMLSchema#string>
<http://mashable.com/2014/02/18/landsat-pictures/>