On the occasion of the 50th anniversary of the National Aeronautics and Space Administration, which began its operations on October 1, 1958, we offer this list of the 50 most memorable images from NASA’s history (see all 50 in the photo gallery below). We recognize that any such ranking is inherently subjective. The rationale for why any one image ranked two slots higher than any other combines several factors, including our attempt to balance the list between human spaceflight, satellite imaging, and planetary exploration. Many wonderful images did not make the final cut—we couldn’t convince the editors to give us 20 pages instead of 10.

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The list omits significant events from space history that were not NASA achievements, such as the famous 1958 photograph of Wernher von Braun and the other architects of the Explorer 1 satellite celebrating their success by holding a model of the satellite over their heads, an event that occurred months before NASA existed. Photos from the Apollo moon program predominate, as well they should—it remains the agency’s crowning achievement. We also recognize that, even though the first “A” in NASA stands for “aeronautics,” our list is light on aeronautical breakthroughs. Our only excuse is that the ranking reflects the affinity of the division of space history staff for space topics.

Topping the list is the view of the whole Earth above, arguably the most influential image to come out of the American space program. Used significantly by the environmental movement (although NOT, as often reported, the inspiration for Earth Day). This particular shot was from Apollo 17, but all of the moon-bound astronauts took similar photos. Although a satellite had returned a picture of the whole Earth in 1967, it wasn’t until humans saw this view for the first time a year later that it entered our collective mind.

We welcome the discussion we know this list will spark. Debating which images should or shouldn’t have been ranked, and how high, would be an appropriate way to mark the past half century of NASA’s accomplishments.