In the annals of astronomy there are a few unforgettable, iconic photos. The “Pillars of Creation” spires taken by the Hubble Space Telescope, for example, or the “blue marble” full-size picture of the Earth taken by Apollo 17 shortly after takeoff. And surely no list could be complete without one of the Earth and Moon together taken by Voyager 1.

On this day, September 18, in 1977 the Voyager 1 craft, two years and 7.25 million miles from home, trained its camera back to Earth and snapped a photo showing our pale blue dot and its crescent moon together for the first time.

The original “photo” was actually a composite of separate images taken through red, green and blue filters, processed at the Jet Propulsion Laboratories in Pasadena, California. More color-correction had to be done to bring the image to life: because the Earth is so much brighter, the moon had to be lit up to three times its actual luminosity to be seen. In the original its crescent was hardly visible at all.