The 1952 X-ray diffraction image of DNA is called Photo 51. It showed the characteristic X-shaped pattern expected from a helical structure and became crucial evidence in determining DNA’s double-helix form.
The image was produced at King’s College London by Raymond Gosling, a PhD student working with Rosalind Franklin in John Randall’s research group. It was made from the hydrated B form of DNA and was recorded on 2 May 1952. The number 51 refers to the 51st diffraction photograph in Gosling’s series, not to the year or a molecular measurement.
Maurice Wilkins later showed the image to James Watson, who recognized its significance alongside Francis Crick’s theoretical work and other measurements from the King’s College team. Watson and Crick published their double-helix model in 1953. Although the image is popularly described as Franklin’s photograph, Gosling actually made the exposure under her supervision; Franklin’s experimental analysis and related data were also essential.
Photo 51 is therefore not a photograph of individual DNA molecules. It is a diffraction pattern created when X-rays interacted with an ordered fiber of DNA.