Conventional ground-based astronomical observations suffer from image distortion due to atmospheric turbulence .
This can be minimized by choosing suitable geographic locations or adaptive optical techniques , and avoided altogether by using orbital platforms outside the atmosphere .
One of the promises of optical intensity interferometry is its independence from atmospherically induced phase fluctuations .
By performing narrowband spectral filtering on sunlight and conducting temporal intensity interferometry using actively quenched avalanche photon detectors ( APDs ) , the Solar g ^ { ( 2 ) } ( \tau ) signature was directly measured .
We observe an averaged photon bunching signal of g ^ { ( 2 ) } ( \tau ) = 1.693 \pm 0.003 from the Sun , consistently throughout the day despite fluctuating weather conditions , cloud cover and elevation angle .
This demonstrates the robustness of the intensity interferometry technique against atmospheric turbulence and opto-mechanical instabilities , and the feasibility to implement measurement schemes with both large baselines and long integration times .