Life as we know it developed on a planet orbiting a G2 V star, the Sun. The cryptic “G2 V” designation is the Sun’s “spectral type.” Based on a star’s spectrum, astronomers group stars by temperature.

In a preparatory step, they used adaptive optics-based optical coherence tomography (AO-OCT) to classify the LMS spectral type of 1000 to 2000 cone cells in a region of each subject’s retina. When ...