The Asahi Illusion. Nothing in the center is actually brighter, but your brain sees a burst of light. Primates and rats react similarly, hinting at shared visual perception across species

Chandrasekhar died exactly 31 years ago today. At 19, on the boat from India to Cambridge in 1930, he worked out that a white dwarf above ~1.4 solar masses could not remain stable. Eddington publicly rejected the result. 53 years later, Chandrasekhar won the Nobel Prize for his work on stellar evolution.

Mars is about 62,000× wider than the International Space Station. Yet in this photo, taken by Tom Glenn in 2020, the ISS appears larger. Here’s why: - The ISS is 109 m across but only ~400 km above Earth, giving it an angular size of roughly 50 arcseconds. - Mars is 6,800 km wide, but was about 62 million km away, giving it an angular size of only ~22 arcseconds. So despite being vastly smaller, the nearby ISS looked larger in the sky. Capturing this photo was not easy: the transit was visible only along a strip of land about 90 meters wide, with the ISS silhouette sweeping across at an equivalent ground speed of 7.4 km/s. Tom Glenn had to be in exactly the right place, point his telescope in exactly the right direction, and nail the timing to a fraction of a millisecond. The final image was extracted from a video frame with an exposure of just 0.00035 seconds.

Voyager 2 launched exactly 49 years ago today - 16 days before Voyager 1, which took a faster trajectory and overtook it. Voyager 2 remains the only spacecraft to have visited Uranus and Neptune and is still communicating with Earth from interstellar space, over 13 billion miles away.