Astronomy

Radiation exposure during the Apollo missions was measured by dosimeters worn by astronauts and fell within survivable, medically documented limits because the missions were timed to avoid major solar events and passed through the Van Allen belts quickly along a trajectory that minimized exposure, contrary to claims that radiation alone would have proven fatal.

Earth's roughly spherical shape has been established since antiquity and is confirmed by satellite imagery, circumnavigation, gravity measurements, and direct observation of Earth's curvature and shadow during lunar eclipses.

Contrary to popular belief, meteorites are typically cold or only mildly warm to the touch when they reach the ground. The intense frictional heating during atmospheric entry is brief and affects mainly the outer surface, while the interior, having spent ages in the cold of deep space, generally remains cold.

Earth's seasons are caused by the planet's 23.5-degree axial tilt, not by changes in its distance from the Sun. In fact, Earth is slightly closer to the Sun during Northern Hemisphere winter in January than during Northern Hemisphere summer in July.

The Great Wall of China cannot be seen with the naked eye from space. Despite its immense length, it is too narrow, generally 5 to 10 meters wide, to resolve visually from low Earth orbit, and China's own astronauts have confirmed they could not see it during spaceflight.

The Apollo 11 Moon landing in 1969, and five subsequent crewed landings through 1972, are supported by extensive physical, photographic, and independently verified evidence, including retroreflectors still used today and lunar samples studied by scientists worldwide.

Polaris, commonly called the North Star, is not the brightest star in the night sky. That distinction belongs to Sirius, which appears roughly 20 times brighter than Polaris. Polaris is notable not for brightness but for its nearly fixed position above Earth's North Pole, which makes it valuable for navigation.

The Moon has a far side that permanently faces away from Earth due to tidal locking, but this side receives just as much sunlight over a lunar month as the near side. The popular phrase 'dark side' historically referred to the far side being unknown or unmapped, not unilluminated.

Gravity exists throughout space and never truly reaches zero. Astronauts aboard the International Space Station experience roughly 90 percent of the gravity felt at Earth's surface, but they appear weightless because the station and everything inside it are in continuous free fall around Earth, the defining condition of orbital flight.

Sound is a mechanical wave that requires a medium, such as air or water, to compress and expand as it travels. The vacuum of space contains far too few molecules for sound to propagate through it, making outer space effectively silent to human ears even during extremely violent events such as supernova explosions.