Planet X Discovered: What It Means for Earth

Explaining The Universe on Instagram: "@ExplainingTheUniverse teaches you something NEW everyday day 🧠💫 The ancient Greek scholar Eratosthenes accidentally became the first person to measure the Earth’s circumference around 240 BCE. He noticed that at noon on the summer solstice in Syene (now Aswan, Egypt), the Sun shone directly into a well, casting no shadow, while at the same time in Alexandria, a stick did cast a shadow. By measuring the angle of the shadow in Alexandria (about 7.2°) and k