The Celestron Rule

The Celestron Rule is a quick way astronomers estimate the true size of an object (like a planet or star) based on its apparent size in the telescope and its distance. It states that the actual diameter equals the product of the object's apparent diameter (in radians) and its distance from Earth. This helps astronomers understand the real size of celestial objects without complex calculations, simply by knowing how big they appear through the telescope and how far away they are. It’s a practical tool for translating observed images into meaningful physical dimensions.