Ask Astro: How do scientists weigh celestial objects?

How do scientists weigh celestial objects? Mike Sackheim Evanston, Illinois It’s true that you can’t simply place a planet or galaxy on a scale to measure how heavy it is. Luckily, astronomers have a few tricks up their sleeves. The first trick is understanding that gravity and mass are inherently linked. It’s important to note that weight — which measures the strength of your local gravitational pull on an object — can change, while mass does not. For example

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