How does astronomy utilize physical laws like gravity or electromagnetism, which are confirmed via Earth testing?

By deriving predictions from these laws and comparing observations against them

Astronomy builds its models upon physical laws, such as gravity or electromagnetism, whose fundamental validity is established through testing on Earth. Since astronomers cannot manipulate the variables of a distant event, like a supernova, they rely on prediction. Physical laws derived from Earth-based testing are used to construct theoretical models that generate specific predictions about what should be observed (e.g., the expected light curve or decay rate). Astronomers then compare the actual measurements of the distant event against these derived predictions. Agreement between observation and prediction validates the application of the physical law across vast cosmic distances.