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Articles on Astrophysics

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Artist concept of Gravity Probe B orbiting the Earth to measure space-time, a four-dimensional description of the universe including height, width, length, and time. (NASA)

Gravitational distortion of time helps tell modified gravity apart from a dark force

The gravitational field can affect space and time: the stronger gravity is, the slower time moves. This prediction of General Relativity can be used to reveal hidden forces acting on dark matter.
Astronomers can estimate ages for stars outside the Solar System, but not planets. Corbis Historical via Getty Images

How do astronomers know the age of the planets and stars?

Measuring the ages of planets and stars is tricky. An observational astrophysicist describes the subtle clues that provide good estimates for how old different space objects are.

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