Astronomers find gravitational effects that cannot be explained by the matter they can see. They propose dark mass to account for these effects.
Which statement best describes this proposal?
It is a guess, because the proposed matter has never been observed directly
It describes ordinary matter that is too dark for telescopes to see
It is an explanation based on evidence that can be tested by further observations
It is a proven fact, because the gravitational effects have been measured
79 exam-style questions on AQA GCSE Physics 8.2 Red-shift, covering 8.2 Red-shift. Each one has a worked solution and a mark scheme showing where the marks go.