Light emitted from distant galaxies is observed to have longer wavelengths than the light emitted by the same elements in a laboratory. This phenomenon is known as cosmological redshift. What is the main conclusion that astronomers draw about the universe from this observation?
The universe is contracting.
The universe is expanding.
The stars within galaxies are cooled down.
The universe is static and unchanging.
59 exam-style questions on CIE IGCSE Physics 6.2.3a Galaxies and the scale of the Universe. Each one has a worked solution and a mark scheme showing where the marks go.