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.
104 exam-style questions on CIE IGCSE Physics 6.2 Stars and the Universe, covering 6.2.1 The Sun as a star, 6.2.2a Galaxies and astronomical distances, 6.2.2b The life cycle of a star, 6.2.3a Galaxies and the scale of the Universe, 6.2.3b Redshift, 6.2.3c The Big Bang Theory and cosmic microwave background radiation, and 6.2.3d The Hubble constant and the age of the Universe. Each one has a worked solution and a mark scheme showing where the marks go.