BRAINCAKEAstrophysics and Cosmology
Revision notes for Astrophysics and Cosmology in OCR Physics A (H556). Read the start of any lesson here, then sign in free for the whole lesson, the R.E.C.I.P.E. recall steps and the quiz.
- The Solar System and GalaxiesThe Solar System consists of the Sun and all the objects that orbit it.
- Formation of a StarStars form from interstellar clouds of dust and gas, mostly hydrogen.
- Evolution of a Low-Mass StarA low-mass star has a mass between about 0.5 and 10 solar masses.
- Evolution of a Massive StarA massive star has a mass greater than about 10 solar masses.
- White Dwarfs and the Chandrasekhar LimitA white dwarf is the hot, dense remnant core of a low-mass star.
- Neutron Stars and Black HolesIf the remnant core left after a supernova has a mass greater than the Chandrasekhar limit (1.44 M☉, where M☉ is one solar mass), electron…
- The Hertzsprung-Russell DiagramThe Hertzsprung-Russell (HR) diagram is a graph of the luminosity of stars (vertical axis) against their surface temperature (horizontal axis).
- Energy Levels in AtomsElectrons in an isolated atom (for example, an atom in a gas) can only exist in certain discrete energy levels.
- Emission and Absorption Line SpectraEmission line spectrum: a hot gas at low pressure emits light at only certain wavelengths.
- Using Diffraction Gratings to Analyse StarlightA diffraction grating is a slide with many equally spaced parallel slits (lines), often hundreds per millimetre.
- Wien's Displacement LawStars behave approximately as black bodies: ideal objects that absorb all the radiation falling on them and emit a continuous spectrum of…
- Stefan's LawThe luminosity L of a star is the total radiant power it emits, in watts.
- Estimating the Radius of a StarThe radius of a distant star cannot be measured directly, but it can be estimated by combining Wien's displacement law and Stefan's law.
- The Astronomical Unit, Light Year and ParsecDistances in astronomy are so large that metres are inconvenient, so three larger units are used.
- Stellar ParallaxStellar parallax is the apparent shift in the position of a nearby star against the background of much more distant stars, caused by the Earth's…
- The Cosmological PrincipleThe cosmological principle states that, when viewed on a large enough scale, the universe is homogeneous and isotropic, and the laws of physics are…
- The Doppler Effect and Red ShiftThe Doppler effect is the change in the observed wavelength and frequency of a wave when its source moves relative to the observer.
- Hubble's LawIn the 1920s Edwin Hubble measured the red shifts of galaxies and estimated their distances.
- The Big Bang TheoryThe Big Bang theory states that the universe began about 13.8 billion years ago from an extremely small, extremely hot and dense state, and has been…
- Cosmic Microwave Background RadiationThe cosmic microwave background radiation (CMB) is electromagnetic radiation in the microwave region that reaches the Earth from all directions in…
- The Age of the UniverseIf the universe has expanded at a constant rate since the Big Bang, Hubble's law can be used to estimate its age.
- Evolution of the UniverseThe universe has been expanding and cooling since the Big Bang.
- Dark MatterDark matter is matter that does not emit or absorb electromagnetic radiation, so it cannot be seen directly.
- Dark EnergyUntil the late 1990s, astronomers expected the expansion of the universe to be slowing down, because gravity between all the matter in the universe…