BRAINCAKEAstrophysics
Revision notes for Astrophysics in AQA Physics (7408). 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.
- Refracting TelescopesAn astronomical refracting telescope uses two converging lenses: • the objective lens, with a long focal length fo, collects light from the distant…
- Angular MagnificationThe angular magnification, M, of a telescope compares the angle subtended at the eye by the image with the angle subtended at the unaided eye by the…
- Reflecting TelescopesA reflecting telescope uses a large concave mirror, instead of a lens, as its objective.
- Chromatic and Spherical AberrationReal lenses and mirrors do not bring all rays to a single perfect focus.
- Resolving PowerThe resolving power of a telescope is its ability to show two close objects (for example two stars) as separate images.
- Radio TelescopesA radio telescope is a reflecting telescope for radio waves.
- Charge-Coupled DevicesA charge-coupled device (CCD) is a silicon chip divided into a grid of millions of tiny light-sensitive picture elements, called pixels.
- Apparent MagnitudeThe apparent magnitude, m, of a star measures how bright it appears from Earth.
- Parsecs and Light YearsDistances in astronomy are so large that metres are inconvenient, so two other units are used.
- Absolute MagnitudeApparent magnitude depends on distance, so it cannot be used to compare how powerful stars really are.
- Black-Body RadiationA black body is an idealised object that is a perfect absorber and emitter of all wavelengths of electromagnetic radiation.
- Wien's Displacement LawThe peak wavelength of a black-body curve, λmax, depends only on the temperature.
- Stefan's LawStefan's law gives the total power emitted (the luminosity) by a black body: P = σAT4 where P is power in W, A is the surface area in m2, T is the…
- Spectral ClassesStars are grouped into spectral classes by the absorption lines in their spectra.
- The Hertzsprung-Russell DiagramThe Hertzsprung-Russell (HR) diagram is a plot of stars' absolute magnitude against their surface temperature (or spectral class).
- Evolution of a StarA star like the Sun passes through the following stages, each showing as a movement on the HR diagram.
- Supernovae, Neutron Stars and Black HolesA supernova is a rapid increase in the absolute magnitude of a star.
- The Schwarzschild RadiusThe boundary around a black hole from inside which nothing can escape is called the event horizon.
- Type Ia Supernovae as Standard CandlesA type Ia supernova happens in a binary system containing a white dwarf and a companion star.
- The Doppler Effect and Red ShiftWhen a source of waves moves relative to an observer, the observed frequency and wavelength change.
- Hubble's LawIn 1929 Edwin Hubble measured the red shifts and distances of many galaxies.
- The Big Bang Theory and the Age of the UniverseThe Big Bang theory states that the universe began about 14 billion years ago from an extremely hot, dense state and has been expanding and cooling…
- QuasarsQuasars (quasi-stellar objects) were discovered in the 1960s as very bright radio sources.
- Detecting ExoplanetsAn exoplanet is a planet orbiting a star other than the Sun.