Astrophysics (13) Flashcards
Lens
can be used to refract light. Lenses are used to focus light and to produce images of various objects.
The Universe
made up of billions of stars and galaxies. The distance between galaxies is measured in millions of light years. The Universe is about 13.8 billion years old.
Converging lens
refracts rays of light to a point.
Principal axis
the principal axis of a lens is an imaginary line that passes through the centre of a lens and through the centres of curvature of the faces of the lens.
Focal point
the focal point of a lens is the point at which rays parallel to the principal axis of the lens are brought to a focus.
Focal length
the focal length of a lens is the distance between the centre of the lens and the point at which rays parallel to the principle axis are brought to a focus.
Collecting power
is a measure of the light intensity gathered by a telescope. This is proportional to the square of the telescope’s diameter.
Brightness
the brightness of a star is a measure of how much visible light from the star reaches our eyes.
Luminosity
the luminosity of a star is the energy it emits per second, in all wavelengths.
Apparent magnitude
a star’s apparent magnitude is a measure of its brightness as it appears on the sky.
Astronomical unit
the average distance from the Earth to the Sun (AU) = 1.5×〖10〗^11m (2sf).
Light year (ly)
the distance travelled by light in one year = 9.46×〖10〗^15m.
Parallax
nearby objects appear to move relative to far-away objects, when viewed from a different angle. If the measured parallax angle is smaller, then the distance to the star is further.
Parsec (pc)
1pc = 3.26ly
Absolute magnitude
a star’s absolute magnitude is the apparent magnitude the star would have if it were 10pc away.
Black-body radiation
the type of electromagnetic radiation that is emitted by a black or non-reflective body, which is held at a constant uniform temperature.
Absorption spectrum
this spectrum is seen as a series of dark lines in a continuous spectrum, when some elements absorb specific wavelengths of light.
Main sequence star
a star in which hydrogen ‘burning’ takes place. This is the thermonuclear fusion of hydrogen nuclei into helium nuclei.
Neutron star
a collapsed star made of neutrons. It has a very high density.
Black hole
a highly condensed state of matter that has an escape velocity higher than the speed of light.
Gamma-ray burst
a brief intense emission of gamma rays from a collapsing supergiant star.
Schwarzschild radius
the radius of a black hole’s event horizon. Light cannot escape from inside a black hole’s event horizon.
Standard candle
a star or supernova of known brightness that can be used to calculate galactic distances.
The Doppler effect
the name given to the apparent change in the frequency, or wavelength, of a moving source of sound (or other type of wave).
Cepheid variable
a bright star whose intensity varies over a matter of days. The period of the variation of intensity is linked directly to the absolute magnitude of the star.
The Big Bang theory
the theory that the Universe originated about 13.8 billion years ago. All the matter we see in the Universe exploded at one point and has been travelling outwards ever since. In the first few seconds after the Big Bang, the Universe was extremely hot, with temperatures in excess of 1011K. As the Universe cooled, atoms of hydrogen and helium were formed. Over billions of years, the force of gravity acted on this matter to pull it together into the stars and galaxies that we see today.
Quasar
a small, very distant object, which emits as much power as a large galaxy.
Exoplanet
a planet outside our Solar System, in orbit around another star.
