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Convex lens

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A lens that causes light to be focused towards a point, an image formed is real, inverted

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Concave lens

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A lens that causes light to spread out, an image formed is vertual and diminished

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Focal point

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The point at which several light rays converge

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Magnifying power

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The ratio of the objective lens focal length to the eyepiece focal length

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Lens formula

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1/focal length = 1/object distance + 1/image distance

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Chromatic aberration

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Aberration caused by the different wavelengths of light refracting differently resulting in the separation of the different wavelengths and distortion of colour

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Spherical aberration

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A problem with circular mirrors, light rays differact to different focal points depending on where they hit on the mirror

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Reflecting telescope

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A telescope that uses mirrors to magnify an image, prone to spherical aberration

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Refracting telescope

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Telescopes that use lenses to magnify an issue, prone to chromatic aberration.

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Cassegrain telescope

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A type of reflecting telescope that uses a parabola mirror with a hole in the bottom which is reflected by a secondary mirror above the whole, allowing for a more compact design for a good focal length.

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Charge coupled device (CCD)

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a light-sensitive integrated circuit that stores and displays the data for an image in such a way that each pixel in the image is converted into an electrical charge the intensity of which is related to a color in the color spectrum.

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Quantum efficiency

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The percentage of photons that hit the object and are registered

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Resolving power

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Capacity of an instrument to resolve two points which are close together.

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Angular resolution

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The ability of any image-forming device to distinguish small details of an object

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Rayleigh Criterion

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The generally accepted criterion for the minimum resolvable detail - the imaging process is said to be diffraction-limited when the first diffraction minimum of the image of one source point coincides with the maximum of another.

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Apparent magnitude

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the magnitude of a celestial object as it is actually measured from the earth.

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Absolute magnitude

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the magnitude of a celestial object as it would be seen at a standard distance of 10 parsecs.

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Luminosity

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The intrinsic brightness of a celestial object

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Nuclear fusion

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a nuclear reaction in which atomic nuclei of low atomic number fuse to form a heavier nucleus with the release of energy.

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P-P chain

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The main type of converting hydrogen to helium within smaller stars, releasing positrons, neutrinos and gamma rays.

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CNO cycle

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A type of fusion that is a more common in more massive stars fusing hydrogen into helium while using carbon, nitrogen and oxygen as catalysts

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Stellar parallax

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the apparent shift of position of any nearby star (or other object) against the background of distant objects, used to measure distance

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Astronomical unit

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A measure of distance in space equal to the average distance between the earth and the sun (1.496x10^11m)

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Light year

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a unit of astronomical distance equivalent to the distance that light travels in one year,(9.4607 × 10^12 km).

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Parsec

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A unit of distance that is equal to 3.26 light years

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Stefan's law

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describes the power radiated from a black body in terms of its temperature. Specifically, stating that the total energy radiated per unit surface area of a black body across all wavelengths per unit time (also known as the black-body radiant exitance or emissive power), j^{star}, is directly proportional to the fourth power of the black body's thermodynamic temperature T

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Black body radiation

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radiation from a theoretical perfect emitter (and absorber) of radiation at all wavelengths.

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Wien's displacement law

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relationship between temperature T of a black body and the peak wavelength (lambda max)

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Spectral classes

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a classification of stars according to the appearance of their spectra. (OBAFGKM)

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Spectral type

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A way of classifying a star by the lines that appear in its spectrum; it is related to surface temperature. The basic spectral types are designated by a letter (OBAFGKM), with O for the hottest stars and M for the coolest, and are subdivided with numbers from 0 through 9.

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Emission spectra

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Produced when electrons are given energy to reach high energy levels which is emitted as light when electrons return to lower levels

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Flux

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the amount of energy per unit area that is received at a distance from it (F=Power/area)

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HR diagram

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A graph that shows the relationship between a star's surface temperature and absolute magnitude

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Spectral class O

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Stars typically blue in colour with a temperature of around 28000-50000 kelvin

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Spectral class B

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Stars usually with a lighter blue colour with a temperature of 10000-28000 kelvin

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Spectral class A

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Stars whitish in colour and a temperature of 7500-10000 kelvin

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Spectral class F

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White stars at around 6000-7500 kelvin

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Spectral class G

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Yellowish stars of around 5000-6000 kelvin

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Spectral class K

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Orange stars of around 3500-5000 kelvin

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Spectral class M

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Red stars of around 2500-3500 kelvin

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Main sequence

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a series of star types to which most stars belong, represented on a Hertzsprung-Russell diagram as a continuous band extending from the upper left (hot, bright stars) to the lower right (cool, dim stars).

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Red Giant

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a very large star of high luminosity and low surface temperature. They are thought to be in a late stage of evolution when no hydrogen remains in the core to fuel nuclear fusion.

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White dwarf

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A small, hot, dim star that is the leftover center of an old star

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Red super giant

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The stage in the life cycle of an already massive star during which the star increases in size and becomes very bright.

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Instability strip

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A region of the H-R diagram occupied by pulsating stars.

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Helium flash

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The runaway helium fusion reactions that occur in the core during the evolution of a red giant.

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Stability curve

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A graph showing average binding energy per nucleon against number of nucleons

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Chandrasekhar limit

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The maximum mass of a stable white dwarf star (1.4 solar masses) and is the mass above which electron degeneracy pressure in the star's core is insufficient to balance the star's own gravitational self-attraction. After this the white dwarf will typically explode into a type 1a supernova.

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Pulsar

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A highly magnetized, rotating neutron star or white dwarf, that emits a beam of electromagnetic radiation. This radiation can be observed only when the beam of emission is pointing toward Earth, and is responsible for the pulsed appearance of emission.

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Neutron star

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The collapsed core of a large (10-29 solar masses) star. The smallest and densest stars known to exist. They typically have a radius on the order of 10 km and can have masses of about twice that of the Sun.

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Black hole

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A region of space having a gravitational field so intense that no matter or radiation can escape.

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Supernova

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The explosion of a star that has reached the end of its life. They can briefly outshine entire galaxies and radiate more energy than our sun will within its lifetime. They're also the primary source of heavy elements in the universe

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Roche Lobe Overflow

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In a binary system matter can be drawn onto a white dwarf.

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Type 1a supernova

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When a white dwarf reaches 1.4 solar masses (Chandrasekhar Limit) the core collapses and explodes. They do not have hydrogen lines and all have similar light curves.

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Type 2 Supernovae

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A type of supernovae that contains Hydrogen Lines in its spectrum, this means that the envelope of the star which contains Hydrogen was intact when the star exploded. The absolute magnitude of these varies with stellar mass.

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Slow process

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A nucleosynthesis process that occurs at relatively low neutron density and intermediate temperature conditions in stars.Nuclei are created by neutron capture, increasing the atomic mass of the nucleus by one. A neutron in the new nucleus decays by beta-minus decay to a proton, creating a nucleus of higher atomic number. The rate of neutron capture by atomic nuclei is slow relative to the rate of radioactive beta-minus decay.

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Rapid process

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A nucleosynthesis process that occurs in core-collapse supernovae and is responsible for the creation of approximately half of the neutron-rich atomic nuclei heavier than iron. The process entails a succession of rapid neutron captures.

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Escape velocity

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The lowest velocity which a body must have in order to escape the gravitational attraction of a particular planet or other object.

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Schwarzschild radius

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The radius of a black holes gravitational field where the escape velocity is equal to the speed of light (R=2GM/c^2)

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Hydrogen lines

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The emission spectrum of atomic hydrogen is divided into a number of spectral series, with wavelengths given by the Rydberg formula. These observed spectral lines are due to the electron making transitions between two energy levels in the atom

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Binary system

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A solar system focused around two stars orbiting eachother

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Hubble constant

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a proportionality constant indicative of the rate of expansion of the universe that is used in relating the apparent velocity of recession of a distant galaxy and its distance

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Doppler effect

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an increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move towards (or away from) each other. The effect causes the sudden change in pitch noticeable in a passing siren, as well as the red shift seen by astronomers.

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Redshift

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the displacement of spectral lines towards longer wavelengths (the red end of the spectrum) in radiation from distant galaxies and celestial objects. This is interpreted as a Doppler shift which is proportional to the velocity of recession and thus to distance.

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Blueshift

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the displacement of the spectrum to shorter wavelengths in the light coming from distant celestial objects moving towards the observer.

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Trigonometric Parallax

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One angle of a triangle and the distance between the two vantage points is one side of the triangle. Basic trigonometric relations between the lengths of the sides of a triangle and its angles are used to calculate the lengths of all of the sides of the triangle.

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Cepheid Variables

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These stars change their brightness on a timescale of days or weeks. It has been discovered (by comparison to the Spectroscopic analysis) that their period is directly related to their size (and hence luminosity)

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Hubble's law

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There is a relationship between how far away a galaxy is and its Red Shift (Redshift v = Hd)

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Quasars

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The most luminous and distant objects in the universe. These objects are believed to be active galaxies, where a super-massive black-hole at the centre are absorbing huge amounts of matter. This creates jets of radiation to be emitted which are detected by radio telescopes. They have the largest red-shift of any objects found in the universe and are hence considered the most distant objects observed

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Exoplanet

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A planet which orbits a star outside our solar system

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Radial velocity technique

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A method for finding exoplanets by measuring the wobble they put onto the star. This works no matter the plane of orbit of the exoplanet

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Transiting method

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A method for finding exoplanets that looks at the light curve for a periodic dip and can tell us the size and orbit length. This only works if the planets orbit is facing earth

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Selection Bias

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The effect caused by large planets in fast orbits being the easiest to see, and being more difficult to detect others.

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