Astrophysics study guide

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in the solar system a planet is a celestial body which: (a) is in orbit around the sun, (b)h as sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and (c) has “cleared the neighborhood” around its orbit
irregular objects a few kilometers across comprising frozen gases, rock, and dust. travel around the sun in sharp elliptical orbits with period of a few to thousands of year.
form when gravity causes the gas in a nebula to condense
red giant
cooler than the sun, higher luminosity than the sun, therefore have much more surface area and a much larger diameter
white dwarf
remnants of old stars and constitute about 9% of all stars. very hot with relatively low luminosity and small surface area. take billions of year to cool down
neutron star
a celestial object of very small radius (typically 18 miles/30 km) and very high density, composed predominantly of closely packed neutrons. Neutron stars are thought to form by the gravitational collapse of the remnant of a massive star after a supernova explosion, that is insufficiently massive to produce a black hole
black hole
A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—not even particles and electromagnetic radiation such as light—can escape from inside it
binary stars
two stars that rotate about a common centre of mass.
planetary system
a set of gravitationally bound non-stellar objects in orbit around a star or star system
a pattern formed by stars that are the same general direction when viewed from earth. more historically significant than physically as many ancient societies attributed them with religious importance
stellar cluster
group of starts positioned closely enough to be held together by gravity. contain a few dozen to millions of stars. all those of the same grouping were formed at the same time by the same nebula.
also know as stellar nurseries because stars are “born” out of them, they are regions of intergalactic cloud of dust and gas.
a creation of stars, gas, and dust held together by gravity and containing billions of stars
galactic cluster
a group of galaxies with a few dozen to a few dozen members. regular clusters consist of a concentrated core and are spherical in shape where irregular clusters also exist with no apparent shape and usually with a lower concentration of galaxies
galactic supercluster
large group of galaxy clusters, among the largest-known structures in the cosmos
fusion (in relation to stellar radiation)
powers stars
stars are stable
because inward gravity and outward radiation pressure balance each other
total energy emitted by the star per second in watt
peak wavelength
peak wavelength formula
= (2.90 x (10^-3))/T
apparent magnitude
number that is a measure of a celestial object’s brightness as seen from earth. the brighter the object appears, the lower its value. sun is -27
absolute magnitude
measure of intrinsic brightness of a celestial object. the brighter the celestial object, the lower is value
stellar parallax
the apparent shift in position of a nearby star against the background of distant objects
spectroscopic parallax
cepheid variables
bing bang definition
describes how the universe expanded from a very high density and temperature state to what it is now, and what it will expand to be
why big band is responsible for creation and expansion of both space and time
doppler effect and red shift (in relation to the big bang)
comic microwave background (in relation to the big bang)
thermal radiation left over from the time of the recombination in big band cosmology
how Hubble’s law can lead to an estimation of the age of the universe
Hubble’s constant shows us how fast the universe is expanding. with relative knowledge of the size of the universe, we can then deduce how long ago the big bang was and hence how old the universe is
cosmic scale factor
function of time which represents the relative expansion of the universe
how Type 1a supernovae provide evidence that the expansion of the universe is accelerating
type Ia supernovae are redshifted and by the doppler affect then seen to be accelerating
light year (ly)
9.46 x E15 meters
astronomical unit (au)
average distance between the sun and earth, really only useful when dealing with the distances of planets from the sun
one of these = 1.50 x E11 meters ≈ 8 light mins
parsec (pc)
most commonly used unit of distance in astrophysics
one of these = 3.26 ly = 3.09 x E16 meters
Stefan -Boltzmann constant
5.67 x E-8 in W(m^-2)(K^-4)
Hubble’s constant
about 500 km(s^-1)(Mpc^-1)
there is still uncertainty in the value of the Hubble constant
red shift value
if z is large there is a large frequency shift and the object in question is moving away from the earth at a high rate of speed
Categories: Astrophysics