Chapter 24, 25: Earth and the Solar System, Stars and Universe Flashcards
axis
the imaginary line between the Earth’s North and South poles
orbit
the path of an object as it moves around a larger object
hemisphere
half a sphere, the earth can be considered to be made of two hemispheres divided by the equator
the equator
an imaginary line drawn round the earth halfway between the north pole and the south pole
phases of the moon
teh different ways the moon looks when viewed from the Earth over a period of one month.
planet
a large spherical object that orbits the sun without another similar object close to it
minor planet
an object which orbits the sun but is not large enough or far enough from another object to be defined as a parent
asteroids and meteoroids
lumps of rock which orbit the sun
comet
a ball of ice, dust and gas which orbits the sun in a highly elliptical orbit
accretion
the coming together of matter under the influence of gravity to form larger bodies
accretion disc
a rotating disc of matter formed by accretion
eccentricity
a measure of how elliptical an orbit is
orbit radius
the average distance of the planet from the sun
orbital period
the time taken for a planet to complete one full orbit of the sun
stable star
a star that is not collapsing or expanding because the inward force of gravity is balanced by radiation pressure which pushes outwards.
plasma
a completely ionised gas in which the temperature is too high for neutral atoms to exist so it consists of electrons and positively charged atomic nuclei.
solar mass
equal to the mass of teh sun (2*1030)
lightyear
the distance travelled in space by the light in one year (9.5*1015)
protostar
a very young star that is still gathering mass from its parent molecular cloud
interstellar cloud
a cloud of gas and dust that occupies the space between the stars
molecular cloud
a cloud of interstellar gas that consists mostly of molecular hydrogen and is cold and dense enough to collapse to form stars
radiation pressure
the outward force due to the high temperature
red giant
a star that began with fewer than eight solar masses and is burning helium in its core its shell of hydrogen has expanded and cooled
main sequence
a stable star that is burning hydrogen in its core; once it has used up 12% of its hydrogen it goes to the next stage of it’s life.
white dwarf
teh final stage of a star that started with fewer than 8 solar masses after all its fuel has been used up
planetary nebula
a bubble of gas surrounded a white dwarf star that used to be the outer shell of a red giant from which it had collapsed.
red supergiant
Similar red giants form when stars with at least 8 times the mass of the sun out hydrogen fuel in their core but fusion of hydrogen continues in the outer shells.
supernova
an exploding star that began life with more than 8 solar masses and has run out of fuel
neutron star
a collapsed almost entirely of neutrons which forms when a star with more than 8 solar masses reaches the end of its life.
black hole
teh final stage in the life cycle of a star that starts with more than 8 solar masses: it has enough mass left over after exploding as a supernova to collapse to a point when gravity is so strong that not even light can escape.
absorption spectrum
dark lines in a spectrum that are produced when light passing through cooler gas is absorbed
redshift
an increase in the observed wavelength of electromagnetic radiation (including visible light) from a star or galaxy because it is moving away from us.
big bang theory
the universe was created at a single point 13.8 billion years ago and has been expanding and cooling every since
hubbles law
distant galaxies are moving away from te earth with a speed v that is proportional to distance s from the earth where H is the Hubble constant (equation)
