Ch19&20: Astrophysics and Cosmology Flashcards
Define a planet.
An object with enough mass for their gravity to make them spherical, no nuclear fusion and with an orbit clear of other objects.
What is the difference between a dwarf planet and a planet.
A dwarf planet is typically smaller with an orbit not clear of other objects.
What are planetary satellites?
Bodies that orbit a planet.
Define an asteroid.
An object too small and uneven to be a planet with a near circular orbit.
What is the difference between asteroids and comets?
Comets have elliptical orbits, and are irregularly shaped. Asteroids are more spherical and have circular orbits.
Define a solar system.
Systems containing stars and orbital objects.
Define a galaxy.
A collection of stars, interstellar dust, and gas held together by mutual gravitational force.
Define emission spectra.
A set of specific frequencies of electromagnetic radiation, visible as bright lines on a dark spectrum, created by excited atoms giving off specific photons as they transition between energy levels. Every element has a unique line spectrum.
Define a continuous spectrum.
A spectrum in which all visible frequencies of light are present.
Define absorption line spectra.
A set of specific frequencies of electromagnetic radiation, visible as dark lines on a continuous spectrum, they are absorbed by electrons moving between energy levels in the form of photons.
Every element has a unique line spectrum.
How many arcseconds in 1 degree?
3600
What quantity do arc seconds measure?
Angles.
What is Wein’s law?
The blackbody radiation curve for different temperatures peaks at a wavelength inversely proportional to the temperature of the object.
What is Stefan’s law?
Total radiant heat energy emitted by a blackbody is proportional to the 4th power of its absolute temperature.
What is the equation for Stefan’s law?
L=4πr²T^4σ
Define a light year.
The distance travelled by light in one year. Speed of light x Seconds in a year
What is 1 Au?
The average distance from the Earth to the sun. 1.5 x 10^11m
What is the first stage in the life cycle of a star?
Nebula, Collection of dust, gas and rock.
How is a protostar formed from a nebula?
Gravity clumps the nebula together, the gpe turns into heat at the centre of the protostar.
What is the approximate make up of a nebula?
75% hydrogen, 25% helium.
What is the requirement for a protostar to become a main sequence, and why?
When the temperature is above 15 Million Kelvin. This is the minimum energy needed to overcome electrostatic force for nuclear fusion.
What keeps a main sequence star stable?
The balance of Gravitational forces inwards and radiation pressure outwards.
What happens to main sequence stars below a mass of 10☉as they run out of hydrogen?
They become red giants. The reduction in energy causes the star to begin to collapse, this increase in pressure allows fusion to take place in shells.
What happens to main sequence stars above 10☉?
They become red supergiants, fusing heavy elements up to and including iron.
