ASTR 1220 Final Exam
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ASTR 1220 Final Exam
astronomy final exam
Terms for the ASTR 1220 Final Exam
rate of energy flow
measure of energy flow (power) equal to 1 joule/s
when a source produces light
when light is absorbed by matter (i.e. your hand absorbing light from a light bulb)
when light passes through a form of matter
when light bounces off something in the same general direction (reflection) or multiple random directions (scattering)
measure of light frequency
Hertz (Hz), cycles per second
a perfect body that completely absorbs every kind of electromagnetic radiation and reradiates the energy as quickly as it absorbs it
The 3 properties of blackbodies are:
1. Every blackbody emits some radiation at every wavelength
2. A hot blackbody emits more radiation at every wavelength than a cool one
3. The peak wavelength of the radiation from a hot body is at a shorter wavelength than that for a cool body
The most common elements in the universe are:
a spectrum from an source like an ordinary light bulb that spans a broad range of wavelengths without interruption
emission line spectrum
the spectrum obtained from a thin, low-density cloud of gas that consists of thin emission lines that depend on the gas' composition
a continuous spectrum that is missing several colors that have been absorbed by a cloud of gas
The total energy emitted per square meter of a blackbody is given by
Therefore, temperature strongly affects the amount of energy emitted
Hotter objects emit photons with a higher average energy (shorter wavelength), given by
A light source moving towards the observer causes
blueshift (shorter wavelengths)
A light source moving away from the observer causes
redshift (longer wavelengths)
the power output of a star, or other blackbody
A nuclear fusion reaction of 1 kg of hydrogen produces
992.9 kg of helium, ~7.1 kg are converted into energy
___% of the Sun's energy is generated in the _____ of the Sun
94% of the Sun's energy is generated in the inner 20% of the Sun
The closest star to our Sun is
Alpha Centauri (4.4 LY or 1.3 parsecs)
Brightness is given by
Kepler's First Law
Planets orbit stars in elliptical orbits, with the star at one of the foci of the ellipse
Kepler's Second Law
The straight line joining a planet and the Sun sweeps out equal areas in space in equal intervals of time
Kepler's Third Law
The squares of a planet's period of revolution is directly proportional to the cube of its semimajor axis.
, where d = distance (AU), p=period (years)
The lifetime of our Sun is
10 billion years
The lowest mass a protostar can have before it becomes a brown dwarf is
Stars with a mass of _______ will leave behind planetary nebulae
Stars whose core has a mass of _______ will form a white dwarf.
Stars with a mass of ______ will die in a supernova.
Stars whose cores have a mass of _______ will form neutron stars.
Stars with a mass of ______ who have cores with a mass greater than _______ will form black holes.
The definition of a black hole is...
an object whose escape velocity exceeds the speed of light.
Escape velocity is
the velocity required for an object to break free from a body's gravity.
The radius at which an object of a certain mass becomes a black hole.
A highly dense, rapidly spinning object, most likely a neutron star, that emits radio signal pulses at very regular intervals.
Used to calculate the distance to objects based on how rapidly they appear to be moving away from us.
The universe is currently accepted to be _______ years old.
13.7 billion years