Fall Exam Review Flashcards
What process creates energy in the sun?
fusion of hydrogen into helium in the Sun’s core generates the Sun’s energy.
Why does the Sun’s size remain stable?
it is in gravitational equilibrium (the outward pressure of hot gas balances the inward force of gravity at every point within the Sun.)
How did the Sun become hot enough for fusion in the first place?
As the Sun was forming, it grew hotter as it shrank in size because gravitational contraction converted gravitational potential energy into thermal energy. Gravitational contraction continued to shrink the Sun and to raise its central temperature until the core became hot and dense enough for nuclear fusion.
at the centre of the Sun, fusion converts hydrogen into?
helium, energy, and neutrinos.
the phase of matter in the Sun is?
plasma.
which is closest to the temperature of the core of the Sun?
10 million K.
how does the sun generate energy today?
nuclear fusion.
suppose you put two protons near each other. Because of the electromagnetic force, the two protons will?
repel each other.
how do we know what goes on under the surface of the sun?
astronomers create mathematical models that use the laws of physics, the Sun’s observed composition and mass, and computers to predict internal conditions, also by measuring dopplers shifts, we observe vibrations of the Sun’s surface that are created deep within the sun.
the light radiated from the Sun’s surface reaches earth in about __ minutes, but the energy of that light was released by fusion in the solar core about?
8 minutes, and about a million years ago.
based on its surface temperature of 5,800 K, what color are most of the photons that leave the sun’s surface?
green.
how does light tell us what things are made of?
every kind of atom, ion, and molecule produces a unique set of spectral lines.
how does light tell us the temperatures of stars?
we can determine temperature from the spectrum of thermal radiation.
what types of light spectra can we observe?
thermal radiation spectrum - looks like rainbow of light.
absorption line spectrum - specific colors are missing from the rainbow.
emission line spectrum - see light only of a specific color.
what is an atom made of?
protons, neutrons, electrons.
what do astronomers learn from spectra?
temperature of a hot body (continuous spectrum)
elemental and molecular composition of stars/hot clouds or absorbing gas/dust clouds (emission and absorption spectrum)
relative velocity of approach or recession (doppler shift)
why is the sky blue during daytime?
small particles scatter blue light more effectively at the position of the sun. Same with sunsets.
what is Stefan-Boltzmann law?
The higher the temperature of an object, the higher the total amount of energy radiated.
why don’t we glow in the dark?
People only emit light that is invisible to our eyes.
do people emit light?
Yes but it is invisible to our eyes.
which is hotter? blue star or red star?
blue.
Dopplers shift tells us only about?
the part of an object’s motion toward or away from us.
for the dopplers shift, what does it mean for a star to be full speed?
moving directly away from us.
for the dopplers shift, what does it measure if the star is moving across our line of sight (going up or down) but not toward or away from us?
measures no speed at all.
the sun is powered by?
nuclear energy.
