Astronomy Test 2 Objectives Flashcards
Relate the color of light to its relative wavelength and energy.
red - longer wavelength, less energy
blue - shorter wavelength, more energy
What is the Doppler Effect and what does it reveal about a star?
The Doppler Effect is the change in wavelength (and frequency) due to relative motion between the source and the observer. It reveals a star’s motion relative to Earth. -blue shift, red shift; the higher the velocity the greater the shift in position.
Relate the color of a star and the total energy it radiates to its temperature.
A hotter star will be brighter with the peak of its radiation toward the blue end of the spectrum. As the temperature increases, more energy is radiated at shorter wavelengths.
If two stars are the same diameter but one is at a temperature of 6,000 K while the other is at 3,000 K, how many times more energy does the hotter star radiate? (Hint: Stefan-Boltzmann Law) If a third star is at a temperature of 9,000 K, how many times more energy does it radiate compared to the 3,000 K star?
the total energy radiated by stars goes up a T to the fourth power
2^4=16
3^4=81
Describe stellar parallax and how it can be used to determine the distance to a star.
Stellar parallax is the apparent shift in position of the closer stars with respect to the more distant stars due to Earth’s revolution. Photograph a nearby star against the background of distant stars. Then, when Earth has moved halfway around its orbit six months later, the same star is photographed again. Compare the two photos to get the parallax angle which you can use with a base line to calculate the star’s distance.
Describe what is meant by the apparent and absolute magnitude of a star.
Apparent magnitude is the brightness of an object as we view it from Earth.
Absolute magnitude is the brightness a star would have at a distance of 32.6 light-years.
What three variables determine the apparent magnitude of a star?
distance
temperature
diameter
Given two stars whose magnitudes differ by a factor of 5 (5, 10, 15, etc), determine how many times bright one star is compared to the other.
A difference of 5 magnitudes equals 100x difference in brightness.
Describe the difference between apparent magnitude and absolute magnitude and qualitatively describe how they can be used to determine the distance to a star.
apparent (m); absolute (M)
If both are known, the distance can be calculated using
d=10(app-abs+5/5) parsecs.
Relate the sizes of the orbits of the stars in a binary system to the stars’ masses.
M1d1=m2D2 (like kids on a seesaw)
Given the mass and distance from the barycenter of one star in a binary system and the mass of the second star, calculate the distance of the second star from the barycenter.
M1d1=m2D2
List the stellar spectral classes in order and relate them to a star’s temperature and color.
Oh Be A Fine Guy Kiss Me
hottest coolest
blue-white yell oran red
Describe the Hertzsprung-Russell diagram.
- scales
- giants and supergiants
- white dwarfs
- most and least massive stars
- main sequence stars
- most luminous stars
- position of sun on diagram
Scales: left y is mag, x is spectral classes, right y is luminosity
Supergiants very top right; giants top right
White dwarfs bottom
most massive top left
least massive bottom right
main sequence stars diagonal
most luminous - giants/supergiants
position of sun - middle of main sequence, luminosity=1, magnitude=4.9
Describe the reasoning used to determine the sizes of giants, supergiants, and dwarf stars from the Hertzsprung-Russell diagram.
Supergiants/giants are very luminous yet have same surface temperature as red stars on main sequence, so they must be large in diameter. Dwarf stars are much less luminous than stars in same spectral class on main sequence, so they must be smaller in diameter.
Describe a neutron star and a pulsar.
Neutron star is the result of an explosion of a star that was originally more than 8x the mass of the Sun. They are incredibly hot and very dense.
Pulsars are the radio waves emited by the rapidly rotating neutron stars.
Beginning with low mass, medium mass, or high mass stars on the main sequence, list the ending stages in each of their life cycles.
low - white dwarfs
medium - planetary nebula with a white dwarf in the center (red giants collapse into white dwarfs which create an expanding spherical cloud of gas)
high - (red supergiant which collapses into) supernova which can result in neutron stars or black holes
List two pieces of data, not their implications, that support the Big Bang model of the universe.
galaxies moving away from Earth
radiation - 3 degree cosmic microwave background radiation
What do the red shifts of the galaxies imply about the universe?
that the universe is uniformly expanding, which in turn meas at an earlier time the universe was smaller
Arcturus verse
Job 38:32; 9:9
Scorpius
scorpion
Cygnus
swan/northern cross
Sagittarius
archer
Lyra
lyra
Bootes
herdsman
