Astronomy Final Flashcards
What are the standard units for luminosity?
Watts
Purpose of adaptive optics
Eliminate distorting effects of atmospheric turbulence for telescopes on the ground
How does the sun generate energy?
Nuclear Fusion
What observations characterize solar maximum?
we see many sunspots on the sun’s surface
When white light passes through a cool cloud of gas, we see
an absorption line spectrum
How are wavelength, frequency, and energy related for photons of light?
Longer wavelength means lower frequency and lower energy
HR Diagram: Cool and Dim
Lower right
Overall fusion reaction by which the sun produces energy
4 H -> He + Energy
Thermal Radiation:
radiation that depends only on the emitting objects temperature.
Layers of the sun from center outward
Core, radiation zone, convection zone, photosphere, chromosphere, corona
What is true of images captured in X-Ray telescopes?
Always displayed in false color
What is the closest temperature to the CORE of the sun?
10 million K
What is NOT an advantage of the Hubble Telescope over ground-based telescopes?
It is closer to the stars
Luminosity
Total amount of light that the star radiates each second
Gravitational Equilibrium
balance between the outward push of pressure and the inward pull of gravity.
On the main sequence, stars obtain their energy by
converting hydrogen to helium
HR Diagram: Largest Radii
Upper right
Lowest energy- highest energy:
Different categories of electromagnetic radiation
radio, infrared, visible light, ultraviolet, x-ray, gamma
Cluster ages can be determines from
main-sequence turnoff
Size of the neutron star
City
What temperature can helium fusion occur?
100 million K
What is the closest in mass to a white dwarf?
the sun
10-solar mass main-sequence star will produce a:
neutron star
Planetary Nebula
expanding shell of gas that is no longer gravitationally held tot he remnant of a low-mass star
What’s the upper limit to the mass of a white dwarf?
1.4 solar masses
How is time affected by gravity?
Time runs slower in places where gravity is stronger
Stages of life for a low-mass star:
Protostar, main-sequence, red giant, white dwarf
How many helium nuclei fuse together when making carbon?
3
How does gravity of an object affect light?
Light from a massive object will be redshifted
Pulsar:
an object that emits flashes of light several times per second or more, with near perfect regularity
What is the closest in size to a white dwarf?
Earth
White dwarfs are called so because
they are both very hot and very small
What happens after a helium flash?
the core quickly heats up and expands
How far is the sun from the center of the galaxy?
28,000 light-years
How did Edwin Hubble measure the distance to the Andromeda Galaxy?
applied the period-luminocity relation to cepheid variables
Diameter of the Milky way?
100,000 light-years
Why do we cal dark matter “dark”
Emits no or very little radiation of any wavelength
Dark Energy
the agent causing the universal expansion to accelerate
Methods for determining distance: nearest to farthest
parallax, main-sequence fitting, cepheid variables, Tully-Fisher, Hubble’s Law
Quasar:
Extremely bright center of a distant galaxy, thought to be powered by a massive black hole.
Spectral Sequence in order of decreasing temperature
OBAFGKM
Hubble’s Law
Recession velocity of a galaxy is directly proportional to its distance from us
Most large galaxies are:
Spiral or lenticular
Galaxy type most commonly found in large clusters
Ellipticals
What happens when a star exhausts its core hydrogen supply?
Its core contracts, but its outer layers expand and the star becomes bigger and brighter
How long does it take the sun to orbit the Milky Way Galaxy?
230 million years
