Astrophysics Sun/Stars Quiz

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Gravitational Contraction
The process in which gravity causes an object to contract, thereby converting gravitational potential energy into thermal energy.

This was a hypothesis proposed in the late 1800’s suggesting the Sun generates energy by contracting in size. However, geologists proved this wrong since the Earth was older than the suggested amount of time the Sun could shine for.

Gravitational Equilibrium
Describes a state of balance in which the force of gravity pulling inward is matched by the force of pressure pushing outward.
How does the Sun shine?
4.6 billion years ago, gravitational contraction made the sun hot enough to start nuclear fusion in its core. Ever since then, energy liberated by fusion has maintained the Sun’s gravitational equilibrium and kept the sun shining steadily
The total power output of an object, usually measured in watts or in units of solar luminosities
Blotches on the surface of the sun that appear darker than surrounding regions.

Best seen during solar maximum

Solar wind
A stream of charged particles ejected from the sun
The tenuous uppermost layer of the Sun’s atmosphere; most of the Sun’s X rays are emitted from this region, in which the temperature is about 1 million K.
But the density of this area is very low
Primary source of sun’s UV rays, 10,000 K
Visible surface of the sun, 6,000 K consists of gas far less dense than Earth’s atmosphere
Convection Zone
Energy in the solar core travels upward
Radiation Zone
Energy carried outward by photons of light
Nuclear fusion transforming hydrogen into helium v dense
Nuclear fission
Splitting a nucleus into two smaller nuclei
Nuclear fusion
Combining nuclei to make a bigger nucleus

Sun does this to make hydrogen into helium

Strong Force
One of the four fundamental forces; it is the force that hold atomic nuclei together
Proton-Proton Chain
The chain of reactions that causes the sun to fuse hydrogen into helium
Solar neutrino problem
Disagreement between the predicted and observed amount of neutrinos
Why do stars appear different from one another?
Differing in mass and different stages of their lives
Apparent brightness
The amount of light reaching us per unit are from a luminous object

Inverse square law with distance (if we viewed sun from 10x Earth’s distance, would appear 100x dimmer)

Parallax Angle
Parallax Angle
Half of the star’s annual back-and-forth shift

distance in parsecs = 1/p

p is parallax angle in parsecs

Approx. 3.26 light years. Distance to an object with a parallax angle of 1 arcsecond
Magnitude System
A system of describing stellar brightness by using numbers, called magnitudes, based on an ancient Greek way of describing the brightness of stars in the sky. This system uses apparent magnitude to describe a star’s apparent brightness and absolute magnitude to describe a star’s luminosity

Originally classified how bright stars looked to our eyes. (First magnitude – brightest; Sixth magnitude faintest)

Apparent Magnitudes
A measure of the apparent brightness of an object in the sky, based on the ancient system developed by Hipparchus
Solar Prominence
Gas trapped beneath loop of magnetic field lines connecting two sunspots
Solar Flare
Emission of X-ray and fast-moving solar particles, occurring in the vicinity of sunspots
Coronal Holes
Regions of the corona that don’t show up in X-ray images
Sunspot Cycle
11 year period between maximum and minimum number of sunspots
Solar Maximum
Time at which sunspots are most numerous
Solar Minimum
Time at which sunspots are least numerous/not visible at all
Total amount of power a star radiates into space
Solar Luminosity
Comparing luminosities to that of the sun (3.8*10^26 watts)
Absolute Magnitudes
Apparent magnitude of a star if it were 10 parsecs from the Earth
Spectral Type
Classification of stars according to temperature–determining OBAFGKM by spectral lines in a star’s spectrum
Annie Jump Cannon
Rearranged spectral classes, from A-Z to OBAFGKM
Showed that the differences in spectral lines reflected hydrogen ionization level of emitting atoms, which are related to changing temperatures (not different internal elements, as was previously thought)
Visual Binary
Pair of two stars seen distinctly rotating around each other
Eclipsing Binary
Pair of stars orbiting in our plane of sight

Helps determine masses, because orbit speed is related to mass of an object

Hertzsprung-Russell Diagrams
Hertzsprung-Russell Diagrams
Graph plotting stellar luminosities on one axis and spectral types (temperature) on the other

*stellar radii increases from high-temperature, low-luminosity (lower left) to low temperature, high luminosity (upper right)

Main Sequence
Location of most stars, upper left to lower right in HR diagram
Very large and very bright stars, above main sequence
Just below supergiants, smaller in radius and lower in luminosity
White Dwarfs
Small in radius (luminosity), high temperature
Luminosity Classes
I. Supergiants
II. Bright Giants
III. Giants
IV. Subgiants
V. Main Sequence
Main-Sequence Lifetime
Stage of star’s life at which it is fusing Hydrogen into Helium
Spectroscopic binary
One star orbiting another but not a visual or eclipsing binary. Must be measured using Doppler shifts (red shift –> moving away, blueshift –> moving towards us)
Pulsating Variable Star
Expanding and contracting star, fluctuating in luminosity.
Star Clusters
Form at about the same time
Are about the same distance from Earth

open= disc of galaxy, several thousand stars
globular=halo of galaxy, more than a million stars

Main Sequence Turnoff Point
Helps us identify age of a star cluster. At this point where stars stop consuming hydrogen, we can use the lifetime of these stars and label it as the lifetime of the star cluster.
Period-Luminosity relation
The longer a Cepheid pulsating variable star’s period, the greater their luminosity
Categories: Astrophysics