PES 106 – General Astronomy II – Exam #2 Study Guide
Measuring Stellar Properties; Stellar Evolution; Stellar Remnants
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Telescopes
What areas of the electro-magnetic spectrum are absorbed by our atmosphere? What telescopes are useful
from the ground? From space?
What is meant by the collecting power of a telescope? By its resolving power?
What are reflecting telescopes and what are their deficiencies?
What are refracting telescopes and what are their strengths and deficiencies?
Are radio telescopes reflectors or refractors?
Understand some of the problems with using telescopes, such as vibration, star tracking and light pollution
What is atmospheric scintillation
Measuring Stellar Properties
How are the distances to stars measured using parallax? How are parsecs, arc-seconds and parallax
related?
How are temperature and color related through Wein’s Law?
How are luminosity and distance related to brightness through the Inverse Square Law?
Know the difference between apparent magnitude and absolute magnitude.
Naming conventions (i.e., Alpha Centauri is the brightest star in constellation of the centaur)
5 orders of magnitude = 100 * brightness
How is stellar composition inferred from spectral absorption lines?
What are Balmer lines, and how are they affected by a star’s temperature?
Know the main spectral classes.
Red shifting (Doppler) measures the relative motion of stars and tells us that the stars near us have the same
motion and direction as Sol.
Spinning stars “fatten” their spectral lines, and we find that young stars rotate faster than Sol.
40% of observed stars are part of a binary system. From binary stars, we can directly measure their mass.
Know the distinction between the types of binaries – visual, spectroscopic, contact, eclipsing (double lines)
Radius: measured from the relationship between its luminosity, radius and temperature (the StefanBoltzmann Law), angular size (using interferometry), or eclipse duration (in eclipsing binaries).
Luminosity: measured from brightness & distance, or from characteristics of its spectrum.
Distance: measured from parallax, or by the method of standard-candles (what is standard-candles
method?).
H-R diagrams – relate {luminosity, brightness, or magnitude} to {temperature, color, or stellar class}.
o Stars may be ordered by radius (increasing from lower left to upper right) on this diagram.
o Stars may be grouped in luminosity classes on this diagram.
What percentage of stars reside on the main sequence?
Mass (for main sequence stars) is related to luminosity. On H-R diagrams, mass increases from bottom to
top.
Know the range of possible mass for a star.
Know the range of possible radius for a star.
Luminosity can be related directly to mass for main sequence stars.
The 5 Luminosity classes are based on the width of their absorption lines (due to density).
The 7 main Spectral Classes are based on the strength of their absorption lines (due to temperature).
more mass = more gravity = more energy to balance = greater luminosity
Luminosity classes – bright supergiants, supergiants, bright giants, giants, sub-giants, main sequence
What is the definition of a variable star? Where do they reside on an H-R diagram?
Cephids (short period 2-3 days) and Mira (long period 1-2 y) are examples of what type of star?
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Stellar Evolution
About how long do the stages of stellar evolution take? (formation, main sequence, death)
Which forces are in balance if a star is in hydrostatic equilibrium?
What are the steps in stellar formation? About how big are the structures during these steps?
Bi-polar flow (heat radiating away from the poles) is characteristic of which stage of stellar formation?
What is a Herbig-Haro object?
What is the definition of a main sequence star?
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PES 106 – General Astronomy II – Exam #2 Study Guide
Measuring Stellar Properties; Stellar Evolution; Stellar Remnants
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What is a T-Tauri star?
What is a brown dwarf?
On what characteristic of a star does its lifetime depend?
About what percentage of a star’s fuel is available for fusion in the core?
Bigger stars – more mass – more gravity – more internal pressure – more fuel burned – shorter life
What stages do small stars (< 10 solar masses) go through?
What stages do large stars (> 10 solar masses) go through?
What causes a planetary nebula?
How are the proton-proton chain (in small stars) and the CNO cycle (in large stars) similar?
What is nucleosysthesis?
Shells of heavier elements in the core of large stars – “ashes” from one layer become fuel for the next
Which element ends the fusion chain in large stars?
Why can neutrons be packed so tightly?
About how fast does the earth-sized iron core shrink to a neutron core (10 km), causing the collapse of a
large star?
When a massive star collapses, the core heats, exploding the star. What is this explosion called?
Characterize the amount of energy released from a supernova.
What property do the stars in a stellar cluster formed from the same stellar nursery have in common?
How is the turnoff point for the stars in a stellar cluster useful?
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Stellar Remnants
What causes white dwarfs to shine? What are they made of, mostly? How big are they?
Where do black dwarfs come from?
About how much would a cubic inch of neutron star material weigh on Earth?
How do normal matter and degenerate matter differ when compressed?
What happens to a white dwarf as more matter is added to it?
Adding mass beyond what limit causes a white dwarf to explode?
What causes a nova?
What causes a supernova of type I? What’s left after the explosion?
What causes a supernova of type II? What’s left after the explosion?
What is gravitational redshift?
How much would a cubic inch of neutron star material weigh on Earth?
What causes a pulsar to “pulse”, or brighten, in the radio spectrum?
The superfluidity in the core of a neutron star causes what remarkable property?
What are the temporary jumps in rotation speed of a neutron star called?
What is an accretion disk? How can it speed up the rotation of a neutron star?
Why is a black hole black? How can a black hole be detected?
The extreme density of stars, neutron stars and black holes cause space to do what?
On what properties of a star do the Schwartzchild radius and event horizon depend?
What are gravity waves and how are they detected?
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