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Midterm 2 Review Questions with Answers

Astronomy & Astrophysics
Course Code
Stefan Mochnacki
Study Guide

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diameter: 100 000 lie and it has around 200 billion stars
distance between central bulge and sun: 28 000 light years away (around 2/3 from the centre)
Inverse square of light: closer= appears brighter
-apparent brightness-tells us how much fusion is going on in the star
-to calculate distance ^2 … dimmer by that much
10AU= 100, 1AU= 1
so the solar panel at 10AU would receive 1/20 the energy compared to if it were at 1AU or its
dimmer by 20watts per meter squared
luminosity depends on temperature and radius
in H-R diagram, most luminous are higher up
brightest in relation to radius – blue stars: higher luminosity
types of binary star systems: spectroscopic (Doppler shifts), visual (telescopes) and eclipsing
(eclipses and diff. in amount of light emitted)
most commonly used is eclipsing because its useful in estimating size, density, luminosity
and distance (can measure distance to other galaxies)
-has an error factor of less than 5%
Spectral classes: O B A F G K M (Oh Be A Fine Girl Kiss Me)- order of hottest to coldest
example: since O is the bluest or hottest, hydrogen electrons would be ionized (weak
absorption line), and would be weak in cool stars (not hot enough to excite)
-thus, strengths of absorption lines depend on the temperature of the star
darker the lines on stellar spectrum the moreabsorbed” the element is by the star
one way:
inverse square law for light: apparent brightness= luminosity/ 4(pi)(distance)^2
-first determine a stars apparent brightness then if we can measure its distance, we can
calculate luminosity
parallax (can only use for nearby stars) if the star position changes a lot then star is close,
if star position changes a little then star is distant
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