ASTR 100 Study Guide - Fall 2018, Comprehensive Midterm Notes - Sun, Orbit, Earth

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ASTR 100
MIDTERM EXAM
STUDY GUIDE
Fall 2018
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Astronomical Unit (AU)
o Average distance between the Earth and the Sun
o 93,000,000 miles
Light Year (ly)- Not used by astronomers
o A unit of distance not time
o Distance light travels in one year
Speed of light (c) = 3x10^5 km/s
1 ly= 9.5x10^12 km
Parsec (pc)- preferred
o 206265 AU
o 3.26 light years
o 1 pc= 3.09x10^13 km
Scales of the universe
o Field width is about 17 ly
o 10 stars in about 17 ly across
o Nearest star
Alpha centauri
4.2 ly away
o Only a handful of stars are visible
o If the sun is a golf ball in chicago then alpha centauri would be in New York City
o Gas Clouds between the stars are called the Interstellar Medium
Rarified gas (1 atom per 1000 cubic centimeters)
Forms new stars
Dominated by hydrogen
Our galaxy
o Massive collection of stars, gas, and dust
Has about 100 billions stars
Gravity holds it together
o Band of “Milky” light
Gives it the name
100,000 ly in diameter
o Sun is in the disk of the galaxy
⅔ of the way out from the center
2.8x10^4 ly from the center
o Is a barred spiral galaxy
We are found in the Orion Arm
Next Interior arn is the Sagittarius Arm
Next exterior arm is Perseus Arm
Arms named after constellations
o Center of the galaxy
Very dense stellar region
Has a massive black hole
o Local group
Our galaxy is a part of about 50 over members in the group
One other galaxy (Andromeda) is in this group
o Andromeda Galaxy
About the mass of the Milky Way galaxy
Has numerous satellite galaxies
Celestial Sphere
o Stars may be many times further away than others and moving through space in
different directions
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o The sky above us appears as a sphere which rotates from East to West
o Stars and planets appear fixed on a sphere
The sky and it’s motion
o Earth’s rotation causes the stars to move in a predictable manner
o Easterly rotation makes us perceive the stars as moving westward
o Stars rise in the east, moves westward, and sets in the west
Geocentric Reference Frame
o Earth’s rotation defines the rotation axis
Intersection of rotation axis and the celestial sphere defines the celestial
poles
Celestial poles appear stationary to an observer on Earth
o The celestial equator
The midpoint between the north and south celestial poles
The Earthbound Observer
o Horizon
Plane of the ground meets the celestial sphere
Observer and time dependent
o Zenith
The point on the celestial sphere directly above the observer
Observer and time dependent
o Nadir
The point on the celestial sphere directly beneath the observer
Observer and time dependent
o Cardinal points
North Point
South Point
o Meridian
Line from North Point through the NCP, Zenith and South point
Observer and time dependent
o The bowl diagram rule
Latitude dependency of the Bowl Diagram
Angle between North Point the observer and the NCP equals your
latitude
o Polaris
North star
Appears stationary
Other stars circle polaris
o Angle between the north point and the north celestial pole is equal to your
latitude
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Document Summary

If two stars differ by one magnitude, then one is about 2. 5 times brighter than the other. If their magnitudes differ by a value of two, then one is 2. 5 x 2. 5 (2. 5)^2 times brighter: greek astronomers. Interpreted as 2 bodies orbiting saturn: milky way, appeared to the human eye as a milky band of light across the sky, phases of venus, disproved the ptolemaic model. Inherited tycho"s detailed observations copernican model: published astronomia nova in 1609, contains the first 2 of 3 laws of planetary motion, laws of planetary motion, 1st, planets follow elliptical orbits. Isaac newton discovered that white light is composed of different colors: composed of many different colors, emitted, reflected, absorbed, light as a particle, light meter reading, count the number of baseballs that strike detector, light as a wave. Interstellar reddening: gives sunsets a red color, stellar structure.

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