ASTR 100 Study Guide - Fall 2018, Comprehensive Midterm Notes - Sun, Orbit, Earth
ASTR 100
MIDTERM EXAM
STUDY GUIDE
Fall 2018
• 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
find more resources at oneclass.com
find more resources at oneclass.com
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
find more resources at oneclass.com
find more resources at oneclass.com
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.