AST 1001 Study Guide - Fall 2018, Comprehensive Midterm Notes - Sun, Solar System, Scattering
AST 1001
MIDTERM EXAM
STUDY GUIDE
Fall 2018
AST 1001: Explore the Universe Lecture Notes
09/05/18
Lecture goals:
1. What is our place in the universe?
a. Earth is a planet in our solar system. The sun and the other visible stars belong to a
huge collection of stars known as the Milky Way Galaxy. On larger scales, we see
chains sheets, and clusters of galaxies separated by huge empty spaces.
2. How did we come to be?
a. Birth of the Universe: The expansion of the universe began with the hot and dense
Big Bang. The cubes show how one region of the universe has expanded with time.
The Universe continues to expand, but on smaller scales gravity has pulled matter
together to make galaxies.
b. From the observed rate of expansion we deduce an age of ~14 billion years~
c. STAR “LIFE CYCLE”: Galaxies make possible the formation of stars, and recycle
material through generations of stars.
3. What are we made of?
a. Atoms (4.6%)
- 98% is Hydrogen (H) and Helium (He)
- 2% in everything else (heavy elements or metals)
- << 0.1% of the Universe in metals
b. Dark Matter (23%)
c. Dark Energy (72%)
d. We are made primarily of carbon, iron, nitrogen
4. How can we know what the universe was like in the past?
a. Light travels at a finite speed (300,000 km/s)
b. At great distances, we see objects as they were when the universe was much younger.
c. Distance and age of the Universe are related.
• Star- a large, glowing ball of gas that generate heat and light through nuclear fusion.
• Solar (Star) System- a star at the center and all the material that orbits it, including its
planets and moons.
• Planet- a moderately large object that orbits a star; it shines by reflected light. Planets
may be rocky, icy, or gaseous in composition.
• Moon (or satellite)- any object that orbits a planet. Ex. Moon orbits the Earth
• Asteroid- a.k.a. minor planets; a relatively small and rocky object that orbits a star. Non-
spherical (gravity)
• Comet- a relatively small and icy object that orbits a star
*chemical composition determines the difference between an asteroid and comet. Also
comets are usually further away, while asteroids are closer
• Galaxy- a great island of stars in space, all held together by gravity and orbiting a
common center.
• Universe- the sum total of all matter and energy; that is, everything within and between
all galaxies.
find more resources at oneclass.com
find more resources at oneclass.com
• Light-Year- the distance light can travel in 1 year → about 10 trillion kilometers (6
trillion miles)
*Unit of distance!
• We can only see up to 14 billion light-years away, because that is the maximum time that
light has to reach us. NO, we cannot see the entire universe.
09/10/18
Q. The size of the solar system reduce by a factor of 10 billion; the Sun is now the size of a
large grapefruit (14 cm diameter). How big is Earth on this scale?
A. a pinhead
• The Sun to Earth distance: 150 million km
• Moon to Earth distance: 450,000 km
• Pluto to Sun Distance: 6 billion km
• The Milky Way has about 100 billion stars
• 1 Month=1.2 billion years
• 1 Day=40mm today
• 1 Second= about 440 years
• We’re moving with the Earth in several ways and at surprisingly fast speeds; EARTH
rotate round its axis once everyday
• .Earth orbits the Sun (revolves) once every year.
- At an average distance of 1 AU = 150 million km
- With Earth’s axis tilted by 23.5 degrees (pointing to Polaris)
- Rotates the same direction it orbits, counter-clockwise as viewed from the north pole
• We are orbiting at a speed of over 100,000 km/hr
• Our Sun moves randomly relative to the other stars in the local solar neighborhood
- At typical relative speeds of more than 70,000 km/hr
- But stars are so far away that we cannot easily notice their motion
• Galaxies move within the universe by being carried along with the expansion of the
universe.
• The farther away places are in space, the faster they are moving away
• Hubble discovered that…
- All galaxies outside our Local Group are moving away from us
- The more distant the galaxy, the faster it is racing away.
• Conclusion: We live in an expanding universe
• With the naked eye, we can see more than 2000 stars as well as the Milky Way
• Milky Way- a band of light that makes a circle around the celestial sphere; it is our view
into the plane of our galaxy.
• Constellation- a region of the sky, not a pattern in the sky; 88 constellations fill the entire
sky.
• The Local Sky (is not the celestial sphere)
- Zenith: The point directly overhead (altitude=90 degrees)
- Horizon: All points 90 degrees away from zenith (altitude=0 degrees)
- Meridian: Line passing through zenith and connect
• Latitude- position north or south of equator
• Longitude- position east or west of prime meridian (runs through Greenwich, England)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Lecture notes: what is our place in the universe, earth is a planet in our solar system. The sun and the other visible stars belong to a huge collection of stars known as the milky way galaxy. On larger scales, we see chains sheets, and clusters of galaxies separated by huge empty spaces: how did we come to be, birth of the universe: the expansion of the universe began with the hot and dense. The cubes show how one region of the universe has expanded with time. 98% is hydrogen (h) and helium (he) 2% in everything else (heavy elements or metals) Planets may be rocky, icy, or gaseous in composition: moon (or satellite)- any object that orbits a planet. Moon orbits the earth: asteroid- a. k. a. minor planets; a relatively small and rocky object that orbits a star. Non- spherical (gravity: comet- a relatively small and icy object that orbits a star.
