PHY 113 Study Guide - Spring 2018, Comprehensive Midterm Notes - Sun, Earth, Orbit

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12 Oct 2018
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PHY 113
MIDTERM EXAM
STUDY GUIDE
Fall 2018
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Chapter 0
What is astronomy, and
why should I care?
• Dictionary definition:
The branch of science that deals with celestial objects, space, and the physical universe as a
whole.
Scientific theories:
Must be testable
Must be continually tested
Should be simple (if possible) Should be elegant (if possible)
Scientific theories can be proven wrong, but they can never be proven right with 100
percent certainty.
Observation leads to theory explaining it.
Theory leads to predictions consistent with previous observations.
Predictions of new phenomena are observed. If the
observations agree with the prediction, more predictions can be made. If not, a new theory
should be made.
What fundamental assumption does science rely on?
Biblical Rooting for “Laws of Nature”:
“This is what the LORD says: ‘If you can break my covenant with the day and my covenant
with the night, so that day and night no longer come at their appointed time, then my
covenant with David my servant [...] can be broken and David will no longer have a
descendant to reign on his throne [....] If I have not made my covenant with day and night and
established the laws of heaven and earth, then I will reject the descendants of Jacob and
David my servant”
- Jeremiah 33:20-26 (NIV)
• In less formal terms:
Astronomy is the study of everything outside of
planet Earth! How big did God make the universe? What are other planets like? What are
stars and how far away are they?
Biblical Rooting:
“For since the creation of the world God’s invisible qualities —his eternal power and divine
naturehave been clearly seen, being understood from what has been made, so that people
are without excuse.” -Romans 1:20 (NIV)
“The heavens declare the glory of God;
the skies proclaim the work of his hands.
Day after day they pour forth speech; night after night they reveal knowledge.
They have no speech, they use no words; no sound is heard from them.
Yet their voice goes out into all the earth, their words to the ends of the world.”
-Psalm 19:1-4 (NIV)
In other words:
The Bible tells us that studying God’s creation in general (and the heavens in particular) tells
us about God’s nature. Studying the vast majesty of the universe helps us understand God’s
amazing power, His consistency, His complexity...
Chapter 1 Charting the Heavens
Scientific Notation
We deal with very large numbers in astronomy. It is often useful to use scientific notation to
express them. As examples, take some properties of Earth:
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Radius of Earth is about 6,400 km
1
Images © Bruce Bryson (www.wordwizz.com)
1. The Universe is much bigger than you or I can possibly imagine.
2. God created it all, from nothing!
à God is much bigger / more powerful than you or I can possibly imagine.
1.3 The ObviousView Simplest observation:
Look at the night sky
About 3000 stars visible at any one time;
Distributed randomly, but God designed our brains to find patterns, even in randomness
We group stars into constellations: Figures having meaning to those doing the grouping
Useful: Polaris, which is almost due north
Useless: Astrology, which makes predictions about individuals based on the star patterns at
their birth
Stars that appear close in the sky may not actually be close in space
Stars seem to be on the inner surface of a sphere surrounding the Earth
They arent, but can use two-dimensional spherical coordinates (similar to latitude and
longitude) to locate sky objects
The Night SkyDefinitions:
Celestial Equator:
extend the Earth’s equator out into space
Declination (Altitude):
angle above or below equator
Celestial Sphere
Positions in The Night Sky
Celestial Equator:
extend the Earth’s equator out into space
Right Ascension α (longitude): angular
position around the Earth.
RA uses odd units: “hours”, “min”, “sec”
Declination δ (latitude): angular position above or below equator.
1.4 Earths Orbital Motion Sun in the same place
again!solar day
Stars in the same place
again!sidereal day
Solar day > Sidereal day by ~ 4 minutes because of Earths rotation
(If we went by sidereal days, soon the time of day wouldn’t correspond to position of sun in
the sky)
Seasonal changes to night sky are due to Earths motion around Sun
Twelve constellations Sun moves through during the year are called the zodiac; path is
ecliptic
Precession (“wobble”): due to gravitational torque from sun/moon. Makes one complete
circle in about 26,000 years. (Bad news for astrology! Your “signis off by about a month)
Ecliptic is plane of Earths path around Sun; at 23.5° to
celestial equator
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