AST-A 100 Study Guide - Spring 2018, Comprehensive Midterm Notes - Wavelength, Watt, Water
AST-A 100
MIDTERM EXAM
STUDY GUIDE
Fall 2018
ASTRONOMY A100
Astronomy
- Assigns meaning to the sun traveling through
- Sky appears as a great hollow dome with stars on the surface
o This dome is referred to as the celestial sphere
▪ Zenith – Top of dome
▪ Horizon – Where dome appears to meet the earth
- Stars the sun and the moon all rise in the east and set in the west
- Looks like the dome of the sky is moving
- Objects in the sky appear to be at the same distance
Constellations
- Sky is divided into 88 regions around identifiable star patterns
- Patterns are only a matter of perspective and stars in constellations are far from each
other
Ptolemy
- 100 AD
- natural philosopher who proposed the geocentric model
o Seemed to accurately predict the movement of planets and sun
o New observations of apparent retrograde motion were hard to explain with this
model
o Used epicycles to explain retrograde motion
▪ Earth was still at center but said all planets also had their own orbit at the
same time
▪ Retrograde motion is the apparent backward motion of planets
- Natural philosophers demonstrated that the earth was a sphere as early as the 3rd
century BC
- Eratosthenes was the first to do an experiment with shadows to calculate the
circumference of the earth
o Step 1: Assume sun is very far away
o Step 2: Imagine two people at different latitudes on earth
o Step 3: Measure shadows
▪ One person has sun at zenith of sphere so no shadow
▪ Other person has shadow due to different location/relative time
Heliocentric Model
- Natural philosophers had proposed the heliocentric model as early as the 3rd century BC
- First model was made by Copernicus
- Explained APPARENT retrograde motion without epicycles
o Retogade otio does’t atuall happe
- Validated by Galileo
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find more resources at oneclass.com
- The planets move along the Ecliptic because they live in the plane of the solar system
Galileo
- Invented the telescope in the 1600s
- Carried out first observations of moons of distant planets
- Used observations of the phases of Venus to validate the heliocentric model of the Solar
System
Tycho Brahe
- In the 1500s before telescopes catalogued the motions of planets for 20+ years
Johannes Kepler
- Studied the catalogued motion of planets
- From studying planetary orbits, he derived three laws of planetary motion
o All planets orbit the sun in ellipses
▪ Aphelion – Place where planet is farthest from sun
▪ Perihelion – Place where planet is closest to sun
▪ Sun sits on one of the focus points
▪ Planet sits on the ellipse
o A line between the Sun and the planet will sweep out in equal areas in equal
time
▪ Plaets do’t oe at ostat speeds
▪ The closer the planet is to the sun, the faster it moves
▪ A planets orbital speed varies in such a way that a line joining the Sun and
the planet will sweep out an equal area each month
▪
o A planets orbital period squared is proportional to its semi major axis cubed
▪ P^2 = a^3
▪ Orbital period – Time it takes to travel once around the sun
Newton’s Laws of motion
- Object in motion stays in motion unless acted upon by outside force
- Force is proportional to acceleration (F=m*a)
- For every action, there is an equal and opposite reaction
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Assigns meaning to the sun traveling through. Sky appears as a great hollow dome with stars on the surface: this dome is referred to as the celestial sphere, zenith top of dome, horizon where dome appears to meet the earth. Stars the sun and the moon all rise in the east and set in the west. Objects in the sky appear to be at the same distance. Looks like the dome of the sky is moving. Sky is divided into 88 regions around identifiable star patterns. Patterns are only a matter of perspective and stars in constellations are far from each other. Natural philosophers demonstrated that the earth was a sphere as early as the 3rd century bc. Natural philosophers had proposed the heliocentric model as early as the 3rd century bc. Explained apparent retrograde motion without epicycles: ret(cid:396)og(cid:396)ade (cid:373)otio(cid:374) does(cid:374)"t a(cid:272)tuall(cid:455) happe(cid:374) The planets move along the ecliptic because they live in the plane of the solar system.
