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Unit 5: ASTRONOMY NOTES
~3,000 B.C.E. People build monuments aligned with
celestial objects.
What we see…
I. Motion of Celestial Objects
A. Definitions:
1. Celestial sphere = an imaginary sphere encircling the
Earth _______________________________________
__________________________________________________________________
2. Celestial Object = an object observable in Earth’s sky but outside its atmosphere.
 Examples: Sun, moon, planets, stars
 Terrestrial refers to objects that are _________________________________
such as ___________, ___________, ___________.
3. Constellation = __________________________________________________
__________________________________________________________________
 Do we see the same constellations at night all year long? Why or why not?
B. Daily Observations:
1. Apparent Motion of all objects: (counterclockwise/clockwise), (N, E, S, W) to (N, E,
S, W), moving at a rate of ______per hour (the speed of Earth’s rotation) in ______
shaped paths.
a. Where does the 15° come from?
i. There are _______ in a circle (or round planet), 360° divided by ____
hours= 15° per hour
2. EXCEPTION: Circum polar stars and Polaris : Polaris is located directly above the
spin axis of the Earth therefore it doesn’t appear to move but all other stars near it
appear to move in a COUNTERCLOCKWISE ______________ path around it.
C. Yearly Observations: The sun appears to take different arcs through the celestial
sphere during different times of the year.
1. In summer, the sun rises _________ of east and sets ________ of west.
a. Summer Solstice:
2. In winter, the sun rises ________ of east and sets ________ of west.
a. Winter Solstice:
3. On the equinox, the sun rises _____ east and sets ____ west.
a. Vernal (spring) equinox:
b. Autumnal (fall) equinox:
Sun’s path on a celestial sphere for Retsof, NY (42ºN)
The sun’s path for other important latitudes:
Things to remember: The altitude of Polaris = Northern Latitude, the altitude of the sun at noon on the
Equinox is 90º from Polaris, the winter and summer solstices are 23.5º from the equinox.
How we explained these motions: Assumptions of Early Models
II. Models of the Universe
A. Geocentric = _____________________________
1. The Planets
The usual motion of planets as they "wandered" on the
celestial sphere was eastward against the background
stars. This is called _______________________
However, it was observed that at times the planets moved
westward for some period on the celestial sphere; this
was termed _______________________
The episodes of retrograde motion were difficult to explain for early astronomers.
~280 B.C.E. Aristarchus hypothesizes that the Earth revolves around the Sun. He
provides first estimation of Earth-Sun distance. Does not have the mathematical skills
to test the hypothesis.
200 C.E. - Ptolemy proposes a geocentric universe. Perfect motion should be in
circles, so the stars and planets, being heavenly objects, moved in circles. However,
to account for the complicated motion of the planets, which appear to periodically
loop back upon themselves, epicycles had to be introduced so that the planets moved
in circles upon circles about the fixed Earth.
B. Better Predictions:
• ___________________________________________________________________
_______________________________________________________________
• The test of all knowledge is ____________________________
~ 1500 C.E. Several astronomers propose a Sun-centered Universe, including
Aryabhata, Bhaskara I (Indian mathematician astronomers) Ibn al-Shatir (Arab Islamic
astronomer) and Copernicus (European).
C. Old models no longer matched what was observed.
1. Heliocentric =____________________________
a. Explained phases of the moon and retrograde motion.
b. Rotation =_______________________________________________________
c. Revolution = _____________________________________________________
2. Proof for Heliocentric Model:
1. Foucault Pendulum: _________________________________________________
_____________________________________________________________________
2. Coriolis Effect : Rotation of the Earth causes deflection to the __________ in the
_______________ hemisphere and to the ________ in the ______________
hemisphere.
3. Still not matching observations because the model moved everything in circles!
D. Angular Diameter of Celestial Objects:
 Objects appear _______________ when they are _____________. Objects appear
_______________ when they are ________________.
III. Apparent Motions of the Sun
A. What causes the seasons?
B. You will need to memorize this chart!
Season
Date
Vertical Sunrise Sunset Daylight
Ray
Hours
December
23 ½ S
South of South
9
21
(Tropic of
East
of West
Capricorn)
March 21
0
Due
Due
12
(Equator)
East
West
June 21
September
23
Seasons Diagram:
23 ½ N
(Tropic of
Cancer)
0
(Equator)
North of North
East
of West
Due
East
Due
West
24 hours of light at
the north pole!
15
12
24 hours of darkness at the
north pole!
IV. The Moon
A. Satellite = _______________________________________________________
The moon is a satellite of Earth.
B. Phases of the Moon:
 Caused by __________________ of the moon around Earth
 Length of one cycle: __________ Length of one orbit around Earth: ___________
 Always seeing the same side of the moon due to equal ____________ and
_____________ of the moon.
 Waxing = __________________________________________________________
 Waning = __________________________________________________________
What earthlings see
2
The diagram to the right shows where the
moon would be in space to show the moon
phases named as seen from Earth, and the
times on Earth. What phases of the moon are
visible during the day?
3
1
4
8
5
6
7
C. Tides:
1. Cause: Gravitational attraction of the ________ and _________. Gravity pulls on
the oceans and the solid Earth.
2. Two per day: Highs on side of Earth where moon is, _________ is pulled toward
the moon and on opposite side from moon, _________ Earth is pulled toward the
moon. Lows are in between.
3. Earth _____________ so one location experiences ___ high tides and ___ low
tides per day.
4. a. Spring tide:
b. Neap tide:
The diagram to the right shows where the positions of the
moon, Sun and Earth to cause spring and neap tides. What
phases of the moon cause each? Which has more
gravitational pull on the Earth, the moon or the Sun?
D. Eclipses:
Lunar:
Solar:
**Why isn’t there an eclipse every full and/or new moon?
V. Orbits:
A. We need better data!
1600 - Tycho Brahe realized that if the Earth was moving about the Sun, then the
relative positions of the stars should change as viewed from different parts of the
Earth's orbit. But there was no evidence of this shift, called parallax. Tycho was not a
Copernican, but proposed a system in which the planets other than Earth orbited the
Sun while the Sun orbited the Earth.
• ________________________________________________________
• Best observations of planetary positions
• Hired someone else to help calculate model (wasn’t interested in math)
B. 1609 - Johannes Kepler discovered the key to building a heliocentric model. The
planets moved in ellipses around the Sun - known as the Laws of planetary
motion.
1. Kepler’s 1st law: _____________________________________________________
__________________________________________________________________
Eccentricity = _____________________________________________________________
Equation for eccentricity:
Eccentricity = 1 ____________________(what shape?)
Eccentricity = 0 ____________________(what shape?)
_______
_____________
__________________
_____________________
____________________
Drawing an Ellipse
Calculating Eccentricity
Formula (ESRT cover):
1. Measure between the thumbtacks (foci)
2. Measure the entire line from one edge to the
other (major axis)
3. Divide
What is the eccentricity of the ellipse below?
2.Kepler’s 2nd Law:_____________________________________________________
________________________________________________________________
Gravity
Force of gravity
Force of gravity
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
3. Kepler’s 3rd Law: ________________________________________________________
1609 - Galileo Galilei observes moons of Jupiter in support of the heliocentric model.
1687 - Newton: Laws of motion, law of universal gravitation, basis for classical
physics
1826 - Heinrich Wilhelm Olbers puts forth Olbers' paradox (Why is the night sky
dark?)
VI. The Solar System
A. Formation of the sun
o 4-5 billion years ago a _______________________________formed.
o Heat from collisions and pressure from the force of gravity caused the center of the
nebula to become hotter and denser.
o _________________________________ began and our sun was born.
o ____________ of the matter in the solar nebula became part of the sun
B.
Planets
 Formation of the planets
o ______________________________________________________________
______________________________________________________________
o Small bodies of matter (planetesimals) in the outer edges of the solar nebula
joined together to for larger bodies called protoplanets, these became planets.
Terrestrial planets: have land
Jovian Planets: gas w/ small cores
•
•
•
•
•
•
•
•
____________________
____________________
____________________
____________________
______________________
______________________
______________________
______________________
C. Other objects:
1. Asteroids:_______________________________________________________
–Rarely cross Earth’s orbit
–Most are in a belt between _______________________________________
–May have caused the ___________________________________________
2. Comets:_________________________________________________________
–Probably provided some of young Earth’s water
–“Tail” created by vaporization when they approach the Sun
–Examples: Halley’s – 76 year orbit (will be back in 2061)
3. Meteoroids: ___________________________________________________
–___________________________________ - Most burn up in the atmosphere
–If they reach the Earth’s surface are called __________________________
–Evidence of meteors on Earth: most craters are eroded away
D. Formation of Earth
1. Solid Earth
a. As the matter from the nebula came together, _____________________
_____________________________________________________________
» giving the planet 3 distinct layers: _________________________________
2. The atmosphere
a. volcanic eruptions released ___________________________________
b. Slowly bacteria and plants increased the oxygen levels to current levels.
c. Some of this oxygen formed _____________________________________
_____________________________________________________________
_______________________________________________________
3. The oceans
a. The earth cooled enough for___________________________________
__________________________________________________________
b. Approx. 3-3.5 billion years ago
c. Condensation fell as rain, which eventually formed our oceans.
d. Comets may also contributed to the water on earth.
1900 - The astronomer and mathematician Bessel finally measured the distance
to the stars by parallax. The nearest star (other than the Sun) turned out to be
about 25 million, million miles away! (By contrast the Sun is a mere 93 million
miles away from the Earth.)
1905 - Albert Einstein publishes the Special Theory of Relativity, positing that
space and time are not separate continuums.
1915 - Albert Einstein publishes the General Theory of Relativity, which requires
a finite spherical universe.
1922 - The Russian mathematician and meteorologist Friedmann realized that
Einstein equations could describe an expanding universe.
1929 - The American astronomer Hubble established that some nebulae (fuzzy
patches of light on the night sky) were indeed distant galaxies comparable in size
to our own Milky Way.
Hubble discovers the red shift with distance. If Doppler shift caused this redshift
then it meant stars / galaxies were moving apart. This is interpreted as evidence
that the universe is expanding.
VII. The Universe
A. Electromagnetic Spectrum (ESRT p. 14)
1. Which type of electromagnetic radiation has the longest wavelength?_______
2. In which list are the forms of electromagnetic energy arranged in order from longest
to shortest wavelengths?
(1) gamma rays, x rays, ultraviolet rays, visible light
(2) radio waves, infrared rays, visible light, ultraviolet rays
(3) x rays, infrared rays, blue light, gamma rays
(4) infrared rays, radio waves, blue light, red light
3. Light’s Fingerprints
a. When white light passes through a glass prism, it separates it into colors
b. _________________________________________________________________
c. This is the visible part of the electromagnetic spectrum
4. Spectra
a. Spectroscope: an instrument that divides visible light into colors.
b. Types of spectra – Continuous, Bright line (Emission) - Used to ID elements, and
Absorption - Used to ID stars
c. Hubble and other astronomers had observed that ______________________
_____________________________________________________________
What Hubble expected (object at
rest)
What Hubble saw - redshift (object
moving away)
d. Doppler shift
i. ________________________________________________________________
__________________________________________________________
ii. ________________________________________________________________
________________________________________________________
Redshift
Blueshift
iii. If everything is _____________________ that means that it is
____________________________________________________________
iv. Hubble figured that this meant the ________________________________
v. If it is, then __________________________________________________
_______________________________________________________________
B. Stars
1. Feuled by _____________ ___________.
2. Closest star to us is ____________.
3. Stars are born, live and die.
4. Classified based on ________________________ and __________________.
ESRT page 15.
C. The Sun
1. Structure of the Sun
• Core
o Temperature:15,000,000°C
Enormous pressure and heat converts
matter into energy through
________________________
• Turns Hydrogen into Helium
2. Solar Activity
a. Solar Wind
o electrically charged particles that
stream out into space through holes
in the sun’s corona.
o _____________________
________________________
b. Sunspots
o ______________________
____________ within the photosphere
caused by powerful magnetic fields
o ___________________________________
 low in 2008, next low 2019
c. Prominences
o cloud of glowing gasses that arches high above the sun’s surface
d. Solar Flares
o Sudden, violent eruption of electrically charged atomic particles from the sun’s
surface.
e. Auroras
o __________________________________________________________________
____________________________________________________
o Occur more strongly just after peak in sunspot cycle