Transcript Day-11

Astronomy 1010-H
Planetary Astronomy
Fall_2015
Day-11
Course Announcements
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SW chapter 2 – due Monday 9/21; 2pm
How is the lunar observing going?
How is the sunset/sunrise observing going?
1st Quarter night – Mon. 9/21 -7:30pm – on campus
Exam 1: Mon. Sept. 21
This Week: APSU-OUR: Research & Creative Activity
Week. Events in the library 2:30-3:30 every day.
Solar Eclipses take hours to
develop but last only minutes
During a total eclipse the
Sun’s corona is visible
Predicting Eclipses
The Saros Cycle…18 years 11.3 days
What Would You See on Mars?
Exam-1 to here
Projected Eclipse Times
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Eclipse Path
Point of Greatest Eclipse
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Lat.: 36.9664° N
Long.: 87.6639° W Total Solar Eclipse
Duration of Totality: 2m40.1s
APSU Observatory
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Lat.: 36.5631° N
Long.: 87.3433° W Total Solar Eclipse
Duration of Totality: 2m23.4s
Projected Eclipse Times
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APSU Observatory
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Lat.: 36.5631° N
Long.: 87.3433° W Total Solar Eclipse
Duration of Totality: 2m23.4s
Magnitude: 1.008
Event
Date
Time (UT)
Alt
Azi (C1) : 2017/08/21
16:56:59.80
62.3°
149.7° (C2) : 2017/08/21 18:25:28.70
64.2°
198.9°
Max : 2017/08/21 18:26:40.50
64.1°
199.5° (C3) : 2017/08/21 18:27:52.10
64°
200.2° (C4) : 2017/08/21 19:52:25.50
53.4°
235.2°
Projected Eclipse Weather
Clarksville, TN
 From our
perspective on
Earth, it appears that
everything in the sky
moves and orbits us.
 Early astronomers
and philosophers
therefore crafted
mostly geocentric
models of the
universe to reflect
this.
 These models became greatly fixed in the
minds of astronomers for millennia.
 Politics and science can clash when cultural
mindsets refuse to be changed.
 Another point unwilling to be conceded was
the idea of “uniform circular motion.”
• Objects moved in perfect circles at uniform
speeds.
 As astronomers viewed the motions of the
planets, the models did not match the
observations.
 Complicated models were needed to explain
phenomena such as retrograde motion.
 Ptolemy developed a system with epicycles
in 150 CE that remained accepted for about
1,500 years.
 Copernicus was the
first to create a
mathematical model
with the Sun at the
center.
 Heliocentric model
with circular orbits.
 Could estimate
relative distances of
the planets from the
Sun and each other.
 Copernicus’s model could explain the
behavior of objects in the Solar System.
 The ordering of the planets could explain
how they sometimes interrupt their prograde
motion with retrograde motion.
Observing Retrograde Motion
Law: pg 99
 Work with a partner!
 Read the instructions and questions carefully.
 Discuss the concepts and your answers with one
another.
 Come to a consensus answer you both agree on.
 If you get stuck or are not sure of your answer, ask
another group.
 If you get really stuck or don’t understand what the
Lecture Tutorial is asking, ask one of us for help.
 Tycho Brahe spent
decades collecting
astronomical data
after building his
own observatory.
 Created his own
geocentric model
with the other
planets orbiting the
Sun, but with the
Sun orbiting Earth.
 Using Tycho’s data,
Johannes Kepler
came up with
empirical rules to
describe planetary
orbits in a
heliocentric system.
 Empirical science
describes how
something works,
not why.
Johannes Kepler
1571 - 1630
Johannes Kepler 1571 - 1630
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Known for -
1. First telescope observations of the
sun
2. First sun centered scientific model
of the solar system or universe
3. Being the world’s best naked-eye
astronomer
4. Creating first a theoretical model to
explain planetary motions
5. Creating first a theoretical model
for explaining gravity
Eccentricity, e
•how squashed or out
of round the ellipse is
•a number ranging
from 0 for a circle to 1
for a straight line
e = 0.02
e = 0.7
e = 0.9
Kepler’s Three
Laws of
Planetary
Motion
Kepler’s First Law: The orbit of a planet about
the Sun is an ellipse with the Sun at one focus.
What is the shape of Earth’s orbit
around the Sun?
Earth, e = 0.017
Nearly circular
SECOND LAW
 A line drawn from the planet to the Sun sweeps out
equal areas in equal times
 orbital speed is not constant for an ellipse only
for a circle
 planets move faster when near the Sun
(perihelion)
 planets move slower when they are far from the
Sun (aphelion)
Kepler’s Second Law: A line joining a planet and
the Sun sweeps out equal areas in equal intervals
of time.
SECOND LAW
 The speed a planet travels during its orbit is related
to the distance from the star
 When the planet is near the sun the planet goes
faster than when the planet is farther from the sun
Planet travels slow here
Planet travels fast here