Astronomy 1010-HFall_2015Day-11

Planetary Astronomy

Course Announcements• 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.

The Saros Cycle…18 years 11.3 days

What Would You See on Mars?

Projected Eclipse Times Eclipse Path Point of Greatest Eclipse

Lat.: 36.9664° NLong.: 87.6639° W Total Solar Eclipse Duration of Totality: 2m40.1s

APSU Observatory Lat.: 36.5631° N

Long.: 87.3433° W Total Solar EclipseDuration of Totality: 2m23.4s

Projected Eclipse Times APSU Observatory

Lat.: 36.5631° NLong.: 87.3433° W Total Solar EclipseDuration of Totality: 2m23.4sMagnitude: 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.

Lecture – TutorialObserving Retrograde Motion

Law: pg 99Work 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 Kepler1571 - 1630

Johannes Kepler 1571 - 1630 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.

Earth, e = 0.017Nearly circular

SECOND LAWA line drawn from the planet to the Sun

sweeps out equal areas in equal timesorbital speed is not constant for an

ellipse only for a circleplanets move faster when near the Sun

(perihelion)planets move slower when they are far

from the Sun (aphelion)

SECOND LAWThe speed a planet travels during its orbit is

related to the distance from the starWhen the planet is near the sun the planet goes

faster than when the planet is farther from the sun

Planet travels fast herePlanet travels slow here