ASTR-1010ASTR-1010Planetary AstronomyPlanetary Astronomy

Day-2Day-2

3 X 5 Card Time3 X 5 Card Time

• Name (legibly)!!

• What is a planet?

Course AnnouncementsCourse AnnouncementsLabs are posted on-line. It is your responsibility to

print it our prior to coming to the laboratory.

Clarksville Astronomy Club meeting Tuesday Jan. 26 @ 7:30pm in the Sears Planetarium

Begin moon observations ASAP … you’ll need them in 2 weeks.

1st Quarter Observing – Monday Jan. 25 – 7:00pm

HOMEWORK (already)HOMEWORK (already)Homework Chapter 1: Due Friday Jan. 22. Get to it.

This tests whether your code works or not.

Chapter 1 lets you practice with the system.

EveryoneEveryone should have tried the SmartWorks site by now … not just the 30 people who are listed as logged on.

Homework Chapter 2: Due Monday Feb. 1

Beginning with chapter 2, you better read the text and THINK before you blindly answer questions.

Phases of the Moon LabPhases of the Moon LabStart observations of the moon ASAP. Record the date, time, angle from the sun and amount of illumination.

Moon Phase Observation FormMoon Phase Observation Form1.Record how much of the moon

you see by shading in the small circle

2.Record date and time

3.Record exactly what it was that you measured

4.Record the angle you measured

What if the sun is below the What if the sun is below the horizon? horizon? •Measure angle of moon from western horizon

(or 180° - angle of moon from eastern horizon)

•Record date, time and amount of illumination

•Go to website and look up time of sunsetSun & Moon Rise & Set Times

•Calculate how far the sun is below the western horizon by subtracting the sunset time from the observing time (as a decimal) and then multiplying the result by 15°

•Add the angle of the moon from the western horizon to the angle of the sun below the western horizon to get angle between sun and moon

What if the moon is on one What if the moon is on one side of the sky and the sun is side of the sky and the sun is on the other side of the sky?on the other side of the sky?

•Measure angle of the moon from western horizon

•Measure angle of sun from eastern horizon

•Subtract the two measurements from 180° to get the angle from the moon to the sun. In this case the moon is west of the sun.

•This will work moderately well until the two are close enough to measure directly.

How do you know which way is How do you know which way is east or west? Where’s the east or west? Where’s the

horizon?horizon?•College Street runs east/west

•direction towards sunrise (east) or sunset (west)

•compass (car or hand held)

•Horizon is along your arm held straight out from your side if you are standing straight up

This is CuteThis is Cute

Who Am I?Who Am I?

How I Got HereHow I Got Here

Time to Get BusyTime to Get Busy

Why Study Astronomy?

ConceptsConcepts

• Scale - # 1 ClassAction Site

Our Place in the UniverseOur Place in the Universe

Stockli, Nelson, HaslerGoddard Space Flight Center/NASA

Earth is a small planet…

… … orbiting a medium-sized star orbiting a medium-sized star ……

NASA/SOHO/ESA

… … in a galaxy of 100 billion stars …in a galaxy of 100 billion stars …

NASA/ESA/ STScI/Science Photo Library/Photo Researchers

… … which is one of billions of galaxies which is one of billions of galaxies ……

NASA/ESA/S. Beckwith (STScI) and the HUDF Team

in a universe that is 13.7 billion years old.

Compared to the universe, the Earth is less than a grain of sand on a beach

ConceptsConcepts

• Lookback Time - # 8 – ClassAction Site

A Vast UniverseA Vast Universe

• The universe is vast.• We need to handle great distances and long

times.• We can do this through the travel time of light.• Light travels 300,000 km every second.• We often use times to denote distances. For

example, we may say a friend’s house is two hours away.

• Astronomy is a time machine!

Light Travel TimesLight Travel Times

Light takes:

• 1¼ seconds to arrive from the Moon.

• 8.3 minutes to arrive from the Sun.

• 5.5 hours to get to Pluto from the Sun.

• 4.3 years (yr) to get to the nearest star.

• 100,000 yr to cross the galaxy.

• 2.9 million yr to get to the nearest big galaxy.

• 10 billion yr to come from distant galaxies.

In order to make sense of what we see we need a Cosmological Principal

An Important AssumptionAn Important Assumption

• The cosmological principle: “There is nothing special about our place in the universe.”

• On one level:– Our view from the Earth is not special or unique.– Distant objects should be like nearby ones which

we can study in detail.

• On another level:– Matter and energy obey the same physical laws

everywhere.

Concept Quiz Concept Quiz Principles Principles

Which of these is a restatement of the cosmological principle?

A. The universe is the same everywhere.

B. The same rules work everywhere in the universe.

C. There are no phenomena remaining to be discovered.

Retrograde Loop – Mars 2003

The (Quiet) Sun

A Dark Sky

Early Astronomy- HistoryEarly Astronomy- History

• If you go out to a dark location at night and look up (for a few years), what do you see?– Sun rises and sets every day; moves across

the sky– Stars rise and set every day; move at a slightly

different rate than Sun ==> Different stars visible at different times.

– Moon goes through monthly phases– Planets meander in a “mysterious manner”– No wind

Conclusions?Conclusions?

• The Earth is flat and motionless.

• But we know the Sun controls life (day/night)

• The Moon influences tides

• Stars are useful for timing agriculture

• Lots of ties to daily life and ritual

GreeksGreeks

• By ~500 B.C.E. the Greek society was well established and philosophy was began.

• Thayles (~624-546 BCE) origin of Greek science– What is the Universe made of?

• Plato & Aristotle - 3 tenets of modern science.– 1. Try to understand nature w/o supernatural expl.– 2. Mathematics, geometry.– 3. Power of reasoning from observations.– ==> Models

ConceptsConcepts

• Greek Universe – ClassAction Site

• Geocentric – swf – ClassAction Site

The Greek UniverseThe Greek Universe• Geocentric

• Celestial Sphere

• Ptolemaic model (100-170 A.D.)– Epicycles

• Aristarchus (310-230 B.C.E.)– Heliocentric – had it right! – But disagreed with Aristotle– Could not measure parallax!