Here and Now

Chapter 1

Science is not…

• A list of previously known facts about nature

• A list of equations handed down from Ancient times

Science• is a body of knowledge• is an ongoing human activity• has beginnings that precede recorded history

What is Science?

The SYSTEMATIC study of the Universe

Gather facts

Modify hypothesis Guess an explanation(Guess=hypothesis)

Test hypothesis

The Scientific Attitude

The scientific attitude is one of• inquiry• experimentation• willingness to admit error

The Scientific AttitudeFact

a close agreement by observers about the same phenomenon

Hypothesis• an educated guess presumed to be factual until

supported by experiment• scientific if there is a test to prove it wrong

Which of these is a scientific hypothesis?

A. The Moon is made of green cheese.

B. Atomic nuclei are the smallest particles in nature.

C. A magnet will pick up a copper penny.

D. Cosmic rays cannot penetrate the thickness of your Conceptual Physics Fundamentals textbook.

The Scientific AttitudeCHECK YOUR NEIGHBOR

Which of these is a scientific hypothesis?

A. The Moon is made of green cheese.

B. Atomic nuclei are the smallest particles in nature.

C. A magnet will pick up a copper penny.

D. Cosmic rays cannot penetrate the thickness of your Conceptual Physics Fundamentals textbook.

Explanation:

All are scientific hypotheses! All choices not only have tests for proving wrongness, but have been proved wrong. Nevertheless, they still pass the test of being a scientific hypothesis.

The Scientific AttitudeCHECK YOUR ANSWER

Which of these is not a scientific hypothesis?

A. Protons carry an electric charge.

B. Undetectable particles are some of nature’s secrets.

C. Charged particles will bend when moving in a magnetic field.

D. All of the above are scientific hypotheses.

The Scientific AttitudeCHECK YOUR NEIGHBOR

Which of these is not a scientific hypothesis?

A. Protons carry an electric charge.

B. Undetectable particles are some of nature’s secrets.

C. Charged particles will bend when moving in a magnetic field.

D. All of the above are scientific hypotheses.

Explanation:

If protons didn’t carry electric charge, they wouldn’t be deflected when crossing a magnetic field. This would be a test for showing the hypothesis wrong. So both A and C are capable of being proved wrong, which makes them scientific. Statement B, however, has no test for wrongness. It is reasonable speculation—but not a scientific hypothesis.

The Scientific AttitudeCHECK YOUR ANSWER

A scientific theory is a collection of ideas that explain a phenomenon in a way that is consistent with laws,

observations and experiments.

Understanding the Universe!!

Viking I Lander Picture from 1976

1999 Picture from the Mars

Pathfinder Lander

Note the remote-control rover,

Sojourner, next to a Martian rock

2004 Opportunity Landing Site – and tracks

We did it!! Huygens takes first images of Titan and survives the crash landing!!

http://www.esa.int/SPECIALS/Cassini-Huygens/index.html

Telescopes gather light emitted from objects in the

universe

Too Much to Comprehend!

The number of stars in the universe today is approximately equal to the number of grains of sand on all the

beaches of Earth!!

The numbers in astronomy are so large, and small, that astronomers use

scientific notation.100 = 1

101 = 10

102 = 100

103 = 1000 5.3 x 103 = 5,300

104 = 10,000 8.9 x 104 = 89,000

and, for small numbers

10-1 = 0.1

10-2 = 0.01 2.1 x 10-2 = 0.021

10-3 = 0.001 6.6 x 10-3 = 0.0066

Astronomical distances and sizes are very very very very large. So,

astronomers use different units.One “Astronomical Unit” (AU)

average distance between Sun and Earth

• 93,000,000 miles

• 150,000,000 km

• 1.5 x 108 km

Distance Light Travels in One Year is a “Light-year” (LY)

•9.46 x 1012 km

•63,000 AU or 6.3x 104 AU

•0.307 parsecs (pc)

At the scale of the size of a planet or moon we describe things in terms of kilometers (km)

At the scale of the Solar System distances are described in terms of the Astronomical Unit or AU (ave. distance from Earth to the Sun).

At the scale of the Milky Way Galaxy distances are described in terms of Light-years which is the distance light travels in one year.

Thousands of km

Astronomical Unit

A few to about 1,000 Light-years

10,000 to 100,000 Light-years

Millions of Light-years

Billions of Light-years

In this chapter, you will meet three essential questions about astronomy:

• Where are you in the universe?

• How does human history fit into the time scale of the universe

• Why should you study astronomy?

Guidepost

Where are You?

To find our place among the stars, we will zoom out from a familiar scene, to the

largest scales in the universe.

From each frame to the next, we zoom out by about a factor 100.

A Campus Scene

16 x 16 m

A City View

1 mile x 1 mile

The Landscape of Pennsylvania

100 miles x 100 miles

The Earth

Diameter of the Earth: 12,756 km

Earth and Moon

Distance Earth – Moon: 384,000 km

Earth Orbiting Around the Sun

Distance Sun – Earth = 150,000,000 km

Earth Orbiting Around the Sun (2)

In order to avoid large numbers beyond our imagination, we introduce new units:

1 Astronomical Unit (AU) = Distance Sun – Earth =

150 million km

The Solar System

Diameter of Pluto’s orbit: Approx. 100 AU

(Almost) Empty Space Around Our Solar System

Approx. 10,000 AU

The Solar Neighborhood

Approx. 17 light years

The Solar Neighborhood (2)

Approx. 17 light years

New distance scale:

1 light year (ly) =

Distance traveled by light in 1 year

= 63,000 AU = 1013 km

= 10,000,000,000,000 km

(= 1 + 13 zeros)

= 10 trillion km

Nearest star to the Sun:

Proxima Centauri, at a distance of 4.2 light years

The Extended Solar Neighborhood

Approx. 1,700 light years

The Milky Way Galaxy

Diameter of the Milky Way: ~ 75,000 ly

The Local Group: Our Cluster of Galaxies

Distance to the nearest large galaxies: several million light years

The Universe on Very Large Scales

Clusters of galaxies are grouped into superclusters.

Superclusters form filaments and walls around voids.

The number 7.14 x 106 is equivalent to:

1 2 3. 4 5

20% 20% 20%20%20%1. 7,140,000

2. 7,140

3. 0.00000714

4. 714,106

5. 75,684

Which of the following descriptions is a definition of an astronomical unit (AU)?

1 2 3 4 5

20% 20% 20%20%20%1. one ten-millionth of the

distance between the equator and the North Pole

2. the distance between the king’s nose and the tip of his middle finger

3. the distance between the sun and Proxima Centauri

4. the average distance between Earth and the sun

5. the distance that light travels in one year

What types of distances are typically listed in astronomical units (AU)?

1 2 3 4 5

20% 20% 20%20%20%1. Distances to stars

2. Distances between galaxies

3. Distances in the solar system

4. The diameter of the Milky Way Galaxy

5. The diameter of the universe

Which of the following lists is in order of increasing size?

1 2 3 4 5

20% 20% 20%20%20%

1. universe - Milky Way Galaxy - solar system

2. Milky Way Galaxy - solar system - universe

3. solar system - Milky Way Galaxy – universe

4. universe - solar system - Milky Way Galaxy

5. solar system – universe - Milky Way Galaxy

Consider the first letter of each of the eight planets’ names. How many entire planet names can be

unscrambled from these eight letters?

1. 0

2. 1

3. 2

4. 31 2 3 4

25% 25%25%25%