Introduction and The Nature of Science. The Nature of Science 1.Science: observation of the world and the constant testing of theories against nature,

Introduction and The Nature of Science

The Nature of Science1. Science: observation of the world and the

constant testing of theories against nature, with the requirement that everything that is to be called science must be testable • Practical, pragmatic, based on evidence• Healthy skepticism

2. Rational approach to questions3. Dull slog through failures to reach a

conclusion4. Answers lead to more questions5. What is a fact, law, hypothesis, theory?6. Can only address question that deal with

the natural world

Astronomy is the oldest science

Ionia – the birthplace of science

What science is not

Pseudosciencee.g. astrology

Limitations of Science

• Science cannot address supernatural phenomena– hypotheses must be testable and falsifiable and

experimental results must be repeatable

Theories in Science

• Broad in scope• Supported by a large body of evidence• Explain• Incorporates confirmed observations, laws, and

successfully verified hypotheses

e.g. Big Bang Theory

• Law – description of how a natural phenomenon will occur

• Fact – natural phenomenon repeatedly confirmed by observation, e.g. Venus takes 225 days to go around the sun

The Culture of Science

• Social activity– Cooperation and competition

Science, Technology, and Society

Technology applies scientific knowledge for some specific purpose

Astronomy

The study of the universe

“We are made of star stuff” Carl Sagan

The Universe

The totality of all space, time, matter, and energy

“The size and age of the Cosmos are beyond ordinary human understanding. Lost somewhere between immensity and eternity is our tiny planetary home. In a cosmic perspective, most human concerns seem insignificant, even petty.” Carl Sagan

"Why is the night sky dark?“

Olbers' Paradox: "Why is the night sky dark?“

• The reason that this question is so important is because it can tell us about the distribution of stars and galaxies in the universe.

• Consider the possibility that the universe is infinite and that it is filled with luminous objects (stars, and the galaxies that contain them). If this is true, then every sight line from the Earth will eventually intersect a bright object. This means that if the universe is infinite and contains an infinite number of bright objects, the night sky will be bright! Since the night sky is dark, this tells us that one of our assumptions about the universe is incorrect.

• We know that the night sky is dark, so that it means that sight lines from the Earth do not all end on sources of light. This could be due to several different possibilities:

• The universe is finite, that is, it ends at some point.

• The stars run out at large distances.

• There hasn't been enough time for the light to reach us from the most distant stars.

• We will find out that we can actually estimate the age of our universe. Because the universe is not very old, the answer is thought to be No. 3 listed above. Since light takes time to reach us, we can see only those objects that are near enough to us that their light has reached us.

• The Wikipedia Page on Olbers' Paradox

Introduction to Astronomy

Universe

Totality of all space , time , matter, and energy

Earth

• 15,000 km diameter

Sun

• 1,500,000 km diameter

1 light year

• a unit of length• distance that light travels in a vacuum in one

year• = 9.5 x 1012 or (9,500,000,000,000 km)

or (9.5 trillion)

Scientific Notation example: 567,000.

5.67 x 105 coefficient base exponent

1. The coefficient must be greater than or equal to 1 and less than 10.2. The base must be 10.3. The exponent must show the number of decimal places that the decimal needs to be moved to change the number to standard notation. A negative exponent means that the decimal is moved to the left when changing to standard notation.

M 81 (a galaxy)

• 100,000 light year diameter

A galaxy cluster

• 1,000,000 light years diameter

Parsec

• 1 parsec = 3.26 light years = 206264.8 AU = 3.086 x 1013 km.

Constellations

• e.g. Ursa major

The Celestial Sphere

Important terms

• Celestial poles – points where the Earth’s axis intersects the celestial sphere

• Zenith - direction pointing directly "above" a particular location

• Polaris – North star or pole star, very close to the north celestial pole

• Horizon - apparent line that separates earth from sky

Earth’s Orbital Motion

• We measure time by the Sun• From one noon to the next is a 24-hour solar day is a consequence of Earth’s rotation

The cause for the seasons?

The cause for the seasons

• The most misunderstood fact in astronomy!• Has nothing to do with the distance of the

Earth from the Sun• Is due to the tilt of the Earth’s axis of rotation

Seasonal changes

Earth’s orbit

• Motion of the Earth around the Sun, at an average distance of about 150 million kilometers, every 365.25 mean solar days

Moon Phases

• http://antwrp.gsfc.nasa.gov/apod/ap040829.html

Moon Phases

Eclipses

• when one celestial object moves into the shadow of another

e.g. when the Sun and Moon line up precisely when seen from Earth

Solar Eclipse

Solar Eclipse

Total Solar Eclipse

Partial Solar Eclipse

Annular Solar Eclipse

Lunar Eclipse

Lunar Eclipse

Eclipses

Distance Measurement

• Parallax - apparent displacement or difference in the apparent position of an object viewed along two different lines of sight