Introduction and The Nature of
Science
The Nature of Science
1. 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
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Practical, pragmatic, based on evidence
Healthy skepticism
2. Rational approach to questions
3. Dull slog through failures to reach a
conclusion
4. Answers lead to more questions
5. 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
Pseudoscience
e.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
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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