,,

2. • First day section 1.1 , 1.2, 1.3 and 1.6
•
Second day 2.1, 4.1,and 4.2
•
Third day 2.2, 2.4, 19.2
•
Fourth day 2.4, 3.1
•

3. First day section 1.1 ,
1.2, 1.3 and 1.6
• THE NATURE OF ASTRONOMY
•
Astronomy is defined as the
study of the objects that lie
beyond our planet Earth and the
processes by which these
objects interact with one
another.
•

4. THE NATURE OF
ASTRONOMY
• We will see, though, that it is
much more. It is also humanity’s
attempt to organize what we
learn into a clear history of the
universe, from the instant of its
birth in the Big Bang to the
present moment.

6. A cosmic inflation took place..after thebig
bang

7. expansion of
the universe
• For the next several billion years, the
expansion of the universe gradually
slowed down as the matter in the
universe pulled on itself via gravity.
More recently, the expansion has
begun to speed up again as the
repulsive effects of dark energy have
come to dominate the expansion of
the universe.

8. THE NATURE OF ASTRONOMY
Galaxy-- UDFj-39546284

9. some 480 million years
• The Hubble Space Telescope captured this image of an exceedingly
distant galaxy called UDFj-39546284. This object has a redshift of
z~10, meaning that it existed some 480 million years after the Big
Bang. Image via NASA/ ESA/ Garth Illingworth/ Rychard Bouwens/ the
HUDF09 Team

10. UDFj-39546284
• .

11. Galaxy GN-z11,
• Here’s another exceedingly distant (and therefore old) object,
captured by the Hubble Space Telescope in 2016. Galaxy GN-z11,
shown in the inset, is seen as it was 13.4 billion years in the past, just
400 million years after the Big Bang, when the universe was only 3%
of its current age. The galaxy is ablaze with bright, young, blue stars,
but looks red in this image because its light has been stretched to
longer spectral wavelengths by the expansion of the universe. Image
via NASA/ ESA/

13. produced using the Hubble telescope.
• MULTIPLE IMAGES of a distant quasar (left) are the result of an effect
known as gravitational lensing. The effect occurs when light from a
distant object is bent by the gravitational field of an intervening
galaxy. In this case, the galaxy, which is visible in the center, produces
four images of the quasar. The photograph was produced using the
Hubble telescope.

14. The hubble
telescope
• Hubble has two primary camera
systems to capture images of the
cosmos. Called the Advanced
Camera for Surveys (ACS) and the
Wide Field Camera 3 (WFC3), these
two systems work together to
provide superb wide-field imaging
over a broad range of wavelengths.

15. The hubble telescope
.

16. the cosmos evolves
• In considering the history of the universe, we will see again and again
that the cosmos evolves; it changes in profound ways over long
periods of time. For example, the universe made the carbon, the
calcium, and the oxygen necessary to construct something as
interesting and complicated as you.

18. Chandra
telescope
Illustration of Chandra

19. modern astronomy.
• Today, many billions of years later, the universe has evolved into a
more hospitable place for life. Tracing the evolutionary processes that
continue to shape the universe is one of the most important (and
satisfying) parts of modern astronomy.
•

20. .
These are the 19 known
galaxies where both Type
Ia supernovae and
individual Cepheid
variable stars... [+]
S.L. HOFFMANN ET AL.
(2016) APJ, V. 830, NO. 1

21. Section 1.2: THE NATURE OF SCIENCE
• Science is not merely a body of knowledge, but a method by which
we attempt to understand nature and how it behaves. This method
begins with many observations over a period of time.

22. Section 1.2: THE NATURE OF SCIENCE
• From the trends found through observations, scientists can model the
particular phenomena we want to understand. Such models are
always approximations of nature, subject to further testing.

23. Earth was the
center of the
universe
• As a concrete astronomical
example, ancient astronomers
constructed a model (partly
from observations and partly
from philosophical beliefs) that
Earth was the center of the
universe and everything moved
around it in circular orbits

24. Earth was the center of the universe

25. Aristotle,
• Aristotle, who lived from
384 to 322 BC, believed
the Earth was round. He
thought Earth was the
center of the universe and
that the Sun, Moon,
planets, and all the fixed
stars revolved around it.
Aristotle's ideas were
widely accepted by the
Greeks of his time.
Aristotle

26. Hipparchus
• . The exception, a century later, was
Aristarchus, one of the earliest
believers in a heliocentric or sun-
centered universe. In the 100s BC,
Hipparchus, the most important
Greek astronomer of his time,
calculated the comparative
brightness of as many as 1,000
different stars. He also calculated the
Moon's distance from the Earth.

27. The Geocentric Universe
• The Geocentric Universe
• The ancient Greeks believed that Earth was at the center of the
universe, as shown in Figure below. This view is called the geocentric
model of the universe. Geocentric means “Earth-centered.” In the
geocentric model, the sky, or heavens, are a set of spheres layered on
top of one another. Each object in the sky is attached to a sphere and
moves around Earth as that sphere rotates. From Earth outward,
these spheres contain the Moon, Mercury, Venus, the Sun, Mars,
Jupiter, and Saturn. An outer sphere holds all the stars. Since the
planets appear to move much faster than the stars, the Greeks placed
them closer to Earth.

28. Section 1.2: THE NATURE OF SCIENCE
• Science is not merely a body of knowledge, but a method by which
we attempt to understand nature and how it behaves. This method
begins with many observations over a period of time.

29. • From the trends found through observations, scientists can model the
particular phenomena we want to understand. Such models. are
always approximations of nature, subject to further testing

30. • As a concrete astronomical example, ancient astronomers
constructed a model (partly from observations and partly from
philosophical beliefs) that Earth was the center of the universe and
everything moved around it in circular orbits.

31. • At first, our available observations of the Sun, Moon, and planets did
fit this model; however, after further observations, the model had to
be updated by adding circle after circle to represent the movements
of the planets around Earth at the center.

32. • As the centuries passed and improved instruments were developed
for keeping track of objects in the sky, the old model (even with a
huge number of circles) could no longer explain all the observed facts.

33. • As we will see in the chapter on Observing the Sky: The Birth of
Astronomy, a new model, with the Sun at the center, fit the
experimental evidence better.

34. • After a period of philosophical struggle, it became accepted as our
view of the universe. When they are first proposed, new models or
ideas are sometimes called hypotheses.

35. • You may think there can be no new hypotheses in a science such as
astronomy—that everything important has already been learned.
Nothing could be further from the truth.

36. • Throughout this textbook you will find discussions of recent, and
occasionally still controversial, hypotheses in astronomy. For example,
the significance that the huge chunks of rock and ice that hit Earth
have for life on Earth itself is still debated

37. • And while the evidence is strong that vast quantities of invisible “dark
energy” make up the bulk of the universe, scientists have no
convincing explanation for what the dark energy actually is.
•
Resolving these issues will require difficult observations done
•

38. • Chapter 1 Science and the Universe: A Brief Tour
•
Page 13
•

39. • at the forefront of our technology, and all such hypotheses need
further testing before we incorporate them fully into our standard
astronomical models.

40. • This last point is crucial: a hypothesis must be a proposed explanation
that can be tested. The most straightforward approach to such testing
in science is to perform an experiment.

41. • If the experiment is conducted properly, its results either will agree
with the predictions of the hypothesis or they will contradict it. If the
experimental result is truly inconsistent with the hypothesis, a
scientist must discard the hypothesis and try to develop an
alternative.

42. • If the experimental result agrees with predictions, this does not
necessarily prove that the hypothesis is absolutely correct; perhaps
later experiments will contradict crucial parts of the hypothesis.