1. Astronomy

2. Theories of Formation of the Universe
Cosmology is the study of the universe, its current nature, and its origin and evolution.
Three Main Formation Theories:
Big bang theory
Steady state theory
Inflationary theory

3. Big Bang Theory
The Big Bang theory is the theory that the universe began as a point and has been expanding ever since. No explosion occurred.
Flash

4. Major evidence of Big Bang
If the universe began in a highly compressed state, as the Big Bang theory suggests, it would be filled with radiation.
As the universe expanded and cooled, the radiation would have been Doppler shifted to lower energies and longer wavelengths.
Cosmic background radiation, which was discovered in 1965, is background noise caused by weak radiation that comes from all directions in space.
This radiation is interpreted to be from the beginning of the Big Bang.

6. The Big Bang Model
Outward momentum of the universe’s expansion competes with the gravity of the universe.

7. Measuring Expansion Rate
An approach to determining the fate of the universe is to measure how much slowing has occurred so far in its expansion.
By measuring the redshifts of the most remote galaxies, it is possible for astronomers to determine the expansion rate long ago.
Astronomers have found that the rate of expansion is speeding up.

8. Steady State Theory
The steady-state theory proposes that the universe is the same as it has always been, has always existed, and new matter is being created as the universe expands maintaining its density.

9. Cosmology
Steady State Theory
Without the creation of new matter, the area within the dotted box would not contain 3 galaxies after a time.
The steady-state theory requires new matter to be added so that the area within the dotted box always contains 3 galaxies.

10. Big Bang vs. Steady State
Evidence currently leans in the favor of the big bang theory.
Proponents of the steady-state theory have not succeeded in explaining the cosmic background radiation.

11. Inflationary Theory
The inflationary theory is an extension of the big bang theory.
The inflationary theory proposes that the universe expanded very rapidly for a fraction of a second before settling into a more orderly expansion.

12. Inflation Theory
When the rate of expansion of the universe is known, it is possible to calculate the time since the expansion started, or the age of the universe. The age of the universe is currently said to be about 13 billion years old.

13. Basic Properties of Stars
Diameter of stars range from 0.1 to 100x diameter of Sun.
Mass of stars range from 0.01 to 20x the Sun’s mass.

14. Gliese 623b

17. Brightness
Apparent magnitude-rates how bright object appears to be; does not take into account distance.
Absolute magnitude-rates brightness of object from a distance of 10 pc (parsecs).

18. Luminosity
Luminosity is the energy output from the surface of a star per second.
The brightness we observe for a star depends on both its luminosity and its distance.

19. A spectrum is visible light arranged according to wavelengths.

21. Spectra of Stars
Stars are assigned spectral types in the following order: O, B, A, F, G, K, and M.
The classes correspond to stellar temperatures, with the O stars being the hottest and the M stars being the coolest.

22. Spectra of Stars
All stars, including the Sun, have nearly identical compositions—about 73 percent of a star’s mass is hydrogen, about 25 percent is helium, and the remaining 2 percent is composed of all the other elements.
The differences in the appearance of their spectra are almost entirely a result of temperature effects
B5 star
F5 star
K5 star
M5 star

23. Spectra of Stars Wavelength Shift
Spectral lines are shifted in wavelength by motion between the source of light and the observer due to the Doppler effect.
If a star is moving toward the observer, the spectral lines are shifted toward shorter wavelengths, or blueshifted.
If the star is moving away, the wavelengths become longer, or redshifted.
flash
If a star is moving toward the observer, the spectral lines are shifted toward shorter wavelengths, or blueshifted.
If the star is moving away, the wavelengths become longer, or redshifted.
flash

25. Spectra of Stars
The higher the speed, the larger the shift, and thus spectral line wavelengths can be used to determine the speed of a star’s motion.
Astronomers can learn only about the portion of a star’s motion that is directed toward or away from Earth.

26. H-R Diagrams
A Hertzsprung-Russell diagram, or H-R diagram, demonstrates the relationship between mass, luminosity, temperature, and the diameter of stars.
Absolute magnitude-vertical axis
Spectral type-horizontal

27. H-R Diagrams LINK
The main sequence, running from the upper-left corner to the lower-right corner, represents about 90 percent of stars.
Red giants are large, cool, luminous stars plotted at the upper-right corner.
White dwarfs are small, dim, hot stars plotted in the lower-left corner.

28. 2) Explain how redshifts and blueshifts indicate motion of objects.
Rate these questions as 1,2,3.
1-completely understand, write down answer to question
2-somewhat understand, write down what you can answer, but also write what you are still not sure of
3-don’t understand, write down what issue you think you have with the question.
1) Explain the basic properties of stars, magnitude, luminosity, composition, and surface temperature and how they are measured.
2) Explain how redshifts and blueshifts indicate motion of objects.

29. Basic Structure of Stars
Fusion
Inside a star, the density and temperature increase toward the center, where energy is generated by nuclear fusion.
Stars on the main sequence all produce energy by fusing hydrogen into helium, as the Sun does.
Stars that are not on the main sequence either fuse different elements in their cores or do not undergo fusion at all.

30. Basic Structure of Stars
The mass and the composition of a star determine nearly all its other properties.
Hydrostatic equilibrium is the balance between gravity squeezing inward and pressure from nuclear fusion and radiation pushing outward.
This balance, which is governed by the mass of a star, must hold for any stable star; otherwise, the star would expand or contract.

31. Stellar Evolution and Life Cycles
A star changes as it ages because its internal composition changes as nuclear fusion reactions in the star’s core convert one element into another.
As a star’s core composition changes, its density increases, its temperature rises, and its luminosity increases.
When the nuclear fuel runs out, the star’s internal structure and mechanism for producing pressure must change to counteract gravity.

32. Stellar Evolution and Life Cycles
A nebula (pl. nebulae) is a cloud of interstellar gas and dust.
Star formation begins when the nebula collapses on itself as a result of its own gravity.
As the cloud contracts, its rotation forces it into a disk shape.
A protostar is a hot condensed object that forms at the center of the disk that will become a new star.

34. Stellar Evolution and Life Cycles
Fusion Begins
Eventually, the temperature inside a protostar becomes hot enough for nuclear fusion reactions to begin converting hydrogen to helium.
Once this reaction begins, the star becomes stable because it then has sufficient internal heat to produce the pressure needed to balance gravity.
The object is then truly a star and takes its place on the main sequence according to its mass.

35. Life Cycle of Sun
What happens during a star’s life cycle depends on its mass.
When the hydrogen in its core is gone, a star has a helium center and outer layers made of hydrogen-dominated gas.
Some hydrogen continues to react in a thin layer at the outer edge of the helium core.

36. Life Cycle of Sun
The energy produced in the thin hydrogen layer forces the outer layers of the star to expand and cool and the star becomes a red giant.
While the star is a red giant, it loses gas from its outer layers while its core becomes hot enough, at 100 million K, for helium to react and form carbon.
When the helium in the core is all used up, the star is left with a core made of carbon.

38. Life Cycle of Sun A Nebula Once Again
A star of the Sun’s mass never becomes hot enough for carbon to react, so the star’s energy production ends at this point.
The outer layers expand once again and are driven off entirely by pulsations that develop, becoming a shell of gas called a planetary nebula.
In the center of a planetary nebula, the core of the star remains as a white dwarf made of carbon.

39. Rate these questions as 1,2,3.
1-completely understand, write down answer to question
2-somewhat understand, write down what you can answer, but also write what you are still not sure of
3-don’t understand, write down what issue you think you have with the question.
1) Explain what occurs in the core of a star. Specifically address the necessity of a equilibrium.
2) Describe the steps, in order, of the formation of a star that is the size of the Sun or less.

40. The Sun’s Life Cycle
A star that has less mass than that of the Sun has a similar life cycle, except that helium may never form carbon in the core, and the star ends as a white dwarf made of helium.
A white dwarf will eventually cool and no longer emit heat, becoming a black dwarf.

41. Life Cycles of Massive Stars
A massive star begins its life just as Sun-sized stars do, from a nebula up to red giant phase.
A massive star undergoes many reaction phases and produces many elements in its interior.
The star becomes a red giant several times as it expands following the end of each reaction stage.

42. Life Cycles of Massive Stars
As more shells are formed by the fusion of different elements, the star expands to a larger size and becomes a supergiant.
A massive star loses much of its mass during its lifetime.
White dwarf composition is determined by how many reaction phases the star went through before reactions stopped.

43. Life Cycles of Massive Stars
A star that begins with a mass between about 8 and 20 times the Sun’s mass will end up with a core that is too massive to be supported by electron pressure.
Once no further energy-producing reactions can occur, the core of the star violently collapses in on itself and protons and electrons in the core merge to form neutrons.
A neutron star results from the resistance of neutrons to being squeezed, which creates a pressure that halts the collapse of the core.

45. Life Cycles of Massive Stars
A neutron star has a mass of 1.5 to 3 times the Sun’s mass but a radius of only about 10 km.
Infalling gas rebounds when it strikes the hard surface of the neutron star and explodes outward.
A supernova (pl. supernovae) is a massive explosion in which the entire outer portion of the star is blown off and elements that are heavier than iron are created.

47. Life Cycles of Massive Stars
A star that begins with more than about 20 times the Sun’s mass will not be able to form a neutron star.
The resistance of neutrons to being squeezed is not great enough to stop the collapse, so the core of the star simply continues to collapse forever, compacting matter into a smaller and smaller volume.
A black hole is a small, extremely dense remnant of a star whose gravity is so immense that not even light can escape its gravity field.

49. Daily Motions Rotation-turning around one’s own central axis.
The Sun rises in the east and sets in the west, as do the Moon, planets, and stars as a result of Earth’s rotation.
One Earth rotation equals a day, but actually only takes 23 hr 56 min.

50. Annual Motions
The annual changes in length of days and temperature Earth’s revolution around the Sun.
Revolution-time it takes for an object to complete its orbit around another object.
The planets revolve around the Sun in an elliptical, or oval-shaped, pattern.

51. Earth’s Revolution
The Earth’s revolution around the Sun takes about days. To compensate for this extra day, we have leap day, February 29th, every four years.

52. Annual Motions The Effects of Earth’s Tilt
Earth’s axis is tilted relative to the Sun’s axis at approximately 23.5°.
As Earth orbits the Sun, the orientation of Earth’s axis remains fixed in space.
As a result of the tilt of Earth’s axis and Earth’s motion around the Sun, we experience seasons.

54. Annual Motions
When the Northern hemisphere is tilted toward the Sun, it experiences summer.
When the Northern hemisphere is tilted away from the Sun, it experiences winter.
Current seasons
experienced in
the N. hemisphere
are opposite in the
S. hemisphere.

56. Annual Motions Summer solstice-June 21st-Sun directly above 23.5°N
Winter solstice-December 21st-Sun directly above 23.5°S

57. Annual Motions Autumnal equinox-September 21st
Vernal equinox-March 21st
Both occur when Sun directly above equator-occur halfway between winter and summer solstice

58. Phases of the Moon
New moon-moon is between Earth and Sun. See the shadow of the moon.
Full moon-Earth is between Sun and Moon. Moon is fully lit by sunlight.
As the moon revolves around the Earth, from new to full moon, portions of the Moon are lit by the Sun.

60. Motions of the Moon Tides
The Moon’s gravity pulls on Earth along an imaginary line connecting Earth and the Moon, creating bulges of ocean water.
When the Sun and Moon are aligned, the result is higher-than-normal tides, called spring tides.
When the Moon is at a right angle to the Sun-Earth line, the result is lower-than-normal tides, called neap tides.

62. Solar Eclipses
A solar eclipse occurs when the Moon passes directly between the Sun and Earth and blocks our view of the Sun.

63. Lunar Eclipses
A lunar eclipse occurs when the full Moon passes through Earth’s shadow.
A lunar eclipse can happen only at the time of a full moon, when the Moon is in the opposite direction from the Sun.