Astr 102 Final

Question 1

Retrograde motion is ___ while prograde motion is ___

Answer 1

the apparent backward motion of planets with respect to fixed stars. Prograde motion is the apparent forward motion of the planets from respect to fixed stars.

Question 2

Aristotle determined ___

Answer 2

The SHape of the Earth

Question 3

Aristarchus deduced ___

Answer 3

Deduced the relative size and distances of the Earth, the Moon, and the Sun.

Question 4

Eratosthenes was the first person to ___

Answer 4

get a rough estimation as to the size of the Earth by measuring the distance between two cities from word of mouth. His estimate was in fact to large though.

Question 5

Hipparchus ___

Answer 5

Revised the findings of Aristarchus, and discovered that the Earth experiences precession.

Question 6

Ptolemy developed the ___

Answer 6

Ptolemaic model which is the geocentric model using epicycles to explain retrograde motion.

Question 7

Copernicus is the one who developed the ___

Answer 7

Heliocentric model.

Question 8

Tycho Brahe’s contribution to astronomy was ___

Answer 8

to observe the stars and made nightly observations for 25 years. He also hired Johannes Kepler.

Question 9

Johannes Kepler’s astronomical contributions were ___

Answer 9

Kepler’s three laws of planetary motion.

Question 10

Galileo made many contributions but five were very notable. What Were they?

Answer 10

Made many discoveries such as discovering Venus went through phases like the moon, discovered Jupiter’s moons, he discovered the moon was not perfect and similar imperfections to Earth, he discovered the Milky Way which was made up of countless stars, when observing the Sun he discovered imperfections known now as Sun Spots which also proved the moon wasn’t a perfect sphere like the moon.

Question 11

Describe how one would measure the size of the Earth.

Answer 11

Measure the difference in the lengths of shadows in two different cities.

Question 12

List and describe each of Kepler’s 3 laws.

Answer 12

1. Planets orbit the Sun in elliptical orbits.
2. The speed of a planet varies inversely with its distance to the Sun.
3. A planet’s orbital period is related to its distance from the Sun. (P2-a3).

Question 13

Describe how astronomers can use light to determine temperature. What would astronomers find if two stars had the same temperature?

Answer 13

Astronomers would look at the intensity of light as a function of wavelength. The position of the peak {towards the short-
wavelength – or blue end for high temperature} can be used to determine the temperature.

Question 14

What is the photosphere? What is the photosphere considered to be? What is its approximate temperature?

Answer 14

The photosphere is the bottom-most layer considered to be the surface of the Sun. the temperature is 4,500 - 6,000 K.

Question 15

What are sunspots and why do they occur? What is the temperature like in sunspots? What is the primary force for sunspots?

Answer 15

Sunspots are magnetically active regions of the sun whose temperature is less than the rest of the photosphere. The primary force of sunspots is magnetism.

Question 16

How long does a single sunspot last? How long do sunspot cycles last?

Answer 16

A single sunspot can last between hours and months. The sunspot cycle is 11 years.

Question 17

. Does the sun rotate? If so, describe its rotation.

Answer 17

The Sun does rotate. However, it is not a solid mass and thus, the poles rotate slower than the equator.

Question 18

How do electrons produce light? What does electron quantization refer to?

Answer 18

As electrons transition from an outer to an inner orbital, it releases energy. Quantization refers to the electrons absorbing or emitting only specific amounts of energy.

Question 19

Describe what an emission spectrum is and discuss why it is different than an
absorption spectrum.

Answer 19

An emission spectrum is a continuous black constant background with strips of color running through it, whereas an absorption background is a continuous bright background with dark lines running through it.

Question 20

How can astronomers determine the direction and speed of a star?

Answer 20

As astronomers collect the spectra of stars, they observe the position of spectral lines. Should the lines be blue shifted, that would indicate that the stars are moving towards us. If the lines are shifted to the red end of the spectrum that would indicate that the star is moving away from us. The greater the shift, the faster the speed.

Question 21

What is one significant discovery binary stars allows us to make?

Answer 21

Binary stars help allow us to determine the mass of stars

Question 22

What is the Hertzsprung-Russel Diagram? What is the significance of the HR diagram?

Answer 22

It’s a diagram that is a plot of the brightness of stars as a function of their temperature. It also shows that stars fall naturally onto certain areas. )

Question 23

What does the magnitude and luminosity of stars mean? How are they similar?
How are they different?

Answer 23

Magnitude refers to brightness, while luminosity refers to energy. They are both measures of light.

Question 24

What do apparent and absolute mean? How do those terms relate to magnitude and luminosity?

Answer 24

apparent means evident from a certain position or view. Absolute means the actual truth regardless of perspective. In terms of luminosity and magnitude, absolute luminosity and magnitude is the intrinsic amount they release, the apparent magnitude and luminosity is what we view here on Earth.

Question 25

What is the one most important parameter to the lifespan of a star? Why?

Answer 25

Mass. The more massive a star the faster it dies and burns its fuel

Question 26

What are the seven (7) spectral classes for stars? Why do stars have different spectral classes?

Answer 26

O B A F G K M (stars have different spectral types because of the differences in temperatures.

Question 27

What is Nucleosynthesis? Under what conditions does it exist?

Answer 27

Nucleosynthesis is the process by which smaller atoms are
combined to form larger atoms. This process occurs in stars
until they have reached the point of having iron in the core.
The process occurs past iron in supernova explosions.

Question 28

Describe what happens when a star exhausts its supply of hydrogen in the core.

Answer 28

It starts burning hydrogen in it’s shell. After that, it depends on the star.

Question 29

Why are stars able to produce fusion reactions?

Answer 29

Because of their mass.

Question 30

What Are White Dwarfs?

Answer 30

White Dwarfs are very hot small stars. (that are core remnants of stars whose fusion has stopped because of electron degeneracy).

Question 31

What is electron degeneracy? What role does it play in the evolution of a star?

Answer 31

Electron degeneracy (or Degenerate Electron Pressure) is the outward pressure exerted by the electrons resulting from their being “crowded together into too small of a volume”. The outward force works against the collapse of the white dwarf. It forces low- to medium-mass stars to stop their fusion process at a certain point. Those stars will then end their life as a white 
dwarf.)

Question 32

What is the Chandrasekhar limit?

Answer 32

The maximum size a white dwarf can have (1.4 MSun).

Question 33

What is a type II supernova? Why do some stars undergo a type II supernova and others do not.

Answer 33

Type II supernova is a supernova of a very massive star after its fusion process has reached a point where t has an iron core. (Some stars aren’t massive enough to fuse iron.)

Question 34

What is a neutron star, and how is Neutron Degeneracy related to it?

Answer 34

(A neutron star is a core remnant from a type II supernova. Neutron degeneracy is the outward force that works against the collapse of the neutron star.)

Question 35

What are Black Holes, and how does the Schwarzschild radius relate to them?

Answer 35

(Black holes are the core remnants of very massive stars that have undergone a type II supernova. These remnants are theorized to have a near 0 volume – near infinite density. The Schwarzschild radius is the minimum distance light can be from an object and still be able to escape. The black hole would have the core remnant that is actually smaller than its Schwarzschild radius.)

Question 36

How would one detect a black hole?

Answer 36

Although we can’t detect a black hole via light because it absorbs it, we can see its effect on surrounding bodies in space. This force is very strong and because we can’t detect it we assume it’s a black hole. You can also see the radiation from mass a black hole is attempting to absorb from its accretion disk.

Question 37

What is one significant discovery binary stars allows us to make?

Answer 37

We can measure the mass of stars.

Question 38

What is the Hertzsprung-Russel Diagram? What is the significance of the HR diagram?

Answer 38

(The Hertzsprung-Russel Diagram is a plot of the brightness of stars as a function of their temperature. It shows that stars fall naturally onto certain areas of the plot.)

Question 39

What is the Milky Way and why is it important to us?

Answer 39

The milky way is our galaxy and it’s important because it’s where we live.

Question 40

How can we determine the shape of the galaxy?

Answer 40

(When observing the Milky Way at night, one notices that the MW can be
described as a narrow band that stretches from one horizon to another.)

Question 41

Name and describe the different types of galaxies.

Answer 41

Name and describe the different types of galaxies.

(Spiral Galaxies: Pin-wheel shaped. Elliptical: Spherical to football-shaped. Irregular: Random shapes.)

Question 42

Briefly explain the Hubble Law and its significance to astronomy.

Answer 42

(If one were to graph the velocity of a galaxy as a function of its distance from us, one would see that the farther out a galaxy is, the faster it’s moving away from us. This suggests
that the Universe is expanding.)

Question 43

Explain the Hubble Constant, H, and its importance to Cosmology

Answer 43

(The Hubble constant is the slope of the line of the Hubble Law.
The Hubble Constant is related to the age of the Universe.)

Question 44

Describe the differences between an Open, Closed, and Flat Universe. What would be required to turn an Open Universe into a Closed Universe?

Answer 44

(In a gravity-dominated Universe: CLOSED: A universe where the expansion will stop and the collapse on itself. OPEN: A universe that will expand forever without significant slowing. FLAT: A universe that will expand forever but with significant slowing {but never stopping}.)