Unit 1 other stuffs

Question 1

Describe what a theory is and how it differs from an hypothesis.

Answer 1

A theory is a tested and refined explanation while an hypothesis is an educated guess that
does not have the depth and breadth of a theory. Hypotheses are tentative while theories
have stood up to more careful scrutiny.

Question 2

Arrange the following objects by their distance from the Earth-
The M13 star cluster, Pluto, Saturn, the Pisces-Perseus supercluster of galaxies, the Andromeda
galaxy, the center of the Milky Way Galaxy, the star Betelgeuse.

Answer 2

1. (Closest) Saturn (0.000015 light years, ly)
2. Pluto (0.0006 ly)
3. Betelgeuse (640 ly)
4. M13 (22,000 ly)
5. Center of the Milky Way (26,000 ly)
6. The Andromeda Galaxy (2.2 million ly)
7. (Farthest) Pices-Perseus Super Cluster

Question 3

Proxima Centauri is 4.22 light-years away. The Sun is 8 light minutes away. Proxima Centauri is then ____ times farther away than the Sun. The solar system is about 1 light day across. The Milky Way galaxy is about 100,000 light-years across. The Milky Way is about ____ times larger than the solar system. The visible universe is about 14 billion lightyears across. The visible universe is then _____ times larger than the Milky Way.

Answer 3

277,000
36,500,000
140,000

Question 4

The sky is mapped out by a grid of two coordinates called ____ and ____. The_____ coordinate is divided into hours, minutes,
and seconds. Its zero point is the Vernal Equinox. The greatest value it can have is ____ hours. The____ coordinate is divided into degrees, minutes, and
seconds. Its zero line is the ____. The greatest value it can have is plus or minus ____ degrees.

Answer 4

• right ascension
• declination
• 24
• declination
• celestial equator
• 90

Question 5

Suppose you go outside after sunset and see the stars. You then arise before sunrise and see the stars again. How have they shifted and why?

Answer 5

The stars have all rotated to the west. The western-most stars have set and new ones have risen in
the east. This is because the Earth spins on its axis.

Question 6

Suppose you see the Moon in the sky on two successive nights. How has its position changed with respect to the stars on the second night? Why?

Answer 6

The Moon will be further to the east by about 12 degrees. This is because the Moon orbits about
the Earth

Question 7

A ___ day is defined as being the time interval between when the Sun is directly
overhead and is exactly 24 hours. A ____ day is defined as being the interval between
times when a star is directly overhead and is about 23 hours 56 minutes. This means that if a star crosses the meridian at 8:00 PM one night, the next night it will cross the meridian at ____

Answer 7

• solar, or synodic
• sidereal
• 7:56

Question 8

Why did the ancient people divide the sky into constellations?

Answer 8

Constellations were originally a means of preserving knowledge and legends that were passed
down from generation to generation among people who did not necessarily know how to read or
write.

Question 9

Why do modern astronomers

continue to use constellations?

Answer 9

We use them today to divide the sky into sectors like the states divide up the USA or like counties divide up a state.

Question 10

describe how the Sun relates to the Arctic and Antarctic circles

Answer 10

The Arctic and Antarctic circles are at 23.5 degrees from the north and south poles respectively. While the tropical zone is the latitude where the Sun can be seen directly overhead at the zenith,
north of the Arctic circle and south of the Antarctic circle are the zones where it is possible to go through a day without the Sun ever setting below the horizon in summer or rising above the horizon in winter

Question 11

What is unique about the Sun inside the tropical zone?

Answer 11

The Sun is seen at the zenith inside this zone.

Question 12

Explain how the Vernal Equinox can be both a time of the year and a place in the sky.

Answer 12

The Vernal Equinox is the location in the sky where the Sun crosses the celestial equator going north. Really, it is when the Earth is at the place in its orbit so that the Sun appears to be exactly
on the celestial equator in spring. It does so on March 21 so we refer to both the time and the place as the Vernal Equinox.

Question 13

Give two reasons why it is hot during the summer in the northern hemisphere

Answer 13

a) The Sun’s rays are more direct, depositing more energy per square meter than in the winter.
b) The days are longer.

Question 14

What is precession and how does it affect the north star

Answer 14

Precession is the slow, regular “wobble” of the Earth’s axis with respect to the stars. It causes the north celestial pole to change position, going in a circle with a period of 26,000 yrs.

Question 15

How dies precession affect when the constellations are

visible?

Answer 15

Because the pointing direction of the Earth’s rotation axis changes, in 13,000 years the northern hemisphere will tilt toward the Sun when the Earth is on the opposite side of its orbit from where
it is now in summer. Calendars are adjusted to keep the seasons on the same days of the years as they are now. So in 13,000 years summer will still be in July and winter in January. However the
night-time constellations will change and in 13,000 years the current winter constellations will
appear in July and the current summer constellations will appear in January.

Question 16

A Moon that is new and getting more illuminated every night, is in the ______ portion of its cycle. When we see exactly half illuminated it is a _____ Moon. After this it enters the _____ portion until the entire face is illuminated at the ____ phase. As it begins to decrease in
illumination, it is in the ____ portion until it is again half illuminated as a ___ Moon. It continues to decrease in illumination as a _____ Moon until it arrives again at the new Moon phase.

Answer 16

• waxing crescent
• first quarter
• waxing gibbous
• full Moon
• waning gibbous
• third quarter
• waning crescent

Question 17

Is the dark side of the Moon the same as the far side of the Moon? Explain your answer.

Answer 17

The dark side is the side facing away from the Sun. The far side is the side facing away from the Earth. As the Moon orbits the Earth the far side is always the same physical side but the dark side is not. The dark half constantly changes with the lunar phases. At new Moon the dark side is the near side and at full Moon the dark side is the far side.

Question 18

If you lived on the Moon would you see the Earth rise and set or would it stay in the same
place? Explain your answer

Answer 18

Since the Moon is in synchronous orbit with the Earth and keeps one face always pointed toward
it, you would always see the Earth in the same place in the sky.

Question 19

A __ eclipse occurs when the Moon passes into the Earth’s shadow. This can be either a
__ eclipse if the Moon is not completely within the umbra of the Earth’s shadow or a
__ eclipse if it is entirely obscured. These eclipses only occur when the Moon is at the __ phase.

Answer 19

• lunar
• partial
• total
• full

Question 20

A __ eclipse occurs when the Earth passes into the Moon’s shadow. These eclipses are called __ at places on the Earth that are inside the umbra of the shadow, __ at places that are inside the penumbra of the shadow and __ if the shadow umbra doesn’t touch the surface of the Earth at all.

Answer 20

• solar
• total
• partial
• annular

Question 21

These eclipses only occur when the Moon is
at the __ phase. The __ , which is the intersection of the plane of the Moon’s orbit with the plane of the Earth’s orbit, must be pointing at the Sun for an eclipse to occur. The yearly path that the Sun traces on the celestial sphere is called the ___ because this is the
only place where eclipses can occur.

Answer 21

• new
• line of nodes
• ecliptic

Question 22

Why is a total eclipse of the Sun visible only from certain parts of the Earth?

Answer 22

A total eclipse is where the umbra of the Moon’s shadow touches the Earth’s surface. It only touches specific places and not the entire surface, so total eclipses are visible only at those locations.

Question 23

Is a total eclipse of the Moon only visible from certain parts of the Earth? Why or why not.

Answer 23

A total eclipse of the Moon is when the entire lunar surface is in the umbra of the Earth’s
shadow. Being in the shadow, it will be dark no matter where on Earth you are looking from.
Of course since the Moon is only visible to half the Earth at a time, lunar eclipses also will only be visible to half the Earth as well.

Question 24

The speed of light in a vacuum is approximately _____ km/sec. This value was first measured accurately by _____ who used eclipses of the _____ of ____ for his estimate.

Answer 24

• 300,000
• Olaus Roemer
• moons of Jupiter

Question 25

The special theory of relativity predicts that nothing can travel faster than this speed. However, under what circumstances can it travel
slower than this?

Answer 25

If it is in a denser medium, such as glass, it will move slower. This change is speed is what causes light to refract.

Question 26

Order the types of electromagnetic radiation from longest wavelength to shortest
wavelength.

Answer 26

(longest) Radio, Microwave, Infrared, Visible Light, Ultraviolet Light, X-ray, Gamma-ray (shortest)

Question 27

A glowing blackbody produces a \_\_\_\_ spectrum of
electromagnetic radiation. If this radiation passes through a rarified gas cloud, then it will have \_\_\_\_ created in it. When the gas re-radiates the subtracted light, it
creates a(n) \_\_\_\_ spectrum.

Answer 27

• continuous
• absorption lines
• emission line

Question 28

Explain how individual atoms create both emission and absorption line spectra.

Answer 28

Emission line spectra arise from electrons falling from higher to lower levels in atoms of low density gasses. They jump to the high levels from either collisions caused by heating or by absorbing light from a continuous spectrum. When they absorb light, it is at the same energy and
hence the same wavelength, as the energy emitted when the electron fell down. But since absorption removes energy from the spectrum it creates an absorption line.

Question 29

Explain what a Doppler shift is and how it affects light from a galaxy that is going away
from us

Answer 29

A Doppler shift is the stretching or compression of wavelength when the emitting or receiving
sources are moving either toward or away from each other. Moving away causes the colors to
become redder

Question 30

How does a doppler shift affects light from a galaxy that is coming toward us

Answer 30

moving toward causes the colors to become bluer

Question 31

How does a Doppler shift affects light from a galaxy that is moving rapidly past us across the sky but not coming closer or farther.

Answer 31

moving across the sky
does not affect the wavelengths. So Doppler shifting only tells us motion toward or away from
us

Question 32

How much greater is the light-gathering power of a telescope with a 20 inch primary mirror than one with a 10 inch primary mirror?

Answer 32

(20/10)2 = 4

Question 33

How much greater is the resolving power of a telescope with a 20 inch primary mirror than one with a 10 inch primary mirror?

Answer 33

20/10 = 2

Question 34

Suppose you have a telescope with a focal length of 40 inches. What is the magnification
when using an eyepiece with a focal length of 2 inches?____. What is the magnification when using an eyepiece with a focal length of 0.5 inches? ____

Answer 34

• 20

- 80

Question 35

List one instrument we have built to observe the universe at Radio wavelengths
and describe what types of objects it is best at studying

Answer 35

The Very Large Array in New Mexico or the 105m steerable dish at Green Bank West
Virginia, etc. Radio telescopes study cool gas clouds. They can also be ganged together to form high resolution interferometers.

Question 36

List one instrument we have built to observe the universe at Infrared wavelengths
and describe what types of objects it is best at studying

Answer 36

The Spitzer Space Telescope. These study warm objects like brown dwarf stars, starforming
regions, planetary surfaces and interstellar dust.

Question 37

List one instrument we have built to observe the universe at Ultraviolet wavelengths
and describe what types of objects it is best at studying

Answer 37

The Extreme Ultraviolet Explorer (EUVE), the Galaxy Evolution Explorer
(GALEX) or Hubble Space Telescope. These study hot objects like hot stars and ionized gas clouds

Question 38

List one instrument we have built to observe the universe at X-ray wavelengths
and describe what types of objects it is best at studying

Answer 38

XMM-Newton or Chandra. These study very hot objects like accreting black holes,
exploding stars and their remnants, and active galactic nuclei.

Question 39

List one instrument we have built to observe the universe at Gamma ray wavelengths
and describe what types of objects it is best at studying

Answer 39

The Compton Gamma Ray Observatory (CGRO), or Swift satellite. This studies
gamma-ray bursts in the early universe and the most extremely hot objects such as exploding stars and active galaxy nuclei.

Question 40

Give three reasons why we orbit satellites to observe the universe

Answer 40

The atmosphere blocks high energy wavelengths, it blurs optical radiation, and it absorbs some radiation at all wavelengths even when it gets through.

Question 41

Describe how geocentric Ptolemy cosmology explains retrograde motion

Answer 41

In Ptolemy’s solar system, the Earth was at the center. The planets pivoted around a
small circle called an epicycle. This small circle moved around the Earth on a large,
perfectly round circle called a deferent. Retrograde motion occurs when the backward motion on an epicycle is greater than the forward motion along the deferent.

Question 42

Describe how heliocentric Copernicus cosmology explains retrograde motion

Answer 42

In Copernicus’ solar system, the planets travel
in circular orbits around the Sun. In this system retrograde motion results when the
Earth overtakes and passes a more slowly moving superior planet. When this happens
planets appear to reverse temporarily their usual eastward direction of motion, and move backwards to the west. It is an illusion, the
planet does not really go backwards.

Question 43

What is Kepler’s first law

Answer 43

Planets orbit in ellipses about the Sun, with the Sun at a focus.

Question 44

What is Kepler’s second law

Answer 44

A line connecting the Sun and planet sweeps out equal areas in equal times.

Question 45

What is Kepler’s third law and explain what it means

Answer 45

P^2 = a^3
. This means that the period of a planet, in years, when squared, equals the semimajor
axis, in AU’s, cubed.

Question 46

Describe 4 discoveries made by Galileo with his telescope.

Answer 46

• The moons of Jupiter
• Sunspots
• Lunar craters and mountains
• Venusian phases and changing angular size
• Rings of Saturn
• The Milky Way is made of individual stars

Question 47

Explain how Galileo’s observations of Venus proved the Copernican heliocentric cosmology was correct

Answer 47

Galileo was able to observe Venus going through a full set of phases, something prohibited by the Ptolemaic system which never allowed Venus to be fully lit from the perspective of the Earth. This observation essentially ruled out the Ptolemaic system, and was compatible only with
the Copernican system.

Question 48

Astronauts in an orbiting spacecraft have
not escaped the Earth’s gravity, so they have weight, yet we refer to them as being “weightless”. Why do they appear as if they have no weight?

Answer 48

They have weight and are falling toward the Earth. However, they are also traveling rapidly in a
perpendicular direction. This velocity carries them eternally beyond the horizon as they fall
downward. The result is that they “fall” in a circle without getting any closer to Earth. Since the capsule or shuttle is falling at the same rate, they appear weightless with respect to it.

Question 49

Explain how Isaac Newton’s law of gravity did away with the old notion of “quintessence”
and thus allowed for space to be completely empty

Answer 49

Before Newton’s law of gravity it was believed that planets were kept in their orbits by contact with quintessence: a material that filled all of space. Planets were like marbles embedded in glass
shells with the quintessence “glass” keeping them at their distance from the Sun. The law of gravity explained how planets could actually be always falling but still remain the same distance
away.