### Earth, Moon, Stars, Sun, Solar System and Galaxy

Some of the topics discussed in this chapter include planet earth, moon, stars, sun, solar system and galaxy.

The average distance between the Earth and the Sun is defined as being one

Astronomical Unit or AU

Consider even the Earth and the Moon. About how many moons would fit across the Earth? (No penalty for wrong guessing.)

4 Moons

The Earth’s diameter is about 13,000 km while the distance between the Earth and the Moon is about 390,000 km. How many Earth’s would fit between the Earth and the Moon?

30

What types of distances are typically listed in astronomical units:

Distances in the solar system

The Sun is

a star.
b. 1 AU from Earth.
c. more than 100 times the diameter of Earth.

List the objects from smallest to largest

Earth, Solar System, Milky Way, Galaxy Clusters

If the nearest star is 4.2 light-years away, then

the light we see left the star 4.2 years ago.

3.9×105 is the same as

390 Thousand

Light takes about 8 minutes to travel from the Sun to Earth.
Light takes about 40 minutes to travel from the Sun to Jupiter.
How many astronomical units is Jupiter from the Sun?

4.95

Light takes about 8 minutes to travel from the sun to Earth.
Mars is approximately 1.5 AU from the Sun.
How many light minutes is Mars from the Sun?

12

One light year is the:

Distance that light travels in one year, approx 10 to the 13th power or 63,000 AU

Our Galaxy is part of

A cluster of a few dozen galaxies. Galaxies are commonly grouped together in such clusters.

Solar System

The sun and its planets

Our Galaxy

Contains our solar system plus billions of other stars and whatever planets orbit around them – in other words, billions of solar systems

Universe

Includes everything: all of the galaxies, stars, and planets
Including our own galaxy
Very small part of it, our solar system

Clusters are grouped into

Superclusters
These are linked to form long filaments and walls outlining nearly empty voids

The nearest star is

4.2 ly from the sun

Galaxies

Contain many billions of stars
Our galaxy is about 80,000 ly in diameter and contains over 100 billion stars

Astronomers describe the brightness of stars using what?

The magnitude scale, a system that first appeared in the writings of the ancient astronomers.

The north pole of the earth is located at the top of this picture.

If you were located on the boundary between daylight and darkness on the right side of the earth in this picture, would you be experiencing sunrise or sunset? Why?

Sunset. Because Earth rotates counterclockwise when viewed from above Earth’s North Pole.

A region of the sky containing a recognizable pattern of stars is called a

Constellation

The apparent visual magnitudes of four stars are listed below. Of these four stars, which one appears dimmest in the sky?

2.8
Compared to -1.2
-0.5
+0.7

The apparent visual magnitude of a star is 7.3. This tells us that the star is

Not visible to the unaided eye

How many arcseconds are there in one degree?

3600

Objects A and B both have the same angular size, and Object A is closer to us than object B. Which of the following can we conclude?

Object A is dimmer than Object B

What is the name of the brightest star in the night sky?

Sirius

The _____is the dividing the celestial sphere into northern and southern hemispheres.

celestial equator

Constellations that do not set and are always above our horizon are called ____ constellations.

Circumpolar

The imaginary boundary between the earth and sky is called the

Horizon

The point on the celestial sphere directly above the north pole of the earth is called the

North Celestial sphere

The ____is the point on the celestial sphere directly above the south pole of the Earth.

South celestial

The point of the sky directly overhead us

Zenith

What is the celestial sphere?

The celestial sphere is a representation of how the entire sky looks as seen from Earth

ou live at a latitude of 730 N. What is the angle between the northern horizon and the north celestial pole?

73

Suppose an astrophotographer hands you a picture with star trails taken looking toward the north celestial pole. If the star trails are 1/6 of a complete circle, about how many hours was the picture exposed?

4

The apparent path of the Sun through the constellations as viewed from Earth is called the

ecliptic

Match the description of the Sun’s position with the name of the special point on the Sun’s path.

The sun is crossing the celestial equator moving north = Vernal Equinox

The sun farthest north = Summer Solstice

The sun is crossing the celestial equator moving south = Autumnal Equinox

The sun farthest south = Winter Solstice

On which of the following days will the Sun appear on the celestial equator.

Autumnal Equinox

The gradual wobble that changes the orientation of earth’s axis in space is called

Are we ever able to view the Sun at our zenith in Los Angeles?

No, we are too far north

Which of the following best describes why we have seasons on Earth?

The tilt of Earth’s axis causes different portions of the Earth to receive more or less direct sunlight at different times of year.

The maximum tilt of the northern hemisphere toward the sun occurs ________.

on the first day of summer

The point on the moon’s orbit farthest from Earth is called

apogee

The region of a shadow that is partially shaded is called the

penumbra

The ___ cycle is the roughly 18-year cycle over which the pattern of eclipses repeats.

Saros

The region of a shadow that is totally shaded is called the

Umbra

The point in the moon’s orbit closest to the Earth is called

Perigee

The points where the moon’s orbit crosses the ecliptic are called

Nodes

If there is a new moon today, in how many days will the next full moon occur?

14 or 15

From the selections below, which one explains why we cannot see a new moon in our sky?

It is too close to the Sun in our sky

What will the phase of the moon be 10 days after a first quarter moon?

waning gibbous

At about what time will the moon rise during a last quarter phase?

midnight

The moon always shows nearly the same face toward earth because ______

the Moon rotates once in the same amount of time that it takes the Moon to orbit Earth

The time for the moon to repeat its cycle of phases is equal to

its synodic period

The Full Moon always occurs

when the Moon is directly opposite the position of the Sun

By approximately how many degrees does the moon’s position change from one day to the next?

13 degrees

During which phase of the moon do lunar eclipses occur?

Full moon

During a total lunar eclipse

The moon is completely in the umbra of the Earth’s shadow and appears to be reddish in color.

The moon’s orbit is not a perfect circle. Therefore sometimes the moon is closer to the Earth than at others.
Perigee is the point in the Moon’s orbit that is closest to the Earth.
Apogee is the point in the Moon’s orbit that is farthest from the Earth.

The angular size of the Moon in our sky will be _________.

greatest at perigee and smallest at apogee

A totally eclipsed moon glows coppery red because

red light is better able to pass completely through Earth’s atmosphere and reach the moon

Scientific thinking is

based on everyday ideas of observation and experiments

Why is Ptolemy important to the history of astronomy?

Developed the first model of the solar system that made sufficiently accurate predictions of planetary positions.

The apparent backward motion of a planet along the celestial sphere is called

According to Copernicus’ model of the solar system a planet undergoes retrograde motion when

Earth passes the planet while they orbit.

Which of the statements below were not made by Copernicus in his formulation of a heliocentric model?

a. The celestial spheres do not have just one common center.
b. The motions of the Sun are not its motions, but the motion of the Earth.
c. All of the spheres revolve around the Sun.
d. What appears to be forward and retrograde motion of the planets is natrually due to their motion around us.
It’s D!

What feature of Aristotle’s model of the universe was included in the model proposed by Copernicus?

uniform circular motion Yes. Copernicus still believed that the planets moved in uniform circular motion.

The apparent shift of a nearby object against the background of more distant stars is called

parallax

Which of the following was a contribution by Tycho Brahe?

Detailed observations

When Tycho observed the new star of 1572, he could detect no parallax. Why did that result undermine belief in the Ptolemaic system?

This star is farther away than the moon and thus the heavens are not perfect and unchanging.

v

Galileo challenged the idea that objects in the heavens were perfect by

observing mountains on the Moon

In his observations of the planet Venus, what was seen by Galileo that could only be explained by Venus revolving around the Sun?

A complete cycle of phases

Galileo discovered that the planet Jupiter

Has moons orbiting it

Kepler’s 1st law states that the orbits of the planets are

Ellipse with the sun located at one focus

Where is the focus of the ellipse?

Off center and along the longer axis

According to Kepler’s 3rd Law, when compared to planets closer to the Sun, those farther away __________

Take longer to revolve around the sun

According to Kepler’s 2nd Law, at which position will a planet move fastest in its orbit around the Sun?

Perihelion

Who used his laws of motion and the Universal Law of Gravity to derive the orbits of the planets, thus explaining WHY the planets moved as they do?

Newton

The number of wave cycles that pass in one second is called the

Frequency of the wave

Light is one form of _____

The distance between two successive peaks of a wave is called a

wavelength

A particle of light is called a

Photon

Red light waves have _____
wavelength, _____
frequency, and travel at _____
speed compared to blue light waves when both are in space.

longer, lower, the same

Light waves with a wavelength of 800 nm would be in which part of the electromagnetic spectrum?

infrared

Which two forms of electromagnetic radiation are useful for observing the stars from the ground?

visible

The units of frequency are given in

cycles per second

The ability of a telescope to make an image appear larger is called the

magnifying power

Telescopes which use a concave mirror to focus incoming light from the stars are called

reflecting telescopes

The ability of a telescope to collect light is called the

light gathering power

The large lens or mirror that is used to focus the light in a telescope is referred to as the ____ lens or mirror.

primary

The brightening of the night sky by light scattered from aritificial outdoor lighting is called

light pollution

The ____ refers to the atmospheric conditions on a given night.

seeing

Which of the following best describes the focal length of a telescope?

It is the distance from the lens or mirror to the image formed of a distant light source.

What does resolving power measure?

The angular size of the smallest features that can be viewed with the telescope.

What is CCD?

It is an electronic detector that can be used in place of photographic film for making images.

Which of the following statements best describes the principle advantages of telescopes over eyes?

Telescopes can collect far more light with far better angular resolution.

What is the purpose of adaptive optics?

It reduces blurring caused by atmospheric turbulence for telescopes on the ground.

Suppose you have two small photographs of the Moon. Although both look the same at small size, when you blow them up to poster size one of them still looks sharp while the other one becomes fuzzy (grainy) looking.
Which of the following statements is true?

The one that still looks sharp at large size has better (smaller) angular resolution than the one that looks fuzzy.

The angular separation of two stars is 0.1 arcseconds and you photograph them with a telescope that has an angular resolution of 1 arcsecond. What will you see?

The photo will seem to show only one star rather than two.

Which of the following best describes why radio telescopes are generally much larger in size than telescopes designed to collect visible light?

Getting an image of the same angular resolution requires a much larger telescope for radio waves than for visible light.

Which of the following is not an advantage of a telescope in space over ground-based telescopes?

It is closer to the stars.

Which power of a telescope is the least important?

magnifying power

We measure the temperature of the stars using the ____ temperature scale.

Kelvin

What is absolute zero?

The temperature at which no more heat energy can be extracted.

Atoms contain three types of particles. In the nucleus there are positively charged ____ as well as ____
which have no charge. Orbiting the neucleus are negatively charged _____
.

Proteins, Neutrons, electrons

The lowest possible energy level an electron can occupy is referred to as the ____
state, while higher energy levels are called ____ states.

Ground, excited

The chemical element of an atom is determined by the number of _________ it contains.

Protons

Carbon-14 is an example of an isotope of Carbon. In this case, fourteen is the number of ___________ in the isotope.

protons and neutrons combined

Considering the transitions in a hydrogen atom, which transition results in the emission of a photon with the shortest wavelength?

n=5 —-> n=1

An atom that has fewer electrons than protons is called ________.

An ion

Which of the following can be determined by examining the spectrum of a star?

(Check all that apply)

Choose all that are correct
a. constellation
b. chemical composition X
c. diameter
d. mass
e. surface temperature X

According to the laws of thermal radiation, hotter objects emit photons with

shorter average wavelengths

Suppose you want to know the chemical composition of a distant star. Which piece of information is most useful to you?

the wavelengths of spectral lines in the star’s spectrum

Which of the following statements is not true regarding the Sun?

It has a spectral class of F2

Betelgeuse is the bright red star representing the left shoulder of the constellation Orion.

All the following statements about Betelgeuse are true. Which one can you infer from its red color ?

Its surface is cooler than the surface of the Sun.

What conditions produce an absorption line spectrum?

a hot solid, liquid, or high-density gas

Examine the figure shown here and consider the following absorption line spectra of four stars.

Star W has medium strong hydrogen lines and weak ionized calcium lines.
Star X has medium strong hydrogen lines and medium strong helium lines.
Star Y has weak hydrogen lines and strong ionized calcium lines.
Star Z has weak hydrogen lines and strong ionized helium lines.

List these stars in order of surface temperature from highest to lowest.

Z, X, W, Y

Suppose that you take the spectra of several stars and identify the 656 nm line of hydrogen. You then measure against the reference spectrum on the same image and find that some of the 656 nm lines are shifted due to the Doppler effect. Of the following shifted locations of this line, which one is that of a star that is moving away from us at the highest speed?

star E at 659 nm

If a certain star emits radiation that has a peak wavelength of 550 nm, the temperature of the star is

5300

The bright, visible surface of the Sun is called the

Photosphere

The outermost layer of the Sun’s atmosphere is called the _____and is made of extremely hot very thin gasses.

Corona

The layer of the solar atmosphere between the visible surface and the corona is called the

chromosphere

The mottled appearance of the Sun’s surface caused by rising currents of hot gas and sinking currents of cooler gas is called

granulation

____are blotches on the Sun’s surface that appear darker than the surrounding regions.

sunspots

______ are composed of ionized gas trapped in a magnetic arch rising above the surface of the Sun. When seen along the edge of the Sun, they appear pink in color. However, when seen against the Sun’s bright surface they appear as dark _____

prominence, filaments

The Sun’s mass is about _________ times that of the Earth.

300,000

What is caused by the effect known as limb darkening.

The Sun appears dimmer at the edge and brighter at the center

The Sun’s surface churns with a bubbling pattern called grannulation. Why?

We are seeing hot gas rising and cool gas falling due to the convection that occurs beneath the surface.

What effect does the formation of negative hydrogen ions in the sun’s photosphere have on solar observations?

The extra electron absorbs different wavelength photons making the photosphere opaque.

As one moves outward from the photosphere to the corona, what happens to the temperature and the density of the gases?

The temperature of the gases increases

The density of the gases decreases

What is responsible for the sunspots on the Sun’s surface?

the sun’s magnetic field

What is the source of the sun’s changing magnetic field?

the differential rotation of the sun and convection beneath the photosphere.

What is the net result of the proton-proton chain?

4 hydrogens are fused into 1 helium + energy

Which statement best describes what was called the solar neutrino problem?

Early experiments designed to detect solar neutrinos found them, but in fewer numbers than had been expected.

Which of the following formulas can be used the calculate the amount of energy produced by the mass lost during nuclear fusion?

E = m c2

The proton-proton chain is ____

the specific set of nuclear reactions through which the Sun fuses hydrogen into helium

What heats the chromosphere and corona to high temperatures?

fluctuating magnetic fields from below that transport energy outward

Enter the spectral classes in order from hottest to coolest.

Put NO SPACING between the letters. For example:

WEISFUN

OBAFGKM

The properties of ____ binary systems are detected by examining a light curve.

eclipsing

A ____ binary system in which both stars can be observed distinctly as they obit each other.

visual

The total amount of energy a star radiates in one second is called its

luminosity

A pair of stars which orbit each other is called a _____star system.

binary

We can detect the binary nature of a _____ binary star system by the dopler shifts in its spectral lines.

spectroscopic

If Star A is closer to us than Star B, then Star A’s stellar parallax is

larger than that of Star B.

32.6 light-years

According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples?

Its apparent brightness will decrease by a factor of 9.

At what distance must a star be to have its apparent magnitude equal to its absolute magnitude?

1 AU

Which magnitude gives the most information about the physical nature of a star?

absolute bolometric magnitude

A star has an apparent magnitude of 3.0 and is located at a distance of 2.5 pc.

If this star were located at the standard distance of 10 pc, it would appear to be ___
to us.

Therefore its absolute magnitude will be ____
3.0.

Dimmer, greater than

Place the colors of the stars in order from hottest to coolest.

Blue, white, yellow, orange, red

Stars with the same spectral class will have the same ____

surface temperature

The spectral classes of several stars are given below.

List the stars in order from hottest to coolest.

Hottest to Coolest
B9, A1, F0, F6, G2, K3, K4, M

Can a cool star be more luminous than a hot star?

Yes, if the cool star is larger than the hot star.

The axes on a Hertzsprung-Russell (H-R) diagram represent ____

Luminosity and surface temperature

Rank the following stars from the H-R diagram in order of temperature from coolest to hottest:

Arcturus, Deneb, Spica, Sun, Wolf 1346

Coolest to hottest
Arcturus, Sun, Deneb, Wolf 1346, Spica

Rank the following stars from the H-R diagram in order of size from largest to smallest:

Antares, Barnard’s Star, Deneb, Procyon B, Sirius A

Antares, Deneb, Sirius A, Barnard’s star, procycon B

Rank the following stars from the H-R diagram in order of luminosity from brightest to dimmest:

Barnard’s Star, Betelgeuse, Pollux, Spica A, Sirius B

Brightest to smallest
Betelgeuse, Spica B, Pollux, Sirius B, Barnard’s Star

The luminosity class of the star Alphard is II which means that

Alphard is a bright giant.

Each choice below lists a spectral type and luminosity class for a star.
Which one is a red supergiant?

Spectral type M2, luminosity class I

Two stars with the same luminosity class will have the same luminosity.

False

What is the distance to a star that has an apparent magnitude of 1.5 and an absolute magnitude of -3.5?

100

Which of the following statments best describes the gas pressures inside of stars?

The gas pressure is greatest at the center and decreases toward the star surface.

The CNO cycle is a series of steps which occur in high mass stars that results in the fusion of __

hydrogen into helium

Which stars produce most of their energy by the CNO cycle?

upper main-sequence stars

Which of the following stars will spend the most time as a main sequence star?

1 solar-mass star

Which property of the star directly indicates the rate at which energy is produced inside that star?

Luminosity

Why is there a lower mass limit of 0.08 solar-masses for main-sequence stars?

Objects below this mass are not hot enough to fuse normal hydrogen.

Why is there an upper mass limit for main-sequence stars of about 100 solar masses?

Objects above this mass fuse hydrogen too quickly and cannot stay together.

What percentage of a stars total fusion lifetime is spent as a main sequence star?

90%

Calculate many years will a star with a mass of 0.7 Msun spend on the main sequence?

24.4 billion years

What happens when a main-sequence star exhausts its core hydrogen fuel supply?

The core shrinks while the rest of the star expands.

What is a helium flash?

The sudden onset of helium fusion in the cores of some giant stars.

As the Sun leaves the main sequence to become a giant, its luminosity will_____
while its surface temperature _____.

Increase, decreases

Which of the following is required in order for a helium flash to occur?

A degenerate helium core.

Which of the following describes a region with a diameter of 25pc containing anywhere between 10 and 1000 stars?

open clusters

galactic clusters

A structure that consists of anywhere from hundreds to thousands of galaxies bound by gravity.

Galaxy clusters are much larger than galaxy groups. One of the key features of clusters is the intracluster medium or ICM. The ICM consists of heated gas between the galaxies and has a temperature on the order of 7-9 keV. Galaxy clusters should not be confused with star clusters such as open clusters, which are structures of stars within galaxies, as well as globular clusters, which typically orbit galaxies.

Which is much larger, Galaxy clusters or galaxy groups?

Galaxy clusters

What should not be confused with star clusters?

Open clusters, which are structures of stars within galaxies, as well as globular clusters, which typically orbit galaxies.

What information about a star cluster can be obtained by examining its turn-off point on an H-R diagram?

The age of the cluster

Which of the following would be classified as an RR Lyrae variable?

a G giant with a period of 14 hours

Any star that changes its brightness in a periodic way is called a____ star.

variable

Which of the following would be classified as an Cepheid variable?

K giant with a period of 14 days

The fairly flat, circular part of the galaxy is referred to as the

disk

The center of the Galaxy is in the direction of the constellation

sagittaruis

Which is the correct description of the Sun’s location in the Milky Way galaxy.

In the disk, about two-thirds of the way out from the center.

The location of the center of our galaxy was first determined by observations of

globular clusters

About how many stars are in the Milky Way?

100 billion

Which of the following is not a part of our Milky Way?

ring

Which of the following is not a part of our Milky Way?

a. galactic bulge
b. disk
c. spiral arms
d. ring
– correct
e. hal

Which of the following is not typical of the Galaxy’s spiral arms?

a. emission nebulae
b. young star clusters
c. O stars
d. globular clusters
– correct

We can estimate the mass of the Galaxy from observations of

radial velocities, proper motions, and distances of stars

How do stars in the galactic disk orbit the center of the galaxy?

In nearly circular paths and in rough

ly the same plane.

How do stars in the galactic halo orbit?

hey have randomly oriented orbits.

What fundamental principle did Shapley use to calibrate the period-luminosity relationship for Cepheid variable stars?

Objects with large proper motion tend to be closer than objects with small proper motion.

What must be measured to determine distance by the Cepheid variable star method?

the apparent magnitude and the period of pulsation of the variable star

What is the approximate diameter of the disk component of the Milky Way Galaxy?

80,000 ly

Which of these two figures illustrates the orbits of population II stars?

3 Model of Galatic plane, ellipses and halo stars

Why do astronomers propose that the Milky Way Galaxy contains a lot of dark matter?

The Galaxy’s rotation curve flattens out at great distances.

How are population II stars different than the sun, a population I star?

Population II stars are lower in metals than population I stars.

What do we observe at radio, infrared, and X-ray wavelengths near the center of the Milky Way Galaxy that leads us to conclude that a supermassive black hole is located there?

⁻A strong source of radio waves called Sagittarius A.
-A rapid rate of star formation.
-Supernova remnants.
-A rapid rate of star formation and supernova remnants.

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