The Solar System

You have learned where Earth is in relation to the Sun. Provide the correct statements.

• The Milky Way is a spiral galaxy

• The orbits of Earth and the other planets around the Sun are not perfect circles

• Galaxies are composed of billions of stars

• The sun is a star

You have learned about the relative sizes of objects and the distances between them. Provide correct statements.

• The sun is about 100 times the diameter of Earth

• Earth is about 4 times the diameter of the Earth

• Our galaxy is thousands of light years across

• The solar system is part of our galaxy

You have learned how astronomers talk about huge astronomical distances. Provide correct statements.

• A light year is larger than an astronomical unit

• The distances to stars are measured in light years

• Astronomers use the metric system for calculations

It is useful to model the sky as a celestial sphere that rotates around the Earth from east to west once per day. Provide correct statements.

• The celestial equator is an imaginary line in the sky directly above Earth’s equator

• Precession is the slow shift in direction of the Earth’s rotational axis, similar to the wobbling of a spinning top

• The apparent rotation of the sphere is caused by Earth’s rotation

• The celestial sphere is still useful even though it is no longer accepted as physical reality

Because the Earth orbits the sun once per year, the sun appears to move through the sky once per year on a path we call the ecliptic. Provide correct statements.

• In the summer the sun is higher in winter

• In the summer the sun is above the horizon longer than in the winter

• The ecliptic’s tilt is caused by the tilt of the Earth’s rotational axis

• The constellations that lie along along the ecliptic are those of the zodiac

What is responsible for the observed motion of a star along the celestial equator?

Earth’s rotation on its axis

At what location on Earth is an observer that has the South Celestial Pole directly overhead?

At Earth’s South Pole (90 degrees South latitude)

At what location on Earth is an observer that has the Celestial Equator pass through the point directly overhead?

At Earths equator (0 latitude)

If the tilt of Earth’s axis were to change from 23.5 degrees to 0 degrees, what celestial circles would coincide for all observers?

The celestial equator and the ecliptic

If you could see the sun and stars during the daytime for several weeks you would notice that the sun does which of the following?

Moves slowly eastward relative to the stars

Why does the sun move relative to the stars as observed from Earth?

It is due to Earth revolving around the sun

Why is the amount of solar heating less on a clear day in January at northern latitudes than on a clear day in July?

Both the sun is above the horizon for less than 12 hours in January in the north and at low sun angles, the received sunlight is spread over a larger surface area

When it is autumn in Asia, what is it in Antarica?

Spring

The fives naked eye planets and three telescopic planets that wander among the stars in the sky are always near which of the following?

Ecliptic

Which of the following descriptions is a definition of an astronomical unit (AU)?

The average distance between Earth and Sun

The way scientists know that a hypothesis in astronomy is a reasonable description of nature is to

Do experiments and observations about the predictions of the hypothesis

By the term universe, astronomers mean

Everything we can observe

The moon goes through a cycle of phases. This occurs because as the moon orbits Earth, differing parts of the side of the moon illuminated by the sun face toward Earth. Provide correct statements.

• Since a full moon occurs when the moon is on the opposite side of Earth as the sun, it is only visible at night

• Quarter phases occur between the new and full phases

• During the new phase, no direct sunlight reaches the side of the moon facing Earth

Why do solar eclipses happen only at new moon?

Since the shadow of the Moon extends directly away from the Sun, a solar eclipse can occur only when the Moon is between the Earth and Sun. Does not occur every new moon due to the moons orbital tilt

Why can’t the Moon be eclipsed when it is halfway between the nodes of its orbit?

When the Moon is halfway between the nodes, it would be approximately 5 degrees above or below the ecliptic, hence, could not be directly opposite of the sun

The moon goes through a cycle of phases. This occurs because as the moon orbits Earth, differing parts of the side of the moon illuminated y the sun face toward Earth. Provide correct statements.

• During the new phase, no direct sunlight reaches the side of the moon facing Earth

• Quarter phases occur between the new and full phases

• Since a full moon occurs when the moon is on the opposite side of Earth as the sun, it is visible at night

Why did Plato propose that all heavenly motion was uniform and circular?

Because he believed the sphere to be the most perfect geometrical form

In Ptolemy’s model, how do the epicycles of Mercury and Venus differ from those of Mars, Jupiter and Saturn?

The epicycles of Mercury and Venus were attached to a line joining Earth and the Sun. The epicycles of Mars, Jupiter and Saturn revolved around Earth independently of the Sun

Why did Copernicus have to keep small epicycles in his models?

His model did not predict planetary positions as well as the Ptolemaic system

• Mars has the shortest duration of retrograde

• Neptune has the longest duration of retrograde

When is Earth closest to the Sun?

January

The seven days of the week are named after what?

The seven “wandering” objects in the Sky that were visible to the ancients

Why does the moon show phases in the course of a month?

The angle the moon makes with the sun changes and we see differing amounts of reflected light

The period of the moons rotation on its axis is?

The same as its revolution around the Earth

When the sun and moon are lined up and pull together, the tides they raise are called?

Spring tides

What phase of the moon must it be to have a solar eclipse?

New Moon

From a particular location on Earth, why can we see many more total eclipses of the Moon than totally eclipses of the Sun?

A total lunar eclipse is visible over a much larger part of the Earth’s surface than a total solar eclipse

Which of the following statements about eclipses of the Sun is true?

For a total eclipse of the sun to happen, the moon must get directly in front of the sun, as seen from Earth

Does Tycho’s model of the universe explain the phases of Venus that Galileo observed? Why or why not?

Yes. In Tycho’s model all planets except Earth orbit the Sun, and the Sun orbits Earth once each day. In this model Venus shows a full set of phases

How does Kepler’s first law of planetary motion overthrow one of the basic beliefs of classical astronomy?

It says that the orbits of the planets are ellipses, rather than perfect circles or series of epicycles

What does Kepler’s second law say about classical astronomy?

It says that the planets speed up and slow down during their orbits, rather than remain in uniform motion

Galileo’s telescopic discoveries contradicted the Ptolemaic theory by:

• Features on the moon - Showing a heavenly body could be imperfect

• Stars that are too faint to be seen with then naked eye - Does not support or contradict the Ptolemaic theory

• Moons of Jupiter - Shows that a heavenly body could have satellites

• Sunspots - Shows that a a heavenly body could be imperfect

• Phases of Venus - showed that planet orbited the sun

What is the difference between speed and velocity?

The velocity of an object indicates both the object’s speed (rate of motion) and its direction of motion

Why did Newton conclude that gravity has to be mutual and universal?

Newton’s third law stated that for every action there is an equal and opposite reaction, so he concluded gravity must be mutual. He reasoned that the sun, the planets and all their moons must also attract each other by mutual gravitation, so he concluded that gravity must be universal

The 17th century astronomer who kept a roughly 20 year continuous record of the positions of the Sun, Moon and planets is?

Tycho Branche

The scientist who formulated the three laws of planetary motion by analyzing the data on the precise location of planets in the sky was?

Johannes Kepler

When a planet in its orbit moves close to the sun it:

Moves faster than average

According to Kepler’s third law, there is a relationship between the time a planet takes to revolve around the sun and its:

Distance from the sun

Newton showed that to change the direction in which an object is moving, one needs to apply:

A force

A single star in the process of forming starts by spinning slowly (while it is quite large and relatively cool.) As the star collapses under the pull of its own gravity, its size decreases. As result, the rate of spinning it:

Will increase

What is the difference between your mass and your weight?

Your mass is a measure of the amount of matter that you contain and your weight is a measure of the amount of gravitational pull you experience.

The detail visible through even the highest quality telescope is limited by which of the following?

the diameter of the telescope

Why does diffraction occur?

Light has wavelike characteristics.

The highest quality telescopes ever made have been termed "diffraction-limited" and can be described by which of the following statements?

• Diffraction fringes are visible around every point of light.

• further improvements in the quality of the optics would not improve the image.

• The telescope has the highest resolution possible for its diameter.

If you had limited funds to build a large telescope, which type would you choose, a refractor or a reflector? Why?

A reflector, because they cost less than refractors of equal size.

The Moon has no sustained atmosphere. What advantages would you have if you built an observatory on the lunar surface?

• Without atmospheric turbulence, there would be no image blur due to seeing.

• There is no atmosphere to absorb or scatter radiation, so all wavelengths of light could be observed with lunar-based telescopes, from radio waves to gamma rays.

• We could observe during the day. Without an atmosphere, sunlight is not scattered and the sky remains dark.

• We could observe continuously, because there would never be any clouds

What might you detect with an X-ray telescope that you could not detect with an infrared telescope?

black holes & hot gas heated by exploding stars

What is a wave?

• The number of crests that move past a given location for each unit of time corresponds to the frequency of the wave.

• The distance between crests (or troughs) of the wave is the wavelength.

• A wave is a repeating disturbance that travels outward.

What are the three basic components of a modern astronomical instrument?

• a device which sorts radiation by wavelength

• a telescope, which collects radiation

• a detector, which senses and records the radiation

What is meant by "reflecting" and "refracting" telescopes?

• A refracting telescope uses lenses to focus light.

• A reflecting telescope uses a mirror as a primary light collector.

Which of the following statements about electromagnetic radiation is FALSE?

the radiation consists of tiny charged particles given off by the nuclei of atoms

The light which allows you to see this very interesting exam is made up of waves. In these waves, the distance between crests is called the

wavelength

How fast do electro-magnetic waves travel?

at the speed of light

We have two waves of light, A and B. Wave A has a higher frequency than wave B. Then wave B must have:

longer wavelength

In the future, several students living on board a space station decide to have a race among different types of electromagnetic radiation. Which of the following travels through space the fastest?

all of these travel through space at the same speed

Which of the following has the highest frequency?

gamma rays  

Not all wavelengths of electromagnetic radiation can penetrate the Earth's atmosphere. Of the following types of waves that come from space, which one are you likely to be able to detect most easily from our planet's surface?

radio waves of the wavelength that carry FM broadcasts

Which of the following is not an advantage that a reflector telescope has over a refractor telescope?

a reflector doesn't have to deal with the twinkling of the stars, as a refractor does

A new technique called adaptive optics allows astronomers to _____.

compensate for changes in the Earth's atmosphere and achieve better resolution

Based on what you know about how astronomers use radio telescopes, select all of the correct statements from the following list.

• Radio waves can travel through obstacles that block out waves of visible light.

• Radio telescopes have to be larger than optical telescopes, since radio waves are longer than visible light waves.

Based on what you know about telescopes located in space, select all of the correct statements from the following list.

• The Chandra X-ray, Hubble, and Fermi Gamma-Ray telescopes are all in space.

• Most types of electromagnetic waves are not visible to ground-based telescopes.

Why are near-infrared telescopes located on mountaintops and ultraviolet telescopes in Earth orbit?

The primary infrared blocker, water vapor, is mostly in the lower atmosphere and the primary ultraviolet blocker, ozone, is located high in the atmosphere, far above mountaintops.

Why is the Bohr atom described as a planetary model?

The electron orbits the nucleus much as a planet orbits the sun.    

The energy stored in an atom depends on which of the following?

the diameter of the electron's orbit  

Why are electrons in an atom only able to occupy certain permitted orbits?

The atom may contain only certain amounts of energy.

When the electron in an atom drops back to a lower orbit, what is true of the photon that is emitted?

It always has an energy equal to the energy difference between the two orbits.   

An atom can absorb a photon only if the energy of the photon equals which of the following?

energy difference between two permitted orbits   

If a source of waves is moving toward you, which of the following will you detect?

slightly shorter wavelengths

The Doppler shift only depends on which of the following?

the relative velocity between the source and observer

Astronomers can detect the Doppler shift of a star by measuring which of the following?

the wavelengths of atomic lines in the spectrum of the object

When does a Doppler shift occur?

• whenever a source of waves is coming closer to or moving away from an observer

• whenever a source of waves is moving radially relative to the observer  

• whenever the distance between a source of waves and the observer is changing

Based on what you learned about atoms, select all of the correct statements from the following list.

• Electrons surround the nucleus.

• Neutral atoms have the same number of protons as electrons.

• The number of neutrons determines the isotope of an atom.

• Protons are positively charged.

Based on what you know about light and matter interactions, select all of the correct statements from the following list.

• The size of an electron's orbit depends on its energy.

• Low-density hot gases produce emission spectra.

• Hot solids emit continuous spectra.

• Electrons will move to higher orbits when an atom absorbs enough energy.

Based on what you learned about light production in stars, select all of the correct statements from the following list

• The temperature of a star can be roughly estimated from its color.

• Stars emit light mostly from their surfaces.

• Hotter stars radiate more energy at higher frequencies.

What conditions produce a dark-line (absorption line) spectrum?

light from a continuous spectrum source passing through a cooler low-density gas

You research the star Sirius and find that its spectral lines are blue-shifted. What does this tell you about Sirius?

It has a radial velocity that is toward us.

Explain how emission lines are formed.

An atom's electron moves to a lower energy level and emits a photon. The wavelength of the photon corresponds to the electron's change in energy.

Explain how absorption lines are formed.

An atom's electron moves to a higher energy level by absorbing a photon. The wavelength of the photon corresponds to the electron's change in energy.

Explain how we can deduce the temperature of a star by determining its color.

The peak wavelength of a blackbody spectrum, which is the color, is inversely proportional to its temperature.    

Explain how we use spectral absorption and emission lines to determine the composition of a gas.

Atoms and molecules in a gas will leave a unique pattern of lines in the spectrum of a gas. We can use these "spectral fingerprints" to deduce the composition of the gas.   

What are the three isotopes of hydrogen, and how do they differ?

Ordinary hydrogen has a single proton for a nucleus. Deuterium is hydrogen with a proton and a neutron in its nucleus. Tritium is hydrogen with a proton and two neutrons in its nucleus.

Explain why each element has a unique spectrum of absorption or emission lines.

• Each element has a unique set of possible energy levels in which an electron can reside.

• The energy differences between the levels will be different for every element.

Describe two ways an atom can become excited.

• collisions

• absorption of a photon

Why do hot stars look bluer than cool stars?

The wavelength that a star radiates the most energy is inversely proportional to the temperature.

What kind of spectrum does a neon sign produce?

an emission spectrum

How can the Doppler effect explain wavelength shifts in both light and sound?

The Doppler effect is produced when the source and observer of a wave are moving relative to each other, regardless of the type of waves produced.

Which of the following statements about the nucleus of a typical atom (such as a carbon atom in your little finger) is FALSE?

the nucleus repels the electrons which move around it

OSAstro1 5.TB.032.

An astronomer discovers a new star and wants to measure its temperature. She would typically do this by _____.

making a blackbody curve and finding the wavelength of the peak (maximum)

Wien's Law relates the wavelength at which a star gives off the greatest amount of energy to the star's _____.

temperature

Why is an absorption spectrum especially useful for astronomers?

It has dark lines in it that allow astronomers to determine what elements are in the star     

Two versions of an element with different numbers of neutrons are called _____.

isotopes

When an atom has lost one or more electrons, it is said to be _____.

ionized

To go from a lower level in an atom to a higher level, an electron must _____.

absorb a photon of energy   

The ground state in an atom is _____.

the electron orbit with the lowest possible amount of energy