Astro Exam 1

The Moon's precise equatorial diameter is 3,476 kmkm, and its orbital distance from Earth varies between 356,400 kmkm and 406,700 kmkm. The Sun's diameter is 1,390,000 kmkm, and its distance from Earth ranges between 147.5 and 152.6 million kmkm. Find the Moon's angular size at its maximum and minimum distances from Earth.

(θMoon)max(θMoon)max = 0.5588,0.4897∘

Find the Sun's angular size at its minimum and maximum distances from Earth. Express your answer using four significant figures. Enter your answers in ascending order separated by a comma.

(θSun)min(θSun)min, (θSun)max(θSun)max = 0.5219,0.5399∘

Find the planet's nearest orbital distance from its star. Express your answer using two significant figures.

0.44a.u.a.u.

The following angles are given in degrees and fractions of degrees. Rewrite them in degrees, arcminutes, and arcseconds. 0.001∘

0∘0′3.6′′

The following angles are given in degrees and fractions of degrees. Rewrite them in degrees, arcminutes, and arcseconds. 0.01∘

0∘0′36′′0∘0′36″

The following angles are given in degrees and fractions of degrees. Rewrite them in degrees, arcminutes, and arcseconds. 0.1∘

0∘6′0′′

Find the planet's farthest orbital distance from its star. Express your answer using two significant figures.

1.0a.u.a.u.

Earth's radius is approximately 6370 kmkm. What distance is represented by each arcminute of latitude?

1.85kmkm

Earth's radius is approximately 6370 kmkm. What distance is represented by each degree of latitude?

111kmkm

The following angles are given in degrees and fractions of degrees. Rewrite them in degrees, arcminutes, and arcseconds. 1.59 ∘

1∘35′23′′1∘35′23″

The following angles are given in degrees and fractions of degrees. Rewrite them in degrees, arcminutes, and arcseconds. 24.7 ∘

24∘42′0′′24∘42′0″

Earth's radius is approximately 6370 kmkm. What is Earth's circumference?

4.00×104kmkm

At latitude 50∘N50∘N, the celestial equator crosses the meridian at altitude:

40∘40∘ in the south.

A newly discovered planet orbits a distant star with the same mass as the Sun at an average distance of 109 million kilometers. Its orbital eccentricity is 0.4. Find the planet's orbital period. Express your answer using three significant figures.

7.46 monthsmonths

What is a scientific theory?

A model that explains a wide variety of observations in terms of a few general principles and that has survived repeated and varied testing

What is a scientific theory?

A scientific theory must: • Explain a wide variety of observations with a few simple principles, AND • Must be supported by a large, compelling body of evidence. • Must NOT have failed any crucial test of its validity.

Which of the following is not true about a scientific theory?

A theory is essentially an educated guess.

Newton's first law of motion:

An object moves at constant velocity unless a net force acts to change its speed or direction.

About how many times larger is the diameter of the Milky Way Galaxy than the diameter of Saturn's rings? (Data: Saturn's rings are about 270,000 km in diameter; the Milky Way is 100,000 light-years in diameter.) Express your answer using two significant figures.

DMilkyWayDSaturn′srings/DMilkyWayDSaturn′srings = 3.5×1012

What makes dark matter and dark energy so mysterious and so important?

Dark matter and dark energy are mysterious because even though we have strong evidence that they exist, we do not know what they are made of.

Choose the correct statement explaining what is dark matter and where does dark matter reside in our galaxy?

Dark matter is a matter that does not emit light and is therefore invisible to our telescopes, but that we can detect because it has gravity that affects other objects we can see. Most dark matter resides in the galactic halo, which is the large, spherical region that surrounds the disk of the galaxy.

How does the force the Earth exerts on you compare with the force you exert on it?

Earth and you exert equal and opposite forces on each other.

When we see Saturn going through a period of apparent retrograde motion, it means:

Earth is passing Saturn in its orbit, with both planets on the same side of the Sun.

An astronomical unit is:

Earth's average distance from the Sun.

Which of the following correctly lists our "cosmic address" from small to large?

Earth, solar system, Milky Way Galaxy, Local Group, Local Supercluster, universe;

The dwarf planet Eris orbits the Sun every 557 years. What its average distance (semimajor axis) from the Sun? Express your answer to three significant figures.

Eris's semimajor axis = 67.7 a.u.a.u.

Newton's third law of motion:

For every force, there is always an equal and opposite reaction force.

According to Kepler's third law:

Jupiter orbits the Sun at a faster speed than Saturn.

How is mass different from weight?

Mass = quantity of matter • Weight = force acting on mass • Objects are weightless in free-fall.

In winter, Earth's axis points toward the star Polaris. In spring, the axis points toward

Polaris

Mercury, synodic period = 115.9 days. Express your answer using three significant figures.

PorbPorb = 0.241 yryr

Use each object's given synodic period to find its actual orbital period. Saturn, synodic period = 378.1 days. Express your answer using three significant figures.

PorbPorb = 29.4 yryr

An asteroid with synodic period = 429 days. Express your answer using three significant figures.

PorbPorb = 6.73 yryr

How did Newton change our view of the universe?

Realized the same physical laws that operate on Earth also operate in the heavens • one universe • Discovered laws of motion and gravity • Much more: experiments with light, first reflecting telescope, calculus...

Angular momentum

Rotational momentum of a spinning or orbiting object is known as ...

How can we distinguish science from non-science

Science means "knowledge" but not all knowledge comes from science

How can we distinguish science from non- science?

Science: seeks explanations that rely solely on natural causes; progresses through the creation and testing of models of nature; models must make testable predictions

Explain your reasoning.

The Earth does not have a perfect orbit; however, the cause of seasons is due to the tilt of the Earth.

What does the fact that we always see the same face of the Moon tells us about?

The Moon rotates with the same period that it orbits Earth.

Define astronomical unit.

The average distance between Earth and the Sun, which is about 150 million kilometers.

Choose the correct definition of precession, and the correct explanation how does it affect what we see in our sky?

The direction in which Earth's rotation axis points in space changes slowly over the centuries, and we call this change "precession." Because of this movement, the celestial poles and therefore the pole star change slowly in time.

Define light-year.

The distance that light travels in 1 year, which is about 9.46 trillion kilometers.

A compact car and a Mack truck have a head-on collision. Are the following true or false?

The force of the car on the truck is equal and opposite to the force of the truck on the car. T 2. The momentum transferred from the truck to the car is equal and opposite to the momentum transferred from the car to the truck. T 3. The change of velocity of the car is the same as the change of velocity of the truck. F

Note

The moon (moon gravity = 1/6 Earth Gravity) Mars (mars gravity = 1/3 Earth Gravity) Jupiter (Jupiter gravity = 2 Earth Gravity) Titan (Titan gravity = 1/8 Earth Gravity)

Explain your reasoning.

The observable universe is around 14 billion light-years. Therefore, it doesn't make sense that the universe would be billions of light-years old.

Beijing and Philadelphia have about the same latitude but different longitudes. What can be said about the tonight's night sky in these two places?

The sky will look about the same.

NASA plans soon to launch a spaceship that will photograph our Milky Way Galaxy from beyond its halo. Choose the correct explanation why does the statement make sense (or is clearly true) or does not make sense (or is clearly false).

The statement doesn't make sense, because even if we could build a spaceship that traveled close to the speed of light, it would take tens of thousands of years to get high enough into the halo to photograph the disk, and then tens of thousands of years more for the picture to be transmitted back to Earth.

The fact that nearly all galaxies are moving away from us, with more distant ones moving faster, helped us to conclude that:

The universe is expanding.

Newton's Second Law of Motion

There are two equivalent ways to express Newton's Second Law of Motion • Force = mass x acceleration (F=ma) (kg*m/s2) • 1 "Newton= 1 kg*m/s2 • Force = rate of change in momentum

Last night I saw Jupiter right in the middle of the Big Dipper. (Hint: Is the Big Dipper part of the zodiac?) Choose the correct explanation why does the statement make sense (or is clearly true) or does not make sense (or is clearly false).

This statement does not make sense, because Jupiter, like all the planets, is always found very close to the ecliptic in the sky. The ecliptic passes through the constellations of the zodiac, so Jupiter can only appear to be in one of the zodiac constellations—and the Big Dipper is not part of the zodiac.

When I looked into the dark lanes of the Milky Way with my binoculars, I saw what must have been a cluster of distant galaxies. Chose the correct explanation why the statement makes sense (or is clearly true) or does not make sense (or is clearly false).

This statement does not make sense, because we cannot see through the band of light we call the Milky Way to external galaxies; the dark fissure is gas and dust blocking our view.

I live in the United States, and during my first trip to Argentina I saw many constellations that I'd never seen before. Choose the correct explanation why the statement makes sense (or is clearly true) or does not make sense (or is clearly false).

This statement makes sense, because the constellations visible in the sky depend on latitude. Since Argentina is in the Southern Hemisphere, the constellations visible there include many that are not visible from the United States.

Explain your reasoning.

We are unable to see distant galaxies in their current form because it takes light time to travel. Therefore, the image we see is light from many years ago and is not current.

The South Celestial Pole is 35 ∘∘ above your southern horizon. What does it tell you?

You are at latitude 35 ∘∘ S.

Consult a map. Based on your position, where is the nearest land?

You are not too far west of the island of Sumatra.

During a vacation, you decide to take a solo boat trip. While contemplating the universe, you lose track of your location. Fortunately, you have some astronomical tables and instruments, as well as a UT clock. You thereby put together the following description of your situation:1) It is the day of the summer solstice.2) The Sun is on your meridian at altitude 6712∘12∘ in the north.3) The UT clock reads 06:00. What is your latitude?

You are on the equator.

What is your longitude?

Your longitude is 90∘∘E.

Mass

a measure of the amount of matter in an object

How does its average distance compare to that of Pluto? Express your answer to three significant figures.

aErisaPlutoaErisaPluto = 1.72

Venus is easiest to see in the evening when it is:

at greatest eastern elongation.

Part complete Jupiter is brightest when it is:

at opposition.

The idealized scientific method

based on proposing and testing hypotheses

You are an astronomer on planet Nearth, which orbits a distant star. It has recently been accepted that Nearth is spherical in shape, though no one knows its size. One day, while studying in the library of Alectown, you learn that on the equinox your sun is directly overhead in the city of Nyene, located 1500 kilometerskilometers due north of you. On the equinox, you go outside in Alectown and observe that the altitude of your sun is 80 ∘∘. What is the circumference of Nearth? Express your answer using two significant figures.

circumference of Nearth = 5.4×104 km

A star's path through your sky depends on your latitude and the star's:

declination.

Decide whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false). If Earth's orbit were a perfect circle, we would not have seasons.

false

Last night I saw Mars move westward through the sky in its apparent retrograde motion.

false

The universe is billions of light-years in age.

false

Although all the known stars rise in the east and set in the west, we might someday discover a star that will rise in the west and set in the east.

false Explanation: If the Earth changed rotation then we might be able to see a star that rises in the west.

When we say that a planet has a highly eccentric orbit, we mean that:

in some parts of its orbit it is much closer to the Sun than in other parts

A torque

is needed to change an objects angular momentum

Net force

is the vector sum of all the forces that act upon an object

If the Sun rises precisely due east,

it must be the day of either the spring or fall equinox.

Momentum

mass * velocity

Two stars that are in the same constellation:

may actually be very far away from each other.

Part complete If you know a star's declination, you can determine your latitude if you also:

measure its altitude when it crosses the meridian

On the moon

my weight is less, my mass is the same.

Based on your answers to parts A and B, is it possible to have a total solar eclipse when the Moon and Sun are both at their maximum distances?

no

The age of our solar system is about:

one-third of the age of the universe.

If there is going to be a total lunar eclipse tonight, then you know that:

the Moon's phase is full.

Weight

the force that a scale exerts upon an object

A week after full moon, the Moon's phase is:

third quarter.

Part complete The time from one spring equinox to the next is the:

tropical year.

Photographs of distant galaxies show them as they were when they were much younger than they are today.

true

How long does it take a message to travel from Earth to a spacecraft at Mars at its farthest from Earth (about 400 million kmkm)? Express your answer to three significant figures and include the appropriate units.

tt = 22.2 min

How long does it take a message to travel from Earth to a spacecraft at Mars at its closest to Earth (about 56 million kmkm)? Express your answer to three significant figures and include the appropriate units.

tt = 3.11 minmin

How long does it take a message to travel from Earth at Pluto at its average distance from Earth (about 5.9 billion kmkm)? Express your answer to three significant figures and include the appropriate units.

tt = 5.46 hh

Suppose you wanted to reach Alpha Centauri (4.4 lyly from the Solar system) in 80 years. // How fast would you have to go, in km/hrkm/hr? Express your answer using two significant figures.

vv = 5.9×107km/hrkm/hr

We are located about 27,000 light-years from the galactic center and we orbit the center about once every 230 million years. How fast are we traveling around the galaxy, in km/hrkm/hr? Express your answer to three significant figures and include the appropriate units.

vv = 7.98×105 kmhkmh

Suppose you wanted to reach Alpha Centauri (4.4 lyly from the Solar system) in 80 years. // How many times faster is the speed you found in part A than the speeds of our fastest current spacecraft (around 50000 km/hrkm/hr)? Express your answer using two significant figures.

vvcurrentvvcurrent = 1200

There are 360∘360∘ in a full circle. What is the Moon's angular size in arcseconds?

θMoonθMoon = 1800 arcsecondsarcseconds

There are 360∘360∘ in a full circle. The Moon's angular size is about 12∘12∘. What is this in arcminutes?

θMoonθMoon = 30 arcminutesarcminutes

There are 360∘360∘ in a full circle. How many arcseconds are in a full circle?

θfullθfull = 1296000 arcsecondsarcseconds

There are 360∘360∘ in a full circle. Part A Part complete How many arcminutes are in a full circle?

θfullθfull = 21600 arcminutesarcminutes