Astronomy Mid-Term

Astronomy is one of the sciences, the study of the Universe, and astronomy is, in many ways, applied physics

What is true about astronomy?

10^40 times smaller

How many times smaller is a proton, compared to the distance from here to the farthest observed reaches of the Universe?

Science

A process to improve understanding of Nature

Observe, hypothesize, predict, test, modify

Which sequence best describes science

Can be tested for correctness

Saturn's radius is 3-5 times larger than Earth's.

Can be tested for correctness

On a clear day, the sky is blue.

Can be tested for correctness

Portents indicate you will be lucky today.

Can be tested for correctness

An astronaut cannot survive on the Moon without life-support systems.

Cannot be tested for correctness

The moon is an uglier place than Earth.

Assumptions that science makes

A) there exist underlying laws of Nature
b) deductive reasoning works
c) inductive reasoning usually works

Moon, planet, star, solar system, galaxy

Considering typical sizes of objects, which lists objects from smallest to largest?
planet, star, solar system, galaxy, moon

an example of deductive reasoning

All stars are fueled by nuclear reactions. Right now, the object I see through my telescope is a star. Therefore, this object must be fueled by nuclear reactions.

An example of inductive reasoning

I have noted that the Sun has risen every day during my whole lifetime. Therefore, it will probably rise again tomorrow.

True statements about astronomy

Astronomy is one of the sciences, the study of the Universe, and Astronomy is, in many ways, applied physics

Scientific notation

2.34x10^4

2.8x10^13

For the product (2.3456x104)(1.2x109), which result has the correct number of significant digits?

24.7

Assuming each of the following numbers has the correct number of significant digits as written, for the sum 23.456 + 1.2, which result has the correct number of significant digits?

400,000 km \= 60 Earth radii

What is the Earth-Moon distance?

Earth radius

6,500 km

1 AU

150,000,000 km

1 light-second

300,000 km

Pluto-sun distance

6,000,000,000 km

1 light year

10,000,000,000,000 km

Planet-moon

Light-seconds

Star-star

Light-years

Sun-outer planets

Light-hours

Sun-inner planets

Light-minutes

Sun-galactic center

10,000's of light-years

Planets from closest to farthest from the sun

Mercury, Venus, earth, mars, Jupiter, saturn, Uranus, Neptune

Gravity

The force that holds the sun in its orbit around the Milky Way Galaxy

electromagnetism

The force that holds atoms together, i.e. that holds electrons in orbit around the atomic nucleus

The weak force

The force involved in radioactive decay of atomic nuclei

Gravity

The force that golds the Earth together

Gravity

The force that holds the planets of our solar system in orbit around the Sun

Gravity

The force that holds out Moon in orbit around the Earth

The strong force

The force that holds the atomic nucleus together

Venus, mars, mercury, the moon, the sun

According to the ancient Greeks, there were seven "wanderers": objects visible to the unaided eye that were observed to move relative to the "fixed stars". Which list contains only "wanderers"?

The moon's phases, beginning with new

Waxing crescent, first quarter, waxing gibbous, full, waning gibbous, third quarter, waning crescent

When the moon phase is full

B) the moon is farther from the Sun than the Earth is
c) to two significant digits, the moon is about the same distance from the sun as the earth is

Stars appear to move in circles around the Celestial poles

Because of the Earth's rotation

Eratosthenes used this to determine the circumference of Earth

the distance between Syene and Alexandria, and the knowledge than one day at noon, the Sun appeared at the zenith in Syene, and 7° from the zenith in Alexandria

Aristarcos

A) argued that the Sun is much farther away from the Earth than the moon is
B) argued that the sun is much larger than the earth
C) was the first person we know of who argued that the Earth goes around the Sun instead of the Sun going around the Earth
D) argued that the stars were much too far away for us to observe their parallax

Aristoteles' arguments that the Earth is spherical

A) faraway ships apparently disappear below the horizon
B) during a lunar eclipse, the Earth's shadow on the Moon is round
C) Northbound travelers saw that stars near the north Celestial pole were higher in the sky

Hipparcos' contributions to astronomy

A) measurements of the directions of objects in the sky
B) a star catalog of about 850 stars
C) the discovery of the precession of the Earth's axis
D) the definition of a system of magnitudes to describe how bright a star is

it employed epicycles on deferents centered just slightly off the Earth

The ancient Greeks assumed that heavenly bodies moved in uniform circular motion (perfect motion), yet the apparent motions of the planets seemed to exhibit various complications including occasional retrograde motion. How did Ptolemy's mathematical scheme solve this problem?

East

Northern hemisphere stars rise in the

East

Southern hemisphere stars rise in the

Between 50% and 100% if the sky

a person standing in Bloomington sees

About 50% of the sky

A person standing on the North Pole sees

about 100% of the sky

A person standing on the Equator sees

in the geocentric model the inner planet would always appear as a crescent, whereas in the heliocentric model the planet would show both crescent and gibbous phases

How would the phases of an inner planet like Venus or Mercury differ in Ptolemy's geocentric model from those in Aristarcos' heliocentric model?

Copernicus' claims about the solar system

A) planets are round worlds, like Earth
B) all planets orbit the Sun
C) Earth is not a special place in the Universe

Accurate measurements of planet motion

Tycho Brahe is most remembered for his

Caternary

What is not a conic section?

Ellipse

Kepler utilized Tycho's data to conclude that the true shape of planetary orbits is an

Hyperbola

A comet is determined to be in an unbound orbit: it will easily escape the solar system. What shape of orbit is it following?

A and B only

A hypothetical solar system contains planets A, B, C, D, E, F, G, and H, orbiting the central star, listed here in order from closest (A) to the central star to farthest (H). As viewed from C, which planet(s) exhibits gibbous and crescent phases?

3 times faster

A hypothetical planet is three times as close to the Sun at perihelion as compared to at apohelion. How much faster is it moving at perihelion, as compared to at apohelion?

8 years

The radius of a rock's circular orbit around the Sun is 4 AU. What is the orbital period?

Kepler's laws of planetary motion

a) the orbits of all planets are ellipses with the Sun at one focus
b) planets sweep out equal areas in equal time
c) the square of the period is proportional to the cube of the semi-major axis

Galileo's discoveries through a telescope

A) many stars exist that are too faint to see with the unaided eye
B) the Moon's surface is uneven and rough, and has mountains
C) the Sun has blemishes (sunspots), and rotates
D) Jupiter has moons of its own

Galileo's discoveries through a telescope

A) planets are disks and not just points of light
B) Venus has both crescent and gibbous phases
C) the fuzzy, nebulous Praesepe patch (the "Beehive") is really a cluster of many stars
D) Saturn has blobs (later shown to be rings)

20 lb

The acceleration due to gravity on the Moon's surface is 1/6 of the acceleration due to gravity on the Earth's surface. An astronaut weighs 120lb on Earth; how much does she weigh on Moon?

55 kg

The acceleration due to gravity on the Moon's surface is 1/6 of the acceleration due to gravity on the Earth's surface. The mass of an astronaut as measured while on Earth is 55kg; what is her mass on Moon?

The same

A skater whose mass is 80 kg and another skater whose mass is 40 kg are standing at the center of an ice rink. We can assume the ice to be effectively frictionless. They push off from each other. Use the following answer choices (hint: apply Newton's laws): During the act of pushing off, the more massive skater feels what fraction of the force that the less massive skater feels?

0.5 times

A skater whose mass is 80 kg and another skater whose mass is 40 kg are standing at the center of an ice rink. We can assume the ice to be effectively frictionless. They push off from each other. Use the following answer choices (hint: apply Newton's laws): During the act of pushing off, the more massive skater feels what fraction of the acceleration that the less massive skater feels?

Mass 0.5M, radius 2R

Object with the lowest escape velocity

it continues to move in its original orbit

Suppose the Sun suddenly becomes a tiny little itsy bitsy black hole. (Don't worry — astronomers think this is extremely unlikely!) All of the Sun's mass is retained; that is, the mass of the black hole is one solar mass. What effect does this have on the Earth's orbital motion?

4 solar masses

In a certain solar system, it is found that a planet is located on a nearly circular orbit with radius 1 AU from the central star. The planet's orbital period is 0.5 yr. What is the mass of the central star? Hint: use Kepler's Third Law as modified by Newton.

4 km/s

An artificial satellite in low Earth orbit (i.e. the orbital radius is just barely larger than the Earth's radius) needs a velocity of about 8 km/s to maintain its nearly circular orbit. What would be the velocity required to stay in orbit if the satellite were much farther out, at an orbital radius equal to 4 Earth radii?

they hit at about the same time

A large cannon ball and a golf ball are dropped from the same height above the surface of Saturn's moon Rea. Which one hits the ground first? (Ignore any possible air resistance.)

it supported Newton's Law Fg \= GMm/R2

What was the significance of Newton's comparison of an apple falling off of an apple tree to the Moon's orbital motion around the Earth?

Forms of light

Photons, electromagnetic radiation, X-rays, radiation from an accelerated charge

γ rays, X-rays, visible light, infrared, radio

Which of the following types of light are listed from highest to lowest energy (left to right):

between 4000 and 7000 Å

Humans best observe light with wavelengths

the Sun is 9 times brighter

Earth is about 3 times farther from the Sun than Mercury is. Compared to the brightness of the Sun as viewed from Earth, from Mercury:

The energy of a photon

proportional to its frequency and inversely proportional to its wavelength

10,000,000,000

How many angstroms are there in one meter?

equal to the angle of incidence

For a thin light beam reflecting off of some surface, the angle of reflection is

blue-shifted by the Doppler effect

The light from a source moving toward us is

They hit at the same time

A basketball and tiny plastic ball are dropped from the same height above the floor. Which hits the floor first? (Ignore possible effects due to air friction.)

The basketball

A basketball and a fluffy feather are dropped from the same height above the floor. Which hits the floor first? (This time pay attention to possible effects due to air friction.)

They hit at the same time

On the moon, a basketball and a fluffy feather are dropped from the same height above the ground. Which hits the ground first?

It would appear white, since the light has not yet gone through the prism.

Suppose the screen is placed between the projector and the prism. How would the light appear on the screen now?

The prism still bends each color (if present) the same way it did before; thus, the red portion of the spectrum remains in the same location as before, and the other colors disappear, because the filter only allows red photons to pass.

The screen is back in the front of the classroom and a spectrum appears on it again. Suppose a red filter is inserted between the prism and the screen. Does anything happen to the spectrum? If yes, describe what happens.

The prism still bends each color (if present) the same way it did before; thus, the red portion of the spectrum remains in the same location as before, and the other colors disappear, because the filter only allows red photons to pass.

The filter is removed; the familiar spectrum is on the screen. Now suppose that, instead, the filter is placed between the projector and the prism. Does anything happen to the spectrum? If yes, describe what happens to the entire spectrum. The answer choices are the same as for question 2.

Since the book is red, it reflects more red photons than any other color; thus it will appear brighter when it is in the red part of the spectrum, and darker when it is in the other parts of the spectrum.

The filter is removed; the familiar spectrum is on the screen. A red book is placed just off the screen but to the edge of the screen, out of the visible beam. The book is then moved across the spectrum from the red towards the blue, and ultimately past the blue. Describe how the book looks as it moves across in this manner, and why.

A white shirt reflects all photons it receives; thus at any moment it will look like the color that it's in.

A volunteer wearing an ordinary white shirt repeats this procedure, i.e. begins off-screen and slowly walks across the spectrum from red to blue and beyond blue. Explain how the white shirt looks during this process.

Blackbody

A perfect absorber of radiation, a perfect emitter of radiation, emits radiation at all wavelengths

A blackbody

Of higher temperature emits more energy at all wavelengths and emits its maximum energy at a shorter wavelength

5200 Å

According to Wien’s law, the maximum energy emitted by the Sun is near the wavelength

Blue star, yellow star, red star

List the stars from hottest (surface temperature) to coolest (left to right)

Infrared

Humans absorb energy from their surroundings, and also generate their own energy (e.g. through chemical reactions occurring in digestive systems).  They then radiate energy away, somewhat like blackbodies.  This energy is mostly radiated at which wavelengths?

Infrared

Planets in our solar system emit energy, somewhat like blackbodies.  This energy is mostly radiated at which wavelengths?

Must have only very specific energy states

Inside an atom, an electron

2\.2 eV

An electron in some particular atom has gone from a state with energy 14.0 eV to one with energy 11.8 eV.  The energy of the photon that is emitted is

At some wavelengths, more energy is being added to the spectrum than taken away

If we observe emission lines, what can we conclude?

A chemical composition, surface temperature, speed toward us or away from us

An analysis of the spectral lines can give information about a star’s:

Hydrogen, helium, oxygen

What are the three most abundant elements in the Universe (and in the Sun), in order  from most abundant  to least abundant?

Both gamma-ray and X-ray telescopes

The atmosphere blocks certain wavelengths, so to observe those wavelengths it is necessary to place telescopes in space.  Which telescopes MUST be launched into space to collect light?