ISP 205 Final Exam

Explain why we see objects at great distances as they were in the distant past.

Because light travels at a finite speed, whatever we see happened sometime in the past. The farther we look, the further we look into the past.

Summarize the major cosmic events that prepared the way for life on Earth.

1) The Big Bang made matter.
2) Gravity pulled the matter into galaxies.
3) Galaxies make stars (gravitational contraction)
4) Early stars make elements necessary for life
5) Our galaxy recycled those elements into new stars and planets. (galactic recycling)
6) Some planets (like ours) are suitable for life

Describe how Earth rotates and moves through space.

Earth rotates once per day (counterclockwise as viewed from above the North Pole

Speed = distance from the Earth's axis X one revolution per day.

Earth orbits the sun once per year at over 100,000 km/hr (counterclockwise)

Earth's orbit is in the ecliptic plane.

Describe how the average distances between galaxies are changing with time.

Expansion of the universe is continually moving the universe's galaxies farther and farther apart.

All galaxies are moving away from one another.

Explain why we cannot observe the entire universe.

Because the universe is 14 billion years old, we can't see anything more than 14 billion light-years away.

This part of the universe we can see is called the Observable universe.

Also, the universe is expanding too quickly we don't have the time or technology to observe the entire galaxy.

Observable universe.

the portion of the entire universe that we can potentially observe. No limit on size of entire universe which may be far larger than the observable universe.

Describe how the daily motions of objects in the local sky depend on Earth's Rotation.

Stars rise and set in a direction opposite to Earth's rotation. Some stars never rise and others never set, depending on your latitude.

Stars that never set are called Circumpolar.

Circumpolar

Stars that never set

Explain how axis tilt affects the number of daylight hours and the path of the Sun in the sky at a particular location on Earth.

When the Earth is tilted toward the Sun, daylight hours are increased.

When the Earth is tilted away from the sun, the daylight hours are decreased.

Predict the approximate rise and set times of the Moon for each of the lunar phases.

New Moon: Rises - 6am, sets - 6pm

Waxing Crescent: Rise - 9am, set - 9pm

First quarter: Rise - noon, set - midnight

Waxing gibbous: Rise - 3am, set - 3pm

Full Moon: Rise - 6 am, set - 6pm

Waning gibbous: Rise - 9am, set - 9pm

Third Quarter: Rise - noon, set - midnight

Waning crescent: Rise - 3am, set 3 pm.

Waxing

"Maxing"
means growing

Waning

Shrinking
means shrinking

Explain how apparent retrograde motion arises from the orbital motion of planets around the Sun.

Occasionally, a planet will appear to drift east to west on the celestial sphere - a behavior known as apparent retrograde motion.

We see apparent retrograde motion when the Earth's orbit carries it past another planet.

Apparent retrograde motion

is the apparent motion of a planet, as viewed from the earth, during the period of a few weeks or month's when it moves westward relative to the star in our sky.

Celestial sphere

An imaginary sphere of very large radius centered on an observer; the apparent sphere of the sky.

Identify the main contribution of Copernicus, Tycho, and Kepler to the Copernican revolution.

Copernicus: Proposed in 1543 that the Sun, not the Earth, was at the center of the solar system

Tycho: The greatest naked-eye observer of all time; his work recorded the motions of planets to better than one arcminute.

Kepler: His system of elliptical orbits greatly simplified our picture of the solar system. (Kepler's first, second, and third law)

Elliptical orbits

The revolving of one object around another in an oval shaped path called an ellipse.

Kepler's first law:

The orbit of each planet around the sun is an ellipse with the Sun as the focus.

Kepler's Second Law:

As a planet moves around its orbit, it sweeps out equal areas in equal times.

Kepler's Third Law:

More distant planets orbit the Sun at slower average speeds obeying the relationship p^2 = a^3

p = orbital period in years

a = average distance from the Sun in AU

Explain why Galileo's observations were inconsistent with the Greek geocentric model.

Galileo saw four moons orbiting Jupiter, proving that not all objects orbit the Earth.

Galileo saw that Venus goes through a full cycle of phases (like the moon), proving that it orbits the Sun and NOT the Earth.

Predict how a rotating system will respond to a change in radius because of conservation of angular momentum.

As radius decreases,
Orbital velocity increases.

As radius increases,
Orbital velocity decreases

Conservation of angular momentum.

The angular momentum of a spinning object will stay constant.

If one of the factors of angular moment goes down, one of the others will go up to compensate.

Predict how the strength of gravity between two objects will change if their distance changes.

More distance = less gravity between the two objects

Twice as much distance = 4x less gravity

Less distance = the more gravity between the two objects

Identify the information needed to measure the mass of an orbiting system using Newton's version of Kepler's law.

You need to measure the orbital period and the distance of another object orbiting around it.

Explain how the composition of an astronomical object can be determined from its spectrum.

Each type of atom, ion, or molecule possess a unique set of energy levels is what causes emission and absorption lines to appear at specific wavelengths in a spectra.

We can match to the spectra of the object to the spectra of the composition to see if they are alike.

Estimate the temperature of an astronomical object from the peak of its thermal radiation spectrum.

The peaks of the spectra are at shorter wavelengths for hotter objects.

For example, the peak for 15,000K star = ultraviolet region.

Peak for 5,800K sun = visible region

Peak for 3,000K star = infrared

Explain how the speed of an object can be determined from shifts in the wavelengths of its spectral lines.

The Doppler Effect tells us whether the object is moving towards us or away from us, but it doesn't tell us the object's speed.

For us to measure how fast the object is moving, we must observe it long enough to notice how it position gradually shifts across the sky.

Identify the forms of light that pass through Earth's atmosphere and those that do not.

Only: Radio waves, visible light, and small parts of the infrared spectrum can be observed from the ground. (and the very longest wavelengths of ultraviolet light)

Describe the major patterns we find among objects orbiting the Sun.

1) All planetary orbits are nearly circular and lie nearly in the same plane.

2) All planets orbit the Sun in the same direction: counterclockwise as viewed from high above Earth's North Pole.

3) Most planets rotate in the same direction they orbit

4) Most of the solar system's large moons have similar properties in their orbits around their planets.

Predict how the temperature of an opaque gas cloud will change as the cloud shrinks.

Temperature increases as clouds shrink

Explain why Earth's Sky is blue and its sunsets are red.

Gas molecules scatter blue light more effectively than red light. When the sun is overhead, the scattered blue light reaches our eyes from all directions, so the sky appears blue.

At sunrise or sunset, when sunlight passes through more air on its way to our eyes., so much of the blue light is scattered away that we are just left with red light to color the sky.

Describe the evidence that water once flowed on the surface of Mars.

The geology of Mars, ancient water flows, dried up river beds, and evidence of martian water today.

Explain Venus is so much hotter than Earth.

Earth has as much carbon dioxide as Venus, but it is mostly locked away in rocks and oceans rather than in our atmosphere.

Explain how Earth's Carbon cycle keeps it climate stable.

The Earth's greenhouse effect and CO2 gets dissolved in oceans and locked into rocks and plants.

Plants = photosynthesis

Describe the scientific evidence indicating that human activity is causing global warming.

Average surface temperature of Earth has been increasing.

Growing seasons have been lengthening. Habitats have been shifting. The last decade has been the hottest on record.

Identify the most likely locations for life among the Joivan moons.

Jupiter's moon Europa

Describe the evidence indicating that a major impact killed the dinosaurs.

Evidence of mass extinction at the K-T boundary, Dinosaur fossils below the layer of iridium from meteorite, no dinosaur fossils above the layer of iridium from the meteorite.

Assess the probability that a major impact will cause widespread devastation or mass extinction with the next century.

about 1 in 1000

Describe how extrasolar planets have been indirectly detected through observations of the host stars.

by looking for periodic wobble, measure the wobble by using doppler shifts of the star's spectrum

extrasolar planets

Planet that orbits a star other than our own.

Identify the two forms of balance that now keep the sun stable.

Pressure balances gravity

Fusion energy balances the energy radiated into space

Predict how the Sun's core would respond to a change in temperature.

If the Sun's core temperature rose slightly, the fusion rate would be higher and the core pressure would rise, which would causes the core to expand and cool.

If the Sun's temperature slightly dropped, there would be a drop in pressure and a decrease of the rate of fusion. The core would shrink and its temperature would rise until the fusion rate returned to normal.

Describe the evidence that supports our understanding of the Sun's interior.

The characteristics of the solar vibrations support our mathematical models of the sun's interior. We observe these solar vibrations through Doppler shifts on the Sun's surface.

Describe how solar activity affects humans.

Coronal mass ejections can tamper with radio communications, disrupt electrical power delivery, and damage the electronic components in orbiting satellites.

They can also heat the Earth's upper atmosphere, making it expand, then causing a drag on low-orbiting satellites, making them crash down to the ground.

Determine the change in apparent brightness that would result from changing the distance to an object of constant luminosity.

Doubling the distance to a star would decrease its apparent brightness by a factor of 2^2 or 4.

Estimate the surface temperature of a star from its color.

Our sun has a surface temperature of 5800 K which causes it to emit strongly in the middle portion of the spectrum, which is why the Sun looks yellow or white.

But stars that are cooler (3650 K), looks red because it emits much more red light than blue light.

Stars that are hotter (9,400 K) emits more blue light than red, thus making it look slightly blue.

Identify the information needed to measure the mass of a star.

We need to measure both their orbital period and separation between them.

Identify on an H-R diagram the regions corresponding to the main sequence, giants, supergiants, and white dwarfs.

O B A F G K M

Oh, boy all frat guys kill me.

Describe how gravitational contraction eventually triggers nuclear fusion in a star-forming cloud.

Stars form in cold clouds where gravity can overcome thermal pressure. Clouds continue to contract because they radiate away energy in the form of infrared light.

Explain why contracting gas clouds with masses less than 0.08 Msun or greater than a few hundred M sun fail to achieve energy balance.

Something stops contraction before fusion stars.

Predict how the central temperature of a star changes after fusion exhausts the fuel in its core.

After exhausting its core hydrogen, the Sun will expand to become a red giant, powered by rapid hydrogen fusion in a shell surrounding the core.

Explain how H-R diagrams of star clusters support our models of how stars change near the ends of their lives.

A star's life track on an H-R diagram shows how its properties change with time.

Explain why fusion in stars of greater mass can produce elements with more protons in their nuclei.

The core of a high-mass star eventually become hot enough for fusion to produce the elements of which we and the Earth are made off.

Describe what ultimately happens to a star with an iron core.

A high-mass star's death is imminent when iron piles up in its core, because fusion of iron releases no energy.

Predict the life history of a star with a given mass.

All low-mass and intermediate-mass stars follow life stages similar to those of our sun, end life as a white drawf.

While high-mass stars live short but brilliant lives and die in supernova explosions.

Define the term "black hole" in terms of escape velocity.

An object whose gravity is so powerful that not even light can escape it.

Predict how the radius of a black hole's event horizon will change if its mass increases.

Add mass = increase in radius of event horizon.

Describe the evidence indicating that some X-ray binary systems contain black holes.

Some X-ray binaries contain compact objects of mass exceeding 3 Msun, which are likely to be black holes. On famous X-Ray binary with a likely black hole is in the constellation Cygnus

Describe how our galaxy recycles gas from dying stars into new stars.

Star-gas-star cycle: Molecular clouds > Star formation > nuclear fusion in stars > returning gas > hot bubbles > atomic hydrogen clouds > and then back to molecular clouds

Interpret the difference between disk and halo stars in terms of basic model for galaxy formation.

Halo stars formed first as gravity caused cloud to contract. Gas left over from the halo formation settled into spinning disk. Stars continuously form in disk as galaxy grows older.

Identify the primary difference between spiral and elliptical galaxies.

Spiral galaxies contain spheroidal and disk components.

Elliptical galaxies is all the spheroidal component and virtually no disk component

Describe the chain of methods used to determine the distance of galaxies.

1) you have to measure the distances to nearby stars through parallax

2) then you use the standard candle method.

Basically we determine the distance by measuring the apparent brightness of an object whose luminosity we already know and then apply the inverse square law for light.

Describe how the age of the universe is related to Hubble's constant.

When the Big Bang occurred, all the galaxies were essentially on top of one another, so by using Hubble's constant, we can determine how fast the universe has been expanding, thus giving us the age of the universe.

Describe the basic assumptions in our current models for galaxy formation.

Most of our successful models of galaxy formation suggest that protogalactic clouds formed in regions of slightly enhanced density in the early universe.

Explain why scientists think the early universe was much hotter and denser than it is now.

Due to Hubble's law that the universe is expanding. As the universe gets less dense, the temperature drops.

Explain why most of the helium in the universe cannot be made by nuclear fusion in stars.

By the time stars formed the universe became too cool for helium to be produced

Describe the observational evidence supporting the idea of inflation.

Patterns in microwave maps show us temperature/density differences that are the seeds of structure formation, Observable patterns of structure in universe agree with what inflation should produce

Explain why the night sky is dark.

Night sky is dark because the universe changes with time.

Describe the evidence for dark matter in galaxies.

Rotation Curves: A plot of orbital velocity versus orbital radius

Orbital speeds decrease with distance from the sun and the center of the galaxy both in the Milky Way and in other galaxies

Dark matter speeds up the center

Describe three methods for measuring the amount of dark matter in clusters

Orbital studies of galaxies

Doppler shifts - temperature measurements of hot gas

Gravitational lensing - bends light beams

Distinguish between recollapsing, coasting, critical, and accelerating models for the expansion of the universe.

Recollapsing - Extremely strong gravitational attraction with no repulsive force, time would eventually slow down, and then completely reverse. In the final stage, the galaxy would look like it did during the Big Bang

Coasting - weak gravitational attraction with no repulsive force. Galaxies would be moving at the same speed they are today.

Critical - gravitational attraction not strong enough to reverse the expansion, leading to a universe that would never collapse but would continue to expand slower and slower as time went on.

Accelerating - repulsive force strong enough to overpower gravity, causing galaxies to recede from one another with an ever increasing speed.

Describe the evidence indicating that the expansion of the universe is accelerating.

Distances measured to faraway white dwarf supernovae indicate that the expansion of the universe is speeding up.

Supernovae indicate that the expansion of the universe is speeding up the farther the object.

Arrange in increasing order the average density in the form of stars, the average density of dark matter, and the average density of dark energy.

1) Average density in stars
2) average density in dark matter
3) average density in dark energy

Identify the necessary ingredients for life on Earth.

1) distance from star that allows water
2) volcanism that releases water vapor and CO2
3) Plate tectonics that support CO2 cycle
4) Planetary magnetic field that protects the atmosphere.

Predict how the habitable zone around a star would change if its luminosity were to change.

Less luminous = closer in and smaller zone

more luminous = bigger zones

All depends on the star's mass

Explain why interstellar travel is far more difficult than portrayed in the movies.

Because it requires 1000x more energy than the current world uses each year, spaceships would have to travel at the speed of light, and new technology would be needed.