Astronomy Exam 3

What is the celestial sphere?

The sphere that all the stars were on around earth that people used to believe in

What is the ecliptic?

Sun's path through the sky

What is the north star and what is notable about it?

AKA Polaris
All stars appear to orbit Polaris because it is is on our celestial axis
Does not appear in Southern Hemisphere

What are circumpolar stars?

Stars that never set

What is the geocentric model?

Earth is the center of the universe, with all objects orbiting around it

Who believed in the geocentric model?

Ancient Greeks until the 16th century

Why does the geocentric system not work?

There is apparent retrograde motion in planets' orbits (they go backwards)

What is the Ptolemaic system?

It explains why planets go backwards—they orbit Earth, but also orbit a smaller point to make a small circle in its bigger orbit
Smaller cycle: epicycle
Larger cycle: deferent

How long did the Ptolemaic system last?

~1000 years

What is the heliocentric model?

The sun is at the center of the universe, with everything else orbiting around it

Who developed the heliocentric model and when?

Nicolaus Copernicus, in the 16th century

Why does the heliocentric model work?

It explains the apparent retrograde motion without epicycles

Is the heliocentric model correct?

Not completely, as it tells that the sun is the center of the universe, which is incorrect

For what three reasons was the heliocentric model rejected?

We do not feel earth move
No evidence of stellar parallax (because stars are too far away)
Predictions of planet locations did not improve—Tycho Brahe's predictions were still a bit off

What is stellar parallax?

The apparent change in a star's position due to change in perspective
We were too far away to detect this with 16th century technology, so we couldn't see Earth move

What was Galileo the first to do?

He was the first one to observe the sky with a telescope, and he adopted the heliocentric model

What were Galileo's five observations?

Observed Jupiter's 4 biggest moons
Observed moon's craters
Observed sunspots
Observed the Milky way as a collection of stars
Observed Venus' phases

What was Galileo forced to do?

He was forced to recount his claims of the heliocentric model by the church and sentenced to house arrest

What did Galileo's observations do?

They casted a doubt on the geocentric model (especially the phases of Venus)

What did Kepler do (his first law)?

He observed that all planets orbit in an ellipse, which fixed all those incorrect predictions

What did Newton do?

He discovered gravity and developed calculus, which he applied to all the planets and got predictions correct (but he still could not get Mercury's predictions correct

What did Einstein do?

He discovered relativity, which allowed him to get Mercury's predictions correct

What is the nebular theory?

The solar system began as a giant molecular cloud

What was the solar nebula and how large was it?

Our stellar nebula that the solar system formed from
50-60 light years thick

What three reasons cause a stellar nebula to collapse into a star system?

Gravity causes it to collapse, but gravity is not strong enough by itself, so there are three more reasons for collapse:
Supernova shockwave
Passing star interacting with the cloud
Passing dwarf galaxy

What three things happen as the nebula cloud collapses?

Heats up
Flattens
Spins faster due to conservation of angular momentum

What is angular momentum and its equation?

Momentum of a rotating object
Mass · Velocity · Distance from rotational axis

What is a protostar?

A star before it becomes a real star

When does a protostar become a star?

When nuclear fusion is achieved and sustained in its core

What is a brown dwarf?

AKA failed star
Objects that do not have enough mass to sustain fusion

What is the circumstellar disk?

The leftover disk of gas and dust spinning around a young star
The dust collides into planetesimals, then they collide into planets

What is absorption?

Electrons absorb a photon and move up and energy level in the atom
More energy in the photon (blue or violet light) equals a higher jump

What is emission?

The photon is emitted and the electron jumps down a level
This is how light is created

What is an absorption spectrum?

A rainbow with certain lines missing

What is an emission spectrum?

Specific lines of color

What is a continuous spectrum?

The continuous rainbow

What is a blackbody?

An idealized object absorbing all radiation, while also emitting perfect radiation
Stars behave close to blackbodies

What is Wien's law?

A higher temperature equals short wavelength (blue)
Cooler temperature equals longer wavelength (red)

What are the three methods of exoplanet detection?

Astrometric method
Doppler method
Transit method

What is the astrometric method?

Looking for a star's "wobble" it gets the gravity of a planet's orbit
Biased towards large planets
Needs a face-on system to detect

What is a barycenter?

The common center of mass between a planet and a star (the Sun actually orbits a point due to Jupiter's huge mass)

What is the Doppler method?

AKA radial velocity method
Waves compress when thin objects approach and widen when they retreat
As a star gets closer to us in its orbit, the light compresses, turning blue
As it gets further away, the light widens, turning red
If the star's light shifts in color, a planet is orbiting the star
Biased towards large planets
Needs an edge-on system to detect

What is the transit method?

Planet passes in front of the star, making the light output dim
Most successful method because it can detect smaller planets in addition to larger planets
Larger planet equals larger light curve dip
Needs an edge-on system to detect

What are the terrestrial planets?

The inner four planets: Mercury, Venus, Mars, and Earth

What are the terrestrial planets' 5 characteristics?

Small
Close to the sun
Made up of metals/rocks
No rings
Little/no moons

What are the Jovian planets?

The outer four planets: Jupiter, Saturn, Uranus, and Neptune

What are the Jovian planets' five characteristics?

Large
Far away from the sun
Mostly hydrogen and helium in gaseous form
Many rings
Many moons

What is the frost line and where is it?

The distance at which volatile elements condense
At 5 AU

What are volatile elements?

Elements that evaporate easily, like water

Why do no planets exist in the asteroid belt?

Jupiter's gravitational pull would tear it apart

What is notable about Mars' and Jupiter's positions?

Mars is at 1.5 AU, while Jupiter is at 5.2 AU—they are super far away from on another because Jupiter's gravitational pull would tear apart any close planet

What three criteria does a planet need to have?

Orbits the sun
Large enough to be round
Has "cleared its neighborhood" of other objects, and is the largest thing in its orbit

Why isn't Pluto a planet?

It has not cleared its neighborhood—it crosses Neptune's and Eris' orbit

What is the Kuiper belt and where is it?

The second asteroid belt, from Neptune at 30 AU to 50 AU
It is huge

What is Eris?

A Kuiper belt object, a little larger than Pluto
Dwarf planet
Part of the reason Pluto was demoted—Eris didn't clear its own orbit and they did not want to make Eris a planet

What are the three dwarf planets?

Pluto, Eris, and Ceres

Where is Ceres?

In the main Asteroid belt

What are Mercury's three characteristics?

Closest planet
No moons
Largest core relative to its size of all the planets

What are Venus' six characteristics?

Second planet
Hottest planet
Intense pressure (more than the Mariana trench)
Slow, retrograde rotation (or flipped upside down so it appears to rotate backwards)
No magnetic field
No moons

What are the three theories for Venus' retrograde rotation?

Collision with a large object (such as a planet)
Tidal forces from the sun slowed it
Flipped upside down on its axis due to the sun's tidal forces

How big is the Moon?

5th largest in the solar system, and this is weird because Earth is small when compared to Jupiter or Saturn

What are the four theories on how the Moon formed?

Fission model, binary accretion model, capture model, and the giant-impact theory

What is the worst theory for the Moon's formation?

Capture model

What is the most accepted theory for the Moon's formation?

Giant-impact theory

What is the fission model for the Moon's formation?

A chunk of early spinning proto-earth broke off

What is the pro for the fission model for the Moon's formation?

Earth's outer layers are similar to the Moon's composition

What are the two cons to the fission model for the Moon's formation?

Conservation of angular momentum fails
Moon's inclined orbit fails

What is the binary accretion model (co-formation) for the Moon's formation?

Earth and the Moon formed at the same time, the Moon coalescing from the dust around a proto-earth

What is the pro of the binary accretion model for the Moon's formation??

Oxygen isotopes are identical on Earth and the Moon

What are the two cons of the binary accretion model for the Moon's formation??

The Moon lacks a dense core like Earth's
Conservation of angular momentum fails

What is the capture model for the Moon's formation?

Earth pulled the moon into orbit, and the Moon formed away from Earth

What is the pro for the capture model for the Moon's formation?

Most moons in the solar system are captured

What are the two cons for the capture model for the Moon's formation?

The Moon is too big to be pulled in by Earth, making angular momentum fail
The Moon is too much like Earth to have formed elsewhere

What is the giant-impact theory for the Moon's formation?

A Mars-sized object hits proto-earth, and a broken off piece forms the moon

What are the four pros for the giant-impact theory for the Moon's formation?

Conservation of angular momentum works
Iron density is consistent with a large impact
The Moon's inclined orbit works
Dry rocks with no volatile elements

What is the con for the giant-impact theory for the Moon's formation?

Lunar samples contain too many volatiles for the energy of a giant impact—they should have all been vaporized

What are solar eclipses?

When the Moon blocks out the sun's light, casting a shadow on Earth

What is a penumbra in an eclipse?

The partial/lighter shadow

What is an umbra in an eclipse?

The full/darkest shadow

What is a partial solar eclipse?

When only part of the sun is blocked

What is a total solar eclipse?

The sun's light is completely blocked by the Moon, making the corona visible

What is an annular solar eclipse?

A total solar eclipse, but the Moon is too far away to completely block the sun's light
This forms a "ring of fire"

When does an annular solar eclipse occur?

At the Moon's apogee (furthest point from Earth, occurring due to its elliptical orbit)

What is a lunar eclipse?

Earth blocks the sun's light, casting a shadow onto the Moon

What is a partial lunar eclipse?

The Moon is in the umbra and the penumbra
This turns red

What is a total lunar eclipse?

The Moon is in the umbra
This turns red

What is a penumbral lunar eclipse?

The Moon is in the penumbra
This does not turn red

Why do eclipses not happen monthly?

The shadow does not hit Earth every time because the moon has an inclined orbit—it only lines up correctly rarely

How long is a lunar month?

28 days

What causes moon phases?

Our viewpoint from Earth—not shadows

What is tidal locking?

Once face of the Moon always points towards Earth because one lunar month equals one lunar day

What are Mars' six characteristics?

No magnetic field
Has the largest volcano in the solar system (Olympus Mons)
It is a big ball of oxidized iron (rust), giving it the red color
It has two moons—the innermost one is too close and Mars will eventually rip it apart
Sunsets are blue
People that land will be immediately exposed to radiation

What are Jupiter's eight characteristics?

Many moons
Gas giant
Largest planet
10-hour day (fastest rotating and shortest day)
Made of hydrogen and helium
Great Red Spot: giant hurricane
Has differential rotation—different latitudes rotate at different speeds
Has bands—dark bands are belts, light bands are zones

What are the Galilean moons?

Jupiter's four main moons, discovered by Galileo
Ganymede, Callisto, Io, and Europa

What are Ganymede's two characteristics?

Largest moon in the solar system
Only moon with a magnetic field

What are Callisto's characteristic?

Oldest and most cratered surface of any object in the solar system

What is Io's characteristic?

Most geologically active object in the solar system, with over 400 volcanoes

What are Europa's two characteristics?

Ocean covered by a 10-mile thick sheet of ice, and water escapes through geysers in the ice
Best chance of life in the solar system

Why is Europa's ocean not frozen?

It gets heat from its core

What are Saturn's five characteristics?

Gas giant
Most prominent rings
Most moons
Ammonia gas gives it a yellow color
Could float in water due to low density