HZ Astron 101 | Final Exam

Explain Karl Popper's theory regarding falsifiability.

A theory must be testable (must be able to prove false); otherwise, it's not scientific. Theories are NEVER proven RIGHT. They're only tested not to be false.

What is Occam's Razor?

The simplest theory is usually correct.

How did the Greeks know that Earth was round?

(1) The mast of the ship went down last. (2) Constellations change as you move. (3) Earth's shadow on the moon is curved

Why did Greeks think that the Earth didn't move/rotate?

(1) They thought that we should be able to feel the movement on Earth. (2) If you drop an object, it falls straight down.

T/F: The Greeks valued observation over theory.

False

Who correctly measured the circumference of the Earth sometime around 240 BCE?

Eratosthenes.

T/F: Aristotle supported the geocentric theory.

True

What was believed about planets' paths in space?

Planets moved in uniform circular motion.

What observation challenged the geocentric model?

Retrograde motion. The path of the planets didn't make sense if Earth was the center of the universe.

What was Ptolemy's contribution to astronomy?

Refined the geocentric model with epicycles to explain retrograde motion.

What was the impact of Ptolemy's model success?

It prevented astronomical advancement for the next 1400 years.

What were the main points of Copernicus' Revolutions?

(1) Planets travel in uniform circular orbits. (2) Heliocentric model (NOT the first person to think of). (3) Earth is a planet just like the other planets/Earth is NOT the center of the universe.

What did Copernicus notice about the planet's velocity?

Planets closer to the sun had a higher velocity.

What were the problems of Copernicus' model?

(1) Couldn't observe parallax. (2) People don't feel movement on Earth. (3) Requires epicycles to match observations.

What is parallax and why was the lack of observation used as a rebuttal against the heliocentric theory?

(1) Parallax is the apparent shift of position of any nearby star against the background of distant objects. (2) If the Earth was orbiting around the Sun, at different positions, the distant stars would seem to shift. But without telescopes, this was hard to observe.

T/F: Copernicus' model was more accurate than Ptolemy's model.

False

What is Tycho Brahe's impact on astronomy?

In Uraniborg, he took the most precise astronomical observations of this time. His data helped Kepler come to his three laws.

What is Kepler's 1st Law?

Planets travel in elliptical orbits, with the sun in one focus.

What is Kepler's 2nd Law?

Line from the sun to the planet sweeps the same area at the same time. Conservation of Angular Momentum

What is Kepler's 3rd Law?

P^2 \= a^3

What are the units of Kepler's 3rd Law?

Period ⇒ Years; a (length of the semi-major axis of the orbit) ⇒ Astronomical units (1 AU \= the distance between the Earth and the Sun)

What did Galileo discover about the acceleration of falling objects?

The free-fall acceleration always equals to 9.8 m/s^2, regardless of the mass of the object.

T/F: Galileo invented the telescope.

False; a Dutch astronomer did, but Galileo improved the magnification.

What did Galileo conclude in his book Starry Messenger?

(1) Sun has sunspots → The sun rotates because the sunspots move. (2) The Moon is 3D. (3) Planets are disks and they change in size (because they're moving). (4) The phases and changes in size of Venus supported Copernicus' heliocentric model.

What was the impact of Galileo's observations about Venus?

It aligned with Copernicus' predictions using the heliocentric model and proved that Ptolemy's predictions using the geocentric model were wrong.

What did Newton invent/formulate to help him make strides in astronomy?

(1) Calculus. (2) "Modern" dynamics (E.g. force, inertia, velocity, acceleration). (3) Developed light and optics.

What is Newton's Universal Law of Gravitation?

F \= {[(m1)(m2)]/R^2} * G

Explain why the moon orbits Earth.

The moon has an optimal tangential velocity that allows it to fall around Earth rather than fall into Earth.

What is Newton's updated Kepler's 3rd Law?

P^2 (M1 + M2) \= a^3

How did the discovery of Uranus and Neptune bolster Newton's universal law of gravity?

Uranus had an imperfect orbit that didn't match the calculations of Newton's universal law of gravity. However, the discovery of Neptune explained what was messing up Uranus' orbit.

How did Einstein's understanding of time and space differ from Newton's?

(1) Time is NOT absolute. (2) Space is NOT just an abstraction that we use to compare different arrangements of bodies constituting the plenum.

Why are Newton's Laws of Motion an example of determinism?

Newton's Laws assume that everything can be predicted if starting conditions are known.

What makes special relativity "special" or what is the difference between special and general relativity?

Special relativity deals with observers who are in uniform motion while general relativity includes accelerated relative motion and gravity.

What are the two postulates of special relativity?

(1) There is no experiment that can be done to differentiate between being at rest or in constant motion. (2) The speed of light is equal to all observers. Disregard speed of the observer or speed of the source of light.

T/F: Nothing can travel faster than the speed of light in a vacuum.

True

What does the zero sum universe tell us about time?

If your speed increases, then time slows down. One of the special relativity corollaries tells us that time slows down for moving clocks.

What experiment supports the theory that time slows down for objects that travel at high speeds?

Cosmic ray muons should not be detected on the surface of the Earth because they have such a short lifespan. However, they are able to be detected since they travel so quickly that their lifespan is "increased" to the point where they can reach the surface of the Earth.

T/F: Mass and energy are not interchangeable.

False; think nuclear bombs.

According to Einstein's theory of General Relativity, what is gravity?

It's the curvature of "spacetime". All matter and energy curves space.

How do masses affect spacetime?

Adding a mass makes spacetime curve. The greater the mass, the greater the curving. Smaller masses follow the curve of spacetime caused by larger masses, which gives us the effect of gravity.

What was the first test that supported the theory of general relativity?

Einstein's theory of general relativity could fully explain the advance of the perihelion of Mercury.

What does the equivalence principle state and what are the implications?

You can't do an experiment to differentiate between being "at rest" and "uniform acceleration". Thus, gravity \= acceleration. If acceleration can make light seem to bend, then gravity can also make light bend.

What experiment supported the theory that gravity can make light bend?

1919 solar eclipse expedition showed that the position of stars seemed to move as a result of the sun's gravity.

How do black holes form?

A massive object collapses in on itself.

How do black holes work/function?

The gravity from a black hole is so strong that not even light can escape it. The escape velocity has to be greater than light but nothing can travel faster than the speed of light. Anything that is pulled into the event horizon will be sucked in the black hole.

How can we detect black holes?

When sufficiently massive objects fall into/merge with black holes, they produce heat in the form of x-rays. Using LIGO, we can detect very small gravitational waves produced by massive objects merging with black holes.

T/F: Newton's laws and principles are wrong.

False; they are incomplete/limited. Einstein's theory of general relativity can explain everything, even in HIGH gravity situations.

Why did Einstein add the cosmological constant to GR?

GR predicted that the universe could NOT be static. However, this would go against traditional scientific beliefs so he added this arbitrary repulsive force that would counteract gravity and keep the universe fixed.

What did Friedmann and Lemaitre believe about the universe?

They believed that the universe would expand or at least it was not static.

What are the implications of an expanding universe?

That implies there was once a beginning of the universe ⇒ primeval atom/Big Bang Theory.

T/F: If the density of the universe is less than the critical density, then the universe will eventually collapse onto itself.

False; Omega is the actual density of the universe divided by the critical density. Thus, if omega is greater than 1, then the universe will expand/be open. If omega is less than 1, then the universe will collapse/be closed.

If the wavelength of a wave decreases, does the velocity of the wave increase or decrease?

Decrease; v \= 𝜆 × 𝑓

What are the two light equations?

(1) c \= 𝜆 × 𝑓 (2) E \= h × 𝑓 (energy of photon \= Planck's constant * frequency

List the spectrum of light from shortest wavelength to longest.

Gamma rays, x-rays, ultraviolet, visible light, infrared, microwaves, radio waves.

Do x-rays have longer or shorter wavelengths than infrared?

Shorter

What was Galileo able to discover in 1609 with his telescope?

(1) Jupiter has moons. (2) Venus has phases and changes in size. (3) The Moon has mountains.

What increases a telescope light gathering power?

Increasing the diameter of the lens thus increasing the area of the lens.

Jeopardy round: Light at different wavelengths focus differently.

What is chromatic aberration?

How to avoid chromatic aberration?

Use mirrors instead of lenses to direct all the light to a focal point.

Who discovered infrared light in 1800?

William Hersehl.

What is bad seeing?

When Earth's atmosphere interferes with seeing.

How did astronomers avoid bad seeing?

They put the Hubble space telescope in space to bypass Earth's atmosphere.

What advantage do infrared telescopes have over visible light telescopes?

Infrared telescopes can bypass dust/gas clouds and see stars within dust clouds.

Which telescope uses infrared light?

James Webb Space Telescope

What are the 3 types of spectra?

(1) Continuous spectra. (2) Emission line spectra. (3) Absorption spectra.

T/F: All colors are emitted with the same wavelength.

False

Why can't we see the light emitted off of ourselves?

We emit infrared.

Jeopardy round: It is each element's specific "code".

What is emission line spectra?

Who determined the composition of the sun in 1859?

Joseph von Fraunhofer.

What did Joseph von Fraunhofer use to determine the composition of the sun?

Absorption spectra.

What are Kirchoff's Laws?

(1) Hot opaque objects (solid/dense gasses) emit a continuous spectra. (2) Hot thin gasses emit an emission line spectra. (3) Cool thin gasses between hot opaque objects and the observer emit an absorption spectra.

What can spectral lines tell us?

Chemical composition, temperature, density, magnetic fields, motion towards/away from the observer.

T/F: All waves exhibit the doppler effect.

True

Explain why the doppler effect happens.

An object that is moving is producing waves of equal wavelength but at different positions. Thus, because of the relative motion to the observer, it seems like the wavelengths are changing.

T/F: If the sound producing object is moving away, the wavelengths of the sound waves will seem shorter.

False; they'll seem longer when the object is moving away and shorter when the objecting is moving towards you.

T/F: You will notice the doppler effect if you're moving with the source or moving perpendicular to the source.

False

What is red shift?

The shift of the absorption spectra of a celestial object towards longer wavelengths when it is moving away from the observer.

What is the cause of red and blue shift?

The doppler effect.

What is the equation for the doppler effect for light?

z \= (received - emitted )/ emitted \= v/c

A star's spectral line normally at 𝜆 \= 600 nm is observed to be 𝜆 \= 700 nm. That means that the star is \_____.

Moving away from the observer.

A star's spectral line normally at 𝜆 \= 600 nm is observed at 𝜆 \= 605 nm. How fast is the star moving?

1/120 of the speed of light away from us.

What is the definition of temperature?

The average speed of random interval motion of the molecules in a substance.

What happens when the temperature of a substance increases?

(1) The amplitude/intensity of every wavelength increases. The radiation of the entire spectrum increases. (2) The wavelength of the peak intensity decreases (higher frequency).

Jeopardy point: The point at which there is no random interval motion of molecules in a substance.

Absolute zero on the Kelvin scale.

How did Max Planck solve the blackbody problem?

He came up with the quantum hypothesis which is the idea that energy can only be exchanged in discrete amounts called quanta, where you can only have whole numbers of energy.

How did Planck's quantum theory differ from classical physics?

In classical physics, you could have fractional energy. In quantum theory, you can only have whole numbers of energy.

What is Wien's Law?

max λ (in nm) \= 3x10^6 (in nm * K)/ T (in K)

What is Stefan-Boltzmann Law?

E is proportional to T^4

What causes blackbody/continuous/thermal spectra?

Electrons vibrating in dense objects.

T/F: All blackbodies at the same temperature emit the same spectra.

True; composition doesn't matter.

T/F: Hotter blackbodies emit more of their light in higher wavelengths.

False; in lower wavelengths/higher frequencies/higher energy.

T/F: Hotter blackbodies emit less total energy.

False; use common sense. If you don't have that like me, use Stefan-Botlzmann Law.

Who discovered the mathematical pattern to explain the emission spectrum of hydrogen in 1885?

J. J. Balmer

What gives the illusion of solidity?

Electrical repulsion between electrons.

T/F: Atoms are mostly empty space.

True

T/F: According to Bohr's hydrogen model, electrons can be at different energy levels at the same time.

False

What happens when hydrogen's electrons jump from a high to low energy level?

The process will release a photon at a certain wavelength.

How does Bohr's model explain the emission line spectrum?

When an electron jumps from a higher energy level to a lower energy level, it'll release light that corresponds to the emission line spectrum of hydrogen. The energy of each single line equals the difference between energy levels.

What is the law of conservation of energy?

Energy cannot be created or destroyed.

How does Bohr's model explain the absorption spectrum?

When an electron jumps from high to low energy it absorbs energy.