ASTR Final Overview

Chapter 1: Universe Basics (4 Questions)

1. What are the relative sizes and scales of different objects in the universe?
Answer: Galaxies > Solar Systems > Stars > Planets. Galaxies are the largest, followed by solar systems, then stars, and finally planets.

2. What are the key units of distance in astronomy, and how are they defined?
Answer:

• Light-year: The distance light travels in one year (~9.46 trillion km).

• Astronomical Unit (AU): The average distance between Earth and the Sun (~150 million km).

• Solar Radius: The radius of the Sun, approximately 696,340 km.

3. What are the ages of the universe, solar system, and Earth?
Answer:

• Universe: 13.8 billion years.

• Solar System: 4.6 billion years.

• Earth: 4.54 billion years.

4. How are elements made in the universe, and which were created during the Big Bang?
Answer:

• Elements are created through nuclear fusion in stars and supernovae.

• The Big Bang produced primarily hydrogen, helium, and trace amounts of lithium.

Chapter 2: Celestial Sphere (6 Questions)

1. What are key concepts related to the celestial sphere?
Answer: The ecliptic (path of the Sun), zodiac, constellations, and north/south celestial poles are essential terms related to the celestial sphere.

2. How do objects move across the night sky?
Answer: Objects appear to move west to east across the sky due to Earth's rotation. Earth rotates counterclockwise on its axis and orbits the Sun counterclockwise.

3. What causes Earth’s rotation, and how does this relate to the movement of stars?
Answer: Earth’s rotation causes the stars to appear to move across the sky from east to west. This movement is an illusion created by Earth’s rotation on its axis.

4. How is Earth’s rotation related to the position of the Sun?
Answer: The Sun appears to move across the sky daily, rising in the east and setting in the west as Earth rotates on its axis.

5. What are declination and right ascension?
Answer:

• Declination: Measures how far an object is from the celestial equator (like latitude).

• Right ascension: Measures the angle of an object relative to the vernal equinox (like longitude).

6. What causes the seasons on Earth?
Answer: Earth’s axial tilt causes different hemispheres to receive varying amounts of sunlight throughout the year, resulting in the four seasons.

Chapter 3: Models of the Universe (4 Questions)

1. What is the difference between geocentric and heliocentric models?
Answer:

• Geocentric: Earth is at the center of the universe.

• Heliocentric: The Sun is at the center of the solar system.

2. What key discoveries led to the "Copernican Revolution"?
Answer:

• Copernicus proposed the heliocentric model, Kepler’s laws confirmed elliptical orbits, and Galileo's observations (e.g., moons of Jupiter) provided evidence for heliocentrism.

3. What causes retrograde motion of planets?
Answer: Retrograde motion is an apparent backward motion observed when Earth overtakes another planet in its orbit.

4. What is the difference between a hypothesis, a law, and a theory in science?
Answer:

• Hypothesis: A testable prediction.

• Law: A consistent, well-supported observation (e.g., laws of motion).

• Theory: A well-substantiated explanation that has stood the test of time.

Chapter 4: Newtonian Physics (8 Questions)

1. What is the difference between mass and weight?
Answer:

• Mass is the amount of matter in an object, measured in kilograms.

• Weight is the force exerted by gravity on an object, measured in newtons.

2. What are Newton’s three laws of motion?
Answer:

1. An object will remain at rest or in motion unless acted upon by an external force.

2. Force equals mass times acceleration (F = ma).

3. For every action, there is an equal and opposite reaction.

3. How does the force of gravity change as you change the masses of objects and their distance?
Answer: The gravitational force increases with the mass of the objects and decreases with the square of the distance between them.

4. How does gravity relate to acceleration?
Answer: Acceleration due to gravity is the same for all objects, regardless of their mass.

5. What causes tides on Earth?
Answer: Tides are caused by the gravitational pull of the Moon and the Sun on Earth’s oceans.

6. What is the difference between velocity and speed?
Answer:

• Velocity includes both speed and direction.

• Speed is the rate of motion regardless of direction.

7. What is the difference between velocity and acceleration?
Answer:

• Velocity is the speed in a given direction.

• Acceleration is the rate of change of velocity.

8. What are the different types of energy?
Answer:

• Kinetic energy: Energy of motion.

• Potential energy: Stored energy.

• Radiative energy: Energy carried by electromagnetic waves.

Chapter 5: Light and Matter (14 Questions)

1. How are wavelength, frequency, and wave speed related?
Answer: Wave speed = Wavelength × Frequency. For light, the speed is constant.

2. How is color related to frequency for light?
Answer: Higher frequencies correspond to bluer light; lower frequencies correspond to redder light.

3. What determines the color of a particular object that we see?
Answer: The color of an object depends on the wavelengths of light it reflects or emits.

4. What are the differences between emission, absorption, transmission, reflection, and scattering of light?
Answer:

• Emission: Light emitted by an object.

• Absorption: Light absorbed by an object.

• Transmission: Light passing through an object.

• Reflection: Light bouncing off an object.

• Scattering: Diffusion of light in various directions.

5. What are the different parts of the electromagnetic spectrum?
Answer: X-rays, ultraviolet, visible light, infrared, radio waves.

6. How does the wavelength and frequency of a photon relate to its energy?
Answer: Energy = Planck’s constant × frequency. Energy is directly proportional to frequency and inversely proportional to wavelength.

7. What is the structure of matter?
Answer: Matter is made up of atoms consisting of protons, neutrons, and electrons. Atoms combine to form molecules.

8. What is the difference between atomic number and atomic mass number?
Answer:

• Atomic number: Number of protons in an atom.

• Atomic mass number: Total number of protons and neutrons.

9. What do electron energy levels represent in an atom?
Answer: Energy levels represent the specific orbits electrons can occupy around the nucleus. Electrons can absorb or emit photons when they transition between these levels.

10. What are the phases of matter?
Answer:

• Solid, liquid, gas, plasma.

• Phases change with temperature and pressure.

11. What is the difference between thermal, emission, and absorption spectra?
Answer:

• Thermal spectrum: Emitted by objects due to their temperature.

• Emission spectrum: Light emitted by hot gases.

• Absorption spectrum: Light absorbed by cooler gases.

12. How does light teach us about stars’ temperatures?
Answer: The color and spectrum of light emitted by a star indicate its temperature.

13. What is a black body?
Answer: An idealized object that absorbs and emits all wavelengths of light. It’s a perfect emitter of thermal radiation.

14. How do we use the Doppler Effect to learn the velocity of an object?
Answer: By measuring the shift in the wavelength of light. Redshift means an object is moving away; blueshift means it is moving closer.

Chapter 6: Telescopes (6 Questions)

1. What are the differences between refracting and reflecting telescopes?
Answer:

• Refracting telescopes use lenses to focus light.

• Reflecting telescopes use mirrors to focus light.

2. How does light-collecting area and angular resolution impact what a telescope can see?
Answer:

• Light-collecting area: A larger area collects more light, allowing observation of faint objects.

• Angular resolution: A higher angular resolution enables the telescope to distinguish between closely spaced objects.

3. What are the three main ways astronomers use telescopes?
Answer:

1. Imaging: Capturing pictures of objects in the sky.

2. Spectroscopy: Analyzing light to determine composition and motion.

3. Time monitoring: Observing changes in objects over time.

4. Why do we put telescopes in space?
Answer:

• To avoid atmospheric distortion, which blurs images.

• To observe wavelengths blocked by Earth's atmosphere, such as X-rays and ultraviolet light.

5. How does Earth’s atmosphere affect ground-based observations?
Answer: The atmosphere causes turbulence, blurring images, and blocks certain wavelengths (e.g., X-rays, ultraviolet).

6. What types of light can successfully pass through Earth’s atmosphere?
Answer:

• Visible light and radio waves pass through relatively unimpeded.

• X-rays, gamma rays, and most ultraviolet light are blocked.

Chapter 14: The Sun (9 Questions)

1. What process powers the Sun?
Answer: Nuclear fusion in the core, primarily the proton-proton chain, where hydrogen nuclei fuse into helium, releasing energy.

2. How old is the Sun? How does its age rule out chemical burning and gravitational contraction as power sources?
Answer:

• The Sun is about 4.6 billion years old.

• Chemical burning and gravitational contraction could not sustain the Sun’s luminosity for this duration; only nuclear fusion provides sufficient energy.

3. What are gravitational equilibrium and energy balance, and how do they relate to the Sun’s evolution?
Answer:

• Gravitational equilibrium: Balance between gravitational force pulling inward and outward pressure from nuclear fusion.

• Energy balance: Energy produced by fusion equals the energy radiated by the Sun.

4. What are the key components of the Sun’s structure, and their temperatures?
Answer:

• Core (~15 million K): Site of nuclear fusion.

• Radiation zone (~7 million K): Energy transported by photons.

• Convection zone (~2 million K): Energy transported by convection currents.

• Photosphere (~5,800 K): Visible surface.

• Chromosphere (~10,000 K): Emits UV radiation.

• Corona (~1-3 million K): Outer atmosphere, visible during solar eclipses.

5. How does nuclear fusion occur in the Sun?
Answer:

• Hydrogen nuclei (protons) fuse to form helium in the Sun’s core through the proton-proton chain, releasing energy.

6. How does fusion energy escape from the Sun?
Answer:

• Energy is carried outward through the radiation zone by photons and through the convection zone by rising hot gas.

7. How long does it take energy to pass through the radiation and convection zones?
Answer:

• Radiation zone: ~100,000 years.

• Convection zone: A few weeks.

8. How do neutrinos provide information about the Sun's interior?
Answer: Neutrinos are nearly massless particles produced in nuclear fusion, carrying direct information from the core. They are hard to detect because they interact very weakly with matter.

9. What causes solar activity, such as sunspots, solar flares, prominences, and coronal mass ejections?
Answer: Solar activity is driven by the Sun’s magnetic field, which creates disturbances in the atmosphere.

Chapter 15: Properties of Stars (14 Questions)

1. How do we measure stellar luminosities?
Answer: By using the inverse square law of light to relate apparent brightness and distance to luminosity.

2. What is the difference between apparent brightness and luminosity?
Answer:

• Apparent brightness: How bright a star appears from Earth.

• Luminosity: Total energy emitted by the star.

3. How are apparent brightness and luminosity related?
Answer: Luminosity = Apparent brightness × (distance)^2.

4. How does stellar parallax measure distances to stars?
Answer: By observing a star’s apparent shift in position when viewed from different angles (e.g., six months apart).

5. How do we measure stellar temperatures?
Answer: From a star’s color and by applying the laws of thermal radiation (e.g., Wien’s Law).

6. What is the spectral sequence of stars?
Answer: O, B, A, F, G, K, M (from hottest to coolest).

7. What spectral type is most common?
Answer: M-type stars are the most common because they are low-mass and long-lived.

8. Who were the Harvard computers, and what did they contribute?
Answer: Astronomers like Annie Jump Cannon helped classify stars and develop the OBAFGKM sequence based on temperature.

9. How are stellar masses measured?
Answer: By studying binary star systems and applying Kepler’s third law.

10. What does the Hertzsprung-Russell (H-R) diagram show?
Answer: It plots stars based on luminosity and temperature, showing patterns like the main sequence, giants, and white dwarfs.

11. How do giant stars and white dwarfs differ from main sequence stars?
Answer:

• Giant stars: Larger, cooler, and more luminous.

• White dwarfs: Smaller, hotter, and less luminous.

12. How can we measure the age of a star cluster from its H-R diagram?
Answer: The main sequence turnoff point shows the age; older clusters have fewer high-mass stars on the main sequence.

13. What are the two types of star clusters?
Answer:

• Open clusters: Young and loosely bound.

• Globular clusters: Old and tightly bound.

14. How do we use binary systems to measure stellar mass?
Answer: By observing their orbits and applying Kepler’s laws.

Chapter 16: Star Formation (10 Questions)

1. Why are molecular clouds ideal for star formation?
Answer: They are dense and cold, allowing gravity to overcome thermal pressure.

2. What is interstellar dust made of?
Answer: Silicates, carbon compounds, and ice.

3. How does dust affect observations of molecular clouds?
Answer: Dust blocks visible light, so infrared telescopes are used to observe them.

4. What are the key steps in star formation?
Answer:

1. Gravity causes a cloud to collapse.

2. A protostar forms.

3. Fusion begins in the core.

5. What is a protostar?
Answer: A forming star where fusion has not yet started.

6. What is the smallest mass for a star to form?
Answer: 0.08 solar masses; anything smaller becomes a brown dwarf.

7. What is the largest mass for a star to form?
Answer: About 150 solar masses, as higher mass stars are disrupted by radiation pressure.

8. How do first-generation stars (Population III) differ from modern stars?
Answer: They lacked heavy elements and formed only from hydrogen and helium.

9. Are low-mass or high-mass stars more common?
Answer: Low-mass stars are more common and have longer lifespans.

10. What role does rotation play in star formation?
Answer: Rotation leads to the formation of disks, jets, and winds that help redistribute angular momentum.

Chapter 17: Life and Death of Stars (11 Questions)

1. How does a star's mass affect nuclear fusion in its center?
Answer: Higher mass stars have hotter cores, allowing fusion to proceed faster and shortening their lifespans.

2. What are the differences in evolution between low-mass, intermediate-mass, and high-mass stars?
Answer:

• Low-mass stars (< 2 solar masses): Become white dwarfs.

• Intermediate-mass stars (2–8 solar masses): Shed outer layers and become white dwarfs after forming planetary nebulae.

• High-mass stars (> 8 solar masses): End their lives as supernovae, leaving neutron stars or black holes.

3. What are the convective and radiative zones in stars of different masses?
Answer:

• Low-mass stars: Convective outer layers and radiative cores.

• High-mass stars: Convective cores and radiative outer layers.

4. What are the key stages in the evolution of a low-mass star?
Answer:

1. Main sequence: Hydrogen fusion in the core.

2. Red giant: Hydrogen shell fusion.

3. Helium fusion: Produces carbon.

4. Planetary nebula: Outer layers are ejected.

5. White dwarf: Carbon core remains.

5. Why don’t low-mass stars undergo carbon fusion?
Answer: Their cores never reach the required temperature for carbon fusion.

6. What is the CNO cycle, and why is it important for higher-mass stars?
Answer: The CNO cycle is a hydrogen fusion process that occurs in high-mass stars, using carbon, nitrogen, and oxygen as catalysts for faster fusion.

7. What is the "onion layer" structure in high-mass stars?
Answer: Layers of different elements fuse at increasing temperatures closer to the core, with hydrogen on the outside and iron at the center.

8. Why is iron significant in the evolution of massive stars?
Answer: Iron fusion does not release energy, causing the core to collapse, which triggers a supernova.

9. What role do neutrinos play in supernovae?
Answer: Neutrinos carry away most of the energy during core collapse and help drive the supernova explosion.

10. What are the two main types of supernovae?
Answer:

• Type I: White dwarf supernova with no hydrogen in the spectrum.

• Type II: Massive star supernova with hydrogen in the spectrum.

11. How can binary star systems affect stellar evolution?
Answer: Mass transfer between stars can alter their evolution, such as forming blue stragglers or triggering supernovae in white dwarfs.

Chapter 18: Stellar Remnants (10 Questions)

1. What are the three types of stellar remnants?
Answer: White dwarfs, neutron stars, and black holes.

2. How does electron degeneracy pressure support white dwarfs?
Answer: Electron degeneracy pressure prevents further collapse by resisting compression.

3. What is the maximum mass for a white dwarf?
Answer: ~1.4 solar masses (Chandrasekhar limit).

4. Why are more massive white dwarfs smaller in radius?
Answer: Greater gravity compresses them further.

5. What are the typical size and mass of a neutron star?
Answer:

• Mass: 1.4–3 solar masses.

• Diameter: ~20 kilometers.

6. What supports neutron stars against collapse?
Answer: Neutron degeneracy pressure.

7. What is a pulsar?
Answer: A rapidly spinning neutron star that emits beams of radiation.

8. What is a black hole’s event horizon and Schwarzschild radius?
Answer:

• Event horizon: The boundary where nothing can escape.

• Schwarzschild radius: The distance from the center to the event horizon.

9. Why does time run more slowly near a black hole?
Answer: Gravitational time dilation occurs due to extreme spacetime curvature near the event horizon.

10. What causes gamma-ray bursts?
Answer:

• Collisions between neutron stars.

• Collapse of massive stars into black holes.

S2/S3: Special and General Relativity (10 Questions)

1. What are the two major absolutes of special relativity?
Answer:

1. The laws of nature are the same for all observers.

2. The speed of light is constant for all observers.

2. What is "relative" about relativity?
Answer: Motion is relative; there is no absolute frame of reference.

3. Why can’t we reach the speed of light?
Answer: Infinite energy would be required, as an object’s mass increases near the speed of light.

4. How does relativity affect space and time?
Answer:

• Objects moving near the speed of light experience time dilation (time slows down).

• Length contraction occurs, where objects appear shorter in the direction of motion.

5. What is the main difference between general and special relativity?
Answer: General relativity includes gravity, describing it as spacetime curvature, while special relativity applies to non-accelerating frames.

6. What is the equivalence principle?
Answer: The effects of gravity are indistinguishable from acceleration in a small, local frame.

7. What is spacetime?
Answer: A four-dimensional combination of three spatial dimensions and one time dimension.

8. How does general relativity explain gravity?
Answer: Gravity is the curvature of spacetime caused by mass.

9. Why is a black hole a "hole" in spacetime?
Answer: A black hole warps spacetime infinitely at its singularity, creating a bottomless pit.

10. How does gravitational time dilation differ near a black hole versus near Earth?
Answer:

• Near a black hole: Time slows significantly due to extreme spacetime curvature.

• Near Earth: Time dilation exists but is negligible