Van Gogh's Starry Night Fall 2000 ASTR 1120-001 Homepage

 Yin Yang Fall 2000 ASTR 1120-001 General Astronomy: Stars & Galaxies Discussion Questions

syllabus | timetable | questions | problems | reviews | hypertext | text


A theme of this course has been the posing of thought-provoking questions which we debate in class. Sometimes it takes as much as half an hour to debate a single question. Some questions are multiple choice, others open-ended. The multiple choice questions do not all have unique answers: sometimes several answers are right; sometimes answers can be partially right and partially wrong. Such ambiguity is the bane of exams, but a boon in discussion.
The Scale of the Universe
red dot What has the speed of air molecules in this room got to do with how fast present day spacecraft go?
  green dot About how fast are individual air molecules in this room moving?
(a) They hardly move;
(b) As fast as the wind;
(c) The speed of sound;
(d) The speed of light.
  green dot About how fast is the speed of sound?
(a) People speed (1 m/s);
(b) Car speed (10 m/s);
(c) Jet speed (1 km/s);
(d) Light speed (300,000 km/s).
  green dot What is the gravitational escape velocity from the Earth's surface?
(a) About the speed of sound (1 km/s);
(b) Several times the speed of sound (10 km/s);
(c) Light speed (300,000 km/s);
(d) Infinity (escape is impossible).
  green dot It is possible to escape the Earth's gravity because:
(a) There is no gravity in space;
(b) Earth's gravity extends to infinity, but it gets weaker as you go farther away.
  green dot About how fast does a spacecraft go? Why?
red dot What difficulties are involved in traveling to the stars?
red dot How do astronomers measure distances to stars:
(a) Spacecraft equipped with long tape measures;
(b) Laser-ranging;
(c) Trigonometric parallax;
(d) ``Standard candles'', plus the inverse square law of brightness with distance.
red dot What is the purpose of the Foucault Pendulum (1851) hanging in the Gamow Tower?
(a) To tell time;
(b) To demonstrate Newton's laws of motion;
(c) To demonstrate that
Period = ę
ē
č
g
length
ö
÷
ų
1/2
 
 
 ;
(d) To demonstrate that the Earth rotates.
red dot This is a part of the Hubble Deep Field. The image is so deep that it goes pretty much all the way to the horizon, the edge of the observable Universe (the horizon is determined by how far light can travel during the age of the Universe). To a certain level, we are seeing all the galaxies there are as far as the horizon. Virtually everything in the image, not only the big bright things, but also all the little faint blobs of light, are galaxies. Estimate roughly how many galaxies there are in the picture.
Part of Hubble Deep Field
The field shown is 150 arcseconds by 38 arcseconds in angular size. Estimate the number of galaxies in the presently observable Universe.
Light
red dot Compare the light from a high wattage tungsten filament bulb to that from a mercury vapor lamp. Which white is whiter?
red dot A filter that absorbs yellow light, when inserted into the path of a spectrum of white light passed through through a prism, will:
(a) produce a dark band of absorption of yellow light;
(b) will absorb not only yellow, but also the yellow part of green, making the green part of the spectrum look blue.
red dot How does fluorescent dye work? The atoms of fluorescent dye:
(a) have an electromagnetic aura;
(b) are hotter than their surroundings;
(c) are extra efficient at absorbing and emitting light;
(d) convert ultraviolet to visible light;
(e) convert infrared to visible light.
red dot The frequencies at which an atom absorbs light:
(a) depend on what type of atom (element) it is;
(b) correspond to the absolute energy levels of the atom;
(c) correspond to differences in energy levels of the atom;
(d) are the same as the frequencies at which the atom emits;
(e) are exacly the oppositve of the frequencies at which the atom emits.
red dot In light waves, what is it that wiggles?
The Sun
red dot How did Eddington estimate the temperature at the center of the Sun?
Hint: The Sun's gravitational escape velocity is 618 km/s.
red dot You are orbiting the Earth in a space shuttle, hard on the heels of another space shuttle. To overtake the space shuttle ahead, do you:
(a) speed up;
(b) slow down?
red dot If a gravitating system loses energy, it:
(a) cools down (temperature decreases);
(b) heats up (temperature increases)?
red dot Why doesn't the Sun explode like a nuclear bomb?
red dot How can the corona at ~ 106 K be hotter than the chromosphere at ~ 5,000 K?
Stars
red dot When should Ha, Hb, Hg, ..., absorption in a star be strong?
(a) When the n = 1 (ground) level is most populated;
(b) When the n = 2 level is most populated;
(c) When the n = 3, 4, 5, ..., levels are most populated;
(d) When H is mostly ionized?
red dot When is the n = 2 level of H most populated?
(a) low Temperature;
(b) intermediate Temperature;
(c) high Temperature?
red dot If Ha is weak in stars both colder and hotter than A stars, how can you tell the temperature?
(a) Wien's law;
(b) the Stefan-Boltzmann law;
(c) the strengths of spectral lines of other elements or ions.
red dot The stars in a star cluster all have the same:
(a) distance;
(b) temperature;
(c) luminosity;
(d) age;
(e) composition;
(f) radius;
(g) composition.
red dot How much brighter (apparently) is the Sun than Sirius?
red dot If you put the Pleiades 2 times further away, they would appear:
(a) the same apparent brightness;
(b) 2 times fainter;
(c) 4 times fainter;
(d) 8 times fainter;
(e) 16 times fainter.
red dot The Main Sequence is a sequence of stars of different:
(a) distance;
(b) temperature;
(c) luminosity;
(d) age;
(e) composition;
(f) radius;
(g) mass.
red dot The Hertzsprung-Russell diagrams of different clusters look different because they have different:
(a) distance;
(b) composition;
(c) age;
(d) range of stellar masses?
red dot What happens to a star when it runs out of H at its core?
(a) The core cools down (core Temperature goes down);
(b) The core contracts and heats up (core Temperature goes up);
(c) The star evolves along the Main Sequence;
(d) The star becomes a Red Giant;
(e) The star becomes a White Dwarf;
(f) The star destroys all life on Earth.
red dot Eddington's Paradox: If a star, when it runs out of fuel, heats up, how can it ever cool down?
(a) It never cools;
(b) It cools, held up by electron degeneracy pressure (the pressure from the quantum-mechanical zero-point motion of electrons);
(c) It cools, held up by nuclear degeneracy pressure (the pressure from the quantum-mechanical zero-point motion of nuclei);
(d) It cools, held up by the `strong' nuclear force;
(e) It eventually collapses to a black hole.
red dot Why is the surface temperature of stars always of order 104 K? It's the temperature where:
(a) thermal velocity = gravitational escape velocity;
(b) H gets ionized;
(c) H fuses into He;
(d) electrons are degenerate.
Relativity and Black Holes
red dot From Einstein's assertion that the speed of light is the same for all observers, it follows that, if light is emitted from a point where an observer is, then the observer will always find self at the center of the expanding sphere of light, irrespective of the observer's motion.
(a) True;
(b) False?
red dot Are these boxes the same?
two boxes
In relativity, how long an interval of space or time appears depends on your perspective. Observers moving relative to each other have different perspectives.
red dot If nothing can get out of a black hole, how come its gravity can get out?
red dot If the Earth were compressed to a black hole, how big would it be? [Hint: 1 Mearth » 3 × 10-6 Msun. The Schwarzschild radius of a black hole of 1 Msun is about 3 km.]
red dot How big/massive/hot are evaporating black holes? How long does an evaporating black hole last? What would an evaporating black hole look like? When an evaporating black hole explodes, how big is the explosion?
red dot What happens to the singularity when a black hole evaporates?
red dot What is the Hawking temperature of the Earth?
red dot If you went near a mini black hole, what would it feel like? Would you feel its gravity? Would you be torn apart? What if you tried to hold it? Would it hurt?
red dot What would happen if a black hole were made in a particle accelerator? Is that likely to happen?
red dot Suppose a mini black hole were dropped into the Earth. What would happen? Would the black hole eat the Earth?


 Van Gogh's Starry Night Fall 2000 ASTR 1120-001 Homepage

syllabus | timetable | questions | problems | reviews | hypertext | text

Updated 21 Nov 2000