Problems & Short-Answer Exam Questions
For each exam, be prepared to solve one problem and answer one of the short-answer questions given for each exam below. You will also get one problem to work out. Be prepared to answer either of the short-answer questions given (if more than one), but I will only ask one of them per exam.
- It would be a very good idea to actually practice writing answers out ahead of time so that you know exactly what you want to say and how you want to say it.
- These may not be discussed on the discussion boards in advance. In this case, you may email me if you don’t understand what any of the questions are asking.
- DO NOT COPY AND PASTE FROM THE TEXT OR ANY OTHER SOURCES! Use your own words. You may, however, prepare the answers to these short-answer questions in advance and copy and paste your own work into the answer box. It will save you time on the exam.
- If I cannot read follow your answer, it’s wrong! Proof read your work.
Below each question is a scoring rubric (aka scoring guide) that I will use to grade your answer. This way, you should have a good idea what I will be looking for.
To answer the following questions (and if you haven’t already done so to do the homework), you might like to download and install the free open-source software Stellarium from www.stellarium.org. Other helpful interactive applets are the Rotating Sky Explorer (in the Daily Motion section of Chapter 2) and the Motions of the Sun Simulator (in the Ecliptic, Equinoxes and Solstaces section of Chapter 2). Physics 106 students should have this to work through the required labs. Setting up the situations below and looking at what is happening may be enlightening. The User’s Guide helps you learn how to set up and control the software.
- Suppose you found yourself at the North Pole of the Earth at noon at the end of December. Describe the sky and the changes in the sky that would occur during a single day. Include in your description the stars motions, what altitude the Celestial equator is, what part of the sky would have circumpolar stars, about what altitude you would look to see Polaris, where the Sun is (above or below the horizon) and whether it will rise or set. (FYI the North Pole is 90-degrees north latitude, longitude doesn’t matter.)
- If you were on the Equator on the first day of spring (equinox), describe the sky and the motion of stars in a single night. Include the altitude and direction you would look to find Polaris, where the celestial equator is, roughly how much of the sky consists of stars that are circumpolar and how the stars overhead move. (FYI the equator is 0-degrees latitude, longitude doesn’t matter.)
Problem (one of the following)
- Use Kepler’s Third Law to calculate the average distance (semi-major axis) of a planet’s orbit given its orbital period
- Calculate its orbital period given its average distance.
- Given the physics of hot glowing objects, explain how it is possible for a star that is cooler to be more luminous than a star that is hotter. Include in your discussion how a star’s luminosity is related to two physical properties (state which two) of the star.
- Very briefly describe what absorption spectra look like and how absorption lines, at the level of the atom, are created. Explain why the visible part of the spectrum of a distant star would have fewer absorption lines in its absorption spectrum when analyzed using the Hubble Space Telescope than it would when using an equally powerful telescope on the ground. Hints: 1) Refer to what conditions create absorption spectra. 2) You will not find much of anything helpful in Chapter 6 other than reminding you that the Hubble Space Telescope orbits in space above the Earth; look in Chapter 5.
Problem (one of the following)
- Given an absorption spectrum estimate the Doppler shift (Δλ) and calculate its radial velocity.
- Given the power spectrum of a thermal emitter, estimate the wavelength at which it peaks and calculate the emitter’s surface temperature.
- Our Solar System consists of planets that orbit in the same direction on roughly the same plane (Pluto is no longer considered a planet). Explain how the Nebular Theory accounts for this.
- Explain why, according to the Nebular Theory, Terrestrial planets formed close to the Sun and Jovian planets formed farther away. Include in your explanation concepts such as condensation temperature and the Frost Line.
Given the velocity plot of a star’s “wobble”, caused by an orbiting planet, and given the star’s mass, calculate the orbital distance of the planet. (This is the only possible problem.)
- Suppose an inventor approached you with an idea for a very strong space probe that could travel to a nearby black hole in ten years and survive the tidal forces experienced when going through the event horizon. The probe, according to our inventor, would then be able to take data and transmit a radio signal giving us information about the interior. There is a basic fundamental problem here. Even if the probe could get there and survive entry, explain why this is not a good invention to invest it. Be sure to include in your explanation what a black hole is, what its parts are (assume a non-rotating black hole), and the most-significant property of each part.
- Two stars, Tom and Jerry, have the same spectral classification. Tom is luminosity class V and Jerry is luminosity class I. Which star is bigger? Which star is more luminous? Which star has a hotter surface temperature? Explain your answers (from the information given and knowledge of the HR diagram).
Given the apparent magnitude and B-V star, use a calibrated main-sequence line on an H-R Diagram to estimate the absolute magnitude of the star and calculate its distance. (This is the only possible problem.)
There will be no short-answer questions on the Final Exam.
Given the red-shift velocity and the value of the Hubble constant, calculate the galaxy’s distance. (This is the only possible problem.)