#1 Homework Teddy Portney Astronomy 22 September 15, 2007 I. Reading: 1. For week 1, we read the introduction to the textbook "An Introduction to the Sun and Stars" as well as chapters 1-3 in the online textbook at www.astronomynotes.com. The latter of these two texts was very hard to read to begin with, as it attempted to give a size and a timescale of the universe to which we can more easily relate. This point was extremely overemphasized and made the text excruciatingly difficult to read. The textbook, however, was much easier to read and provided some valuable information alongside relevant and interesting photographs. Specifically, I did not know that you can see different images of the same point in space depending on what type of electromagnetic radiation is received by different telescopes. 2. For week 2, we read chapter 7 in the online textbook and chapter 4 in "Readings on Stellar Astrophysics" textbook. Most of the topics discussed in the Swihart textbook were things I had already studied; as we spent about a week in Chemistry 1 discussing Quantum Mechanics. The same goes for the online textbook, which dealt with the electromagnetic spectrum. The most valuable piece of information from the online book was the chart of exact cutoff values for wavelengths, energies, and frequencies of different colors of visible light. II. Descriptions and Explanations: 2. When the sun can be observed directly above Earth's equator, it is known as an equinox. This usually occurs in March and September of every year. When this occurs, day and night are almost exactly equal in time. 3. Precession of the equinoxes describes the precession of Earth around its axis with respect to the space around it. Ancient astronomers noted that as time progressed, stars seemed to move. They were not exactly in the same place every night, and over greater periods of time, their locations varied even more greatly. It is now estimated that this precession varies at about 1 degree every 71 years. III. Determinations: 4. I measured the elevation of Jupiter to be approximately 65 degrees. 5. Using this value of the elevation, we can calculate the declination of Jupiter as viewed from Medford, MA. The formula for this calculation is: Declination = elevation + Latitude 90 degrees; or 42.5 degrees + 65 degrees 90 degrees = declination of Jupiter; or 17.5 degrees. 6. I measured the elevation of Vega to be approximately 85 degrees above the horizon, and using the equation in number 5 above, I calculated the declination to be approximately 37.5 degrees.
7. Using values found on www.wikipedia.org and other websites containing astronomic information about the relevant celestial I bodies, calculated the distance to size ratios for Jupiter and Vega. These came out to be 0.042 and 20.32, respectively. The ratio for Vega came out to be a significantly larger number than that for Jupiter because Vega is much farther away from Earth than Jupiter. 8. Comparing the angular resolutions of the human eye and the Hubble Space Telescope is relatively easy, as the ratio of the angular resolutions is the inverse of the ratio of diameters of the lenses. The ratio of the resolution of the Hubble telescope to the human eye is approximately 1/1000. This means that the human eye has 1000 times the angular resolution of the Hubble. Conversely, because the diameter of the Hubble is 3 orders of magnitude greater than that of the eye, its light-gathering power is 9 orders of magnitude greater, as the light-gathering power increases with the area and area is a function of radius squared. 9. In a hydrogen atom, an electron moving from energy levels 2 to 1, it will produce a photon with a fixed wavelength. This wavelength can be calculated with the Bohr formula. This formula is given as: hv = 2.18x10-11 Z2 (1/n22 1/n12) and is given in units of ergs. We know from chapter 4 in the textbook by Swihart that hv = hc/ so we can set this as the left-hand side of the equation and solve for wavelength. The resultant wavelength is approximately 121 nm, which corresponds with ultraviolet light. IV: More Descriptions and Explanations: 10. Kirchhoff's Laws of Spectroscopy describe three distinct phenomena. The first phenomenon occurs when there exists a hot, solid object. According to Kirchhoff's laws, this object will produce a continuous spectrum of light, that is to say that the electromagnetic radiation produced by the object will correspond with every wavelength in the electromagnetic spectrum. The second phenomenon occurs when there exists a cloud of hot gas. This gas will emit photons at specific wavelengths. These wavelengths depend on the energy levels of the electrons in the atoms of the gas. This is what Kirchhoff named "The Emission Spectrum." The third phenomenon is a combination of the two previous phenomena. When a hot, solid object is surrounded by a hot gas, the resulting spectrum will be almost a continuous one, although there will be gaps corresponding to the wavelengths of the light produced by the gas. This is what Kirchhoff referred to as "The Absorption Spectrum." These laws come in handy for astronomers when dealing with stars and their nebular surroundings because this is an easy way to determine if a star is solid or a gas. It also is an easy way to determine whether or not a cloud of gas surrounds a solid star.