AST 1002 -- MISCELLANEOUS WEB SITES

1. This animation illustrates uniform circular motion. The blue arrow ahead of the moving point represents the point's velocity; the arrows marked v0 and vf are the velocity at the beginning and end of some time interval, and the green arrow marked "-v0" is the negative of v0, essentially subtracting it from vf. The red arrow represents the change in velocity; it points towards the center and marks the direction of the centripetal acceleration.
2. Diagrams showing the conic sections may be viewed (along with some of the relevant math, which you can skip).
3. A diagram of tidal forces superior to the one in the text (IMHO) is this one.
4. The trajectories of the Voyager spacecraft are shown on this page. The basic idea of gravity assist (otherwise known as the "slingshot effect") is explained (sort of) in this article from Wikipedia, a Web open encyclopedia. (If you don't understand everything in the article, don't worry about it.)
5. The Doppler effect is familiar to us from sound, as in the case of an ambulance siren.
6. This is another illustration of the Doppler effect, this time showing the waves in a simplified version.
7. Chromatic aberration is shown in this diagram. A partial solution is the achromatic objective, which with two different kinds of glass can bring two colors to a focus at the same point. It reduces, but doesn't completely eliminate, chromatic aberration. (The diagram is slightly inaccurate because it suggests all colors are brought together.)
8. With either lenses or mirrors that have spherical surfaces one can have spherical aberration, where rays that come in to the mirror at different distances from the central axis are brought to a focus at different distances from the center. The solution is to use a paraboloidal mirror. The mathematical shape of the paraboloidal surface is shown in this diagram.(WARNING: There's some scary-looking stuff on this page about "partial derivatives" and whatnot. Pay it no mind.)
9. Here are an illustration and diagram showing what images look like as a result of coma with the Newtonian design of reflector. I haven't been able to find any diagrams showing the paths of rays in a paraboloidal mirror setting that illustrate it, at least not yet.
10. Another technique for looking for exoplanets (planets orbiting stars other than the Sun, or free-floating planets not bound to a star) is microlensing. It uses the bending of light when it passes near matter -- i.e., by gravity. When light from a distant star passes by a nearer one, the latter "focuses" the light on the Earth for a while, making the distant star seem brighter than usual. If there's a planet orbiting the closer star it'll briefly contribute a "spike" of extra light. Here's a fairly recent news story from the UK about it.
11. This page contains a number of tables and graphs about asteroids, including a couple of pretty good ones showing the Kirkwood gaps and the Hirayama families, which are towards the bottom. (There's one minor typo in the table of properties towards the top: for the diameters the units should be kilometers instead of kilograms. Also, the rotation period is in hours, not days; the word "Day" should be in quotes.)
12. A page with graphs of asteroid albedos. Note especially the decrease in average albedo with increasing semimajor axis. (In case you're wondering, the term"osculating" refers to the instantaneous orbital elements, which are affected by the gravitational effects of the planets, while the term "proper" refers to the orbital elements taking out those gravitational effects.)
13. It's disappointing that the text doesn't have any pictures of the Sun's chromosphere. Maybe the authors thought they would be too confusing. Anyway, here's a link to a couple of images. The second one down is at the wavelength of the center of the H-alpha absorption line of hydrogen, the line in the red part of the visible spectrum. The one beneath it is at the wavelength of a strong absorption line of ionized calcium in the violet. If you're puzzled by light at an absorption line, keep in mind that even strong absorption lines aren't usually completely dark. Here's a page about spicules with some better images than the ones in the text IMHO.
14. A compilation of solar images in the different parts of the electromagnetic spectrum is at this Web page.
15. Here are some links to some neat animations: eclipsing binary; spectroscopic binary. We're indebted to Terry Herter of Cornell for these. There are also some neat animations of visual binaries.
16. Here's Fig. 5.19 from the text in the original from NASA. WARNING: It's a rather large file, so it might take a while to load unless you have a high-speed connection. Notice how bright it is in Florida. The only place where the light pollution is fairly low is to the west of Gainesville. The explanatory material is here.