ASTR 1010 – Homework Assignment 5 – Spring 2009

Question 1 - #4. In everyday life, a particle is a localized object, while a wave extends over space. The wavelength is the size of the repeating pattern in the wave train. The frequency is how many wave patterns go by in one second. The speed of a wave is the wavelength times the frequency.

Question 2 - #6. A photon is when light manifests particle properties. A photon is like a particle in the sense that it is localized at any given moment. A photon is like a wave in that it has a wavelength and frequency.

Question 3. - #7. From lowest to highest energy light: radio waves, microwaves, infrared radiation, optical light, ultraviolet radiation, x-rays, gamma rays. It would be the same order if we listed the various types of light by increasing frequency. If we listed the various types from shortest to longest wavelength, the list would be in reverse order.

Question 4. - #14. The three types of spectrum are continuous, absorption, and emission spectra. A continuous spectrum is produced by directly observing a source of thermal or blackbody radiation. If the previous source is surrounded by a thin gas, then absorption lines are produced when the line of sight cuts through the thin gas to the thermal source. If you look directly at only the thin gas without looking at the source of thermal radiation, then you see an emission line spectrum.

Question 5. - #45. (a) The pattern of spectral lines (either in emission or absorption) identifies each element or molecule in the source uniquely. (b) The surface temperature is determined by comparing the strength of lines of a given species. (c) A low-density gas cloud would produce emission lines. As the gas density increases, the spectrum becomes a continuous spectrum. (d) If the object has a hot upper atmosphere, you will see emission lines. (e) If the spectrum shows very little red light and a lot of blue light, then it is likely reflecting the blue light from a nearby source. (f) By looking at the Doppler shift of either emission or absorption lines you can calculate the speed of the emitting source. (g) By looking at how wide each individual line is, one can infer the rotation rate of the object.

Question 6. - #48. The rest wavelength is 121.6 nm.

Star A has the line at 120.5 nm

Star B at 121.2 nm

Star C at 121.9 nm

Star D at 122.9 nm

Because the wavelength decreases for Star A and B, those objects are moving towards us. For Star C and D, the wavelength has increased and those objects are moving away from us. The star that is moving the fastest is the one with the greatest shift. In this case, that would be Star D.