Answer to Question 1
Seyfert galaxies were first identified because they are very bright at radio wavelengths. Eventually it was found that they emitted unusual amounts of energy at all wavelengths and were termed active galaxies or active galactic nuclei.
Seyfert galaxies are spiral galaxies that have a small, highly luminous nucleus with peculiar spectra. Most galaxies only show absorption lines; Seyfert galaxies also display emission lines. Seyfert emission lines are very broad, indicating that they come from a gas rotating at high speed.
Two types of Seyfert galaxies are observed. Type I has strong X-ray emission and very broad emission lines, Type II do not show as much X-ray emission and have emission lines that are not as broad.
Answer to Question 2
The Doppler effect uses a measured change in the wavelength of photons to determine the speed of an object. The effect is only able to detect motion toward or away from the receiver, not motion directed side to side.
If the officer positioned himself far from the roadway, he would be viewing an oncoming car from an angle. In this situation, part of the velocity of the automobile would be side-to-side across the officer's line of sight. The Doppler effect would measure only the velocity of the car along the line of sight, and underestimate the true speed of the car. If the road was curved, the same situation would apply.
The officer can only get a true measure of the car's velocity if the velocity of the car is directly along the line of sight.
Furchgott's discovery that endothelial cells produce a vasodilating substance.
Part of the Hubble Ultra-Deep Field image showing a typical section of space containing galaxies int
Aurora australis observed from the Space Shuttle Discovery, on STS-39, May 1991 (orbital altitude: 2
Galaxies Forming by Combining Smaller Units
Properties of some naturally occurring RNA molecules
Functions and Properties of Blood