What is the Doppler effect?.

<P> To learn more about the Milky Way, we must study the method to determine stellar campaign. .When Halley comet discovered in motion, he can only measure them through the visual route (intrinsic motion) away, as if they are sliding along the celestial. .However, once the object does not exist, and the distribution of stars across a vast space close to or away from the more distant we become very clear, the question arises: is a particular star is moving towards our movement, or departure from our movement .him? .This movement (opposite or backward) is known as radial motion, because the stars are seen along the spokes (or radius) in motion toward or away from us, round the earth as the center, extending out away from us. .</ P> <P> How can we detect this movement? .If a star is us or towards the back straight to our movement, then it's position in space is constant. .Of course, if they deviate from our movement, it will become increasingly dark in the sky. .If it is stable towards our movement will become more and more light, but the stars so far away from us, but in terms of the relative distance of a huge movement that is so slow, then the stars change with the brightness of thousands of precision can .instrument detected. .Moreover, even if a star is a natural movement through space, it can also be movement toward or away from us that it exists in three dimensions tilt movement. .How can observe this movement? .</ P> <P> the answer is observed from Earth, a phenomenon was found, as if nothing to do with the stars. .If a cavalry charge under military attack, a trumpet to inspire the morale of their troops while the enemy threat, when he moved to a stationary listener, the number seems to change the pitch of the sound. .When passing, the sound is suddenly showing a lower pitch. .</ P> <P> This phenomenon is most intense when the war was not found, but in 1815, the British engineer George Stephenson invented the locomotive, it is not the kind of run up years ago, the speed with the same or gallop .a bit more speed locomotives. .More importantly, when they pass through densely populated areas, it is usually given a whistle to warn people, so when the locomotive passed suddenly heard the sound reduction is very common. .Why does this happen? .Questions emerged. .</ P> <P> Joanna Austrian physicist Christian Doppler is very accurate solution to the problem, determine when the motorcycle approaching, each successive sounds are a little catch up with it in front of that, so they .than the stationary locomotive passed more often ears. .Therefore, when at rest than the locomotive whistle is higher. .When the motorcycle through the back or start, each successive sound waves that are pulled away from the front, then when the spread than the stationary locomotive fewer ear, so to a lower pitch sound. .Then there is the sound in the locomotive through the natural process of change, from a high than normal to lower than normal, from treble to bass. .</ P> <P> in 1842, Doppler solve the mathematical relationship between speed and pitch, and at different speeds through the engine back and forth pulling flatbeds and successfully verified this relationship. .Trumpeters blowing in the flatbed truck on a variety of tone, on the ground, a sense of absolute pitch musicians have recorded the sound changes when the train passed. .Therefore, this change in pitch is called the Doppler effect. .</ P> <P> to the present, it was discovered that light is constituted by the waves, although it's Bobby wave is much smaller. .In 1848, French physicist Bose Litefeizuo Oman Technip for Renhe Bo pointed out that the Doppler effect, the movement, including light. .So often the way of light known as the Doppler motion - fee Junior effect. .</ P> <P> If a star is neither close to nor far away from us, then it's the black line on the spectrum remain in place. .If the stars back our movement, it sends the light of longer wavelength (the lower the value of the pitch, etc.), and the black line is always the red end of the spectrum of movement (red to mobile). .The more you move, the faster the movement away from us. .On the other hand, if the stars closer to us, it sends a shorter wavelength of light (a higher value of the pitch, etc.), spectral lines toward the violet end of the spectrum move. .Moreover, the shift farther, faster close to our movement. .</ P> <P> if we know the radial motion (opposite or back), they know the inherent movement (toward the side), we can calculate the three-dimensional space, the stars in the real sport. .In fact, the radial velocity is one of the very important. .Only stars from us and it is close enough to the movement across the sky fast enough to be aware of it, the proper motions can be measured, but only a very small part of the star is away from us so close. .On the other hand, no matter how far away are the stars, only its spectrum could be obtained in order to determine the radial motion. .In 1868, William Huggins confirmed for the first time radial velocity of stars. .He found Sirius to about 46 km / s away from us the second strongest pace. .Currently, we have good graphics, very close to the first attempt. .</ P>.