Group Light Quiz 3

Red Shift

    1. Christian Doppler (1803-1853), in 1842, stated that if a light sources approaches an observer, then the light waves will crowded closer to each other. While if a light source moves away from an observer, then the light waves will spread out from each other. This is known as the Doppler effect. In Figure 1, the Doppler effect is demonstrated with a stationary light source to an observer (Fig.1a), and with a moving light source (Fig 1b), S1, S2, S3, and S4. So to observer A (Fig 1b), the wavelengths appear shorten. But to Observer C, the wavelengths appear to lengthen. While Observer B saw no change in the wavelengths. The Doppler effect is the main law that astronomers use to explain the Red Shift. Astronomers also use the Doppler effect to hypothesis the existence of binary star systems, and star systems with planets. If a star comes closer to us, the starís stellar spectrum seems to shift towards shorter wavelengths. When a star moves away from us, the starís stellar spectrum appears to shift towards longer wavelengths. Using the atomic spectrum for Hydrogen as an example, draw and explain how a starís stellar spectrum changes because of stellar wobble. Again, explain how the stellar spectrum helps astronomers detect binary star systems, and star systems with planets.

Table 1

 

To Observer C

 

 

 

 

To observer B

(a) To observer

(a) To observer A

 

 

Several astronomy students were looking at stellar spectrum charts that were taken over several days from a star that was in the Andromedae Galaxy. What they saw (fig 1) made them jump up and down and cheer in celebration. Look at Figure 1, then tell me what made them so happy.

Figure 1

a

b

c

d

Figure 1: Figure 1a shows a hydrogen spectrum taken on 3-3-99. Figure 1b shows a hydrogen spectrum taken on 7-3-99. 1: Figure 1c shows a hydrogen spectrum taken on 10-3-99. Figure 1d shows a hydrogen spectrum taken out of one of the astronomy students chemistry textbooks.