Our Solar system contains eight planets, several dwarf-planets, thousands of asteroids and comets, but it seems that our system is not unique, and in fact most other stars also have planets orbiting them. Figure 5:The light curve from two binary stars, one much brighter than the other. This transit method produces light curves similar to the one below with periodic dimming, which again can be used to measure the orbital period and radii of the stars. When the more luminous star is partially eclipsed the reduction in brightness is larger than when the dimmer star is eclipsed. As one star transits in front of the other, some of its light is absorbed and the apparent magnitude is reduced. The constantly shifting pattern of spectral lines can also be used to find the period of the the stars’ orbit and the mass of the system Figure 5: As two binary stars orbit each other spectral lines are shifted depending on whether they are approaching or receding.īinary systems can also be investigated looking at how the apparent magnitude of the two star varies over a long period of time. This is called the radial velocity method. The time between two consecutive peaks on the wave can be given by: The equation for the amount of red shift can be derived if we imagine a star, moving away from Earth with a velocity, $v$, which is emitting light of a wavelength $λ$ and speed $c$. The fractional change in the wavelength is called the red shift, whether or not the object is moving towards or away from the observer, and is given the symbol $z$. Wavelengths in the direction of the object's motion are compressed and appear 'bluer'.Īs the amount that the wavelength changes is directly proportional to the speed of the source, observations in the shift of spectral lines can be used to determine its speed. As this would move the wavelength towards the red end of the spectrum this is called red shift. When the source is moving away from the observer the relative speed between the source and the wavefront is greater, and the observed wavelength also increases. As the wavelength would move towards the blue end of the visible spectrum this is called blue shift. As the source still emits at the same frequency the observer will see a shorter wavelength than when observing the stationary source. The wavefront moves out at equal speeds in all directions, but as the source moves, its relative speed to the wavefront in the direction of its motion is lower. If the light source is moving towards the observer, as the source emits a wavefront, it continues moving. However, if the source of light is moving relative to the observer, the observed wavelength changes depending on whether the motion of the light source is towards or away from the observer. When an object is stationary emits light, or has light reflected off its surface, that light spreads out uniformly so that wherever an observer receives the light it would appear to have the same wavelength. However it is also possible to discover information about the motion of stars, and other astronomical bodies by making careful observations of their light. In the following sections, we shall explore the Doppler effect and how to calculate the Doppler shift frequency.So far within this module we have examined how we find out about the composition, distance to, and the temperature of stars by observing their colour and brightness. While calculating the Doppler effect on sound in air, keep in mind that the speed of sound in air depends on many factors, including the humidity and dew point.
0 Comments
Leave a Reply. |