My word, I've almost forgotten about this thread. But to be honest, I was actually hoping that more people would share some trivia. C'mon guys and gals, I'm sure you've got something to gooi in.
So by the way, are you the same deefstes as the deefstes on the SB forums?
Yup, you got me
My cover is blown
OK, so let's look into Redshift a bit. It's a very well known and commonly referenced principle in astrophysics but perhaps not something that the everyday casual skygazer knows.
So, have you ever heard of the Doppler Effect? If so, you understand Redshift already. If not, you certainly have heard the Doppler Effect even if you haven't heard of
The Doppler Effect describes the perceived change in pitch (frequency) of a sound when the observer and the source are moving relative to each other. More precisely, when the observer and source are moving towards each other the perceived frequency of the sound is higher while, conversely, when the observer and source are moving away from each other the perceived frequency is lower.
This can be very clearly observed when a police car sounding its siren passes you. As the car approaches you can hear a certain frequency of the siren which then rapidly drops to a lower frequency once the car passes you. The explanation for this is as follows.
Sound waves move at a fixed speed through any given medium (air in the above example). This means that any sound wave emanating from the police siren will move towards you at a fixed speed (more or less 340 meters per second). The frequency of the sound is determined by the wavelength (physical distance between peaks -or throughs- of the waveform). If the sound source is moving towards you, the waveform gets "compressed" so to speak. In other words, while one peak in the waveforem is travelling towards you, the sound source is also moving towards you so that, when the next peak emanates and starts travelling towards you, it is closer to the previous peak than it would have been had the sound source been motionless. This has the effect that the sound wave has a shorter wavelength, resulting in a higher frequency.
Similarly, if the sound source is moving away from you, the waveform is "stretched out" so to speak resulting in a longer wavelenght and lower frequency.
This image illustrates the principle. The sound source is moving from the bottom of the image to the top. Sound waves would have emanated in concentric rings from a motionless source but because this one is moving the waves are compressed towards the top of the image and stretched at the bottom of the image. An observed standing at the top of the image would hear a higher pitched sound that an observer standing at the bottom of the image.
This principle applies exactly to the propagation of light as well. In the sound spectrum long wavelengths equate to low frequencies while short wavelengths equate to high frequencies. In the light spectrum long wavelengths (low frequencies) equate to red colours (outside edge of the rainbow) while short wavelengths (high frequencies) equate to blue colours (inside edge of the rainbow). Because light travels so much faster than sound (almost a million times as fast) the effect is not as readily observed as with say a police siren. Had police cars been moving almost a million times as fast as they do, their colours would have been affected (and no robber would ever have gotten away
In the vast expanses of space things actually do move at those types of speeds and by this very principle their perceived colours are indeed affected. According to the theory of the Big Bang, objects in space are rapidly moving away from a specific point in space, resulting in their perceived colours to be redder than they really are. Conversely, when an objects are moving towards us at such speeds (and thank goodness there are rather few of those) their colours are shifted towards the blue end of the spectrum (blueshift).
An important thing to note is that, to the naked eye, stars appear white. Some stars do seem to have a bit of redder tinge but by and large we can't really tell the colour of a star with the naked eye. The thing is, all stars have varying levels of just about every colour, combined which gives the impression of white (remember, if you mix all colours you get white). But if you were to break down the full spectrum seen of a star into its various colour components, you'd see that some colours are represented more so than others. Here is a spectral breakdown of a type K4III star for instance with the spectral breakdown of pure white light for comparison. You will see that some colours are more prominent than others in the star's spectrum.
When a star like this gets redshifted, the entire spectrum gets shifted towards the red side of the spectrum, meaning that all the bands appear on different wavelengths than they really are.
And that's Redshift. The spectral breakdown of a star tells us a lot about its composition as certain elements that they star may contain will absorb or emit certain wavelengths of light. It is therefor crucial to know by how much the spectrum is redshifted (or blueshifted for that matter) to really know what elements are present, which in turn can tell us about the age, history or relationship to other stars of that particular star.