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Lesson 3 - Observing the Universe
Transcript of Lesson 3 - Observing the Universe
Observing the Universe Last lesson we talked about waves... Amplitude Wavelength
or Period ...and we learned a couple of formulae that help us describe wave characteristics frequency speed period wavelength But how do these characteristics translate to light? Well it turns out that if you change the wavelength of a photon of light, you change its colour.
That is, different wavelengths have different colours. so what colour is what wavelength? Red - 650nm Orange - 590nm Yellow - 570nm Green - 510nm Blue - 475nm Violet - 400nm But this is all just one small part of... The Electromagnetic Spectrum Visible Light Infrared Microwaves Radio Waves Ultraviolet Gamma Rays X-Rays So what is a ? A spectrum is the separation of light into its individual wavelengths. The full electromagnetic spectrum contains all possible wavelengths of light...
...but not all spectra are like this. Some have gaps This is the spectra of light from our Sun. As you can see, there are black lines appearing everywhere. These black lines are 'holes' or missing wavelengths why are they missing? Each element emits only specific wavelengths (colours) of light that are determined by the structure of the atom itself.
As such, each element has a spectrum that is specific to it, a bit like a barcode. Neon Mercury Hydrogen We can use this to our advantage as just by looking at an object's spectra, we can figure out what elements are required to make the observed patterns
So the Sun, while it contains lots of different elements, doesn't contain enough to create a full spectrum Hence why it looks like this. The Doppler Effect So by looking at an objects spectra, we can determine what elements that object is made up of. BUT THIS IS NOT ALL IT TELLS US When we look at an objects spectra we can also determine how quickly the object is moving towards or away from us through and effect known as As can be seen in the animation below, when an object moves towards you, the waves emitted from it become bunched up and appear of shorter wavelength. If the object is moving away from you, the waves appear longer. This is the Doppler Effect. longer wavelengths shorter wavelengths "It's the apparent change in the frequency of a wave caused by relative motion between the source of a wave and the observer." The Equations For objects moving towards the observer For objects moving away from the observer observed frequency speed of wave speed of source emitted frequency speed of wave Red Shift and Blue Shift This effect manifests itself in the spectra we observe by causing the lines to move position.
If the object is moving away from us, the lines move towards the red end of the spectrum (red shifted).
If the object is moving towards us, the lines will be moved towards the blue end of the spectrum (blue shifted) The greater the amount of shifting that has occurred, the faster that object must be moving towards or away from you. And so, just be looking at an object's spectra, we can determine what it is made of and how quickly it is moving.