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Spectral Interpretation 101: Doppler effects
Echelle spectra
To make these spectra the light from the object is collected by a telescope and enters the spectrograph through a slit. Inside it bounces off some reflecting surfaces before arriving at the detector (a CCD chip like the one in your digital camera). These reflecting surfaces have lots of fine lines etched onto their surface and these split the light up into a rainbow. If you have ever held a CD upto some light and seen a rainbow it's the same principle at work: red light and blue light bounce off of the lines at different angles and so you get to see a rainbow, spectrum in astronomine.
Saturn
The slit means that we can have some spatial resolution. Stars are just points and so make nice lines on the detector. Extended sources like Saturn fill the slit (and a bit more) and so I took two spectra to get the whole thing. In the pictures below the planet is the brighter part of the strips and is separated from the fainter rings by a slight gap. They lie above the planet in the east side view (next picture) and below it in the west side (the one below that). The little insets try to show this. The spectrum spreads perpendicular to the slit.
![[Eastside
of Saturn]](./images/SaturnE_mod.jpg)
These two spectra are of Saturn and its rings are here to illustrate the Doppler effect. What we're seeing is largely the Sun's spectrum reflected off of Saturn and its rings. Rotation of the rings around Saturn causes provides a velocity along the line of sight- with the west side coming towards us and the east moving away. You can tell this by using the lines from the planet as a reference point. In the top spectrum the ring spectrum lies to the right (red) of the planet's, in the bottom they are on the left (blue). The velocity is higher the further the ring is from the planet.
![[Saturn
Westside]](./images/SaturnW.jpg)