MATERIAL FROM CLASS 10: Wednesday October 11
Light waves travel more slowly in glass or water than in air, so the light is bent towards the perpendicular line of the two surfaces:![[light is refracted]](http://www.astro.wisc.edu/~sparke/ast103/Light_Refracting.gif
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Model of the SALT telescope: the large primary mirror is 11 meters across, made of 91 segments. Light is reflected up towards the prime focus instrument package (cylinder at the top); this is carried on the tracker to follow stars across the sky. Right, the telescope with the dome open, at dusk.
![[SALT telescope model]](http://www.astro.wisc.edu/~sparke/ast103/SALT_model_withflags.jpg
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![[SALT telescope at dusk]](http://www.astro.wisc.edu/~sparke/ast103/SALT_dome_lights_on.jpg
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Putting SALT's dome on, then lifting the tracker into place:
![[putting the dome on]](http://www.astro.wisc.edu/~sparke/ast103/SALT_dome_on.jpg
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![[lifting SALT's tracker into place]](http://www.astro.wisc.edu/~sparke/ast103/SALT_trackerlift1.jpg
){kind=tracking}