Cool Photo of Telescope Guide Stars

A good scientist is a person with original ideas. A good engineer is a person who makes a design work with as few original ideas as possible. There are no prima donnas in engineering.

— Freeman Dyson, from Disturbing the Universe. He clearly did not work at any of the companies I have – engineering is full of prima donnas.

Figure 1: Laser Creating a Guide Star.

Figure 1: Laser Creating a Guide Star.

The use of adaptive optics requires that precise measurements be made of the disturbances present in the atmosphere so that they can be compensated for – a process known as deconvolution. These measurements are often made by reflecting light off of sodium atoms in the upper atmosphere. These reflections effectively create artificial stars known as guide stars (Figure 1).

The Wikipedia article on guide stars has a good description of how a sodium guide star works, which I quote here:

Sodium guide stars use laser light at 589 nm to excite sodium atoms in the mesosphere and thermosphere, which then appear to "glow". The LGS [Laser Guide Star] can then be used as a wavefront reference in the same way as a natural guide star – except that (much fainter) natural reference stars are still required for image position (tip/tilt) information. The lasers are often pulsed, with measurement of the atmosphere being limited to a window occurring a few microseconds after the pulse has been launched. This allows the system to ignore most scattered light at ground level; only light which has travelled for several microseconds high up into the atmosphere and back is actually detected.

I saw a great photo from the Gemini telescope showing the five guide star pattern it generates (Figure 2). I think this is really cool.

Figure 2: Gemini Telescope's Five Guide Star Pattern.

Figure 2: Gemini Telescope's Five Guide Star Pattern.

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