In this picture, we see that the sun comes out as a hexagon. I am sure it is not arbitrary. What does the hexagon tell us about the instrument that captured the image?
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It tells us that the aperture contains either three or six blades and that where these blades meet there is a corner which results in Fraunhofer diffraction. This is discussed mathematically in Physics SE.
It also tells us that the lens was stopped down, as if it were wide open there would be no corners to cause diffraction, regardless of the number of aperture blades.
Incidentally the number of (distinct) points to the star is equal to double the total number of unique orientations* in the sides of the aperture shape i.e. three blades would be six points, six blades would also be six points as a hexagon has only three unique orientations in its sides.
* a hexagonal aperture has six sides but only three unique orientations as there are three pairs of parallel sides.
The shape of the lens flare is related to the shape of the aperture while the characteristics of the flare as a whole have more to do with the elements used in the lens.
The lens in that image would be using a six blade aperture.
The lens is using an aperture with six blades (or, theoretically, three - see comments); most probably six, since there are very few, if any, lenses with three aperture blades.
The lens is stopped down, and the aperture blades aren't rounded (or not enough for this aperture setting).
OR someone is using a star filter (though probably not, they are not very widely used).
This is an addendum to Matt Grum's answer, which I generally agree with:
Lens was stopped down.
Number of aperture blades is likely three or six.
The aperture most likely has six blades because a six-bladed aperture is the most common aperture configuration that would produce six-pointed sun stars. However, there are apertures with three blades. There are also apertures that form a triangular shape with a greater number of blades.
The shape of bokeh balls may indicate the number of blades. (At least, it indicates the aperture shape.) The bokeh cannot be examined because the resolution of the sample image is too low.
If the number of spikes is divisible by four, the aperture likely has the same number of blades as there are spikes. This isn't helpful in this case because six is not divisible by four.
If the spikes are approximately the same length, the number of blades is likely equal to the number of spikes. If they alternate short-long, then the number of blades is likely half the number of spikes. (At least, the pattern indicates that the aperture is an odd-sided polygon.)
Since the spikes in the sample image are all the same length, the aperture most likely has six aperture blades.
It tells us they may not be photographing a natural light source.