Wednesday, August 27, 2014

Star Shaped Stars?

Ever wondered why when we look at stars or a bright point light source it has pointy edges? Read on to find out.
As we know, stars are giant balls of plasma in space and do not have pointy edges. Point light sources also do not have pointy edges. So why do we see the pointy edges? Well, it is due to the diffraction of light.

Light has both a wave-like and particle-like nature. When light passes through an opening, it is diffracted and creates a diffraction pattern. This diffraction pattern can be seen when photographing a picture such as the following.

This is sometimes called a sunburst or starburst pattern which can only be observed when the lens is stopped down (shot using a small aperture). We can not only observe the effect using cameras, even the Hubble Space Telescope has this effect.

This is due to the design of the telescope itself where the secondary mirror is supported by 4 trusses perpendicular to each other. Hence we see the cross pattern as per the image above.

You may argue that our eyes do not have an "aperture" with sharp edges or trusses that may cause diffraction patterns. Well that is true but we must realize that the lens of our eyes are not perfect. There are imperfections in the lens called "suture lines" which are transparent. Suture lines are where the lens fibers join which grow from the periphery to the center.

Source: Journal of Optometry

Everyone's suture lines are unique, it is even unique between both eyes. Therefore, everyone will observe a slightly different star pattern but the same person will see the same pattern for every star.

This post is based on the following video:

Hubble Image | Journal of Optometry | STScI

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