![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhZvyvSgwdmopsv6JMRVYoxK49oLNeR8S1lZ_z8fiEhsq1hwAhcrO5hE_2qAA_vkoH2no1izcBMZNOy3Vg_cTFVnOknSbLDBFWfaThlkAlUvmChZjRgD0diPJ5H4t65hHEf8Hs1nk6Se2s/s400/DSC_3719.jpg)
When you have the sun in your shot, using a small aperture (like f/18 - f/22) creates a "star burst effect". Basically when your aperture is wide open the hole is more like a circle. However, when it is closed, the blades of the aperture create a polygon. This shape is what what creates the sun burst.
Here is a sample of one I tried this out on today. (shot at f/18)