What is the aperture and how does it impact sunrise/sunset photos? what is generally considered an ideal aperture for sunrise/sunset photos?

  
Aperture is a hole or an opening through which light travels.   
Shooting at a wider angle will also accentuate the starburst effect for more dramatic sunset images.  
f/8, f/11 is generally considered an ideal aperture for sunrise/sunset photos.

Aperture, which is the first step to taking better photos refers to the lens of the diaphragm opening up inside a photographic lens. An ideal aperture with exposure compensation for sunrise or sunset photos is when the sun is still in the sky. Once the sun sets below the horizon, one can switch to manual. It allows the photographer to have the convenience of shooting in aperture priority as light levels adjust very fast before the sun dips. Switching to the manual mode allows the photographer to get a more precise exposure after the sun sets. Setting a larger aperture f-number such as f13 or f16 gives the sun a starburst effect, and this fraction will depend on the lens on is using. 

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