[dave9t5]

I see Canon people will still be using the Nikon 14-24mm for astro and aurora photography as this is not f/2.8. It is wider, I wonder how big it would have been with an f/2.8 aperture.

I'm no BC or Scythels, but roughly: 

 

Area is the aperture, but elements are roughly proportional to the aperture.  

+1 stop => 2x the area => 1.414x the diameter

 

So roughly expect for every stop increase: the diameter of the lens increases 41% and the weight doubles.