Neil, The Harvest Moon was kickin' our butts that night. Longer exposures were washed out even with lower ISO or higher -stops. You can see some of that in the lower portion of the image. There is a slight bluing of the sky.
I have shot the 24mm on the D700 for Aurora as well as the 28mm /2.0 AI MF. Both do fairly well wide open but there can be a bit of distortion of bright lights near the edges unless I stop down. I am not sure if it is barrel or CA I see but the lights appear to have what I call "bat wings". The distortion is present on both the D300 and D700 with the 24mm /2, the 28mm /2, and the 35mm /1.4. I have not checked it on my 50mm /1.4 (I have both the MF and AF-D versions).
The only fast lens I have that performs great wide open in the dark is the Noct-Nikkor 58mm /1.2. I will use the Noct if I am going for a small section of the Aurora display.
Here is one from the same night with the Noct on the D700 - 58mm /1.2 - ISO 1600 - .5sec. The moon was really difficult as longer exposures were showing "glow".
If the distortion is symmetrical then it is a bit of astigmatism. If the distortion looks like small comets, all pointed toward the optical center, then it is coma. My understanding is that wider than f/4 or so almost all lenses will show one or the other. Lenses are basically designed to have one or the other- it's a designer's choice.
Except the Noct of course . You are blessed to have that lens.