Not sure what the center lighted area is?

Took this image with my C8 SCT using a 25mm eyepiece and I set Iso on my phone around 800; exposure is 3sec. Anyone know what the brighter center area might be? Should I have lowered the Iso for the exposure? Any advice welcome. Thank you.

Honestly this is out of my realm of understanding. But I have to wonder if there is a light source nearby that might be getting captured?

A C8 SCT, even with the 42mm camera adapter on, has a very small “imaging circle”. The center is the brightest with rapid light fall-off and vignetting. When using an eyepiece, especially one as narrow-field as a 25mm, the center “hot spot” is very bright, the light falls off and vignetting is way more severe than even the camera adapter. If you were to shoot a bright object like the moon, you wouldn’t notice this severe light fall off as much.

Thanks Andy. Any way of correcting for this in camera, scope, or photo editing?