Both Kodak Astro Zoom AZ651 and Nikon 1 J5 have 21.0 MP resolution sensors but Kodak Astro Zoom AZ651's sensor is 1/2.3" (6.17 x 4.55 mm ) and Nikon 1 J5's sensor is 1" (13.2 x 8.8 mm ).
Since Nikon 1 J5's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Kodak Astro Zoom AZ651.
Another difference between these two cameras is that Nikon 1 J5's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the Astro Zoom AZ651 and J5 sensor size comparison.
As seen above, Nikon 1 J5 has a 4.1x Larger sensor area than Kodak Astro Zoom AZ651. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.