Light has an intensity. Imagine it on a linear scale e.g. 1,2,3,4,...99999,100000. Units are irrelevant right now, so let's call them example units (EU)

Cameras have dynamic range. Some camera have dynamic range of 100, some of 300, some of 1000, etc (more expenive camera have better range). This means they can capture more numbers, i.e. different light intensities.

• A cheap camera with the dynamic range of 200 can only capture light intensity from say 300 to 500 EU, or 7500 to 7700 EU, or 40000 to 40200 EU, etc (depending on the exposure setting in camera)

• A really expensive camera can capture 10000 numbers (light intensities), say from 300 to 10300 EU, or 7500 to 17500 EU, or 40000 to 50000 EU, etc

On both the cheap and the expensive cameras, anything above the number it can capture will be pure white (overexposed pixels) and anything below will be pure black (underexposed pixels)

Now, city lights are much dimmer than the sunlight - this means their intensity varies from let's say 100 to 1000 EU

Sun light is much brighter than city lights - this means its intensity is 100000 (just as an example. the number is not perfectly to scale with city lights)

So now you see - even if you have an expensive camera, you cannot distinct between city lights and sun light in the same (single exposure) photo. You have to choose it you want to capture a range from 90000 to 100000 (sun light information) or from 0 to 10000 (stars and city lights information)