system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do really long exposure photos weigh more MB? Shouldn't every pixel have the same amount of information regardless of how many seconds it was exposed?

I noticed that a regular photo weighs a certain amount of MBs, while if I keep the shutter open for 4, 5 minutes the resulting picture is HUGE.  
Any info on why this happens?
gpt
The jpeg format we store photos in is designed to store a good photograph efficiently. A good photo has large areas of smooth, even gradients, and Jpeg does a great job of *compressing* these to take up less space.

A long exposure photo will have more random 'roughness' in the picture. It will be much more *noisy*, with small, random changes in individual pixels. Jpeg is not designed for this, so it takes more space to store the noise.