Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
You should watch this video from Smarter Every Day, where he conducts a number of experiments that can be copied by anyone: youtu.be/eNK2LI7VeX4?si=WULNICu6teecsTOU
This does not answer the question at all. Chris, please read our tour and How to Answer pages to understand how this site works, and what answers need to be.
Vladimir - those are very obviously planes, and as a pilot and aero enthusiast who has flightradar open almost all day every day, I can tell you that your comment re density only being like that near airports is just wrong.