A few points I wanted to make, specific to the HN context (and a lot of this is in the "nerd mode" donation page at https://skycircl.es/donate-nerd-mode/):
1. This seems like a classic "low effort, high impact" project. It's super easy to detect aircraft flying in circles, in real-time, and post it to twitter. But it turns out to be an entry-point into a "strangely interesting" (according to pg) world of aircraft activity.
The current #1 comment sadly only gets to see general aviation pilots practicing, but my bots have tweeted military aerial refueling, STOL practice in the wilderness, float-planes practicing on rivers and lakes, military drones flying over the desert, planes dropping sterile fruit flies as a way to reduce the fruit fly population, news helicopters following a highway pursuit, U.S. Forest Service AH-1Z Viper attack helicopters fighting fires, helicopters dropping mosquito pesticide, aerial tankers over Manhattan for the president's combat air patrol, FBI surveillance planes registered to front companies, Coast Guard helicopters doing search & rescue, crop dusters, scientists observing sea life over the ocean, planes doing Gorgon Stare-style persistent surveillance over Baltimore, sheriff's helicopters rescuing hikers, power line inspections, pipeline inspections, military aircraft doing surveillance over protestors, stealth jet test flights, a Grumman HU-16 Albatross seaplane that belongs to the USAF over the Mojave desert, a U-2 test flight, and a B-29. That is not even close to a complete list.
2. All the code is open source. See https://gitlab.com/jjwiseman/advisory-circular/ and https://gitlab.com/jjwiseman/whatsoverhead
3. As far as I know, this comment on HN is the first time anyone published any significant detail about the FBI's secret aerial surveillance program: https://news.ycombinator.com/item?id=9508812