[coolspot]

2I/Borisov was not discovered by Zwicky Transient Facility .

The comet was discovered on 30 August 2019 by amateur astronomer Gennadiy Borisov at his personal observatory MARGO in Nauchnij, Crimea, using a 0.65 meter telescope he designed and built himself.

[zeven7]

That’s interesting. If it was possible to do on a homemade telescope, then why were no interstellar objects discovered before 1A?

[MalbertKerman]

The hard part isn't having a telescope, but analyzing the images for objects that have moved between successive observations. Digital astrophotography and analysis software have been getting steadily cheaper and better, which leads to more amateur comet hunters each watching more sky, which has rapidly improved the odds of catching rare objects.

I'm not sure how the progress of institutional and amateur observations compare. Obviously the big guys benefit from the same technological advancement, but I don't know whether the fraction of new objects discovered by amateurs has been growing or not. I suspect the odds of the first interstellar object being found by an amateur were still pretty long.