I don't understand the concept of first pass. Do they really mean "first pass ever" which I suppose would also mean humanity will never ever interact with this comet ever?
[emphasis mine] Why? (Assuming humanity lives in harmony on Earth for another few million years) It's non-periodic (the 'C' in C/2013 A1 (Siding Spring)) comet, so as far as we know, it will be the first and only pass through the inner Solar System.
22/7 is misleading, in that people often think it's an exact value.
Who says Pi or 22/7 don't have an exact values? 22/7 is mileading because it's a rational number while Pi is not.
It is impossible to enjoy idling thoroughly unless one has plenty of work to do. -- Jerome Klapka Jerome