What is the furthest observable phenomenon from Earth that is Earth Science?
It appears the Earth's magnetotail, which is a part of its magnetosphere, is on the Earth's nightside; lengthwise exceeds 6,300,000 kilometers (3,900,000 miles); and is the furthest known observable feature of Earth.

I am unable to explain why is it commonly not included in the "spheres" of Earth Science.



Note: The gravitational pull of Earth in theory spans the known Universe, though it's unlikely to have any observable affect, unlike the Earth's magnetotail.