Newbie here wondering if there's some consensus answer to the following:

Given a planet similar to Earth (I'll call it Searth), exists in a star system S light years distant...

With our current technology, what's the value of S?

- How dependent would S be on the Searth's sun's magnitude or other characteristics?

- How would the value of S change in 10 years? 20 years? 100 years?

Another question:

How far distant could Earth be detected by an alien civilization with technology 50 years more advance than our current? (I'm assuming they had some sort of orbiting telescope with a clear view at a stable Lagrange point).