[Kunama]

Originally Posted by OICURMT

Two words... "apparent magnitude"

If we consider that our sibling was cast out at any sort of significant velocity say 4 billion years ago (let's allow it to grow up with Sol for 500million years), at a velocity of say 20km/s (a low velocity for a cast out star), it would be about 82000 parsecs away by now...

Even at 1 billion years ago, it would be at 23000 parsecs away.

The Sun's apparent magnitude is 4.7... if our sibling is the same G-type star, it would be very very very very faint...

Trying to get a spectra of such a faint star would require many minutes, if not hours of exposure. Only a space telescope (maybe Magellan on Earth) could manage that...

Merlin, care to comment on exposure times for spectra?

OIC!

Don't you mean absolute magnitude (4.83)