A question

[xnamkrad]

Having a discussion here and maybe one of you could help

Comments

[captainlucy]

One possibility is to make the same assumption that SETI does, and assume that the alien Signal is a "Hello Universe, we're here!" signal which will presumably include one of a number of universal indicators (eg. it's broadcast will include something at the emission frequency of Hydrogen, or one or more of its energy states) which gives us a measurable yardstick. If we then analyse the signal's redshift, we can determine how fast the signal source is moving either towards or away from us, and use this against figures for the expansion of the universe to obtain an approximate figure. Obviously this only works with objects at great distances (probably extra-galactic); for objects closer to us we can analyse the known relative motion of stars and match them to the signal that way.

For much closer objects (within a couple of hundred parsecs), if the signal lasts long enough we can use stellar parallax (the difference in angle of a nearby star to "fixed" distant background stars caused by the orbit of the Earth around the Sun) to gauge the distance by simple triangulation.

[xnamkrad]

For purposes of the discussion, the second option sounds like the answer for this.

Thanks