[chris (OP)]

I received this question from Adrian in an email during this evening's programme.

Assuming we could travel fast enough to make the journey feasible, how could we navigate to a distant star since don't we see that star as it was in the past? Do we simply have to keep recalculating it's position? As we get closer are we basically shortening the viewing time as well as distance - the star effectively comes closer to the present :/

Adrian

What do you think?

[alancalverd]

Simply aiming at the apparent source will get you there in the end, but via a "banana approach", not the most efficient or direct path. However if you know how far away it is (or "was then") and you set off in a straight line, you can estimate its movement after you have travelled, say, 25% of the initial track, calculate where it will be by the time you arrive, and make a single course correction to rendezvous. It's a standard technique for flying to a radio beacon with an unknown crosswind, complicated a bit by the  very long travel times and apparent acceleration of distant stellar objects, but the principle is sound.

[chris (OP)]

Also, we need to assume that it'll still be there when we arrive too!

[Colin2B]

Also, we need to assume that it'll still be there when we arrive too!

We could probably get an idea of that from the current life stage of the star.
Also, if the star is not moving directly away from us we should be able to estimate a likely shift e.g. Barnard's Star has a movement of 10.25 arcsec/yr when compared to more distant stars.

[evan_au]

If the star is close enough to measure its position and velocity in 3 dimensions (eg via the Gaia satellite), then you can set off in the correct direction so the star will be there at the time you arrive, with no course corrections (in theory).

In practice, no rocket firing is ever exactly right, and collisions with the gas and dust in interstellar space will change the spacecraft course slightly, so some minor course corrections will be necessary.