Re: How close will the star Vega pass by our sun when it arrives in our system.

Hi Donald,

You heard right that we are getting closer to Vega.
The Sun's motion is about 20 km/s, pretty close to the
direction of Vega, and Vega is approaching the Sun at about 14 km/s.

Vega isn't moving directly towards the Sun, however: its
transverse velocity (ie at right angles to the line between
the Sun and Vega) is about 2.71 AU/year (1 AU= 1 "astronomical
unit" = distance from the Earth to the Sun).
So the distance of closest approach is (2.71 AU/year)*(time to closest
approach), where (time to approach) = (current distance)/(approach speed)

I calculate the number of years as about 250 000, so the
distance is about 650 000 AU, which is 3.2 parsec or 10.4 light years.
This is a little under half the current Vega-Sun distance of
7.8 parsec. So it's not as though Vega will be screaming through the
solar system, but it will be about 4 times brighter being only
half as far away.

This is only a rough calculation, since it assumes that the Sun and Vega
will not deviate from their current velocities in the next quarter million
years. This isn't quite true, because the other stars in the neighborhood
will also have some (small) gravitational effect on both stars. I don't
know of any caulcation that attempts to map the local stars' positions
out in detail for the next 250000 years. But in principle it could
certainly be done.

I got the numbers for this calculation from "Abell's Exploration of the
Universe", 7th Ed. by Morrison, Wolff and Fraknoi. This college astronomy
text is a very good general reference.

Pauline