Determining past and future positions relies on accurate astrometric measurements of their parallax and total proper motions (how far they move across the sky due to their actual velocity relative to the Sun), along with spectroscopically determined radial velocities (their speed directly towards or away from us, which combined with proper motion defines their true movement through the sky relative to the Sun).
[2] Based on results from the Gaia telescope's second data release from April 2018, an estimated 694 stars will approach the Solar System to less than 5 parsecs in the next 15 million years.
[4] It is currently predicted to pass 0.1696±0.0065 ly (10635±500 au) from the Sun in 1.290±0.04 million years from the present, close enough to significantly disturb the Solar System's Oort cloud.
Absolute magnitude (with electromagnetic wave, 'light' band denoted in subscript) is a measurement at a 10-parsec distance across imaginary empty space devoid of all its sparse dust and gas.
[6] Over long periods of time, the slow independent motion of stars change in both relative position and in their distance from the observer.
This can cause other currently distant stars to fall within a stated range, which may be readily calculated and predicted using accurate astrometric measurements of parallax and total proper motions, along with spectroscopically determined radial velocities.
[2] Inaccuracies of these measured parameters make determining the true minimum distances of any encountering stars or brown dwarfs fairly difficult.