In Star Trek: The Original Series, what technique lets a starship travel through time by slingshotting around a star?

In Star Trek: The Original Series, the gravitational slingshot effect lets a starship travel through time by using a star’s gravity and extreme warp speed.

The method is demonstrated in “Tomorrow Is Yesterday” and later referenced in “Assignment: Earth.” The Enterprise approaches a star, accelerates to high warp, and uses the star’s gravitational field to alter its trajectory and temporal position. The maneuver is fictionalized far beyond real spacecraft navigation.

In real astronautics, a gravity assist changes a spacecraft’s speed and direction relative to the Sun or another body. It does not normally send a spacecraft through time, although relativity means that high speeds and strong gravity can affect elapsed time.

This technique is often confused with ordinary warp travel. Warp drive supplies the fictional faster-than-light motion; the star’s gravity provides the slingshot geometry that produces the time shift.