Final answer:
The apparent shift in a star's location as observed from Earth is called parallax, which is particularly known as stellar parallax when referring to stars. It occurs because of Earth's orbit around the Sun and is measured by observing the star from different points in Earth's orbit.
Step-by-step explanation:
The apparent shift in location of a star that we observe is called parallax. This phenomenon is due to the Earth's motion around the Sun. As our planet orbits, a nearby star seems to shift position against the backdrop of more distant stars. This apparent motion is observed because we are viewing the star from different positions in space at different times of the year.
Stellar parallax is the specific term for the shift in the apparent direction of a star caused by Earth's orbital motion. The Greeks were among the first to attempt to detect this motion, but the effect was too small to observe with the nak'd eye. Astronomers define the parallax angle as half of the total angular shift observed over a six-month period as Earth moves from one side of its orbit to the other, effectively using a baseline of 1 Astronomical Unit (AU) rather than 2 AU.