This movie was developed by Professor Rick Pogge at the Ohio
State University Astronomy Department.
The top portion of the movie shows what you would see looking at a nearby
star over time from Earth. The nearby star, whose distance you are trying
to measure, is in red and can be
observed to move against the fixed background stars. The bottom portion
shows the view of the Earth/Sun/star system from above. The Earth is shown
in blue orbiting the Sun (yellow).
The line of sight from the Earth to the nearby star, and
onto the distant background stars, is shown in red. As the Earth orbits
the Sun, the line of sight to the nearby star changes, and the apparent
position of the star on the sky (in the top portion of the diagram) can be
seen to change as well.
Notice that in the movie two different cases are shown, one after another.
In the first, the nearby star is closer to the Earth, while in the latter,
it is further away. Observe how the size of the apparent shift changes in