
Stellar Aberration 2D
General Description
This simulation illustrates the phenomenon known as the aberration of
starlight, first reported by James Bradley in 1729. Aberration occurs because light has a finite speed, and
thus light from a star takes a finite amount of time to travel through
the tube of a telescope. During this time, the telescope moves as a
result of Earth's rotational and orbital motions (in this case, the orbital motion
is more important because it is faster). Therefore, if the telescope
is pointed directly at the star the starlight will hit the sides of
the tube before reaching the eyepiece. To see the star the telescope
must be pointed forward (ie in the direction of Earth's motion) very slightly.
The simulation shows a telescope (depicted as a red rectangle) and a
star (white point) directly overhead. When the simulation is run a
pulse of light is emitted from the star and travels straight downward
to Earth. The telescope moves to the right due to Earth's motion. As
a result, if the telescope is pointed straight up (ie toward the
actual location of the star) the pulse of light will not reach the
bottom of the telescope. Controls allow the user to set the speed of
Earth and the tilt of the telescope. The user can modify the tilt
until the starlight reaches the bottom of the telescope. Alternately,
the user can use the Options menu to set the telescope to the correct
tilt for the current speed setting.
Stellar Aberration 2D Frame
- Options Menu
- Tilt Telescope to Correct Angle: sets the tilt of the
telescope to the correct angle for viewing the overhead star.
- Visual Elements
- Red rectangle: the telescope tube.
- White points: the star (directly overhead) and the pulse
of light sent out by the star.
- White line: path that the starlight travels from the
star to Earth.
- Cyan arrows: displacement vectors showing how the
telescope moved during the time the light was traveling
through the tube.
- Magenta point/line: apparent location of the star and
the line of sight from the observer to that apparent location.
- Controls
- Play/Pause: start and stop the simulation.
- Step: advance the simulation by one time step.
- Reset: reset the simulation to its initial state.
- Speed: the speed of Earth divided by the speed of light.
- Tilt: tilt angle of the telescope (in degrees).
Todd K. Timberlake (ttimberlake@berry.edu)