Figure 14 is a screen grab from the running applet. To try this virtual experiment, select the ATLAS icon to start the applet.

See the list of other virtual experiments.

VIRTUAL EXPERIMENT 6
Comparing the Eccentricity of the Parallax Path for Alpha Centauri A and Tau Ceti

• Understand how the eccentricity of the parallax path is determined by the declination coordinate for the star.

• Set the operation mode to parallax measurement.
• Set the Field of View to 2 arc seconds.
• Set the selected target star to Alpha Centauri A and observe the eccentricity of the parallax path in the display window. Also note the star's declination in the data window.
• Set the selected target star to Tau Ceti and observe the eccentricity of the parallax path in the display window. Also note the star's declination in the data window.
• Repeat this observation for a variety of other stars.

• The declination of Alpha Centauri A is -60 deg 38.0 min
• The declination of Tau Ceti is -16 deg 12 min
• Because Tau Ceti is closer to the Celestial Equator, it has a more eccentric parallax path than Alpha Centauri A, which is closer to the southern celestial pole.
• Note that a star on the Celestial Equator would appear to move back and forth, rather than sweeping out an ellipse!