FIGURE 12. Calculating the distance to Tau Ceti

Figure 12 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 4
Calculating the Distance to Tau Ceti using the Parallax Timer

• Demonstrate that multiple exposure images such as those in Experiment 4 and Figure 8 are artificial. That is, multiple exposure images do not directly convey that many images must be taken over a period of at least six months to make a single parallax measurement.
• Understanding how nearby stars appear to move against the background of fixed stars on a month by month basis.
• Calculate the distance to Tau Ceti using virtual parallax measurements made over a period of many simulated months.

• Set the selected star to Tau Ceti.
• Set the field of view to 2 arc seconds.
• Set the operation mode to parallax with timer.
• Repeatedly click the clock icon in the upper left-hand corner of the display window. Each click of the clock icon advances the virtual month.
• When the clock reads Dec, use two mouse clicks to measure the Tau Ceti parallax angle. To do this, click the mouse once in the centre of the ellipse and once at the end of the major axis.
• Use the measured parallax angle and Equation 3 to calculate the distance to Tau Ceti.

• Although the clock icon appears to give the time in calendar months, the clock icon refers to no particular month or year. The clock icon is intended to be a convenient mechanism to denote the passing of the months.
• Measuring parallax requires taking multiple images!

In Figure 12, the Tau Ceti parallax angle was measured to be 0.275 arc seconds. The distance to Tau Ceti can be calculated using this measurement and Equation 3 according to:

Appendix 4 of Kaufmann and Freedman (1999) reports the distance to Tau Ceti as 11.9 ly. In this case, the virtual experiment produced an error of only 0.3%.