A circle with a radius of 10cm was drawn on a sheet of paper and used to simulate the orbit of the earth. A cardboard star was placed 1metre from the centre of the circle. A Kodak DC40 Digital Camera was placed on opposite sides of the circle, and two images were taken. These images simulated the view of the "nearby star" from the "earth" in January and July.

FIGURE 5. Homemade calibration instrument

A calibration instrument to measure the Field Of View (FOV) of the DC40 camera was created using household items. A cardboard tube with protruding arrow was fixed with a paper clip to pivot about the origin of a protractor. A needle and thread was used to create a crosshair for sighting in the centre of the tube.

The calibration instrument was placed on top of the camera on a sturdy tripod. The left and right boundary of the camera FOV was sighted through the calibration instrument and the camera view finder. The camera FOV was found to be 44 degrees.

FIGURE 7. Left and right parallax images

Two images were taken on opposite sides of the circle simulating the orbit of the earth. These images are shown in Figure 7. The football goal posts at the end of the field represent distant stars, which were used to register the two images. The parallax shift of the nearby star was found to be 26.5% of the camera field of view. Since the camera's field of view was found to be 44 degrees, this means the nearby star exhibited a total parallax shift of 11.68 degrees.

Recall from Equation 1 that the distance to the nearby star can be found using:

where:

d = distance to nearby star
r = radius or earth's orbit or 0.1 metres
= 11.68 degrees/2 or 5.8 degrees

The distance d is therefore calculated to be 0.98 metres, with an error of 2%

Note that the parallax shift is off-centre in these images because the focal plane of the digital camera is not directly above the point where the camera is attached to the tripod.

FIGURE 8. Simulated multiple exposure.

In his version of the experiment, de Jong (1972) reported that some students preferred having parallax images presented using two images similar to those shown in Figure 7.

De Jong reported that other students preferred a double exposure to simplify the measurement process.

In the version of the experiment presented here, the equivalent of a multiple exposure was produced in Adobe Photoshop and is shown in Figure 8.

To produce Figure 8, the image corresponding to the right-hand camera position was made to be a semi-transparent layer over the top of the left-hand camera position. The football goal posts were used for registration.