The figure illustrates the effect of parallax on the apparent position of a star which is located in the plane of the Earth's orbit (ie on the ecliptic)
The red object on the top is the projection of the real star (red) on the sky. When the Earth (blue) is revolving around the Sun (yellow), the star looks like moving on the sky. For example, when the Earth is on the position A, the star appears to be near the background star "A" (yellow). You can press the button "Show" to see the line-of-view from the Earth to the star. This line can be turned off by clicking on the button "Clear". The yellow button "Change" allow you to change the distance between the Earth and the star. You can see that the parallax angle is proportional to the distance from the star. The closer the star, the greater the parallax effect.
You can stop the planet motion by clicking on the image at any time, and then press the mouse again to activate it.
This animation was created by Ming Zhu . Send questions or comments to: zhu@astro.utoronto.ca.
This page was selected by the SciLinks program, a service of National Science Teachers Association. Copyright 2001.