World Science Scholars
1.3 Parallax

PLEASE NOTE: For better performance, you may download the demonstration by clicking here. If you have not already downloaded and installed the free CDF player, it is available here.

How can we estimate the distance of a cosmic object? The method of stellar parallax exploits the revolution of the Earth around the Sun to observe the apparent shift of a nearby object against the background of distant stars. In this demonstration, three stationary bodies are placed at fixed distances from you, the observer. As you move your viewing angle left and right, notice how the nearer objects appear to shift against the colored background much more than the further objects. For instance, the furthest sphere never seems to leave the blue region, while the middle sphere appears to be in front of the red region from one side and in front of the green region from the other. Stellar parallax is a fairly accurate technique for objects closer than ~100 parsecs (326 light-years) but begins to lose accuracy beyond that.


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