How do you demonstrate parallax?

Answer 1

Look at two objects, say one about a foot away, and the other about two feet away. Move your head until the objects appear to be lined up with each other.

Now, cover and uncover one eye. Repeat it a couple of times. Then do the same thing with the other eye.

Depending on which eye is dominant, in one case the two objects will stay lined up, and in the other case they will appear to move with respect to each other.

That is parallax, which is simply the difference in perception between the viewpoints, in this case, the eyes.

Astronomers use parallax to measure long distances in space. They take pictures of an area of space they are interested in, wait 6 months, and take pictures of the same area of space. They compare the pictures. Most far distant stars will appear to be in the same position, so they line up the two pictures based on the far distant stars. Then they notice that some stars appear to be in different positions. They use trigonometry to measure the parallax error between the two pictures. Since they know the distance between the two observation points is about 186 million miles, and they know the angles of both observations, they have enough information to calculate distance to the star.

Answer 2

Hold up your hand in front of your face, and alternately close your left and right eyes.

Answer 3

Haha, very funny