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Design a Way to Measure Parallax Shift and Use It to Determine the Distance to an Object

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Author: Janice VanCleave

What You Need to Know

The apparent change in position of an object when viewed from two different points is called parallax shift. The distance between the two points is the baseline.

How Does Parallax Shift Work?

Hold your thumb at arm's length in front of you. Close your right eye and look at your thumb with your left eye. Notice how your thumb lines up with the distant objects behind your thumb. Without moving your thumb, close your left eye and open your right eye. Again, look at your thumb. Your will notice a change in the objects behind your thumb. This apparent change in the position of your thumb in relation to the distant object is parallax shift.

What Does This Have to Do with Measuring Distance?

Parallax shift can be used to determine the distance to an object using the following formula:

d = 57.3° × baseline distance ÷ parallax shift

When the baseline distance is divided by the parallax shift, the answer is a number without a unit. To express the answer in degrees, the number is multiplied by 57.3°. The smaller the parallax shift, the farther away the object is. For example, if the baseline is 2 inches, an object with a parallax shift of 5° is closer than an object with a parallax shift of 10°.

d = 57.3° × 2 inches (5 cm) ÷ 5° = 2.292 inches (5.73 cm)
d = 57.3° × 2 inches (5 cm) ÷ 10° = 1.146 inches (2.865 cm)

Real-Life Science Challenge

When Sedna was discovered in 2003, scientists were challenged to determine if it was part of our solar system, meaning that it orbits the Sun. On March 16, 2004, the Hubble telescope took 35 pictures of Sedna. When scientists looked at the pictures in order, Sedna appeared to move slightly, indicating a parallax shift, which demonstrated to scientists that it was a member of the solar system.

Fun Fact

Our solar system no longer has nine planets. Pluto continues to be part of the solar system, but it has been demoted from a regular planet to a dwarf planet. This came about because of the discovery of Sedna, a celestial body that is smaller than Pluto but that, like Pluto, orbits the Sun. Astronomers decided that if Pluto and Sedna were called planets, then asteroids orbiting the Sun should also be called planets.

Experiment

Now, start experimenting with ways to measure parallax shift and use it to determine the distance to an object.

Hints

• You could use a pencil eraser to represent the object whose distance is being measured.
• You could draw stars on a piece of paper and secure it to a wall to represent distant stars.
• The farther away the background objects are, the greater the parallax shift will be.
• Design a way to change the length of the baseline.
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