# Suppose the semi-major axis of the Earth was 1.3 A.U. Would it be easier to measure parallax? A) Yes, it would be slightly (1.3 times) easier to measure parallax.B) Yes, it would be more than 10...

Suppose the semi-major axis of the Earth was 1.3 A.U. Would it be easier to measure parallax?

A) Yes, it would be slightly (1.3 times) easier to measure parallax.
B) Yes, it would be more than 10 times easier to measure parallax.
C) No, it would be slightly (1.3 times) harder to measure parallax.
D) No, it would be more than 10 times harder to measure parallax.
E) It would make no difference -- the star are so far away, it would be just as hard to measure parallax.

Asked on by sruland

### 1 Answer

caledon | High School Teacher | (Level 3) Senior Educator

Posted on

Note that the Earth has two semi-major axes; that of its orbit, and that of its radius. Both of them would result in the space occupied by the Earth, and the observations conducted from it, being larger, and therefore making parallax easier to measure.

Parallax is the same principle that your eyes use to attain depth perception; because your eyes are a certain distance apart, they perceive the world from a slightly different perspective. Your brain is capable of merging the two images into one that compensates for the differences by creating depth of field, allowing you to interpret how far away things are. The closer they are, the greater the difference that your eyes perceive. Likewise, if your eyes were farther apart, you would perceive a greater difference due to the distance of objects.

If the Earth's average orbit was 1.3 AU, it would be farther from the sun. This would be just like saying that your eyes were 1.3 times farther apart. When we looked at stars from the 1.3 AU earth, the angle created by their parallax would be 1.3 times greater than from the 1.0 AU earth.

Thus, A) It would be 1.3 times easier to measure parallax.

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