Question

How is stellar parallax defined?

Answer 1

The shift of a star against a background of distant stars when measured at different viewpoints, usually 6 months apart from each other

Explanation:

Using stellar parallax, we can calculate the distance to close stars with simple trigonometry.

It's sort of like looking through one eye and then the other. The object(s) appear in different places. When you see through both eyes, your brain constructs an image combining the two together.

By calculating the parallax angle, and knowing the distance between our two vantage points, we can use the equation:

(where)
`theta` is the parallax angle,
`x` is the distance between vantage points divided by 2 {because you want to create a right-angled triangle} and;
`y` is the distance from our Sun to the star

`tantheta=x/y`

If the star is too far away, the angular displacement will be too small, so other methods are used, for example Cepheid variables.