Stellar Parallax

Astronomy 1101/1103 __________________________ Yervant Terzian/Terry Herter

Example to try

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Stellar distance estimates are crucial to understanding stellar properties and underpin the whole distance network for galactic and extragalactic astronomy. The simulation above shows the orbit of the earth around the sun, a "nearby" star, and background stars. The view is from the north galactic pole. The foreground star is shown as a filled orange circle and the background star field on the right-hand image. As the earth moves around the sun the foreground star will change position relative to the background (more distant) stars. This is illustrated in the lower image.

Astronomers measure this movement by taking a picture of the star field at different times of the year. The greatest parallax occurs when the earth is at the ends of its orbit. Proper motion (space motion) of the star relative to the sun could contaminate the parallax measurement. However, picture can be taken again after one year (so that the earth is the same position) to remove proper motion effects.

This simulation greatly exaggerates the amount of parallax. A typical motion is much less than the size of the star in the image.



Start the animation and turn on the Show Bounds feature. This will produce an arrow which tracks the star against the background stars. Now drag the star to different distances from the earth-sun system. Note how the parallax decreases as the star moves further away and increases as the star move closer to the earth.