Complex sentence: This observable movement implied it was relatively close to the Sun, making it a star of interest for the purpose of trigonometric parallax measurements--recording the position of the star as the Earth moved about the Sun, which would allow the distance to be estimated.
Split into simpler sentences: This observable movement implied it was relatively close to the Sun, making it a star of interest for the purpose of trigonometric parallax measurements. This process involves recording the position of the star as the Earth moved about the Sun, which would thereby allow the star's distance to be estimated.