How do astronomers use parallax to calculate a stars distance?

Astronomers can measure a star's position once, and then again 6 months later and calculate the apparent change in position. The star's apparent motion is called stellar parallax. The distance d is measured in parsecs and the parallax angle p is measured in arc seconds.

The characteristics of groundwater is said to be: are weak turbiditya constant temperaturechemical composition and almost overall absence of oxygen.