Distances to nearby stars can be determined from

Distances to nearby stars can be determined from Stellar parallax. 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 arcseconds.

Because the dept in the ocean

That depends on what kind of environ meant it is in  in space it has the same force that was applied when the velocity was gained