Which technique relies on combining proper motion observations with radial velocities for distance determination?

Answer

The moving cluster method

The moving cluster method is a crucial geometric technique used to determine the distance to open clusters, especially those too far for precise parallax measurements. This method hinges on the principle that all stars within the cluster share a common velocity vector through space. By observing the apparent proper motion of these members across the sky, astronomers can determine the direction towards a vanishing point where these motions appear to converge. When this geometric information (the convergence angle) is then combined with the measured radial velocities of the stars (determined via the Doppler shift in their spectra), simple trigonometry allows for a precise calculation of the cluster's absolute distance from Earth. This calibration step is vital for extending the entire astronomical distance ladder.

Which technique relies on combining proper motion observations with radial velocities for distance determination?

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