The Hubble flow: an observer's perspective

Abstract

In this methodological note we discuss some details and peculiarities of the cosmic expansion as viewed by a realistic observer. We show that the velocity $v_\Theta$ related to a change (measured by observer's clock) of the angular distance, plays an important role in formation of a meaningful observed picture of the expansion of the universe. Usage of this velocity and the angular distance (in addition to the standard approach --- proper distance and corresponding velocity) allows to present the cosmic expansion in a more illustrative manner. These parameters play a key role in visualization of the expansion.