The concept of using petametres (abbreviated as Pm) as a unit of distance in astronomical measurements is not commonly used because it does not offer any significant advantages over existing units such as light years or parsecs.
Both light years and parsecs are widely used in astronomy and astrophysics because they provide practical and meaningful ways to express vast distances on the astronomical scale. Here's a brief explanation of why these units are preferred:
Light Year (ly): A light year is the distance that light travels in one year in a vacuum. Since the speed of light is constant, using light years allows astronomers to easily relate distance and time. It provides a convenient way to understand the scale of astronomical objects and events, especially when discussing objects within our own galaxy or relatively nearby stars.
Parsec (pc): The parsec is another commonly used unit of distance in astronomy. It is defined as the distance at which an object would have an annual parallax of one arcsecond. Parallax is the apparent shift in the position of a nearby object when observed from different vantage points. The parsec is particularly useful for measuring distances to objects beyond our own galaxy. It allows for more precise calculations of stellar distances and is often used in cosmological contexts.
Petametres, on the other hand, are not specifically designed for astronomical purposes. The prefix "peta-" denotes a factor of 10^15, which is an extremely large value. While it is technically possible to express astronomical distances in petametres, it would not offer any significant advantages over existing units. Light years and parsecs have become standard units in the field of astronomy, and there is a vast body of knowledge and research built around them.
In scientific fields, it is generally preferable to use established units and conventions to ensure consistency and facilitate communication among researchers. Therefore, unless there is a compelling reason to introduce a new unit, such as the need for improved precision or simplification of calculations, there is typically no need to replace existing units like light years or parsecs with petametres.