Parsec
A parsec (pc) is a unit of distance used in astronomy, equal to about 3.26 light-years or roughly 31 trillion kilometers. The name “parsec” comes from “parallax of one arcsecond,” referring to the method astronomers use to measure distances to nearby stars based on their apparent shift when viewed from different positions in Earth’s orbit. Parsecs are commonly used to measure distances to stars and galaxies. For example, the nearest star system, Alpha Centauri, is about 1.3 parsecs away. The symbol for parsec is "pc". It’s a convenient unit for expressing large astronomical distances beyond the reach of light-years.
Planck Length
The Planck length is the smallest meaningful unit of length in physics, representing a fundamental scale at which classical ideas about gravity and space-time break down and quantum effects dominate.
It is defined as approximately 1.616 × 10⁻³⁵ meters.
The Planck length is derived from fundamental constants: the speed of light, Planck’s constant, and the gravitational constant.
It sets a theoretical limit below which the very concepts of space and distance may lose conventional meaning.
Used mainly in theories of quantum gravity and string theory.
Key facts:
1 Planck length ≈ 1.616 × 10⁻³⁵ m
Smallest scale in quantum physics and cosmology
Represents a scale where quantum effects of gravity become significant
The Planck length is crucial for understanding the fabric of the universe at its most fundamental level.