The term "platypus" is not used as a unit of measurement in astronomy.

Parsecs

A parsec (pc) is a unit of distance used in astronomy. It is defined as the distance at which an object has a parallax angle of one arcsecond. In other words, if you were to place the Sun and the Earth at opposite ends of a 1-parsec baseline and look at a distant object, it would appear to move by one arcsecond in the sky as the Earth orbits the Sun.

Parsecs are used to measure the distances to stars, galaxies, and other objects in the universe. They are much larger than the units we use to measure distances on Earth, such as kilometers or miles. One parsec is equal to about 3.26 light-years, or about 206,265 astronomical units (AU).

MilliCrab

A milliCrab (mCrab) is a unit of flux density used in radio astronomy. It is defined as one-thousandth (1/1000) of a Crab, where the Crab is a bright radio source in the constellation Taurus.

Flux density is a measure of the amount of energy that an object emits per unit area per unit time. It is usually expressed in units of watts per square meter per hertz (W/m2 Hz). A milliCrab is equal to about 1.6 mJy (millijanskys), where a jansky (Jy) is a unit of flux density equal to 10-26 W/m2 Hz.

MilliCrabs are used to measure the flux density of radio sources, such as stars, galaxies, and quasars. They are particularly useful for measuring the flux density of weak radio sources, such as those that are located at great distances from Earth.