Various measures: obscure to unknown

Some examples, from the site:

Attoparsec
Parsecs are used in astronomy to measure enormous interstellar distances. A parsec is approximately 3.26 light-years or about 3.085×10¹⁶ m. Combining it with the "atto-" prefix yields attoparsec, a conveniently human-scaled unit of about 3.085 centimeters (about 1-7/32 inches) that has no obvious practical use but does have a proper SI symbol, apc. Interestingly, 1 attoparsec/microfortnight is nearly 1 inch/second (the actual figure is about 1.0043 inches per second, or approximately 2.55 cm/s).

Siriometer
The siriometer is a rarely used astronomical measure equal to one million astronomical units, i.e., one million times the average distance between the Sun and Earth. This distance is equal to about 15.8 light-years, about twice the distance from Earth to the star Sirius.

Light-nanosecond
The light-nanosecond was popularized as a unit of distance by Grace Hopper as the distance which a photon could travel in one billionth of a second (roughly 30 cm or one foot): "The speed of light is one foot per nanosecond."