Farther superl. : More remote; more distant than something else.

Farther superl. : Tending to a greater distance; beyond a certain point; additional; further.

Farther adv. : At or to a greater distance; more remotely; beyond; as, let us rest with what we have, without looking farther.

Farther adv. : Moreover; by way of progress in treating a subject; as, farther, let us consider the probable event.

Farther v. t. : To help onward. [R.] See Further.

Example:
How much Farther away could Hipparchos probe our galaxy relative to measurement on the Earth?

Taxonomy
Merriam-Webster Online Dictionary, Dictionary, adverb, webster, interchangeably, Word Games, Webster Online Dictionary with audio pronunciations, Middle English, thesaurus, adjective, glossary, language, ESL, Search, fär, Etymology, ferther, alteration.

Defination from the web:
farther from the Merriam-Webster Online Dictionary with audio pronunciations, thesaurus, Word of the Day, and word games. ... usage Farther and further have been used more or less interchangeably throughout most of their history, but currently they are showing signs of diverging. ...