Special is to ordnary as approximate is to

'Special' is an antonym (an opposite) of 'ordinary'. So, for 'approximate' (approximation is something you explain, calculate or guess with a great deal of certainty), the opposite could be 'exact'.

word choice -uses unfamiliar words such as husbandman instead farmer

tone - has the tone of a biography and is more of a narrative than an informational text

sentence structure - long sentences with multiple ideas that reflect the fashion of speaking in Victorian England

writer’s attitude toward the subject - writer shows great knowledge about the development of astronomy and great admiration for the astronomers mentioned in the work

how the writing reflects the writer's period versus how it might come across to modern readers -

use of formal language reflecting the more formal customs of the time; words such as protracted, illumined, verisimilitude, sagacity not likely to be used in a modern equivalent like Carl Sagan’s Cosmos

text difficult to read for many modern readers because of long-winded sentences and unfamiliar words