I'd like to know the precise meaning of "raw" in the following excerpt from the Chapter 8 of The Great Gatsby:
"He must have looked up at an unfamiliar sky through frightening leaves and shivered as he found what a grotesque thing a rose is and how raw the sunlight was upon the scarcely created grass."
It will help to understand the particular meaning of raw as used to describe sunlight, a part of nature, by putting the passage in context with the events it relates to in the story.
Daisy has run over Myrtle. Wilson has gone out '"acting sort of crazy".' He has discovered Gatsby's name in association with the yellow car. He has turned up in West Egg asking for directions to Gatsby's house.
Gatsby has been waiting for a phone call from Daisy, who has, by this time, left East Egg with her husband Tom, thereby implicitly making her choice between Tom and Gatsby. Gatsby goes to float in the pool on this blisteringly hot afternoon while he continues to wait for her phone call, which, according to Nick's speculations, he no longer hopes to receive.
Gatsby himself didn't believe [the call] would come and perhaps he no longer cared.
In the emotionally and physically exhausted state Gatsby is in, coupled with his probable disliiusionment that Nick hints at--"he must have felt that he had lost the old warm world"--he floats in the heat of the day in his pool on a "pneumatic mattress" his party guests had used all summer long.
Nick speculates about what Gatsby must have done and felt in his newly disillusioned state. Nick speculates that Gatsby would see the world in all its stark realism, unfiltered now by the rose color (or green light-lit shade) of his "single dream" of Daisy's love being restored to him. He would see a rose in all the harshness of unfiltered glaring sunlight, the same glaring sunlight that scorched them all as they went to and came from New York and that bathed Myrtle as she fatefully ran into the road. Fitzgerald here describes the sunlight illuminating Gatsby's disillusionment and disillusioned perceptions as "raw": "how raw the sunlight was" [this description of sunlight is reminiscent of Camus' The Stranger].
One of the several definitions of "raw" applies to nature. In a nature related usage of the word "raw," nature and elements of nature are said to be harsh, brutal, painfully exposing. For an understanding of this, think of a harsh winter scene during and after a blizzard; think of the Sahara or Mojave desert sun, brutal, beating down upon a stranded person; think of the detail exposed in a rose's petals when held up to and exposed to the painful mid-day sun of July or August.
Thus what Fitzergerald means by "raw" in the sentence Nick speaks is that the sunlight was brutal, harsh, painlfully exposing as it beat upon newly emerging blades of grass, blades that could easily be scorched and burned by such merciless sunlight. This is a metaphor for how Gatsby will be affected by his new perception of the merciless light of the reality of life that beats down upon him, Daisy, Myrtle and Wilson.
He must have looked up at an unfamiliar sky through frightening leaves and shivered as he found what a grotesque thing a rose is and how raw the sunlight was upon the scarcely created grass. A new world, material without being real, where poor ghosts, breathing dreams like air, drifted fortuitously about . . . like that ashen, fantastic figure gliding toward him through the amorphous trees.