Is it correct to use the countable noun "sun" in the uncountable meaning to express its function as the source of light and warmth to the earth?
They went trying to soak in some sun.
The alternation of sun and snow continued for the rest of our holiday.
… a glimmer of sun on a frost-bound field…
Is it correct to precede the nouns "sun" and "moon" with the indefinite article in order to desribe their looks at this particular moment?
...a strange-looking blue sun...
We all got scared and knew something would go wrong because for a few minutes we saw glimpses of a bloody red moon.
Please comment on this.
"sun" is short for sunlight:
 soak in some sun(light)
 sun(light) and snow
 a glimmer of sun(light) on a frost-bound field
"sun" and "moon" are in the solar system.
 a strange-looking blue sun ~ a blue sun ~ a sun
 a bloody red moon ~ a red moon ~ a moon
Student or Learner
Sorry for butting in, but I have a countable/uncountable question too: when the word response used as reply/answer, is it countable or uncountable?
EX: There were several replies/answers/responses. (plural)
EX: There was a reply/an answer/a response. (singular)