The most common and most likely answer to this crossword clue is the 6 letter word QUASAR
I've seen this crossword clue in The Guardian
Q
U
A
S
A
R
Buddy explains!
The straight part
We know that "that’s gigantic and awfully distant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case that’s gigantic and awfully distant = quasar.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does QUASAR mean?
QUASAR noun- An extragalactic object, starlike in appearance, that is among the most luminous and (putatively) the most distant objects in the universe.