Cryptic crossword clue
Fireworks in the sky make Penny nervous, excited — even gassy 10

The most common and most likely answer to this crossword clue is the 10 letter word SUPERNOVAS

I've seen this crossword clue in The Guardian
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Buddy explains!

The straight part
We know that "Fireworks in the sky" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fireworks in the sky = supernovas.
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 SUPERNOVAS mean?

SUPERNOVAS noun
  1. The explosion of a star, which increases its brightness to typically a billion times that of our sun, though attenuated by the great distance from our sun. Some leave only debris (Type I); others fade to invisibility as neutron stars (Type II).

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