Turning light again as it was losing mass, a scientific phenomenon (5)
I believe the answer is:
euler
This clue could be a double definition.
'turning light again as it was losing mass' is the first definition.
I can't judge whether this defines the answer.
'a scientific phenomenon' is the second definition.
The definition suggests a singular noun which matches the answer.
Can you help me to learn more?
(Other definitions for euler that I've seen before include "Leonhard --, C18 Swiss mathematician" , "Swiss mathematician; sounds like lubricator" , "Noted blind Swiss mathematician" , "Swiss scientist" , "18th-century Swiss mathematician and physicist" .)