Astronomer broadcast Mars latest info, then spoke (11)

I believe the answer is:

hertzsprung

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'astronomer broadcast mars latest info' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'spoke' is the wordplay.
I cannot really understand how this works, but
'spoke' could be 'rung' (synonyms) and 'rung' is present in the answer.
This may be the basis of the clue (or it may be nonsense).

'then' is the link.

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I've seen this clue in The Times.

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