Spotted this:
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BBC Radio 4, Tuesday 19 August, 11:00am to 11:30am
'Aubrey Manning joins archaeologists investigating strange cairns with three arms of stone on the moors of Northumberland. Were they linked to ancient farming methods or do the arms pick out astronomical alignments from the Bronze Age?'
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Sadly I won't be able to listen live, but I think you can 'listen again' from the BBC website for up to a week after the broadcast.

Enjoy!