We would never have got the theme – Bert only knew the Martian Chronicles.

Well done Eimi and thanks NealH – we needed you to explain 4ac.

And I now see that Shuchi @ 13 beat me to it whilst I was writing this!

I haven’t solved the puzzle, got the theme from looking at the answers: titles of Ray Bradbury‘s works.

It is certainly an odd grid. Apart from the two pairs of lights with less than 50% cross-checking, I regard it as undesirable if there is even one pair of lights whose removal would split the grid into two disjoint parts. Here there are no fewer than six such pairs: 10/30ac, 13/25ac, 14/22ac, 16/20ac, 8/24dn, and 9/19dn.

Maybe my dislike of grids that lack full interlocking comes from my preferred solving method, which is to solve one clue only from scratch, and then work outwards from that answer without having to start again somewhere else. As usual, I have no quarrel with people who work differently and are not bothered by such niceties of grid construction.

There appears to be some sort of theme to do with (American) popular music, but this is not an area about which I have much knowledge.

26dn: Should there not be an indicator for initial letters of Crosby and Nash?

Speaking as someone with a physics degree, I could never remember whether a cathode was positive or negative. I remembered electrons are negative and move out of the negative terminal of a battery, but that was it.

I’d heard of Donna Summer and knew she’d died recently, which gave me the answer to 4ac, but although I’d heard of REM, I’d no idea that they’d recently disbanded and didn’t see how the clue worked.

I noticed the odd grid but couldn’t see anything special about it.

Both Collins and the COED have country as an acceptable definition of ‘shore’ in the singular.

I’m still waiting for someone to work out why the odd grid, some abstruse entries and marvel at the quick turnaround since the event that prompted the grid-fill.