HOW big is Professor Brian Cox’s brain? From the looks of his normal sized head I would plump for average. That is in reality. What about metaphorically?

At this point it would be handy to have a series of rocks for illustrative purposes, as the good professor himself had in his new series, The Planets (BBC2, Tuesday, 9pm). Then again, he had taken the trouble to be in a desert location where there were tons of rocks, ranging in size from pebbles to boulders. Clever, see? Whereas I am typing this in an office conspicuously short of the items. Something about the danger in throwing them at colleagues, or some such ‘elf and safety nonsense.

Prof Cox used his rocks to show us the distance between various planets and the sun, causing me to finally understand the title of the sitcom, Third Rock From the Sun. He explained how the terrestrial planets began life as collections of powdery material that got bigger and bigger, like giant dust bunnies (my phrase, not his).

There were lots more fascinating facts, such as on Mercury, a day is twice as long as a year. At that point I confess to becoming completely lost. The beauty of Brian, however, is that he has so much information and wisdom to impart you can always catch him up later and start again. But by the end I had picked up a few things I did not know before, so well done Prof, and well done Auntie Beeb for public service broadcasting at its finest. At this rate I’ll be an astrologist by Christmas (boom, boom).

Comedy of a similar poor quality was on offer on Coronation Street (Bank Holiday Monday, 9pm) when Lorraine Kelly made a guest appearance. She does quite a few cameos, does Lorraine. Usually, as in Murder in Successville, she is content just to be her cheery, giggly self, but lately she has been showing worrying signs of trying to act. On this occasion, Gail, holidaying in the same forest park as Lorraine, shot the daytime television star in the leg with a bow and arrow. Lorraine attempted “furious”, and threw in a limp for good measure, but she still made the surrounding trees look like the Royal Shakespeare Company. Stop now dear.

The documentary Confessions of a Serial Killer (Channel 4, Monday, 9pm) told the story of Samuel Little. As reporter Ben Zand said, most people will probably never have heard of him, yet he claims to have killed more than 90 women, which would make him America’s most prolific serial killer. The claims were made in police interviews with Little, recordings of which had been obtained by Zand. How had Little been able to get away with his crimes for so long, he wanted to know.

The deeply depressing answer was “because he could”. By his own admission, Little preyed on women, mostly African-American women, who were working as prostitutes, had drug habits, or were otherwise vulnerable. His betting was that no one would miss them, and even if the body was found before he escaped over state lines, the police would not bust a gut looking for the perpetrator.

I am usually war of such true crime documentaries. There is always the risk that they somehow glamourise scumbags who deserve to be forgotten. But then the victims deserve to be remembered. Zand’s heart and head were in the right places, even if he did keep referring to women as “ladies”, and he was essentially covering the same themes as the far superior The Yorkshire Ripper Files, which aired in March.

“I’ll name that tune in one.” Those familiar with that catchphrase would have been right at home with the concept behind The Hit List (BBC1, Saturday, 7.30pm). Presented by real life former pop stars Rochelle and Marvin Humes (nope, me neither), it was described as “the music quiz where all you have to do is name the song and artist”. As opposed to what, transmitting it telepathically? Imparting it through the medium of contemporary dance?

It was easier than Name that Tune because the song clips were longer and the tunes fairly recognisable, as long as you had a spread of ages in the team, as dad and daughter combo Jason and Jasmine did. One of the show’s gimmicks is that the teams come on to a song that is special to them, or sums them up. Fran and Danielle chose Simply the Best. They came second, while Jason and Jasmine walked away with a very nice prize of almost £7000. In the old Tom O’Connor version the winners could take home up to £1200.

Wonder how much Prof Brian Cox knows about pop music. Probably nothing. Probably about as much as I know about Jupiter. Hang on … there’s something here about him playing the keyboards in the band D:ream, of Things Can Only Get Better fame. Nobody likes a show off, mate.

How good is Years and Years (BBC1, Tuesday, 9pm) turning out to be? Emma Thompson’s monstrous politician Vivienne Rook is proving terrifyingly seductive, and the plotlines are heading in intriguing directions. Very clever. Brian Cox clever. So there.