“Now, anybody seen a full eclipse? Anyone been in the path of totality, when the sun is just wisps and tendrils of light peeking out from behind the moon? You, sir? Pretty impressive, sight, yeah? Yeah, mind-blowing indeed. Changes some people’s lives. They become shadow chasers – people who track down as many eclipses as they can, journeying to every corner of the world just to experience more examples of this uncanny and unique phenomenon.

“So let’s think about eclipses for a moment. Even if we haven’t seen an eclipse personally, we’ve seen the photographs in magazines and the footage on television or YouTube. We’re almost blasé about them; they’re just part of the stuff that happens to our planet, like weather or earthquakes, only not destructive, not life-threatening.

“But think about it. What an incredible coincidence it is that our moon fits exactly over our sun. Talk to astronomers and they’ll tell you that Earth’s moon is relatively much bigger than any other moon round any other planet. Most planets, like Jupiter and Saturn and so on, have moons that are tiny in comparison to themselves. Earth’s moon is enormous, and very close to us. If it was smaller or further away you’d only ever get partial eclipses; bigger or closer and it would hide the sun completely and there’d be no halo of light round the moon at totality. This is an astounding coincidence, an incredible piece of luck. And for all we know, eclipses like this are unique. This could be a phenomenon that happens on Earth and nowhere else. So, hold that thought, okay?

“Now, supposing there are aliens. Not E.T. aliens – not that cute or alone. Not Independence Day aliens – not that crazily aggressive – but, well, regular aliens. Yeah? Regular aliens. It’s perfectly possible, when you think of it. We’re here, after all, and Earth is just one small planet circling one regular-size sun in one galaxy.