When you think of hard sf you don't usually associate it with Doctor Who, but this piece of fan-fic by an astronomer has the Doctor and Martha witnessing supernova SN 2007gr firsthand. Definitely worth a read.
Doctor Who and the Silver Spiral
'Far across the universe, something big was about to happen. The explosion would outshine an entire galaxy and be visible billions of kilometers away. Its light would travel across the universe for millions of years but, aside from a few astronomers, it would go unnoticed on the Earth.
With a grating, wheezing noise, a small blue box flickered into existence.
"So, where are we?"
"Have a look..." the Doctor replied, tapping a control, "but... don't step outside."
The door of the TARDIS clicked open, and Martha gave him a quizzical look. "Why, what's out there?"
"Take a look" he said, a lopsided grin on his face.
Gingerly, she pulled open the door of the police box and looked out.
"Oh my God," exclaimed Martha. "Is that real?" She was looking out at a vast star-scape, hundreds of stars embedded in swirling clouds of gas, stretching out as far as she could see.
"What? Of course it's real!" he laughed, looking out over her shoulder.
"It's amazing! Where are we?"
"A long time ago, in a galaxy far, far away..." he quoted thoughtfully.
"Sorry. We're in a galaxy the local species call the 'Silver Spiral'. From Earth, it's a tiny, faint speck in the sky, somewhere in the constellation of Perseus. You'd never even notice it without a telescope. These stars are part of a cluster formed just a few million years ago, out in one of the spiral arms."
"It's beautiful. But... why are we here?"
"Why not?" he said. "Have you ever seen a star explode?!"
She stared at him.'