Poor health has forced Professor Stephen Hawking to miss a second party celebrating his 70th birthday.
The renowned cosmologist was due to attend a VIP reception on Thursday at the Science Museum in London in honour of his birthday and work, with a new exhibition, Stephen Hawking: A 70th Birthday Celebration, opening to the public the following day.
Prof Hawking, who was diagnosed with motor neurone disease at the age of 21, turned 70 on 8 January. He was unable to attend a birthday symposium in Cambridge on that day because of health problems.
The professor's daughter, Lucy, represented her father at the event at the Science Museum.
She said: "It's really sad that he can't be here this evening. He would have loved to have been here with you all."
Lucy Hawking, an author and journalist, accepted a special gift on behalf of her father from the Science Museum's inventor in residence, Mark Champkins.
Entitled "black hole light", it was an illuminated model depicting spirals of light falling into a black hole.
Guests then raised their glasses to Prof Hawking in a "happy birthday" toast.
The new museum display includes a wide range of objects, papers and photos sourced from Prof Hawking's own collection and previously unavailable to the public.
Among them is the blue suit he wore for a zero-gravity flight in 2007, a rarely seen 1978 portrait by David Hockney, and Prof Hawking's annotated script for a 1999 guest appearance as a cartoon character on The Simpsons.
Also shown are a drawing of the mechanism of Hawking radiation, which Prof Hawking theorised should be emitted by black holes.
Prof Hawking recorded a personal message to be featured in the exhibition in which he credits the museum for "introducing young people to the wonder and excitement of scientific discovery".
Alison Boyle, curator of astronomy at the Science Museum, said: "We have been very privileged to explore Prof Hawking's archives, discovering early drafts of his hugely influential scientific papers alongside a rich array of popular material.
"We hope that the selection we have chosen to display will offer a unique insight into the career of the world's best-known scientist."