Pupils from two schools in Wales joined a UK-wide viewing of the Deep Impact probe's collision with a comet in an event organised in Powys.
This image was taken 16 seconds after impact
Pupils from Llandrindod Wells and Pontypool watched at Knighton's Spaceguard Centre as Nasa's "impactor" crashed into comet Tempel 1 on Monday.
The event also involved children in Birmingham, Edinburgh and Armagh.
Pictures were beamed from the Faulkes telescope in Hawaii.
Each town and city received images of the encounter in near real time, giving them the earliest data in the country.
Students then analysed the raw images to try to detect any changes to the comet.
Jay Tate of the Spaceguard Centre, which examines the threat to earth from comets, said: "In Knighton, we had 10 pupils from Llandrindod Wells High School and 10 from West Monmouth Comprehensive School in Pontypool.
DEEP IMPACT FACTS
The Nasa probe hit the comet at 25,000mph
It penetrated 15-20m into the surface before exploding
It carved out an 100m diameter crater
The comet lost 100,000 tonnes of material
The comet is estimated to be 4.6bn years old
"The Faulkes telescope had some of the first images and the children enjoyed analysing the pictures.
"They saw the comet brighten significantly as the Nasa craft vaporised on impact."
Mr Tate said the probe would help experts learn about the composition and construction of the 4.6-billion-year-old comet.
"In the future it will be necessary to divert comets away from earth and now Nasa has proved that it can target one," he added.
Children also watched from the Thinktank in Birmingham, the Planetarium in Armagh, Northern Ireland, and the Royal Observatory in Edinburgh.
Twenty children saw the historic event at the Spaceguard Centre
Meanwhile, Professor Chandra Wickramasinghe and Dr Max Wallis, from Cardiff University, are involved in monitoring the comet before, during and after the impact and interpreting the results.
"Not only is Deep Impact a spectacular experiment, it is also a test for our long-standing arguments," said Professor Wickramasinghe before impact.
"It will show, we believe, that a comet is not a rubble pile, nor a conglomerate of ices, but a porous mass of organics and ice under the black asphalt crust."
Comets are thought to have accumulated from a mixture of ice and organic interstellar dust at the time the solar system was formed some 4.6 billion years ago.