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...work, shocked to see the dark February morning lit by something originally thought to be a missile. The rock exploded in the atmosphere, with many meteorite fragments scattered across the region. The largest piece, of about 600kg, was recovered several months later in an ice-covered lake. Although many people were hurt when the object powered its way through the...

...Work is held at a negative potential of 400–800 V with respect to the chamber. Operating temperatures up to 1050°C, but usually below 950°C. Carbon source is hydrocarbon gas (methane or propane), often diluted with nitrogen, hydrogen and argon, which is bled into the vacuum chamber at a few litres per minute. Very little exhaust gas results, hence no risk of...

...working in the same office. The numbers of children each of us has are 0, 2, 4 and 2. The mean number of children per person is the number we’d each have if they were divided out evenly between the four of us. In total there are 8 children, so the mean number is 8 divided by 4 - which is, of course, 2. What happens if a new colleague joins us, and the new colleague has...

...work, and that’s where the second type of gravitational lensing observations came in. The authors repeatedly took images with Hubble for six years, measuring how far the star appeared to move as its light was deflected. Eventually this let them calculate the mass and distance of the object which caused the lensing effect. They found it was about seven times the mass of...