The Astronomical Unit, or AU, is well-known as the distance between the earth and the sun. But when astronomers turned that loose idea into an actual and complex calculation it created several problems. The complex formula ran into trouble with general relativity, the fact that the sun is losing mass and even that the formula itself was incredibly hard to understand. Now astronomers have given the AU a fixed definition: exactly 149,597,870,700 metres. The metre is defined as the distance travelled by light in a vacuum in 1/299,792,458 of a second. Now let's just hope everyone agrees on the length of a second and the nature of a vacuum.

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NOBODY HOME: Engineers from the US National Institute of Standards and Technology built a fairly ordinary two-storey family dwelling on campus. Where it's not ordinary though is that it produces as much energy as it consumes over the course of a year. The net zero energy house incorporates energy-efficient construction and appliances and solar panels. The house is sealed — no-one actually lives there — but a computer simulation runs it as though a family of four were leading normal lives. It's great to test one building, but perhaps the next step is to test it in widely differing environments. US National Institute of Standards and Technology explains. Check out the video.


OUR ROBOT COLLEAGUES: Baxter, from Rethink Robotics in the US, is heading for the assembly line, to work next to its human colleagues. The robot can apply common sense, adapt to its environment and quickly be trained by workers without robotic expertise. To teach Baxter a human guides its arms to simulate the desired task, then presses a button to save the pattern. And its human co-workers whose jobs may be threatened absolutely won't make mistakes in its programming, I'm sure. BBC has further info. Video here.

BEAT THE CLOUD: Backyard astronomers know the problems with inclement weather, light pollution and even just getting an unobstructed view of the sky. Many give up on seeing interesting astronomical events. The MYSky iPad app will allow anyone to take control of one of Slooh's robotic telescopes and capture an image for as little as 99 cents a time. Slooh's telescopes are in Chile and the Canary Islands. The images are delivered as processed png format files within minutes of the request. Their telescope's probably bigger than yours anyway. Slooh details. Here's the video.

TAXI CAN: One taxi driver from Gaza City was so sick of queuing for scarce petrol he decided an electric car would be a better choice of vehicle. But rather than buying one he made his own, the first hand-built electric car in Gaza, from recycled parts at a total cost of less than $1000. The car carries two passengers and needs five hours of charging to run for four hours at up to 19 Kph. The frame's made of wood, the wheels came from wheelbarrows and the steering wheel's recycled from gym equipment. He'd like to upgrade the car to use solar energy, but can't afford to. Necessity is the mother of invention indeed. PhysOrg elaborates. Click here to watch the video.

Miraz Jordan,