Swans on Tea

Optics basics: Inverse problems at Skulls in the Stars.
Plenty of other techniques exist for measuring the internal structure of objects, using a variety of different types of waves. Magnetic resonance imaging (MRI) subjects a patient to an intense magnetic field, and makes an image by measuring the radio waves emitted when the field is [...]

Unknotting Knot Theory
One of the reasons knots have given mathematicians fits is that the same knot can appear in very different guises. Tug here, tug there, and soon a knot will become unrecognizable, but remain fundamentally unchanged. To allow a knotted string to wiggle around without danger of untying, mathematicians seal its two ends together, [...]

Space station trash plunging to Earth

NASA and the U.S. Space Surveillance Network are tracking the object — a 1,400-pound (635-kilogram) tank of toxic ammonia coolant thrown from the international space station — to make sure it does not endanger people on Earth. Exactly where the tank will inevitably fall is currently unknown, though it is [...]