Category: Seein’ the light
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The weather on HD 189733b
Our old friend HD 189733b is in the news again this week. As a Jupiter-sized gaseous planet orbiting a yellow dwarf in the constellation of Vulpecula, HD 189733b has become one of the best studied exoplanets. The reason is that it’s relatively big and close to its sun, which shines through the atmosphere as the…
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Dark energy and the bitterest pill
It’s hard to get your head around dark energy, this universe-accelerating stuff that is supposed to fill the cosmos. Dark energy was invented to explain measurements that seem to show that the most distant supernovas all appear to be accelerating away from us. The thinking is that something must be pushing them away and…
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Simple mod turns diode into photon counter
Counting photons is a tricky business. They’re slippery beasts that arrive silently, often and in packs, in ways that are almost impossible to count. One of the most widely used of devices that can spot the arrival of a single photon is the avalanche photodiode. These cheap and easy to use devices rely on the…
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Why black holes could be antimatter factories
Here’s an interesting chain of thought… Imagine a black hole sucking in protons and electrons. With their higher mass, protons are likely to be preferentially sucked, giving the black hole a positive charge. (That’s not so unusual in space: a similar mechanism can give planets a charge because electrons escape their gravity more easily.) But…
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The embarrassing lightness of photons
Here’s a conundrum for you. What is the momentum of light in a transparent dielectric medium? If the answer doesn’t trip off your tongue, that might be because nobody else knows either. Amazingly, there are two lines of thought: In 1908, the German mathematician Hermann Minkowski guessed that the momentum was equal to nE/c (where…
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Supernova echoes give first glimpse of ancient explosions
Back in 2005, Armin Rest from Harvard and a few mates, spotted the echo of a supernova in the Large Magellanic Cloud. The explosion had kicked off some 900 years ago but what Rest and co were seeing was its reflection from cold dark dust in the cloud. Since then, the team has even measured…
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How to turn a narrow slit into a large window
How do you turn a narrow slit into a large window? Fill it with a metamaterial that captures and transmits as much light as the bigger window. At least, that’s what Xiaohe Zhang and colleagues at Shanghai Jiao Tong University in China tell us. Metamaterials are substances constructed in a way that gives them exotic…
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The mystery of the Plutonic color scheme
Pluto’s three satellites, Hydra, Nix and Charon, are all a similar shade of grey. In fact, Nix and Hydra have exactly the same colour to within our ability to measure it. Pluto, on the other hand, is a beautiful shade of red. How come? The current thinking is that Charon, Hydra and Nix are a…
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The trouble with optical invisibility cloaks
You could be forgiven for thinking that invisibility cloaks are a few R&D dollars away from hitting the high streets. Not so. While it’s true that a number of high profile cloaks have been built, the best of these work only in the radio and microwave regions of the spectrum and then only in at…
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A new class of photon gun
Photons are easy to produce, at least en masse. But making them one at a time in a controlled fashion is much harder. Until recently the only trick physicists had for this was to reduce the brightness of a beam until it contained only one photon at a time, on average. Of course, the “on…