Bhangmeter

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A bhangmeter is a radiometer, a device that measures the power of electromagnetic radiation. Most people are already familiar with one type of radiometer, the Crooke’s radiometer, which detects infrared radiation.

crookes-radiometer

A Crooke’s radiometer. The higher the flux of infrared radiation the faster it spins.

Bhangmeters are placed on reconnaissance satellites* in order to detect nuclear weapon detonations and to measure their yield. Bhangmeters are designed to look for the characteristic “double flash” created when nuclear weapons detonate: the first initial bright flash being caused by the actual detonation of the weapon and the second being caused when the ionised gas shock wave cools enough to allow light from the fireball to escape.

The name “bhangmeter” was created by Frederick Reines (who later won the Nobel Prize for Physics for his work on detecting neutrinos), who suggested that one would have to be on bhang (an Indian drink made from marijuana) to believe that the detector would work.

* The US Department of Defense’s GPS satellites also carry bhangmeters.

Halley VI Research Station

brunt-ice-shelfThe Brunt Ice Shelf, with the Brunt Ice Falls behind it.

One of the problems with building a research station located* on the Brunt Ice Shelf in Antarctica is that the Brunt Ice Shelf is floating on the Weddell Sea. Not only do you have to keep jacking-up the base of the station to prevent it from being buried by accumulating snow, but you also run the risk of the entire ice shelf calving away as an iceberg.

The UK’s Halley VI Research Station, which was officially opened on 5th February, has been designed to combat both of these issues. The base sits on legs that can be hydraulically raised to prevent it from being submerged by snow, and at the end of each leg are skis that allow the entire base to be moved to a new location if and when it becomes necessary.

halley-wide

halley-leg

Close-up view of Halley VI’s legs.

halley-section

The station is designed to be modular, making construction and maintenance easier. The blue modules are science modules, and the central red module is the main space for eating, drinking and recreation.

halley-interior

Halley’s primary purpose is atmospheric research. It was at Halley in 1985 that the hole in the ozone layer was discovered.

* The Brunt Ice Shelf is in the north-west quadrant of Antarctica, in an area claimed by the UK but also by Argentina and Chile.

Standby power

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We are constantly being bombarded with messages to turn devices off at the mains, rather than leaving them on standby. But is it worth it? How much energy does this actually save?

standby-light

According to the Lawrence Berkeley National Laboratory a television left on standby uses about one-and-a-half watts. For comparison purposes, a power shower uses between 7500 and 10800 watts. That means that for one fewer ten-minute (9 kW) shower you can leave your TV on standby for another forty-one days and still have used less electricity than you would have.

A study published in 2010 in the Proceedings of the National Academy of Science showed that people were far more likely to select curtailment activities (turning things off) rather than efficiency savings (like cutting a minute off your shower), despite efficiency savings being more likely to reduce energy consumption. Turning devices off at the mains, rather than making choices that would save far more energy, is another example of this.

 

Rifling

The first firearms (e.g. muzzleloaders and muskets) were smoothbored, with barrels that were essentially smooth metal tubes. Towards the end of the fifteenth century rifling was invented, creating spiralled grooves in the barrels that caused the projectile being fired to spin along its axis.

105mm-rifling

A cutaway cross-section through a 105-millimetre tank gun, showing the barrel’s rifling.

A projectile that spins along its axis is gyroscopically stabilised and therefore more aerodynamic and accurate; for example, the stabilising effect of the spin prevents the projectile from “tumbling” in flight. Short, large-diameter projectiles (e.g. lead shot) require only low twist rates, whereas longer and thinner projectiles (e.g. rifle rounds) require faster twist rates, one turn per twenty centimetres or more.

rifling

In some cases the twist rate will increase down the length of the barrel, this is known as gain twist and helps reduce wear and tear on the barrel.

Dawn, dusk, sunrise, sunset and twilight

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Dawn occurs before sunrise, before the top of the Sun reaches the horizon. Astronomical Dawn is the point at which it becomes possible to detect light in the sky, when the sun is 18° below the horizon. Nautical Dawn occurs at 12° below the horizon, when it becomes possible to see the horizon properly and distinguish some objects. Civil Dawn occurs when the sun is 6° below the horizon and there is enough light for activities to take place without artificial lighting.

Dusk occurs after sunset, once the top of the Sun has passed the horizon. As with dawn there is astronomical dusk, nautical dusk and civil dusk, occurring at 18°, 12° and 6° below the horizon respectively.

Twilight is the name given to the period between dawn and sunrise, or between sunset and dusk, when light is still visible in the sky due to sunlight scattering off the atmosphere. It can also be separated in astronomical, nautical and civil sections by how far below the horizon the Sun is.

dawn-dusk

Sunrise and sunset are the points at which the top edge of the Sun reaches the horizon; the only difference between them is the direction in which the Sun is moving at the time. It actually occurs when the top of the Sun is 0.57° below the horizon due to refraction of the Sun’s light by the atmosphere.