The Sun (the big floaty fireball, not the awful “newspaper”) has been in the news lately as it’s been predicted that the Sun may interfere with the 2012 Olympics. It’s been suggested that solar flares, ejections of material from the Sun’s surface; and the solar wind, a fast-moving stream of charged particles (normally responsible for the Northern and Southern Lights (Aurora Borealis and Aurora Australis)), could affect the satellites that are responsible for relaying television footage from the Games around the globe.
Over the last few years the Sun has been in an unusually quiet mood, but recently it seems to be “waking up”. Looking at images from the Solar and Heliospheric Observatory (SOHO) Large Angle Spectrometric Coronagraph (LASCO) you can see a clear difference between images taken now and images taken in past months.
SOHO picked up its largest solar flare in two years on January 22nd:
At the time of writing the solar wind is running at somewhere between 300km and 400km per second with between 2 and 4 protons per cubic metre [source]; this is nothing to worry about. The concern is that by the time the Olympics come around we might be experiencing periods of solar weather like in January 2005 during a severe solar storm.
If you’ve ever been involved with weather monitoring you’ll know that a spherical lens can focus sunlight to a point. The Campbell-Stokes sunlight recorder counts the hours of sunlight per day by burning a trail across a calibrated sheet of paper.
When teaching vision I use a large spherical flask full of dyed water and a number of different lenses to simulate the eye, including short- and long-sightedness.
Until very recently this flask was stored on a windowsill in direct sunlight. Can you guess why we moved it?
The corona of the Sun is a layer of plasma that extends millions of kilometres into space above the Sun’s surface.
The problem is that the temperature of the corona is between one and three million kelvin, whilst the temperature of the surface is much, much cooler, only about 6000K.
There doesn’t seem to be any good explanation as to why the region above the surface is hotter than the surface itself. The Second Law of Thermodynamics says that thermal energy cannot flow from the cool surface to the hot corona so a different explanation is needed.
There are two competing theories as to what is responsible: wave heating, and magnetic reconnection. The first, wave heating, says that energy is transferred by waves in the plasma a bit like sound waves; the second, magnetic reconnection says that energy is released as electrical currents induced by the collapse of the Sun’s magnetic field. This is the same phenomena that creates coronal loops like the one shown in the photograph below.
Most scientists think that a combination of the two theories is responsible; it is hoped that NASA’s Solar Probe+ will solve the coronal heating problem for good.