Astronomy 101: Solar Flares
A recent Hollywood blockbuster has suggested that Solar Flares, also known as Coronal Mass Ejections (CME’s) can destroy Earth. But, how many of us actually know what a CME is, what causes it and what the real dangers are? Thats what I’m here to tell you, in laymans terms.
Lets start here on Earth. As you should know, the earth has a magnetic field. This is why compasess point north, how birds migrate and why we have something called ‘the magnetosphere’. As you can clearly see, our compasses and GPS’s point to one spot, so it’s safe to say that our nice rotating ball of solid rock and molten iron has a stable magnetic field.
Now lets look at our sun. It’s a big ball of burning hydrogen and helium (with a little bit of other stuff) thats burning over 5000C on the surface and 15700000C at the core. It weighs the same as 33000 Earths, but this mass keeps getting less as light and gas are emmitted. And finally, because it is a big ball of plasma and not solid like Earth, it doesn’t rotate properly. In fact it spins faster at its equator than at the poles (the opposite of Earth). This doesn’t sound very stable, and as a result the magnetic field of the sun changes constantly.
Now what happens is that the burning gas follows these field lines, but sometimes this leaves ‘cold spots’ on the surface of the sun where less gas goes. These are called Sun Spots and can usually be seen as black dots on most star photos. But as with all things in nature, the sun wants to be at equilibrium. This means that the magnetic field rushes to close the gap, resulting in fields that are ‘abnormal’. These abnormal fields often extend far beyond the surface of the sun, and they are the root cause of a Solar Flare.
So now we have a stray magnetic field line. What happens now? Well, as on the surface of the sun the burning gas is going to follow this line out into space. Although the field does loop back and return to the Sun, we must remember that the burning gas is taking this corner at thousands of km/h and inevitably a lot of this gas and plasma is shot out into space. This is a Coronal Mass Ejection, and is a big danger to Earth if it hits us.
Luckily for us, we have the magnetosphere here on earth. This is actually the magnetic field the Earth’s iron core makes and it reaches out beyond the ozone layer. This field absorbs most of the radiation from the CME, so we don’t all burn up or die of skin cancer every time this happens. A problem is that this radiation can easliy cripple satellites and spacecraft and can kill astronauts (which is why everthing in space is radiation shielded).
There is also a phenomenon linked to a CME called a ‘Proton Storm’. This is becasue when the gases on the sun become plasma, all the bits pf the atoms break up. One of these bits is called a proton, and this can pass through an substance until it finds something to join up to. Once again, our magnetosphere saves the day, but if an astronaut is caught in this, no amount of shielding will save him from cancer. (A Proton Storm can take as little as 15min to reach earth from the sun, thats almost half the speed of light!)
Finally, back here on planet Earth we have only 1 real threat posed by CME’s. That threat is known as EMP (ElectroMagnetic Pulses). As I said earlier, gas moleules are released during a CME and these are caught in another layer of our atmosphere called the ionosphere. Here a bunch of chemical reactions take place and we can see them as the Northern or Southern lights. What these lights are is actually a massive electic charge being stored ad the outher limits of our atmosphere. Under normal circumstances this is fine, but when a large CME takes place, it can increase this charge to abnormal levels, creating a new magnetic field in the air. This magnetic field can affect powerlines and phonelines through a process called electromagnetic induction and this can raise or lower the voltage of a line for a long period of time. This results in massive power surges and outage, which as we know can pretty much cripple any city on Earth.
So can this end the world? No. The biggest ever recorded flare from our sun was classified X45 and took place on 4 November 2003. This flare was twice as large as any our sun has ever made before, and it is unlikely to ever happen again. I bet you didn’t even notice it though, but us South Africans did experience a power outage in most of the country. To get an idea of the power behind that, the amount of radiation soaked up by our magnetosphere on that day was 5000 times the normal amount. Our sun cannot make a so-called ‘super flare’ until it turns into a Red Giant Star, which only happens in several million years, so relax we’re safe!
Check out the following site for updates on the current solar cycle: http://www.solarcycle24.com/