It occurred to me I posted a video featuring auroras without writing about the science associated to them. Here’s a recycled post from the old Dinner Party Science that provides a short explanation about northern lights and the events behind them, which start some 150 million kilometres away from the Earth, in the Sun.
An earlier version of this post was published at Dinner Party Science on Blogspot on 15 September 2010.
You’ve probably heard of auroras or northern lights, or are even lucky enough to have seen one of these events. They are proof positive of the existence of some sort of weather in space. The term space weather refers to changes in the near-Earth space environment which are driven by the Sun. On a calm day, only a breeze of radiation and energetic particles — the solar wind — flows from our star. Sometimes particles from this wind stream into the Earth and interact with the gas in the planet’s atmosphere. These interactions release particles of light causing auroras.
But not all days are calm and the northern lights are by far the least threatening effect of space weather. Trouble starts when our very active star decides to rebel and begins to emit large amounts of energy, not to mention electrically charged material into space. That’s when you get the space weather equivalent of hurricanes.
The Sun is made out of a material called plasma. Plasma is the fourth state of matter: a solid can be heated up to become liquid, a steaming liquid becomes a gas, and a hot enough gas transforms into plasma. This happens because the atoms that form the gas are separated into their constituents, electrons and nuclei. It is of this, electrically charged, material that the Sun is composed of.
In the solar interior, plasma is in constant motion. If you recall your physics lessons from high school you may remember that moving electric charges generate magnetic fields. In fact, the Sun is a ball of plasma with tangled magnetic field lines breaching through its surface. One of the interesting things about magnetic fields is that they can store a lot of energy. Every now and then the tangled lines of the magnetic field break and the energy they store bursts into space. These explosions are what solar physicists call “solar flares” — the storms of space weather.
It gets worse. Sometimes the magnetic field lines break so violently that they drag along some of the solar plasma. In this case, a coronal mass ejection (CME), the equivalent of a hurricane, occurs. CMEs cause the most damage when they are directed towards the Earth. When they hit, the electrically charged material and energetic particles of the solar wind and solar plasma surge into the Earth’s atmosphere and surface. While this can cause brighter auroras, the more beautiful northern lights come at a price. The radiation associated with CMEs can be harmful to astronauts, and even to airline crews and passengers. CMEs can also affect satellites, interfere with communications and cause power blackouts.
Fortunately, these situations are rare — most days are calm when it comes to space weather. Terrestrial storms and hurricanes are much more likely to cause damage than solar flares and CMEs.
But the weather can always affect you. Even if it’s in space.