As the title suggests, our topic for today is Earth’s aurorae (pronounced auh-ror-eye). These stunning displays generally occur in two symmetrical oval rings about the planet’s far northern and southern regions–Earth’s magnetic north and south poles. When they happen in the north, aurorae are often referred to as the northern lights or Aurora Borealis. Likewise, southern aurorae are called the southern lights or Aurora Australis.
How are they formed?
Coronal mass ejections, solar flares, and other features of solar weather can violently hurl electrically charged plasma into the void of space at speeds up to 2000 km/sec. Sometimes these ejections travel on a collision course with Earth which, in extreme cases, can wreak havoc on electrical and telecommunications systems. (Interested in learning more? Check out NOAA’s article on the 1859 Carrington Event.)
Fortunately, though, the Earth has a magnetosphere–shaped in part by the interaction of Earth’s magnetic field and solar wind–that protects the matter below from the effects of all but the most severe solar weather. Earth’s magnetosphere–like those of Mercury and the outer giant planets–occurs due to material spinning within its hot molten core. These conditions essentially turn the planet into a large electromagnet. Charged particles become trapped in the magnetic field lines and race along them to the poles (1), where they then interact with gasses in our atmosphere to produce aurorae.
Wait, what about the colors?
When the charged particles from the sun mingle with the gasses in Earth’s atmosphere, their interaction induces excitation. During this process, electrons impart energy to the gaseous atoms. When the electrons of the gaseous atoms return to a lower state, they release energy in the form of a photon–a particle of light. The color of the emitted light depends on the amount of energy released and the type of gas that was exited. In large concentrations–such as during aurora events–these emissions can be seen with the naked eye. The greenish-yellow hue that characterizes typical aurorae results from the oxygen in our atmosphere. Emissions from high-altitude oxygen create vibrant red aurorae. And nitrogen emissions cause blue and purple-hued aurorae.
Closing
If you made it to the end, congratulations! I’m aware of my aversion to short descriptions–it’s a problem that’s exacerbated when I’m excited about a topic. But I hope this post was informational! If you want to learn more or get involved in some citizen science, NASA operates aurorasaurus, where you can help filter and classify real tweets as (non)sightings of aurorae. Zooniverse’s aurora zoo is another cool citizen science opportunity where you can help classify features of auroral images and videos for use in further scientific research. (It’s also a great way to procrastinate while still feeling productive!) Let me know if you’ve ever seen the aurorae in person or if you decide to participate in either aurorasaurus or aurora zoo.
Until next time,
7smessier45
