"Ask the Expert" articles provide information and insights from MSU scientists, researchers and scholars about national and global issues, complex research and general-interest subjects based on their areas of academic expertise and study. They may feature historical information, background, research findings, or offer tips.
It’s not often to see a green or purple sky, so what actually are the Northern Lights, why are they so special and what’s the science behind them?
What exactly are the Northern Lights, and what causes them?
Northern lights, also known as aurora borealis, are an interaction between Earth's magnetic field and charged particles emitted by the sun. The sun has its own solar wind that sends out charged particles. These particles then spiral around Earth's magnetic fields. When they hit atoms in our atmosphere, electrons in those atoms are excited to a higher energy level. The electrons then settle back down to their normal energy level and, in the process, release light. We see that light as aurora.
Do they ever change colors or patterns?
They can be different colors, depending on what atoms are being excited. Yellow and green light will be from the electrons in oxygen atoms being excited and purple, blues and reds are from nitrogen.
How often are Northern Lights visible – and where are they most easily seen?
They can happen any time of year – it just depends on the sun's solar wind and what it is doing. That said, when the sun has solar flares or solar storms a huge number of charged particles are sent into space. If these hit Earth, we can get a particularly good show.
They are most easily seen near the poles. Just like there are Northern Lights, there are also Southern Lights (or aurora australis), so very northern or very southern latitudes are the best places to see them. Think places like Alaska, Northern Canada, Greenland, Iceland and the Nordic countries. This is where the magnetic field lines are most concentrated on Earth, so normal amounts of wind will allow you to see them at those latitudes. The stronger the storm the farther south you can see them. There was one solar storm so strong in 1859, known as the Carrington Event, people in the Southern United States saw aurora!
What’s making them visible in Michigan this week? Can we see them without a telescope?
The sun is always sending outs winds, but solar storms and solar flares are less common. They occur when the sun has sunspots. These dark spots on the sun are areas where the sun's temperature is a little less hot than the surrounding area are caused by the sun's magnetic field. These magnetic fields can get tangled and snap, sending out solar flares. The sun has been boring the past few years with few spots. But recently spots have been spotted! And one of these spots resulted in a particularly large flare, meaning some nice aurora!
Aurora are a naked eye phenomenon, so no telescope needed!
What don’t most people (both in the science world or not) know about Northern Lights?
Other planets have aurora too! We have observed aurora on Venus, Mars, Jupiter, Saturn, Uranus and Neptune. They seem to work similarly to Earth's aurora, with the planets' magnetic fields interacting with solar wind. But Jupiter's aurora seems a lot more complex and could be caused by other factors, like its very volcanic moon Io (pronounced "EE-oh").