My wife and I will be traveling to Iceland later this week, hoping to see the Northern Lights. There are many astronomical phenomena that don’t require travel, but for the few that do, there are plenty of travel agencies waiting to accommodate you. When we traveled to the South Pacific in 2009 to see a total solar eclipse, it was with a group organized by Sky and Telescope magazine. This trip is also under the auspices of Sky and Telescope, which insures that I will be around people whose enthusiasms match mine. In other words, astronomy nerds.
Why Iceland? And why now? I posted earlier about aurorae, and here I want to give a basic primer in the form of a question-and-answer session.
What are aurorae?
These are glowing lights in the sky caused by charged particles colliding with atmospheric atoms. These particles come mostly from the sun and are trapped in the Earth’s magnetic field. They impart energy to the atoms; when the atoms return to a lower-energy state, they emit light. The aurorae can take the form of a generalized sky glow or of sharply defined features that look like waving curtains. The most we ever see at the latitude of Lynchburg (37.5° N) is this generalized glow when the sun is especially active and the region in which aurorae are most active shifts farther south. When I have seen it, it looks like a late sunset or a fire on the northern horizon.
Aurorae are best seen at high latitudes, either very far south or very far north. For someone living in the United States, Iceland is a lot more accessible than the southern equivalent, which is the Antarctic Peninsula. Aurorae mostly occur in a band called the auroral zone, a ring centered on the Earth’s magnetic (not geographic) pole. Here is a “weather forecast” of the ring from last year, courtesy of NOAA (National Oceanic and Atmospheric Administration—your tax dollars at work again).
The ring’s location is not absolutely fixed, but varies between 10° and 20° from the magnetic pole. You can see that Iceland (just to the right of Greenland in this view) is well within this range. For the current forecast, click here. The northern magnetic pole does not stay in a fixed location, and is currently in the Arctic Ocean as seen in this image generated in Google Earth.
Why do aurorae occur in a ring?
I hope that at some time in your life, perhaps in school, you sprinkled iron filings around a magnet and saw them arrange themselves along the invisible lines of the magnetic field.
The Earth’s magnetic field also exhibits these lines of force.
You can picture the Earth as having a big bar magnet whose poles are deep beneath the surface. The lines of magnetic force dive into the surface and converge at a point far underground. The points on the surface, or in the atmosphere above it, describe a ring rather than a point.
Solar activity goes through an 11-year cycle, and aurorae are most active when the sun is most active, sending more charged particles our way. One measure of this solar activity is the number of sunspots.
Having gone through a minimum in 2009, these data (current through 2011) show that we are due for a livelier sun, and indeed those predictions have been borne out.
Why April, 2013?
Auroral activity is greatest near the spring and autumn equinoxes. No one is entirely sure why, but part of the reason is thought to be the interaction of the sun’s magnetic field with that of Earth, opening a path for particles to more easily enter the Earth’s atmosphere.
Why the week of April 7th-14th, 2013?
Does this lunar phase calendar give you a clue?
We hope to capture some good images and videos while we are there. Failing that, we hope to make friends with fellow travelers who do so!