What are Northern Lights?
Should you be outdoors one evening during winter, take a minute and glance up at the skies. If you're lucky, you might catch a glimpse of some flickering curtains of lights, apparently dancing across the dark sky. You are watching the Northern Lights, a celestial phenomenon that has amazed people for centuries. ”No pencil can draw it, no colors can paint it and no words can describe it in all its magnificence.” (J. von Payer).
The Northern Lights, alias Aurora Boreali,s are natural displays of light in the sky, particularly observed in a Artic circle that surrounds the North Pole (near the South Pole they are called Southern Lights or Aurora Australis). The Aurora Borealis is named after the Roman goddess of dawn, Aurora, and Boreas, the ancient Greek personification of the north wind.
The solar wind is the ultimate source of the Northern Lights. During large explosions and flares, huge quantities of solar particles are thrown out of the sun and into deep space. These plasma clouds travel through space with speeds varying from 300 to 1000 kilometers per second. But even with such speeds (over a million kilometer per hour), it takes these plasma clouds two to three days or more to reach our planet. Earth’s magnetic field typically deflects the charged particles streaming out from the sun, but some amount escapes into our atmosphere around the poles. That is where the Northern Lights (or the Southern lights) can be created.
Click here to see a five minute video by Peter Byhring that offers an explanation of what causes the beautiful imagery of the Aurora Borealis.
A sunspot is an area on the Sun’s surface that is marked by intense magnetic activity, which inhibits convection, forming areas of reduced surface temperature. They can be visible from Earth without the aid of a telescope, and appear as dark spots. Solar winds often originate around the sunspots.
A gas of electrons and ions — at supersonic speed — is continuously emitted from the sun. This stream of gas is called the solar wind. The solar wind is filled with gusts and gales, and when a strong eruption from the sun hits earth, the stable situation - which may have existed for several days - is strongly disturbed. The most spectacular result of this interaction is an intense Aurora significantly closer to the equator than during normal conditions.
The Auroral Oval
The Auroral zones represent the places on earth where Auroras occur most often and with greatest intensity. The Auroral oval is nearly twice as wide and twice as far from the magnetic pole at midnight as at midday. On the night side the oval is roughly 10 degrees (about 1100 kilometers) closer to the equator than at the day side. The Auroral oval can be regarded as fixed in space with reference to the sun. As the earth revolves underneath, the daily variations in the Aurora's position occur.
The different colors depend on temperature and density of the local atmosphere. They correspond to different quantum transitions in excited atoms of oxygen and nitrogen. As the charged particles (electrons and protons) of the solar wind escape through the magnetic field, they run into gas in Earth’s upper atmosphere (above 80 km). Ionized nitrogen atoms can regain an electron and oxygen and nitrogen atoms can return from an excited state to ground state. Exitation energy is lost by the emission of a photon of light or by collision with another atom or molicule. The colors can range between green, red and multiple shades of purple. Altitude also affects Auroral color. Green or yellow is the most frequently observed color. The strong, green light originates at altitudes of 100 to 180 km. Red Northern Lights occur at even higher altitudes, while blue and violet occur mostly below 120 km. When the sun is “stormy”, red colors occur at altitudes of 90 to 100 km. Entirely red Northern Lights may sometimes be seen, particularly at low latitudes. In earlier times, people often mistook this red light for fire on the horizon. They are something truly marvelous to experience.
Compared to the light from the sun and the moon, the brightness of the Aurora is rather weak.
With new optical instruments, we can now study weak Auroras with intensities well below the threshold of our eyes.
Weak Northern Lights have a brightness comparable to that of the Milky Way, our galaxy, which can be seen as a diffuse band of light across the sky on clear winter nights.
Medium-strength Northern Lights are brighter than most stars. Thus, during a medium-strength Aurora Borealis we cannot see stars that lie behind the Aurora in the line of sight.
Strong Northern Lights are comparable to light from the moon. The Northern Lights are then
much stronger than starlight and 100 to 1000 times stronger than the weakest observable light.
How to Observe the Aurora Borealis in Iceland
Chasing the Aurora is difficult, since the phenomenon seems to have a mind of its own, hiding from observers who wait for a week or two, only to reveal itself in a spectacular display the day after they leave. We get a lot of questions regarding the best time to visit Iceland to see the Aurora. There is no simple answer, because we simply do not know for sure. No one does, not until a few hours before the actual display. But there are some things you can do to improve your chances of observing a wonderful Auroral display. A little bit like salmon fishing, sometimes you must wait for the perfect conditions to “catch the big one” and get them at their finest. But, if you get lucky, you will see why it is well worth the wait.
What complicates things for us observers is two things. One: the oval isn't fixed in one place, because it rotates with the sun, and, two: it may grow and shrink in size considerably in only a matter of hours. On (very) rare occasions the oval can cover the entire hemisphere down to Mexico.
11-Year Solar Cycle - “The Age of the Aurora”
The sun has a heartbeat. This is known as the solar cycle and is measured by the number of sunspots visible on the sun. Solar activity goes through regular cycles of increasing and decreasing magnetic activity periods. When solar activity is at it’s peak we refer to it as solar maximum. The least active period we call a solar minimum. Each cycle is approximately 11 years. The probability of seeing Northern Lights is higher during the years close to the solar maximum than during a solar minimum. Nevertheless we can have periods of great Northern Lights during the dark hours of winter, at any stage of the solar cycle.
Aurora Borealis season in Iceland runs from August through the very first days of May. These are the nights with darkness. From the 20th of May until the 20th of July, the sun never goes lower than 6° below the horizon — making the skies basically bright all night and eliminating any Auroral viewing. During these summer months it is just too bright to see them at higher latitudes. Auroras can still be spotted south of about 50° latitude during the summer. Once every hundred years during solar storms the Aurora Borealis can reach as far south as Cuba.
Statistically, the equinox months of September and March are best for Aurora activity. The winter months of October-thru-February are of course also good (there is definitely no shortage of darkness!). A mythbuster is that contrary to popular belief, it does not have to be cold to see the Aurora Borealis, just dark and clear... and clear skies usually mean it’s cold, hence the association between Auroras and chilly nights.
What Time of Night?
The peak hours are between 11pm and 2am, however, anytime it’s dark there is hope. We have seen the Northern Lights at Hotel Rangá as early as 7pm and as late as 9am.
Current Viewing Conditions
To see the current status of Northern Lights – go to the following web link and view the image of the Northern hemisphere (the site is updated every 10 minutes) –
Stay tuned for solar news on http://spaceweather.com/
Follow the solar cycle on http://www.swpc.noaa.gov/SolarCycle/index.html
Another good website we like to visit is the http://solarham.com/