If you don't see an index on the left, click here.

Aurora Sentry FAQ

This FAQ is a work in progress... please check back for updates

General Questions
   What is the aurora?
   What does aurora look like?
   What causes the aurora?
   Are there any other effects of aurora?
   When and where could I see the aurora?
   What is radio aurora?
   Why is there so much interest in radio aurora?

Aurora Sentry
   What happened to the Kiruna Magnetogram? It was on the old Aurora Monitor site.
   Why isn't data from [some site] included in the Aurora Sentry?
   The data on this site looks impressive, but what does it all mean?
   There are many aurora alerting services. What purpose does Aurora Sentry serve?

What is the aurora?
The aurora borealis or northern lights (aurora australis or southern lights in the southern hemisphere) is one of nature's most spactacular and beautiful sights. The aurora forms huge oval halos of radiation around the earth's magnetic poles.

What does aurora look like?
It can range from a faint glow just above the northern horizon to overhead arcs, rays, streamers and other forms dancing in the sky. Colors vary from white to green to red and occasionally others. There are many excellent collections of aurora photographs on the web. Check the galleries section to explore some online collections of aurora photographs.

What causes the aurora?
The sun is a very hot and stormy place, with its own type of weather. It is so hot and stormy that it cannot keep its atmosphere completely contained by its gravity. Hot, ionized gas (plasma) escaping the sun carries electrically charged particles and magnetic fields out through the solar system. We call this ever present stream of charged particles the solar wind. Earth is constantly bathed in the solar wind, and when certain types of violent 'weather' occur on the sun the wind blows harder. The earth is surrounded by a large magnetic field called the magnetosphere which protects it from the full blast of the solar wind.

The earth's magnetic field captures some of the particles streaming by in the solar wind. Once captured, these particles spiral down along magnetic field lines toward the polar regions of earth, gaining speed (and energy) in the process. When these particles collide with certain gases in the earth's atmosphere, some of the energy is converted to light. The color of the light produced is dependent on the type of molecule involved. It takes billions of such collisions to produce the visible light show we know as the aurora.

Are there any other effects of aurora?
Yes. Aurora can cause problems with power distribution systems, pipelines, navigation systems, communications, and more. See Practical Consequences of Space Weather for more information.

When and where could I see the aurora?
That has to be the most commonly asked question of all. No wonder! Aurora truly is a spectacular sight, and one that relatively few people ever get to see.

The aurora is more or less always visible if one gets close enough to the polar regions. Visiting the arctic or antarctic isn't always practical though. During times of stormy space weather, the auroral ovals expand, reaching further from the polar regions. During the most intense storms, for example, aurora has been seen from all parts of the United States and even into the northwestern Caribbean! Unfortunately, it isn't possible to know very far in advance when such a storm might occur.

There is no simple answer to this question, really. One of the best I have seen is in the Aurora FAQ of the Poker Flat Research Range (Poker Flat, Alaska). Also check out Tips on Viewing the Aurora at the Space Environment Center.

What is radio aurora?
If there are enough charged particles (electrons) spiralling down the earth's magnetic field lines, the ionization may be sufficient to reflect VHF and lower UHF radio waves (generally in the 25 to 500 MHz freqency range). This usually occurs in conjunction with visual aurora, but the mechanism is a bit different and it is possible to have one (visual or radio) without the other. This is how auroral radars work - they send a VHF radio signal toward the auroral oval and record the strength of the signal reflected back from the aurora.

Why is there so much interest in radio aurora?
For ham radio operators who like to contact stations over greater distances than would ordinarily be possible on the VHF frequencies, radio aurora is great! Besides the thrill of making contacts that most poeple would consider impossible, the phenomenon itself is fascinating - and like its visual counterpart, very unpredictable. It's the thrill of the chase!

What happened to the Kiruna magnetogram? It was on the old Aurora Monitor site.
Aurora Sentry only uses data if it is considered public information or specific permission has been obtained for its use. It will be included in the future if proper authorization can be obtained.

Why isn't data from [somewhere] included in Aurora Sentry?
That could be for several reasons:

The data on this site looks impressive, but what does it all mean?
A Guide to the Data is available. If you have a specific question you may email the Aurora Sentry webmaster.

There are many aurora alerting services. What purpose does Aurora Sentry serve?
There are several very good aurora alerting services. Most send alerts by email and work very well. However, email can get delayed, and (in some cases) only one alert is sent at the onset of a storm. Aurora Sentry provides a more or less continuous flow of real time data which is useful in monitoring the progress of a storm. A combination of both the email services and frequent checks of Aurora Sentry is a good idea for those who want to make sure they don't miss an aurora event.