Aurora: How to See A Display

Photos of aurorae can be stunning. Why wouldn’t you want to see this for yourself? But there’s a problem: You have to be in the right place at the right time to see them, and there is no guarantee at any time as to what might happen.

Dedicated aurora chasers learn when the best chances of seeing aurorae occur, mostly by monitoring several key indices of space weather activity on the internet. But firstly you need to assess your geographic location in relation to the magnetic poles of the planet, not the geographic ones.

The magnetic poles do not line up evenly with the geographical north and south poles, and are known to measurably wander around over short periods of time. At the moment the north magnetic pole is in Canada and the south magnetic pole is in the Southern Ocean just off the coast of Antarctica to the south of Tasmania. So the first thing to do is find a map of magnetic latitude. You might be surprised how far from the pole you really are! Looking at the southern hemisphere, the South Island of New Zealand and Tasmania are the closest areas of land to the south magnetic pole. In the northern hemisphere there is a lot more land, so mainland Canada, Alaska and across the Atlantic the Scandinavian countries of Norway and Sweden usually fall under the auroral circle.

World Magnetic Chart

Source: NOAA

The next thing to consider is the current space weather. As we discussed in Part 1, aurorae are caused by the solar wind colliding with the Earth’s magnetic field. This wind of energetic particles streaming off the Sun is not constant, it varies greatly in strength from hour to hour but is nearly always there (it very rarely shuts down completely, but it has been recorded doing so. This is actually a bad thing, as although it can do a lot of damage, on the other hand offers some protection from cosmic rays, random particles of gamma radiation that are scattered across the universe.)

There are three main sources of bursts of strong solar wind that cause aurorae: the first is solar flares from sunspots, the second is a stream of wind from a coronal hole and the third is a blob of energy from a coronal mass ejection.

Big sunspots have long been associated with auroral displays. Whenever a particularly large group of sunspots form astronomers will watch it closely as it transits across the face of the Sun. The bigger the sunspot complex the greater the chances of a solar flare erupting from it, as the tangled magnetic lines of the sunspots collapse back onto the surface of the Sun. These flares are difficult to see visibly in white light but contrast well as bright flares of light against the darker surface of the Sun itself and the relatively dark sunspots in the narrow bandwidth of the spectrum known as Hydrogen-alpha light, or H-alpha light for short.

It’s interesting to note that solar flare of Carrington’s event was so bright he was actually able to see it as a patch of white light over the top of the sunspot he was observing at the time by projecting an image of the Sun through a refractor onto a white background. Usually the flares are not bright enough for us to detect them just using white light observation, so this is an indication of just how big this solar flare was!

Coronal holes show up as wide areas free of coronal streamers, so the solar wind speeds up out of here, and Coronal Mass Ejections (CMEs) are huge blobs of energetic material not related to sunspots or solar flares that are sometimes ejected from the Sun as well.

 

What Indicators to Watch Online:

Watch the Kp index. This will give you an idea of activity. Depending on how far you are from the magnetic pole you might need a higher Kp level before you see anything. For example I learnt by experience when I lived in Perth, Western Australia, at magnetic latitude 44, that the Kp index needed to be 7 or above for there be any chance of seeing an aurora. Even at Kp 7 it might only be detectable photographically, not visually. However observers in Dunedin, New Zealand will see nice displays at Kp 4, and Tasmanian observers have no trouble seeing displays at Kp 5.

The solar wind speed  – speeds up to 400km/hour or more are needed, too. The higher the better.

An increase in Density of the solar wind is also desirable. That information will probably be available where you get your solar wind speed.

You also need the Bz level to swing to magnetic south (or negative). If it stays oriented to the north you are unlikely to get a good display.

Displays can occur at any time of the year but for some unknown reason the best aurorae tend to occur around the time of the equinoxes. Scientist don’t yet know why, but if you’re planning a trip to see them, that would increase your chances.

 

Online Resources:

Aurora Australis Tasmania is a closed group on Facebook but you can read their posts publicly, so you can see if there is anything happening.

Aurora Hunters Victoria is also a closed and private Facebook group and you will need to apply to join them to read their posts.

NASA’s Space Weather site is excellent for beginners which displays a current solar activity summary

If you would like an app there is  “Aurora Alert” for Android platforms

On Twitter I get warnings from Halo CME @halocme and SpaceWeatherLive @_spaceweather_

The Australian government runs Space Weather Services, formerly known as IPS, which sends out activity warnings via an email service. Originally for radio operators so they would know when their transmissions might be affected, they soon realised they were helping a lot of amateur astronomers as well and have modified the warning system. So you now get a heads up as well as a notice when a storm is in action.

For predictions of expected activity levels in the next day or so try Aurora Service

If you know of any other good sources of information online leave a note in the comments below.

 

 

Leave a Comment