Part 2 of my aurora chasers guide is all about what causes the aurora – ie when an aurora might appear in Tasmania.

When does the aurora appear in Tasmania?

The million dollar question. Unfortunately we cant simply check an upcoming aurora schedule, book a flight to Tassie and sit back and enjoy the show. That said, it is worthwhile knowing a little bit about what causes the aurora and what to look out for to recognise when one might occur.

Beautiful display of the aurora during a dark – new moon – night

Solar Maximum

Every 10-11 years or so the sun goes through a cycle of sunspot activity. The reason this is important is that sunspots are a sign of increased solar activity (such as solar flares) which result in auroras being visible here on earth. You can read more about sunspots here. 2024 is predicted to be solar maximum which means an increase in solar activity and a high chance of auroras.

The aurora usually appears 2-3 days after a significant solar flare on the earth-facing side of the sun. Nobody can predict exactly when a sunspot will erupt with a solar flare, but once the flare has occurred we can keep an eye on things and wait to see if an aurora eventuates.

What do I mean by “keep an eye on things”?

Solar flares often launch a “Coronal Mass Ejection (CME)” which contains magnetically charged particles. When these particles hit the earth, we see an aurora – as long as a few things go exactly right.

Here are a couple of screenshots of great aurora numbers from previous auroras. To me, “keeping an eye on things” pretty much means monitoring the Bz value. Without going into all the details, basically the Bz must be negative, and the further negative the better.

October 2021 – note the the sudden shift in the graphs

April 2023 – a huge display!

You can see in October 2021 (top image) the Bz was steady at around -5 or so until a sudden drop to -14. If you see that on the graphs its time to get off the couch and out the door! The April 2023 image above was even wilder at -25 (and I am pretty sure it topped -30 at points during the display!).

Rule of thumb summary of Bz values: Minimum of -5ish to capture a bit of a glow in camera; -10 or lower to get a really exciting display. -25 or lower is just bananas!

To Moon or not to Moon

The aurora can appear all year round regardless of earths weather, seasons and moonlight etc so obviously as long as it is dark outside with clear skies you should get out if you get wind of an aurora happening.

The moon adds an interesting variable, as a full moon will interfere dramatically with the light of the aurora with only the strongest of displays visible through the moonlight. A partial moon can be a great asset as it lights up the landscape just a little bit, and the new moon allows you to capture all the glory of the aurora – perhaps with landscape features in silhouette. My personal favourite is new moon – and most of my workshops are set at new moon for this reason.

Aurora during a nearly full moon

In part 3 I will share some advice about locations.