Eclipses explainedUSA 2017

What is Solar Minimum and how will it affect August’s eclipse?

The Sun has a cycle that lasts roughly 11 years, and right now we’re heading towards the trough. Does it matter?

Will August 21 reveal our Sun to be weaker than normal? It’s highly possible that the mighty Solar Corona – the star attraction of a Total Solar Eclipse – will be smaller than seen in previous years, but there’s no need to get concerned; the event will still be the most spectacular natural event you have ever witnessed.

You see, the Sun has a cycle that lasts between 9-14 years. At the peak of that cycle – solar maximum – the Sun spits-out more electrons and protons as huge solar flares and coronal mass ejections. These are responsible for the displays of Northern Lights and Southern Lights; the more charged-up the solar wind headed towards Earth, the brighter and more frequent are the displays. What’s known as the ‘auroral oval’ gets larger, so people in more southerly latitudes can see them.

A solar maximum is historically when aurora are at their most frequent and spectacular, and if there’s a Total Solar Eclipse during that peak, you can expect to see ‘prominences’ – huge solar flares and coronal mass ejections in action.

“The Sun has an 11-year cycle where it gets more active and more prominences, but that doesn’t mean that towards minimum there’s no action going on,” says Eddie Mahoney, the only Nasa Ambassador, and Director of Astronomy and host of Tour of the Stars at the Hyatt Regency Maui.

There’s less activity than there is at the peak but there’s still activity – it’s not zero – so we may still get some dazzling effects from the corona.”

However, predicting the solar maximum is difficult because although 11 years is the average cycle, it can vary between 9-14 years, so August’s Total Solar Eclipse could help astronomers determine exactly where the Sun is in that cycle. During Totality the Sun’s corona can be small and tightly bound to the surface, or flared and stretching away from the Sun. “The Sun can tricks us, it can surprise , and even at absolute minimum,” says Mahoney. “Perhaps the solar corona will be a bit smaller, that’s likely.”

The next solar maximum is expected to peak in the mid 2020s.

Photo credit: J. Vilinga (Angola, IAP), LASCO, NRL, SOHO, ESA, NASA; Processing: R. Wittich; Composition & Copyright: S. Koutchmy (IAP, CNRS)