solar cycle 25 Archives

Solar SDO — A (nearly) naked Sol… more the norm than the exception these days. Credit: NASA/SDO AIA 512/1600 imager.

Have you been keeping an eye on Sol lately? One of the top astronomy stories for 2018 may be what’s not happening, and how inactive our host star has become.

The strange tale of Solar Cycle #24 is ending with an expected whimper: as of May 8^th, the Earthward face of the Sun had been spotless for 73 out of 128 days thus far for 2018, or more than 57% of the time. This wasn’t entirely unexpected, as the solar minimum between solar cycle #23 and #24 saw 260 spotless days in 2009 – the most recorded in a single year since 1913. Cycle #24 got off to a late and sputtering start, and though it produced some whopper sunspots reminiscent of the Sol we knew and loved on 20^th century cycles past, it was a chronic under-performer overall. Mid-2018 may see the end of cycle #24 and the start of Cycle #25… or will it?

solar minimum — The story thus far… and the curious drama that is solar cycle #24. Credit: David Hathaway/NASA Marshall Spaceflight Center.

One nice surprise during Cycle #24 was the appearance of massive sunspot AR 2192, which popped up just in time for the partial solar eclipse of October 23^rd, 2014. Several times the size of the Earth, the spot complex was actually the largest seen in a quarter century. But just as “one swallow does not a Summer make,” one large sunspot group couldn’t save Solar Cycle #24.

The Sun goes through an 11-year sunspot cycle, marked by the appearance of new spots at mid- solar latitudes, which then slowly progress to make subsequent appearances closer towards the solar equator, in a pattern governed by what’s known as Spörer’s Law. The hallmark of a new solar cycle is the appearance of those high latitude spots. The Sun actually flips overall polarity every cycle, so a proper Hale Cycle for the Sun is actually 11 x 2 = 22 years long.

A big gaseous fusion bomb, the Sun actually rotates once every 25 days near its equator, and 34 days at the poles. The Sun’s rotational axis is also tipped 7.25 degrees relative to the ecliptic, with the northern rotational pole tipped towards us in early September, while the southern pole nods towards us in early March.

An animation of massive susnpot AR 2192 crossing the Earthward face of Sol from October 17th to October 29th, 2014. Credit: NASA/SDO.

What’s is store for Cycle #25? One thing’s for certain: if the current trend continues, with spotless days more the rule than the exception, we could be in for a deep profound solar minimum through the 2018 to 2020 season, the likes of which would be unprecedented in modern astronomy.

Fun fact: a similar dearth of sunspots was documented during the 1645-1715 period referred to as the Maunder Minimum. During this time, crops failed and the Thames River in London froze, making “frost fairs” along its frozen shores possible. Ironically, the Maunder Minimum also began just a few decades after the dawn of the age of telescopic astronomy. During this time, the idea of “spots on the Sun” was regulated to a controversial, and almost mythical status in mainstream astronomy.

Keeping Vigil on a Tempestuous (?) Star

We’ve managed to study the last two solar cycles with unprecedented scrutiny. NASA’s STEREO-A and -B spacecraft (Only A is currently active) monitors the farside of the Sun from different vantage points. The Solar Dynamics Observatory (NASA SDO) keeps watch on the Sun across the electromagnetic spectrum. And our favorite mission, the joint NASA/European Space Agency’s SOHO spacecraft, has monitored the Sun from its sunward L1 Lagrange vantage point since it launched in 1995—nearly through one complete 22 year Hale Cycle by mid- 2020s. Not only has SOHO kept a near-continuous eye on Sol, but it’s also discovered an amazing 3,398 sungrazing comets as of September 1^st, 2017… mostly due to the efforts of diligent online amateur astronomers.

A guide to features on the Sun. The left view in Calcium-K shows the photosphere and is similar to a standard whitelight view, and the right view shows features in the chromosphere in hydrogen-alpha. Credit: Paul Stewart Instagram: @Upsidedownastronomer/annotations by Dave Dickinson

…and did you know: we can actually model the solar farside currently out of view from the Earth to a high degree of fidelity thanks to the advent of powerful computational methods used in the nascent field of solar helioseismology.

Unfortunately, this low ebb in the solar cycle will also make for lackluster aurora in the years to come. It’s a shame, really… the relatively powerful cycles of the 1970s and 80s hosted some magnificent aurorae seen from mid-latitudes (and more than a few resulting blackouts). We’re still getting some minor outbursts, but you’ll have to venture “North/South of the 60” to really see the aurorae in all of its splendor over the next few years.

But don’t take our word for it: get out there and observe the Sun for yourself. Don’t let this discourage you when it comes to observing the Sun. Even near its minimum, the Sun is a fascinating target of study… and unlike most astronomical objects, the face of the Sun can change very quickly, sometimes erupting with activity from one hour to the next.

We like to use a Coronado Personal Solar Telescope to monitor the Sun in hydrogen-alpha for prominences and filaments: such a scope can be kept at the ready to pop outside at lunch time daily for a quick look. For observing sunspots and the solar photosphere in white-light, you’ll need an approved glass filter which fits snugly over the aperture end of your telescope or camera, or you can make a safe solar filter with Baader Safety Film.

Solar scopes — Safe ways to observe the Sun: a homemade whitelight filter (left) and a Coronado PST solar telescope (right). Images by author.

Does the sunspot cycle tell the whole picture? Certainly, the Sun most likely has longer, as yet undiscovered cycles. For about a century now, astronomers have used the Wolf Sunspot Number as calculated mean average to describe the current state of activity seen on the Sun. An interesting study calls this method into question, and notes that the direction and orientation of the heliospheric current sheet surrounding the Sun seems to provide a better overall depiction of solar activity.

Other mysteries of the Sun include: just why does the solar cycle seem baked in at 11 years? Why don’t we ever see spots at the poles? And what’s in store for the future? We do know that solar output is increasing to the tune of 1% every 100 million years… and a billion years from now, Earth will be a toasty place, probably too warm to sustain liquid water on its surface…

Which brings us to the final point: what role does the solar cycle play versus albedo, global dimming and climate? This is a complex game to play: Folks have literally gone broke trying to link the solar cycle with terrestrial human affairs and everything from wheat crops to stock market fluctuations. Many a climate change-denier will at least concede that the current climate of the Earth is indeed changing, though they’ll question human activity’s role in it. The rather ominous fact is, taking only current solar activity into account, we should be in a cooling trend right now, a signal in the data that anthropogenic climate change is working hard against.

See for yourself. You can keep track of Sol’s daily activity online: our favorite sites are SpaceWeather, NOAA’s space weather/aurora activity page, and the SOHO and SDO websites.

Be sure to keep tabs of Sol, as the next solar minimum approaches and we ask the question: will Cycle #25 occur at all?

Well, we’re finally emerging from our self-imposed monastic exile that is editing to mention we’ve got a book coming out later this year: The Universe Today Ultimate Guide to Viewing the Cosmos: Everything You Need to Know to Become an Amateur Astronomer, and yes, there’s a whole chapter dedicated to solar observing and aurora. The book is up for pre-order now, and comes out on October 23^rd, 2018!

Our nearest star has exhibited some schizophrenic behavior thus far for 2013.

By all rights, we should be in the throes of a solar maximum, an 11-year peak where the Sun is at its most active and dappled with sunspots.

Thus far though, Solar Cycle #24 has been off to a sputtering start, and researchers that attended the meeting of the American Astronomical Society’s Solar Physics Division earlier this month are divided as to why.“Not only is this the smallest cycle we’ve seen in the space age, it’s the smallest cycle in 100 years,” NASA/Marshall Space Flight Center research scientist David Hathaway said during a recent press teleconference conducted by the Marshall Space Flight Center.

Cycle #23 gave way to a profound minimum that saw a spotless Sol on 260 out of 365 days (71%!) in 2009. Then, #Cycle 24 got off to a late start, about a full year overdue — we should have seen a solar maximum in 2012, and now that’s on track for the late 2013 to early 2014 time frame. For solar observers, both amateur, professional and automated, it seems as if the Sun exhibits a “split-personality” this year, displaying its active Cycle #24-self one week, only to sink back into a blank despondency the next.

This new cycle has also been asymmetrical as well. One hallmark heralding the start of a new cycle is the appearance of sunspots at higher solar latitudes on the disk of the Sun. These move progressively toward the Sun’s equatorial regions as the cycle progresses, and can be mapped out in what’s known as a Spörer’s Law.

The sunspot number "butterfly" graph, illustrating Spörer's Law that susnpots gradually migrate towards the equator of the Sun as the solar cycle progresses. (Credit: NASA/MSFC). — The sunspot number “butterfly” graph, illustrating Spörer’s Law that susnpots gradually migrate towards the equator of the Sun as the solar cycle progresses. (Credit: NASA/MSFC).

But the northern hemisphere of the Sun has been much more active since 2006, with the southern hemisphere experiencing a lag in activity. “Usually this asymmetry lasts a year or so, and then the hemispheres synchronize,” said Giuliana de Toma of the High Altitude Observatory.

So far, several theories have been put forth as to why our tempestuous star seems to be straying from its usual self. Along with the standard 11-year cycle, it’s thought that there may be a longer, 100 year trend of activity and subsidence known as the Gleissberg Cycle.

The Sun is a giant ball of gas, rotating faster (25 days) at the equator than at the poles, which rotate once every 34.5 days. This dissonance sets up a massive amount of torsion, causing the magnetic field lines to stretch and snap, releasing massive amounts of energy. The Sun also changes polarity with every sunspot cycle, another indication that a new cycle is underway.

But predictions have run the gamut for Cycle #24. Recently, solar scientists have projected a twin peaked solar maximum for later this year, and thus far, Sol seems to be following this modified trend. Initial predictions by scientists at the start of Cycle #24 was for the sunspot number to have reached 90 by August 2013; but here it is the end of July, and we’re sitting at 68, and it seems that we’ll round out the northern hemisphere Summer at a sunspot number of 70 or so.

Some researchers predict that the following sunspot Cycle #25 may even be absent all together.

“If this trend continues, there will be almost no spots in Cycle 25,” Noted Matthew Penn of the National Solar Observatory, hinting that we may be on the edge of another Maunder Minimum.

Looking back over solar cycles for the past 500 years. (Credit: D. Hathaway/NASA/MSFC).

The Maunder Minimum was a period from 1645 to 1715 where almost no sunspots were seen. This span of time corresponded to a medieval period known as the Little Ice Age. During this era, the Thames River in London froze, making Christmas “Frost Fairs” possible on the ice covered river. Several villages in the Swiss Alps were also consumed by encroaching glaciers, and the Viking colony established in Greenland perished. The name for the period comes from Edward Maunder, who first noted the minimum in papers published in the 1890s. The term came into modern vogue after John Eddy published a paper on the subject in the journal of Science in 1976. Keep in mind, the data from the period covered by the Maunder Minimum is far from complete— Galileo had only started sketching sunspots via projection only a few decades prior to the start of the Maunder Minimum. But tellingly, there was a span of time in the early 18^th century when many researchers supposed that sunspots were a myth! They were really THAT infrequent…

Just what role a pause in the solar cycle might play in the climate change debate remains to be seen. Perhaps, humanity is getting a brief (and lucky) reprieve, a chance to get serious about controlling our own destiny and doing something about anthropogenic climate-forcing. On a more ominous note, however, an extended cooling phase may give us reason to stall on preparing for the inevitable while giving ammunition to deniers, who like to cite natural trends exclusively.

Down but not out? Sol looking more like its solar max-self earlier this month on July 8th. (Photo by author).

Whatever occurs, we now have an unprecedented fleet of solar monitoring spacecraft on hand to watch the solar drama unfold. STEREO A & B afford us a 360 degree view of the Sun. SOHO has now monitored the Sun for the equivalent of more than one solar cycle, and NASA’s Solar Dynamics Observatory has joined it in its scrutiny. NASA’s Interface Region Imaging Spectrograph (IRIS) just launched earlier this year, and has already begun returning views of the solar atmosphere in unprecedented detail. Even spacecraft such as MESSENGER orbiting Mercury can give us vital data from other vantage points in the solar system.

Cycle #24 may be a lackluster performer, but I’ll bet the Sun has a few surprises in store. You can always get a freak cloud burst, even in the middle of a drought. Plus, we’re headed towards northern hemisphere Fall, a time when aurora activity traditionally picks up.

Be sure to keep a (safely filtered) eye on ol’ Sol— it may be the case over these next few years that “no news is big news!”

Tag: solar cycle 25

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