{"id":59067,"date":"2024-05-14T08:55:06","date_gmt":"2024-05-14T08:55:06","guid":{"rendered":"http:\/\/fa4a29e8-9a5b-40ea-9cf3-ab33bb12a356"},"modified":"2024-05-14T09:10:07","modified_gmt":"2024-05-14T09:10:07","slug":"what-causes-peaks-in-activity-on-the-sun-scientists-are-still-trying-to-fully-understand-the-11-year-solar-cycle","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/what-causes-peaks-in-activity-on-the-sun-scientists-are-still-trying-to-fully-understand-the-11-year-solar-cycle\/","title":{"rendered":"What causes peaks in activity on the Sun? Scientists are still trying to fully understand the 11-year Solar Cycle"},"content":{"rendered":"

The Solar Cycle peaks and troughs roughly every 11 years, and is an indicator of a rise and fall in activity as observe on the surface of the Sun. <\/p>

By <\/p>

Published: Tuesday, 14 May 2024 at 08:55 AM<\/p>

\n\n

Sunspots have been observed for thousands of years, even before the development of the solar telescope provided a way to safely view our dazzling local star.<\/p>

Systematic records of sunspot numbers and their positions didn\u2019t begin, though, until the mid-1800s.<\/p>

Still, these records represent the longest running dataset of any cosmic phenomenon and reveal an intriguing side to the Sun\u2019s character.<\/p>

The number of sunspots<\/a> observed on the surface of the Sun follows a roughly 11-year pattern of peaks and troughs known as the solar cycle.<\/p>

100 days of sunspots, photographed by Soumyadeep Mukherjee, Kolkata, India, December 2020\u2013April 2021<\/figcaption><\/figure>
While we still have a lot to learn to accurately estimate the patterns of future solar cycles, predictions over the past decade suggested that our current cycle would be smaller than average.<\/p>
And the numerous missions dedicated to the study of the Sun<\/a> are only making our predictions more accurate.<\/p>
Does this mean an overall waning of solar activity? New research over the coming years may help us get a better idea of what the future holds for our host star.<\/p>
Perhaps you could get involved in capturing images of the Sun for scientific study. For more on this, read Pete Lawrence’s fascinating guide on how to photograph the Sun<\/a>.<\/p>
**How the Solar Cycle was born<\/strong><\/h2>** $\"Illustrated$
Illustrated plate based on observations of the Sun by British astronomer Richard Christopher Carrington (1826-1875), showing a group of sunspots, taken from ‘Memoirs of the Royal Astronomical Society’, 1861. Inspired by the discovery by Heinrich Schwabe in 1843 of the sunspot cycle, Carrington made detailed observations and drawings of the positions of sunspots between 1853 and 1861. Photo by SSPL\/Getty Images<\/figcaption><\/figure>
That the solar cycle was ever noticed is thanks to astronomers spurred on by the possibility of discovering a new planet.<\/p>
In 1846 Neptune had been discovered in the search to understand whether irregularities in the orbit of Uranus were due to problems with Newton\u2019s theory of gravity<\/a>, or the gravitational effect of a then undiscovered planet.<\/p>
The latter idea won. So when irregularities were discovered in Mercury\u2019s orbit, it seemed only sensible to take the same approach and the existence of the planet Vulcan orbiting close to the Sun was proposed.<\/p>
The theory could be tested observationally by looking for Mercury as it transited the Sun<\/a>.<\/p>
$\"Mercury$
Mercury in Transit by Phil Benson, Essex, UK.<\/figcaption><\/figure>
One person who took up this challenge was German pharmacist-turned-astronomer Heinrich Schwabe, who observed the Sun every clear day from 1826 to 1843.<\/p>
Although he found no evidence for the hypothetical planet Vulcan, his sunspot records did reveal a 10-year period or so during which their numbers rose.<\/p>
A repetitive process seemed to be at work. Soon astronomers across Europe were being encouraged by the director of Bern Observatory \u2013 Rudolf Wolf \u2013 to make regular observations of the Sun and record their findings.<\/p>
Wolf combined the new sunspot records with those taken in the centuries before and was able to reconstruct sunspot cycles back to 1755.<\/p>
He called this \u2018cycle 1\u2019 and numbered all the following cycles consecutively.<\/p>
$\"Solar$
Solar cycle 23, captured in extreme ultraviolet light by NASA\u2019s SOHO spacecraft, reveals maximum activity in 2001. Credit: SOHO (ESA & NASA)<\/figcaption><\/figure>
What causes sunspots?<\/strong><\/h2>
Solar cycle studies focused for many years on data collection, such as sunspot number, location and shape, until the true origin of sunspots was shown by George Ellery Hale in 1908.<\/p>
Hale discovered that these dark spots on the Sun are actually the intersection of colossal tubes of magnetism penetrating the photosphere.<\/p>
This discovery started a revolution in solar physics and showed us that the solar cycle is actually a magnetic one.<\/p>
Today we understand that flows of electrically charged gas inside the Sun both sustain and evolve the global magnetic field<\/a>.<\/p>
$\"The$
The dynamo effect of the Earth\u2019s spinning molten core produces our planet\u2019s magnetic field, which prevents the solar wind from stripping away our atmosphere. Credit: Naeblys \/ Getty Images<\/figcaption><\/figure>
The solar cycle captures all the stages of this evolution. At the start of the cycle, the Sun\u2019s global field is aligned in a north-south direction.<\/p>
The flows then drag out this field so it becomes more aligned with the east-west direction.<\/p>
When portions of the interior field grow too strong, they become buoyant and a loop rises to penetrate the Sun\u2019s surface.<\/p>
Sunspots form at the two foot points of the loop: one sunspot with a south magnetic pole next to a spot with a north pole. Just like the configuration of a magnet.<\/p>
$\"Sunspots$
Sunspots captured by Arturo Buenrostro, Dallas, Texas, 27 March 2022<\/figcaption><\/figure>
The fluid nature of the Sun means sunspots don\u2019t live forever. The solar cycle progresses because flows at the surface of the Sun start to tear apart the magnetic fields of the sunspots, spreading the field over ever-larger areas.<\/p>
As the field disperses, the sunspots disappear. Eventually, more fluid flows take the magnetic field up towards both poles of the Sun where it gets reprocessed, ready to feed into the next cycle.<\/p>
Overall, the evolution of the Sun\u2019s magnetic field that drives the solar cycle might seem straightforward.<\/p>
But consider this: cycles can be large or small, and cycles of different sizes do not follow each other at random.<\/p>
Instead, a few large cycles will be followed by a few small cycles.<\/p>
Analysing this trend has also revealed an 80-year so-called \u2018Gleissberg cycle\u2019 on top of the 11-year cycle.<\/p>
And on top of this are the 200-year de Vries and the 2,300-year Hallstat cycles too. Developing a model that can explain all these details is an important area in modern solar physics.<\/p>
How the solar cycle works<\/strong><\/h2>
$\"How$
How the solar cycle works. Credit: Paul Higgins<\/figcaption><\/figure>
The diagram above reveals the inner workings of the Sun during the solar cycle.<\/p>
The magnetic field evolves from being aligned north-south at solar minimum (a) to aligning east-west (b), and eventually being multipolar at solar maximum (c). <\/p>
The photosphere is the visible layer of the Sun that we are familiar with, where sunspots are formed; the tachocline is a region inside the Sun where the magnetic field gets distorted and moved.<\/p>
$\"The$
The 11-year solar cycle (shown here as black lines) can be further grouped into 80-100 year Gleissberg cycles (shown here as a yellow arc) as seen when we look back at the last 200 years of sunspot data. Credit: Paul Wootton<\/figcaption><\/figure>
The discovery of the Sun\u2019s magnetism was also key to understanding the violent side of the Sun\u2019s character: solar flares and coronal mass ejections (CMEs) driven by colossal releases of energy stored in the solar magnetic field.<\/p>
The frequency of solar flares and CMEs peaks at the apex of each solar cycle, as does the amount of light that the Sun emits.<\/p>
At cycle maximum, with the most sunspots, the Sun is fraction of a per cent brighter.<\/p>
Certain rules are obeyed during a solar cycle. Sunspots appear at high latitudes at the start,<\/p>
with the sunspots that form during subsequent years appearing at progressively lower latitudes.<\/p>
This pattern is shown wonderfully clearly in the so-called \u2018butterfly\u2019 diagram published by astronomers Annie and Walter Maunder in 1904 (see below).<\/p>
When pairs of sunspots appear, one with a north pole and one with a south, sunspots in each hemisphere will nearly always appear in the same order as the Sun rotates.<\/p>
$\"The$
The \u2018butterfly\u2019 diagram shows the latitude of sunspot occurrence versus time in years. When pairs of sunspots form, one with a north pole and one with a south, they appear at the same place in each hemisphere.<\/figcaption><\/figure>
Solar Cycle 24<\/strong><\/h2>
For cycle 24, pairs of sunspots in the northern hemisphere that came into view as the Sun rotated had the south pole spot appear slightly ahead of the north.<\/p>
In the southern hemisphere, it was the opposite way round.<\/p>
This swaps every solar cycle, meaning you can use the magnetic field of sunspots to determine which cycle they formed in.<\/p>
The rules apply to the overall global field of the Sun too, and at the peak of each cycle the polar magnetic fields swap their magnetic polarity.<\/p>
All this prompted the American National Oceanic and Atmospheric Administration and NASA to form a \u2018Solar Cycle 24 Prediction Panel\u2019 to see what models and theories are best able to predict solar cycle size, duration and peak.<\/p>
Prediction methods vary. One uses the finding that the number and frequency of sunspot formation at the start of a cycle is linked to the size and timing of that cycle\u2019s peak.<\/p>
$\"NASA\u2019s$
NASA\u2019s Solar Dynamics Observatory captured this image of a solar flare on 10 May 2024. Credit: NASA\/SDO<\/figcaption><\/figure>
Another assesses the strength of the polar magnetic field, that is the \u2018seed\u2019 from which each cycle grows. Another looks at the strength of the gas flows that ultimately drive the cycle.<\/p>
Yet, another approach is to consider solar activity over timescales much longer than a single 11-year cycle.<\/p>
The challenge is that it is easier to forecast once the sunspots of a new cycle have started to appear.<\/p>
Then the rate at which the sunspots are forming can be compared with that of previous cycles to get an idea of how the new cycle will play out in terms of size and duration.<\/p>
Initial predictions for cycle 24 came in 2006, even before the first sunspots of that cycle formed.<\/p>
$\"Solar$
Solar flare in sunspot region 3590\/3586 Harold Soto, Jacksonville, Florida, USA, 24 February 2024<\/figcaption><\/figure>
Solar minimum \u2013 when the number of sunspots is lowest \u2013 was forecast for March 2008 with a moderately large maximum in 2011.<\/p>
In January 2008 the first sunspots of the cycle were seen and by 2009 there were enough to be used in cycle prediction methods.<\/p>
A revised statement from the Solar Cycle Prediction Panel followed in May 2009, downgrading the forecast to a smaller than average cycle that would peak in May 2013.<\/p>
Another slight downgrade came again in 2011.<\/p>
At this time the solar physics community was feeling pessimistic about the status of the Sun\u2019s cycles.<\/p>
Some even suggested in the coming decades we might experience a strong downturn of the type seen in the Maunder Minimum, when the solar cycle appeared to switch off for several decades in the mid-1600s.<\/p>
It felt like the Sun was fading in front of our eyes.<\/p>
$\"Solar$
Solar flares on the Sun captured by NASA’s Solar Dynamics Observatory, 10, 11 May 2024. Credit: NASA\/SDO<\/figcaption><\/figure>
The Sun eventually reached solar maximum in April 2014 and although the predictions didn\u2019t do too badly, it was clear we have a lot to learn.<\/p>
It is never possible to say exactly when minimum occurs until we have passed that point.<\/p>
We need to see the sunspot number drop and then start to rise again with spots that have the new cycle\u2019s magnetic field orientation.<\/p>
$\"Looking$
Looking back at recent solar cycles reveals a decline in sunspot numbers. Early indications suggest this trend is likely to continue in cycle 25<\/figcaption><\/figure>
Solar Cycle 25<\/strong><\/h2>
Solar Cycle 25 is well underway, but what might it yet have in store?<\/p>
The challenges with predictions in previous years have motivated new research.<\/p>
New physical models are being developed along with new analysis of the observations.<\/p>
With still so much to learn about processes that play out over the full surface of the Sun is it clear that we need more data.<\/p>
$\"Solar$
Solar flares on the Sun captured by NASA’s Solar Dynamics Observatory, 12 May 2024. Credit: NASA\/SDO<\/figcaption><\/figure>
But one of the limiting factors comes from our viewpoint.<\/p>
Many of our telescopes take images from close to the plane of the Sun\u2019s equator, when many of the important processes take place near the poles.<\/p>
The solution to this predicament is the European Space Agency\u2019s Solar Orbiter mission, the first spacecraft to take images of the Sun from a high-latitude vantage point.<\/p>
We will be able to track the magnetic field that drives one cycle into the next, filling in the gaps in our knowledge.<\/p>
From this new physical theories will be developed and, we hope, we will finally unlock the secrets of the solar cycle.<\/p>
Prof Lucie Green is a Professor of Physics at Mullard Space Science Laboratory. This article originally appeared in the May 2019 issue of BBC Sky at Night Magazine.<\/em><\/strong><\/p> <\/body><\/html>\n
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