Solar maximum is in sight but when will it arrive (and when will we know)?

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We explore the latest solar maximum predictions and look into why it could be a couple of years before we can confidently state when solar maximum occurred.

graphic of the sun in space shows a large orange sphere against a black background.
It could be a couple of years before we can confidently say when solar maximum occurred. (Image credit: Canva Pro)

May and June 2024 saw the highest sunspot numbers on the sun since 2002, but is the peak of the solar cycle here yet? 

The sun follows an 11-year solar cycle of increasing and decreasing activity. Although not the first astronomer to discover the solar cycle, the solar cycle numbering and naming convention was first introduced in 1852 by Swiss astronomer Johann Rudolf Wolf. Within his new solar cycle numbering system, he set the historic 1755-1766 solar cycle 'Solar Cycle 1'. By the time of his work, the sun was already in Solar Cycle 9. As of December 2019, we are now in Solar Cycle 25.

A given solar cycle begins at solar minimum, where the sun is near sunspot-less. During this window, there can be no solar flares or coronal mass ejections (CMEs) for months at a time. From this period of solar minimum, solar activity gradually ramps up over several years, to a period of solar maximum. During solar maximum, large solar flares and CMEs are at their most frequent. 

How is solar maximum defined? 

Solar maximum has a very specific scientific definition, it's the peak of the 13-month smoothed sunspot number curve. What does this mean? Sunspot numbers are calculated daily, but not as simply as just counting the number of sunspots on the sun. 

The international sunspot number is calculated through the equation R = 10g + s, where g is the number of sunspot groups, and s is the number of individually distinct sunspots. There is also a scaling factor applied, dependent on the local observatory conditions. This sunspot metric is consistent with the scaling used by Wolf himself and is designed to reduce the effect of a single fragmented sunspot region inflating the individual sunspot count.

A monthly sunspot number is then calculated from the average of each daily sunspot number. This monthly sunspot number is published monthly by official sources, e.g. the National Oceanic and Atmospheric Administration (NOAA). Because the monthly sunspot numbers can oscillate quite considerably from one month to the next, it is difficult to extract the exact point of solar maximum from the data. Instead, longer sunspot trends are examined through the 13-month smoothed value. This number is calculated for a given month by taking an average of the monthly sunspot number from 6 months prior, to 6 months later (13 months total). This smoothed value is therefore only available for a given month, 6 months later. Solar maximum and minimum are formally defined by the high and low points of this smoothed curve.

Related: Solar maximum is coming, but we won't know it happened until 7 months after it's over

Although this is the formal definition of solar maximum, the same term is also used less formally to describe the year or so of heightening activity around the specific solar maximum peak. 

NOAA ISES Solar Cycle Sunspot Number Progression: Solar cycles 24 (left hump) and 25 (right hump) are clearly visible.  Black dots show individual monthly sunspot values, whilst the purple line shows the 13-month smoothed value.  (Image credit: NOAA)

When is solar maximum? 

M class solar flare Nov. 28, 2023. (Image credit: NASA/ESA/SDO/SOHO)

Because solar maximum is defined by this peak of the 13-month smoothed curve, solar maximum may not actually occur in the month with the highest sunspot count. Taking Solar Cycle 24 as an example, the highest monthly sunspot number was recorded in February 2014, but the official solar maximum arrived in June 2014.

Meanwhile, in the current Solar Cycle 25, May and June 2024 saw the highest monthly sunspot counts since September 2022. It is possible that these months are the highest monthly sunspot numbers that we'll see, even if the 13-month smoothed value (which defines solar max) continues to rise for a few months. Alternatively, it is still also possible that upcoming months will see sunspot numbers greater than May and June.

The newest modeling efforts from NOAA, which use existing sunspot data to predict the peak of the solar cycle, estimate a solar maximum between July 2024 to January 2025. However, although the peak of the solar cycle could be imminent, it will be some time beyond this timespan before we can confirm when solar maximum actually occurred. Why is this?

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—Astrophotographer captures stunningly detailed photos of our 'fuzzy' sun

In any given month, it's impossible to know if you're at the peak of the solar cycle. This is because you never know for certain if the next month's sunspot activity will exceed the activity of the month you're currently in. Even several months after the suspected solar maximum, we can't know if sunspot numbers will accelerate once again. Our current solar cycle shows a good example of this, with an initial peak in June 2023, followed by several months of decreasing sunspot activity until a resurgence of activity in April/May 2024. This double peak in sunspot numbers is seen frequently in historic solar cycle data, but never guaranteed. In some cases, a year or two of sustained declining sunspot numbers are needed to confidently state the peak has passed. Because this trend analysis uses the 13-month smoothed sunspot values, there is also the 6-month wait to consider before we even have the data point for a given month.

With an expected solar maximum between July 2024 to January 2025, we could easily reach the end of 2025 or 2026 before we can confidently state when solar maximum occurred. 

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Ryan French
Ryan French
Contributor

Dr. Ryan French is a solar physicist, science communicator and author. He is pursuing the mysteries of the sun at the forefront of modern solar physics research, using cutting-edge telescopes on the ground and in space. Ryan also works to share the wonders of the sun and space with the public, through museums and observatories, television, and social media on Twitter and TikTok. Ryan's first book, "The Sun: Beginner's guide to our local star" was published in 2023.

6 Comments Comment from the forums
  • CircuitBurner
    Seriously, this is the 1st time in my 56 years that the 11 year solar cycle has gone rogue. The truth is we really have no control over the sun and what our star will do next. I find it curiously worrisome to observe our science institutions fraying at the edges not able to definitively dictate the natural behavior of our closest star, and the subsequent lack of coverage in main stream media. It might very well turn out that global warming wasn't driven by human activities after all....
    It doesn't require the sun to get more than 10% brighter and hotter to really wreak havoc with an apocalyptic vibe. To make things clear, that the sun will do whatever TF it wants to do, which certainly could include making everyone understand how we had been lied to and mislead regarding the true cause of the global warming phenomena. No, it hasn't been your diesel Cadillac or coal burning power plants, you know the things certain power players have been circling in on, for elimination...cheap transport is a big problem for anyone wanting to obtain control over a populace. They want to take that away from you, and replace it with much more limited means...to keep you securely within reach and in order.
    It's actually nice to see the sun doing something that strains the narrative, threatening to make us aware of an evil power grabbing scheme when the lies become apparent... It was never us, it had always been from the source all along. It will be the sun that decides when playtime is over, and when carbon based life on this planet is to end.
    It is something that has taken place throughout the cosmos and throughout its history, life created and ended...stories begin and then end.
    Reply
  • Classical Motion
    I didn't know anything was wrong with this cycle. I haven't paid attention to it since the 70s while hamming. Is there something strange about it this time?

    And I would have thought that with a much less percentage of increase....we would notice it right away. But I am no expert.

    The prediction of the temp increase with CO2 will be seen in about 10 years. We will see.

    The rise of CO2 doesn't worry me. But the smog and smell in Asian cities does. Some cities have a visibility of about two hundred yards.......meters.

    No one should live in that. They make LA in the 70s look like pristine air.
    Reply
  • billslugg
    Classical Motion said:
    No one should live in that. They make LA in the 70s look like pristine air.
    Dad drove us up to LA in 1964, the sky was red. The redness in the air could be seen inside a building. The eyes hurt. Everyone had red eyes. Positive crankcase ventilation on cars sold in CA started in 1961. EGR didn't start until 1970. It's much better now.
    Reply
  • CircuitBurner
    Yes, it was amateur radio that brought my attention to the dynamics of our sun originally. Then from there I have watched somewhat consistently the ebbs and flows for many years now, thanks mainly to the space weather prediction pages by NASA. Of particular interest has always been the LASCO instruments with their occulter disks that produce full frontal imaging of the corona, in sequenced series. These motion pictures provide excellent awareness of CME dynamics coupled to a specific timeframe, for visualizing the stuff streaming outward from our star. Lately, our star has been having unprecedented fits. As my attention became focused on this subject, I noticed some days last year that just seemed abnormally bright outside... Like really really abnormally bright. It was when I had left a jug of red colored koolaid outside during work for a duration of no more than 4 hours one day, and returned to retrieve it later in the evening that peaked my awareness.
    It has lost its red color completely, and appeared as water. It also lost about half its flavor. There had been no ice in that drink also. This was the march before this past march. The temperature that day was around 55 degrees F. That event is what made this most concerning to me. An acquaintance had a similar observation that day in the form of a bottle of dawn dishwashing detergent getting it's typically dark blue coloration bleached to a light blue hue in the same short time frame of just several hours.
    Whatever the sun had blasted us with that day was remarkable and makes me wonder about it's potential role in driving genetic mutations. This was where some deep diving into the oceans of past recorded solar observation data and the different data point variables further improved my awareness. It's very easy to see, for me, how this kind of thing could be going on, with detailed data available, with the general public remaining oblivious.
    No one's sounding an alarm really, yet.
    I may be just a lucky observer that noticed the bigger picture early... But I do not take any credit, the data has been collected continually for decades.
    With my intensified attention, I have also witnessed alterations in charts days after an event occurred, almost like someone buffering the result to maybe not cause an alarm or something. I had screenshots of the data to compare, so I noticed. This caused me to save frequent screenshots daily in order to catch these types of editing.
    I have not looked at the sun the same since. We grew up thinking the light levels and radiation levels coming from this star were steady and constant... And for many periods it essentially has been. But the realization that our star fluctuates is rather intriguing. Then with all the past talk about the star in Orion, Betelgeuse, fluctuating and suggesting some kind of supernova event taking place soon, there is an itching irony here.
    Classical Motion said:
    I didn't know anything was wrong with this cycle. I haven't paid attention to it since the 70s while hamming. Is there something strange about it this time?

    And I would have thought that with a much less percentage of increase....we would notice it right away. But I am no expert.

    The prediction of the temp increase with CO2 will be seen in about 10 years. We will see.

    The rise of CO2 doesn't worry me. But the smog and smell in Asian cities does. Some cities have a visibility of about two hundred yards.......meters.

    No one should live in that. They make LA in the 70s look like pristine air.
    Reply
  • Wistiu
    CircuitBurner said:
    Seriously, this is the 1st time in my 56 years that the 11 year solar cycle has gone rogue. The truth is we really have no control over the sun and what our star will do next. I find it curiously worrisome to observe our science institutions fraying at the edges not able to definitively dictate the natural behavior of our closest star, and the subsequent lack of coverage in main stream media. It might very well turn out that global warming wasn't driven by human activities after all....
    It doesn't require the sun to get more than 10% brighter and hotter to really wreak havoc with an apocalyptic vibe. To make things clear, that the sun will do whatever TF it wants to do, which certainly could include making everyone understand how we had been lied to and mislead regarding the true cause of the global warming phenomena. No, it hasn't been your diesel Cadillac or coal burning power plants, you know the things certain power players have been circling in on, for elimination...cheap transport is a big problem for anyone wanting to obtain control over a populace. They want to take that away from you, and replace it with much more limited means...to keep you securely within reach and in order.
    It's actually nice to see the sun doing something that strains the narrative, threatening to make us aware of an evil power grabbing scheme when the lies become apparent... It was never us, it had always been from the source all along. It will be the sun that decides when playtime is over, and when carbon based life on this planet is to end.
    It is something that has taken place throughout the cosmos and throughout its history, life created and ended...stories begin and then end.
    Well, that is a handful.
    No , we have no control over the Sun will do. Truth.
    Our scientists "Fraying at the edges" What? It's a progression you know, like all science. We know now, so much more than we did pre SDO launch than we could have imagined. We are deciphering coronal heating , and pretty much know the answer now, It was an enigma 25 years ago. Nobody is "Fraying at the edges" They are progressing with the best available information, as the technology and and ability to study this tech improves. Science.
    Lied to? You are going to need to substantiate that. I mean, come on.
    And yes , there is absolutely no doubt that the atmospheric co2 levels have gone past and are effecting global warming, it is a fact, and not up for speculation. And its not just the Cadillac or the coal burning. Its a conglomeration of a myriad things.
    Recent Global warming is being steered by man made influence. That really isn't up for debate anymore. There are number of papers that actually predicted this Solar cycles intensity pretty accurately. Hathaway seems to have been wrong at this point , but he is only one of so many, and many saw this as a bigger cycle than was predicted. Sol is not straining the Narrative. We are just getting better at understanding the physics.
    Reply
  • CircuitBurner
    I accept what your saying.
    It's not like I'm claiming to know if all.
    It's something to consider based on personal experience. The choice of words might be sensationalized a bit.
    The red liquid getting bleached out so quickly on certain days but not on others really peaked my interest.
    It won't be the fault of science if it cannot save us from a fitful star that strips away our atmosphere and changes the appearance of the landscape rather drastically.
    Maybe there's a need to market a new category of sunscreen, like 'extra heavy duty, for those angry sun days...now with chromium!'
    Reply