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Solar cycle 25

Solar Cycle 25 is the current and 25th recorded solar cycle since systematic sunspot observations began in 1755, spanning approximately 11 years of varying solar magnetic activity that influences on . It commenced in December 2019 with a , a period of low sunspot numbers and subdued solar output, as determined by the joint NASA-NOAA Solar Cycle 25 Prediction Panel. Initial forecasts from the 2019 panel anticipated a relatively weak cycle akin to , with a maximum smoothed number of 115 expected around July 2025 (ranging from November 2024 to March 2026). However, activity escalated more rapidly than predicted, with numbers and events surpassing expectations by late 2024. In October 2024, and NOAA announced that had entered its phase, characterized by heightened coverage, frequent solar flares, and coronal mass ejections (CMEs), though the precise peak month remains under evaluation due to the need for retrospective smoothing of data. This maximum is projected to persist for up to another year, gradually declining toward the next around 2030-2031, when 26 is expected to begin. As of November 2025, remains active in its post-peak phase, evidenced by strong X-class flares including those in June 2025 (peaking on June 17 and 19) and more recently in November 2025, such as an X5.1 on November 11 (the strongest of the year) and an X4.0 on November 14, along with associated storms that may indicate a double-peaked maximum; these events potentially disrupt radio communications, GPS signals, and power infrastructure while enhancing global auroras. Notable earlier events include the strongest in two decades on May 10-11, 2024, triggered by multiple CMEs, and an X9.0 flare on October 3, 2024. The cycle's unexpectedly vigorous output, including stronger since 2008, has prompted researchers to investigate underlying mechanisms, as it deviates from long-term trends of declining solar activity. This period coincides with key observations from 's , which completed close solar approaches in 2024 and continues to sample the corona during heightened activity, aiding understanding of solar dynamics and forecasting.

Overview

Start and minimum

Solar Cycle 25 officially began in December 2019, following the that concluded Cycle 24, as determined by the Solar Cycle 25 Prediction Panel using monthly sunspot data from the World Data Center for the Sunspot Index and Long-term Solar Observations (SILSO). The panel identified this minimum based on the 13-month smoothed International Sunspot Number (ISN) falling to 1.8, one of the lowest values recorded in recent cycles, signaling the transition to the new cycle. This minimum period, spanning late 2019, featured exceptionally low sunspot activity, with the Sun frequently spotless for extended periods, reflecting the overall quiet state of solar magnetism. Accompanying this were reduced solar flares and coronal mass ejections, contributing to diminished disturbances. The during this time exhibited a simpler structure, with lower speeds and reduced magnetic complexity, allowing for easier propagation of galactic cosmic rays. Signs of emerging Cycle 25 activity preceded the official minimum date, with observations detecting the first sunspots of reversed polarity—indicative of the new cycle—at mid-latitudes around 30° in both solar hemispheres as early as November 2019. These initial active regions were captured in magnetograms from the Global Oscillation Network Group (GONG), showing the characteristic poleward migration of sunspot zones that defines the onset of a new solar cycle. Supersynoptic maps further corroborated this shift, revealing nascent magnetic flux patterns consistent with Cycle 25's leading polarity emerging from the remnants of Cycle 24.

Duration and end

Solar cycles typically last between 9 and 14 years, with an average duration of about 11 years, as determined by long-term observations of activity and reversals. For Solar Cycle 25, which began in December 2019, experts anticipate a similar length of approximately 11 years based on its progression mirroring that of the preceding Cycle 24. This expectation aligns with historical patterns where cycles of comparable intensity, like Cycle 24, maintained durations around 11 years from minimum to minimum. The projected end of Solar Cycle 25 is around 2030, coinciding with the that will mark the transition to Cycle 26, expected to commence sometime between January 2029 and December 2032. This timeline reflects updated forecasts using nonlinear curve fits to observed numbers and radio data, which indicate a full cycle span of 10 to 13 years from the 2019 minimum. During this minimum, solar activity will decline to low levels, facilitating the onset of the next cycle's rising phase. Several factors influence the duration of Solar Cycle 25, including its observed rising phase, which progressed more rapidly than that of Cycle 24 due to stronger initial activity trends. This quicker ascent, exceeding initial predictions, suggests the cycle may conclude at the shorter end of the typical range, potentially slightly under 11 years. Early indicators for the end include the current phase, reached in 2024, which is anticipated to persist for another year before transitioning to the declining phase around late 2025 or early 2026, as sunspot numbers begin to wane.

Context and Predictions

Comparison to prior cycles

Solar cycles are approximately 11-year periodic variations in the Sun's magnetic activity, driven by the solar process in which convective motions in the Sun's interior generate and regenerate its . This operates through the interaction of and convection, producing a of reversals every 22 years, with the 11-year representing half of that full magnetic oscillation. Solar activity is primarily measured using the International Sunspot Number (ISN), calculated by the formula R = k(10g + s), where g is the number of sunspot groups, s is the number of individual sunspots, and k is a correction factor for observational differences between stations. Over the past century, solar cycle strength, as indicated by maximum numbers, has shown a general declining trend since the peak of cycle 19, which reached a smoothed maximum of 201.3 in 1957. Subsequent cycles followed this pattern: cycle 20 peaked at 196.0, cycle 21 at 164.5, cycle 22 at 158.5, cycle 23 at 180.3, and cycle 24 at a notably low 116.4 in April 2014, representing a roughly 20% decrease per cycle on average since the . This decline aligns with broader observations of reduced solar activity in recent decades compared to the mid-20th century "." Solar cycle 24, which began in December 2008 and ended around December 2019, was one of the weakest cycles in the , with its maximum smoothed number of 116.4 occurring in April 2014—substantially lower than the averages of preceding cycles. Initial forecasts anticipated that cycle 25 would be of similar modest strength to cycle 24, but observations have shown it exceeding those expectations. Cycle 25, which started in December 2019 following the minimum between cycles and 25, has demonstrated a faster rise and higher overall activity in its early years compared to cycle at equivalent points. For instance, by mid-2024—approximately 4.5 years into the cycle—the smoothed monthly number for cycle 25 reached 152.8, representing roughly 68% more spots than the 90.9 recorded for cycle at the same in mid-2013. This quicker ascent and elevated activity mark a departure from the ongoing decline, positioning cycle 25 as stronger than its immediate predecessor and breaking the pattern of weakening cycles observed since cycle 19.

Initial forecasts

In December 2019, the NOAA/NASA/ISES Solar Cycle 25 Prediction Panel released its consensus forecast following meetings that began in , in March 2019. The panel, comprising international solar physicists, synthesized dozens of submitted models to predict a weak cycle comparable to the preceding 24. This expectation stemmed from observations of a prolonged and deep between cycles 24 and 25, forecasted to occur around April 2020 with an uncertainty of ±6 months. The core prediction called for a maximum smoothed sunspot number (SSN) of 115, peaking in July 2025 with a timing uncertainty of ±8 months. Across the individual models considered by the , the forecasted maximum SSN varied widely, ranging from 65 to 233, reflecting diverse approaches and inherent uncertainties in solar forecasting. The consensus emphasized a moderate overall intensity, with the cycle's rise phase anticipated to be gradual, leading to a lower peak activity level than stronger historical cycles. These initial estimates relied on established precursor techniques, including assessments of polar strength at minimum, which serve as indicators of the subsequent cycle's amplitude, and counts of polar faculae as proxies for emerging magnetic activity. Additionally, dynamo models simulating the Sun's internal magnetic were incorporated to project cycle evolution. The panel anticipated fewer intense geomagnetic storms relative to Cycle 24, implying reduced impacts during the .

Revised estimates

As observations of Solar cycle 25 accumulated, forecasters revised their predictions upward, reflecting a more rapid and intense ascent than the initial estimate of a maximum smoothed sunspot number (SSN) of 115 in July 2025. By 2021 and 2022, sunspot activity had ramped up much faster than anticipated, prompting early indications of stronger performance. In December 2023, NOAA issued an updated forecast, projecting the cycle's peak between January and October 2024 with a maximum smoothed SSN ranging from 137 to 173, acknowledging the quicker rise observed in prior years. These adjustments continued into 2023, with some models raising the expected maximum to around 140-160 SSN based on accumulating data. By 2024, revisions confirmed the peak occurring in with a smoothed SSN of 160.8, while the unsmoothed monthly maximum reached 216 in . These changes stemmed from elevated production rates—significantly higher than in , particularly in the cycle's fifth year—and a corresponding increase in activity that exceeded early projections. As of November 2025, holds that Solar cycle 25 is overall stronger than initially predicted, with the maximum phase having passed but high activity levels suggesting a potential extension of elevated output into 2026 before a clearer decline.

Activity Progression

Sunspot trends

Sunspot numbers in Solar Cycle 25 are primarily tracked using the International Sunspot Number (ISN), with smoothed 13-month monthly averages calculated by the Solar Influences Data Analysis Center (SILSO) at the Royal Observatory of Belgium, and daily spot counts compiled by SILSO and NOAA's Space Weather Prediction Center. These metrics provide a standardized measure of solar activity, focusing on the number and size of sunspots visible on the solar disk. The rising phase from 2020 to 2023 exhibited marked year-over-year growth in activity compared to 24. By October 2024, overall levels in Cycle 25 were about 40% higher than in Cycle 24 at the same cycle stage, indicating a more vigorous progression. Key observational data underscore this intensification: the 2024 yearly average smoothed number (SSN) reached approximately 150, surpassing initial forecasts and reflecting heightened magnetic complexity. Early 2025 data indicate a decline, with the October 2025 monthly mean SSN at 114.6, yet levels remain elevated compared to Cycle 24's declining phase. However, as of mid-November 2025, daily numbers have shown a resurgence, averaging around 100, suggesting ongoing variability. Emerging trends suggest a potential double-peaked structure in the cycle, driven by hemispheric asymmetries where the has shown leading activity in sunspot emergence during the ascent, with recent November 2025 activity providing further evidence of a possible second peak. This pattern aligns with historical cycles exhibiting prolonged maxima, though confirmation awaits further decline in smoothed values.

Peak phase

The peak phase of Solar cycle 25, or , is defined as the period encompassing the highest values of both unsmoothed and smoothed numbers (SSN), with the maximum typically confirmed retrospectively once sufficient data establishes the trend reversal. The unsmoothed monthly SSN, which reflects raw daily observations averaged over a month, reached its cycle high of 216 in August 2024. Meanwhile, the smoothed SSN—a 13-month running average used to filter short-term fluctuations and identify the true maximum—peaked at 160.8 in October 2024, marking the official declaration of by and NOAA in October of that year. During this peak, solar activity exhibited elevated levels across multiple indicators, underscoring the cycle's intensity. The 10.7 cm radio , a key measure of solar emission in the microwave spectrum that correlates with overall magnetic activity, achieved a smoothed monthly maximum of 203.6 solar flux units (sfu) in September 2024, surpassing the peak of 23. This period also saw a proliferation of complex active regions on the Sun's surface, such as AR3664 in May 2024, which produced the cycle's most powerful X-class flares to date and contributed to heightened eruptive behavior leading into the maximum. Overall, the sunspot rise culminating in this phase built on progressive increases observed earlier in the cycle. By late 2025, Solar cycle 25 continues in its post-peak phase, with monthly SSN values having declined from the 2024 maxima but showing signs of resurgence. For instance, in November 2025, active regions have generated multiple X-class solar flares, including an X5.1 on November 11 and an X4.0 on November 14, indicating persistent magnetic complexity and potential for a double-peaked maximum. This transitional phase aligns with historical patterns where solar maximum can extend variably before a sustained decrease toward minimum.

Key Events

2020

Solar cycle 25 officially began in December 2019, transitioning from the deep minimum of the previous cycle into a period of gradually increasing activity. Throughout 2020, solar activity remained low, characterized by sporadic groups primarily emerging in the southern hemisphere, signaling the initial rise of the new cycle. These early were small and short-lived, with the smoothed sunspot number averaging below 5 for much of the year, well below levels seen in prior cycles' ascending phases. The year's first notable solar flares occurred on May 29, marking the onset of flaring activity in cycle 25 with C-class events, followed immediately by the cycle's initial M-class flare, an M1.1 eruption from a newly formed . This event ended a prolonged quiet lasting over 900 days without M-class or stronger flares. Activity escalated modestly toward year's end, with active region AR2781—a large sunspot group in the —producing multiple C-class in early . The strongest flare of 2020 followed on November 29, an M4.4 from an just behind the southeastern limb (later designated AR2786), which also generated a . This late-year CME reached on December 10, impacting the and producing a sudden detected by ground magnetometers, along with minor geomagnetic disturbances rated at G1 (minor) levels. No significant auroral displays or disruptions to were reported, consistent with the weak orientation of the .

2021

In 2021, solar activity during Solar Cycle 25 continued its upward trajectory in the rising phase, marked by a growing number of and associated phenomena that signaled the cycle's intensification. The year saw the emergence of the first X-class on July 3, when AR2838 produced an X1.59 event that peaked at 14:29 UTC, causing radio blackouts over the sunlit side of and a rare magnetic crochet effect in the . This flare represented a significant escalation from prior C- and M-class events, highlighting the increasing potency of sunspot regions as the cycle progressed. Throughout 2021, multiple M-class flares erupted from various active regions, contributing to heightened solar radio emissions and occasional coronal mass ejections (CMEs) that began to interact with . One such CME from an M1.4 on October 9 arrived at on October 12, triggering a (moderate) with a index of 6, which enhanced auroral activity at higher latitudes. The most intense event of the year occurred in early , when a series of CMEs from late October activity—stemming from active regions like AR2887—impacted on November 3-4, producing the first G4 (severe) of Solar Cycle 25 with a Kp index reaching 8. This storm, characterized by high-speed speeds exceeding 700 km/s, expanded the auroral oval dramatically, making visible at mid-latitudes across northern U.S. states, , and parts of . The event also posed risks to operations and power grids due to induced geomagnetically currents.

2022

In 2022, Solar Cycle 25 continued its ascending phase with moderate solar activity, marked by a noticeable increase in the number of sunspot regions, particularly in the northern solar hemisphere, though overall output remained subdued relative to the cycle's subsequent intensification. A prominent event was an X1.3-class that erupted on March 30 from Active Region 2975, near the Sun's western limb; this flare, peaking at 17:37 UTC, triggered a that arrived at the following day, resulting in a G1 (minor) despite initial forecasts for stronger conditions. Later that spring, on April 20, 2992—positioned just beyond the southwest solar limb—produced the cycle's strongest flare to date, an X2.2-class event peaking at 03:57 UTC, which caused strong radio blackouts across Earth's sunlit side but had limited geoeffective consequences due to its off-disk location. These isolated X-class flares highlighted emerging complexity in active regions, yet the year's geomagnetic disturbances were fewer and milder than in prior or later periods of the cycle.

2023

In 2023, Solar Cycle 25 exhibited intensifying activity, marked by severe geomagnetic storms and powerful solar flares that highlighted the cycle's approach toward its maximum phase. Early in the year, a G4 (severe) geomagnetic storm occurred on March 23-24, triggered by a coronal mass ejection (CME) from an earlier solar event, leading to widespread auroral displays visible as far south as New Mexico in the United States. This event was the second G4 storm of the cycle, underscoring the increasing solar influence on Earth's magnetosphere. Activity escalated further with another G4 storm on April 23-24, resulting from a CME that arrived at Earth following a solar eruption on April 21; this storm produced vivid auroras across northern latitudes and into mid-latitude regions, including parts of the United States and Europe. These storms disrupted high-frequency radio communications and highlighted the growing potential for space weather impacts as the cycle progressed. Toward the end of the year, sunspot region AR3514 produced two significant X-class flares, signaling heightened solar explosivity. On December 14, an X2.87 flare erupted from AR3514, peaking at 17:02 UTC and generating one of the strongest solar radio bursts ever recorded, which caused widespread radio blackouts across Earth's sunlit side. Just over two weeks later, on December 31, sunspot region AR3536 unleashed an X5.0 flare—the strongest of Solar Cycle 25 up to that point—peaking at 21:55 UTC and further disrupting radio communications globally. These December events from AR3514 and AR3536 exemplified the cycle's ramp-up, with the X2.87 flare's radio emission standing out for its exceptional intensity.

2024

In 2024, Solar Cycle 25 reached its maximum phase, characterized by heightened solar activity including some of the most powerful X-class flares observed in the cycle to date. This year saw multiple intense eruptions from large active regions, leading to significant events that produced widespread geomagnetic storms and auroral displays visible at unusually low latitudes. Early in the year, on February 9, Active Region 3590 produced an X3.4-class , one of the strongest up to that point in the cycle, accompanied by a (CME) that triggered a G2 (moderate) . Just two weeks later, on February 22, the same region unleashed an X6.3 flare, the most energetic detected in Solar Cycle 25 at the time, which ionized Earth's upper atmosphere and caused temporary radio blackouts across the Pacific region. These events highlighted the escalating intensity as the cycle approached its peak. Activity intensified dramatically in May with the emergence of 3664 (NOAA designation AR13664), one of the largest sunspot complexes of the cycle, spanning over 150,000 kilometers in size and containing numerous magnetic knots prone to reconnection. On May 14, AR3664 erupted in an X8.7 , ranking among the top flares of the cycle and producing a fast CME that contributed to subsequent geomagnetic disturbances. Six days later, on May 20, the region—now rotated to the Sun's farside—emitted an X12 , the strongest of Solar Cycle 25, detected by instruments like those on the spacecraft; although Earth-directed effects were limited due to its position, the event released high-energy particles that impacted Mars, causing planet-wide auroras observed by NASA's rovers. These May flares were part of a barrage from AR3664 that included several other X-class events, underscoring the region's hyperactive nature. Later in the year, October brought further peaks in activity, with Active Region 3842 producing an X7.1 flare on October 1 and an X9.0 flare on October 3—the latter briefly holding the title of the cycle's strongest Earth-visible flare before later events. Solar activity crested around August and October, aligning with smoothed sunspot number maxima exceeding 150. The flares and associated CMEs throughout 2024 drove multiple severe geomagnetic storms, including G4 (severe) events in March, May, August, and October, which expanded auroral ovals to mid-latitudes across North America, Europe, and even parts of the Southern Hemisphere. For instance, the May 10-11 storms, fueled by CMEs from AR3664, reached G5 (extreme) levels—the strongest since 2003—resulting in vivid auroras visible as far south as Mexico and Florida, along with minor disruptions to power grids and satellite operations. Similarly, the October 10-11 G4 storm, linked to the AR3842 flares, produced auroras over northern California and Alabama, with potential impacts on high-frequency radio communications. These storms exemplified the cycle's space weather impacts during its zenith.

2025

In 2025, Solar Cycle 25 entered a post-peak phase following its maximum activity in late 2024, characterized by declining but still elevated levels of solar flares and numbers compared to the prior year. According to data from the Solar Influences Data Analysis Center (SIDC), the cycle maintained notable activity, with multiple M- and X-class flares recorded throughout the year, though at a reduced frequency from the 2024 peak. The top solar flares of 2025 included an X2.7 event in May and several X1- to X2-class eruptions, underscoring the cycle's lingering intensity despite the overall downward trend. A significant X-class solar flare erupted from the Sun on January 4, 2025, peaking at 7:48 a.m. ET and classified as an X1.85 event, which highlighted early-year activity. This flare, originating from an on the solar disk, contributed to disruptions in polar regions but did not produce a major (CME) directed toward Earth. In June 2025, activity remained notable with strong X-class flares on June 17 and June 19, peaking during periods of heightened complexity. These events caused radio blackouts, potential GPS signal disruptions, and enhanced auroral displays at high latitudes, aligning with the cycle's post-peak vigor. Activity intensified again in , with two powerful X-class flares occurring on November 4, 2025—the first such events since —triggering widespread radio blackouts across the and Pacific regions. These flares, estimated at X1.1 and X1.8 magnitudes, emanated from AR4274 and disrupted high-frequency communications for up to an hour in affected areas. In the ensuing days, multiple CMEs associated with these and preceding M-class flares began impacting on November 5-6, enhancing geomagnetic activity and producing vivid auroras visible at mid-latitudes. The (NOAA) forecasted potential G4-level geomagnetic storms during this period, with Kp indices reaching 7-8, leading to widespread auroral displays across and . Later in November 2025, activity escalated further with an X5.1 on from AR4274—the strongest of the year—causing extensive radio blackouts over and , followed by a G4 . On November 14, an X4.0 from the same region added to the month's intensity, contributing to ongoing effects as of November 19, 2025.

Impacts

Space weather effects

Solar Cycle 25 has produced several severe geomagnetic storms, classified as G4 on the NOAA scale, which have extended auroral displays to unusually low latitudes, including sightings in Texas during events in March and May 2024. These storms arise from coronal mass ejections (CMEs) interacting with Earth's magnetosphere, inducing rapid changes in the geomagnetic field that energize particles in the auroral ovals. G4-level disturbances pose risks to power grids by generating geomagnetically induced currents (GICs) that can overload transformers, potentially causing voltage instability and outages in vulnerable high-latitude infrastructure. X-class solar flares during this cycle have triggered widespread radio blackouts, disrupting high-frequency (HF) communications essential for and maritime operations. For instance, two X-class flares on November 4, 2025, caused blackouts over the and Pacific regions, ionizing the and absorbing radio signals for up to an hour. In mid-November 2025, produced its strongest flare of the year, an X5.1-class event on November 11, along with multiple other X-class flares, leading to additional radio blackouts across , , and other regions. These events highlight the cycle's elevated flare activity, which scatters electrons in the D-layer of the , leading to signal attenuation particularly on the sunlit side of . CMEs from Solar Cycle 25 have increased atmospheric density in low-Earth , enhancing drag on satellites and accelerating . In 2022, a minor led to the reentry of 38 satellites due to heightened drag at 210 km altitude, underscoring vulnerabilities for constellation operators during the cycle's rising phase. Similarly, the May 2024 geomagnetic storm amplified thermospheric density, affecting LEO satellite maneuvers and necessitating frequent orbit boosts. The November 2025 geomagnetic storm, the strongest of the year with a Dst index of -225 nT, further increased drag risks and prompted orbit adjustments for satellites. Radiation from (SEPs) during these events poses acute hazards to astronauts, with exposure limits for Mars missions strained by cycle 25's frequent SEPs, potentially exceeding 300 mSv for a round trip without adequate shielding. The peak phase of Solar Cycle 25 has broadened aurora viewing opportunities, making vivid displays visible farther south than typical, as seen in multiple G4 events from 2023 to 2025, including auroras reaching Florida during the November 2025 storm. This enhanced activity stems from stronger solar wind interactions with Earth's magnetosphere, energizing auroral particles over expanded regions.

Scientific implications

The unexpected strength of Solar Cycle 25, which exceeded initial forecasts of a weak or moderate cycle similar to Cycle 24, has significant implications for dynamo models that underpin long-term activity predictions. Early ensemble predictions based on flux transport simulations anticipated a maximum number of around 115, aligning with a trend of declining solar activity observed in recent cycles. However, updated observations revealed a peak smoothed number of 160.9 in October 2024, challenging these models by highlighting potential underestimations in meridional circulation and polar field recovery rates during the . This discrepancy prompts refinements in theories, particularly in incorporating nonlinear effects and elements to better capture cycle-to-cycle variability, as evidenced by comparative analyses of physics-based forecasting approaches. Key observations during Cycle 25, including the completion of polar magnetic field s and enhanced heliospheric imaging, provide critical data for validating solar models. The northern hemisphere's polar field reversal occurred between June and November 2024, centered around August, while the southern hemisphere's reversal occurred in early 2025, centered around February, marking the transition to the cycle's declining phase and confirming the overall process typically spanning one to two years. Complementing these, missions like Solar Orbiter's Heliospheric Imager (SoloHI) have delivered unprecedented wide-field views of the inner , capturing electron-scattered light from structures and interplanetary shocks during the rising phase, which reveal heightened propagation and warping beyond pre-cycle expectations. These insights underscore the cycle's vigor and aid in calibrating surface flux transport models for more accurate magnetic evolution tracking. More robustly, the cycle has driven improvements in space weather predictions via NOAA's Space Weather Prediction Center panels, which incorporated real-time and radio flux data to revise forecasts upward, enhancing probabilistic alerts for geomagnetic storms and events with reduced uncertainty bands. These advancements stem from nonlinear curve-fitting techniques updated monthly, providing better statistical estimates for operational decision-making. Data from longstanding missions like and SDO continue to inform predictions for 26, expected to commence between January 2029 and December 2032, by supplying high-resolution magnetograms and imagery that track evolution and axial dipole moments into the upcoming minimum. These observations, spanning from Cycle 24's end through Cycle 25's peak, enable precursor-based forecasts that could anticipate Cycle 26's amplitude more reliably, potentially reversing the recent weakening trend if polar field strengths recover robustly.

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