False color image of the sun in the Extreme Ultraviolet part of the spectrum. Bright Pink plumes of gas show the 1.1 magnitude X-class Solar Flares associated with two separate sunspot groups and originate from deep in the solar interior with gas temperatures above 2.3 million Kelvin. The composite image (and corresponding video) was produced from three separate wavebands at 9.4 nanometers, 19.3 and 33.5 nanometers wavelength. Click the image to download the original 4 Mb image (2048 x 2048 pixels).
Increasing magnitude and frequency of solar flares heralds approaching solar maximum
Using data, video and imagery from the Solar Dynamics Observatory, we’ve produced a video featuring two 1.1 magnitude X-Class solar flares (video link at foot of page). As part of its mission, the Solar Dynamics Observatory observes the sun in the extreme Ultra Violet region of the spectrum. These observations show regions of the solar interior in the million-degree range.
A Remarkable Star
We orbit a remarkable star, remarkable in many ways. Many stars with the same classification as our sun are quite variable, variable in ways that would make life impossible on a hypothetical earth with a similar orbit as our home planet. Our sun is relatively benign in this regard, but it does exhibit a mild variability in energy output with an 11-year cycle. Every 11 years, the sun’s energy output peaks and then sinks to a minimum 5.5 years later. This mild variation is well understood and has been observed and scientifically documented for over 175 years.
The first systematic scientific observations of sunspots were made by Galileo and other astronomers in the early 17th century, (c 1610). However, the cyclical nature of sunspots, leading to the identification of the 11-year solar cycle, was first noted by Samuel Heinrich Schwabe in 1843 after 17 years of observations.
Historical records, including those from ancient civilizations and medieval scholars, suggest that sunspots and solar activity were noticed and described long before the 17th century, though these observations were not systematic or understood in the context of a solar cycle.
Coincidentally, with the astronomical beginning of spring this year on the vernal equinox, a series of M and X class flares has occurred, heralding the approach of the solar maximum in mid-2025.
Recent solar activity, illustrating the variations in solar output since 2010. The image links to the NOAA web portal that chronicles the 11-year cycle since 1750.
Solar Flares
Million-degree gas produces X-rays. Solar flares, short-lived and temporal, are often associated with sunspots, cooler regions of the sun’s photosphere resulting from magnetic anomalies that cause a breach in energy transmission from the solar interior. Solar flares emit radiation in the visible, ultraviolet, x-ray and gamma ray regimes of the electromagnetic spectrum. The X-rays and gamma rays, being of the highest energy, are associated with localized, super-heated gas. Solar flares are thus categorized according to a logarithmic x-ray intensity scale, from A being the weakest to X being the strongest.
The measured flux at the Earth/Sun distance is
X = 1.0×10-4 (Watts per sq. meter)
M = 1.0×10-5 (Watts per sq. meter)
C = 1.0×10-6 (Watts per sq. meter)
B = 1.0×10-7 (Watts per sq. meter)
A = 1.0×10-8 (Watts per sq. meter)
Sunspots as a Bellwether of Solar Activity
Sunspot numbers are an indicator of internal solar activity; increased sunspot numbers are an indicator of increased solar output and activity. Our sun has an 11-year activity cycle. Currently, solar activity is on the rise and will peak in the summer of 2025. Considering the sun’s nature as a giant, roiling, super-heated, self-regulating ball of plasma that is modeled as a fluid we expect certain irregularities in the sun’s behavior and activity, aspects of solar dynamics that give rise to solar storms and outbursts, phenomena whose frequency of occurrence are directly linked to the solar cycle.
Solar Flares vs. Coronal Mass Ejections
While they are both indicative of a dynamic and changing environment, they are, at the same time, quite different in nature, yet have certain commonalities. A CME is a huge bubble of magnetized gas that is ejected into space, an event that may take several hours to complete. A solar flare is far more temporal and short-lived and much smaller in scale. They both have associated with them streams of high-energy protons, electrons and alpha particles (helium nuclei). Hence, the large difference between solar flares and CMEs is mostly one of size. Both can occur together but can also occur in the absence of the other.
Sources
https://www.swpc.noaa.gov/products/solar-cycle-progression
https://espo.nasa.gov/content/Solar_radiative_output_and_its_variability_evidence_and_mechanisms
A quick, interactive web-based version of Stellarium is available here Tonight's Sky. When you launch the application, it defaults to north-facing and your location (on mobile and desktop).
Astronomy For Change: https://astronomyforchange.org
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