Peering into the Heart of the Sun with The SDO (with video)

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This composite view of the sun in visible and EUV (Extreme UltraViolet) light illustrates the dynamism of the sun, unseen in visible light but revealed in the extreme ultraviolet. Note the coronal streamers and loops, the “Bridges” between sunspot groups, where the super-heated plasma follows the twisting and turning of the sun’s magnetic lines of force. Note: this image links to the accompanying video.

The Solar Dynamics Orbiting Observatory continuously monitors the sun in 10 wavebands, mostly in the extreme ultraviolet part of the spectrum. These UV emissions correspond to super-heated gas in the million-degree range. Our full-featured video is linked below.

When observing the sun in visible light, it seems benign enough and is something we’re used to seeing on our home star. What we don’t see, is what’s actually happening in the solar interior, what is causing these super sunspot regions, solar flares, coronal loops and coronal mass ejections (CMEs).

Coronal loops and Sunspots

This excerpt from the video shows a well-defined coronal loop visible on the western limb (right side) of the sun.

Coronal loops occur when the sun’s electrically charged, super-heated gas and plasma follow the sun’s magnetic lines of force, often between one sunspot and another. This is not a random occurrence. Sunspots, as described below, represent a breach in the solar photosphere and are caused by these magnetic lines of force. Coronal loops generally occur during periods of increased solar activity.

Sunspots represent slightly cooler regions of the solar photosphere where the hot columns of gas, convecting up from the solar interior, are interrupted by twisting and overlapping magnetic lines of force. This effect is observed in the video and the accompanying still above. Their frequency and number are a direct bellwether of solar activity.

In this video of the visible-EUV composite, the sun is very active. A direct correspondence can be seen between the active, flaring regions observed and the large “Super Sunspot” groups visible on the solar photosphere, the flaring regions and the Coronal Loops.

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)

Solar Flares vs. Coronal Mass Ejections

While they are both indicative of a dynamic and changing solar environment, they are, at the same time, quite different in nature, yet have certain commonalities. A CME is a huge bubble of superheated 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. They both can disrupt telecommunications and have been known to disable the power grid (The Carrington Event, 1859).

Solar Cycle 25

August 2024 has seen largest sunspot number of any month in the current Solar Cycle, cycle 25, and since September 2001, 23 years ago!

The Solar Cycle peaks every 11 years and it is being suggested that the maximum for the current solar cycle is occurring now. Previously, it was predicted to occur next Summer but, based on observed activity and the published sunspot counts for August, it may be occurring now and may be among the strongest on record.

This activity, with solar flares and Coronal Mass Ejections, gives rise to the spectacular Aurorae recently observed, observed as far south as Alabama and Northern California.

Technical Details about the video

Video via NASA’s orbiting Solar Dynamics Observatory: https://sdo.gsfc.nasa.gov from 9/1/2024 through 9/7/2024 (23:59:59) inclusive.

EUV wavebands observed: 9.4 nanometers (red), 19.3 nanometers (blue), and 33.5 nanometers (green). One nanometer is one billionth of a meter (1 x 10^-9) meter. These wavebands correspond to super-heated gas in the million-degree range that originates deep in the solar interior.