Sunday, November 23, 2014

Largest Sunspot in 24 Years Returns for 2nd Month

By Glenn A. Walsh
Reporting for SpaceWatchtower

The largest sunspot on our Sun, in nearly a quarter-century, is now rotating back into view for the second month in a row. Actually, it attained the largest sunspot distinction last month, while it appears somewhat smaller this month.

Last month, Sunspot Active Region 2192 (AR-2192)  was more than ten times the size of the Earth, when it rivaled the October 23 Solar Eclipse in prominence. This month, the sunspot, re-numbered AR-2209, is about one-third its original size.

However, last month Sunspot AR-2192 produced six major solar flares, called X-Flares (the strongest magnitude of solar flares), and also some radio blackouts (R-1 to R-3) in late October. The area of the Sun with Sunspot AR-2209 continues to be active, with several intense M-class Solar Flares. A large M5.7-class Solar Flare peaked early last Monday morning (November 17)  at 12:48 a.m. EDT / 5:48 UTC. So, scientists continue to monitor this sunspot region, to watch for additional solar activity that could be directed towards Earth.

Such solar activity as solar flares and Coronal Mass Ejections (CMEs) can adversely affect radio communication, satellites and GPS systems, and in severe cases can disrupt electrical grid systems. In March of 1989, a large solar storm, known as a geomagnetic storm, caused power failures over large sections of the Canadian province of Quebec, while less severe storms occurred in 1921 and 1960 when there were widespread reports of radio disruptions.

However, the largest effects felt on Earth occurred, at the very beginning of the electrical age, in the first couple of days of September of 1859, when ground-based magnetometers recorded one of the largest geomagnetic storms ever. This is known as the "Carrington Event" for English Amateur Astronomer Richard Carrington, who made among the first observations of a major solar flare on September 1 that is associated with a huge CME that led to telegraph system failures, electric shocks to telegraph operators, and even fires in some telegraph offices. The Carrington Event also resulted in Aurora observations throughout the world, particularly in lower latitude locations unaccustomed to such displays.

This-past April, NASA announced that an event possibly similar to the Carrington Event may have missed the Earth in 2012. On 2012 July 23, NASA's STEREO-A spacecraft recorded a huge CME that sped four times faster from the Sun than a normal solar eruption. Fortunately, the Earth was not in the path of this CME, which Daniel Baker of the University of Colorado claimed "might have been stronger than the Carrington Event itself," as was the spacecraft.
The Spaceweather Prediction Center of the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA, which also administers the National Weather Service), commented on Sunspot AR-2209 on November 16:

Although not quite as impressive in size, it is still a large region with a complex magnetic structure, and is capable of producing even more X-ray flare activity. It has already produced two M-class flares (R1-Minor radio blackouts), and has only been on the Earth-side of the sun for a couple of days. And, unlike its previous transit, it appears to have coronal mass ejections (CMEs) associated with some of its flare activity.
This could mean an increased probability for elevated geomagnetic storming. Forecasters will be monitoring this region closely over the next week and a half as it makes its way across the visible disk.

Sunspots and large sunspot regions are huge magnetic storms on the visible surface of the Sun's photosphere, some as large or larger than the planet Earth, such as the one now visible on the Sun. Sunspots appear darker than the rest of the Sun's photosphere, often with a black or brown coloration, because they are cooler than the rest of the photosphere, due to convection currents in the sunspot. When a sunspot reaches the Sun's surface, the convection is then inhibited resulting in less heat and consequently lower temperature.

However, sunspots are not cold or even cool. It is the contrast between the cooler sunspots ( at ~ +2,700 to +4,200 degrees Celsius) and the hotter photosphere (at ~ + 5,500 degrees Celsius) that makes the sunspots appear dark. A sunspot, if it could be removed from the Sun, is so hot that it would appear as a mini-star on its own!

The Sun is not solid like the Earth, and it is composed of hot plasma interwoven with magnetic fields. Like the Earth, the Sun does rotate on its axis, and because this rotation is uneven throughout the solar disk, the magnetic fields twist and turn, and when these magnetic fields break the solar surface the result is a sunspot. This is somewhat analogous to how the Earth's axial rotation affects weather systems in our atmosphere. The intense and twisted magnetic fields, which form the sunspot region, are usually the source of solar flares and CMEs. 

Sunspots, particularly the larger ones, sometimes, but not always, appear in pairs (a "leader" first develops, followed by a "follower" or "trailer," with respect to the direction of solar rotation), each with opposite magnetic polarity. The dark central portion of a sunspot is known as the umbra, while the lighter, outer portion of the sunspot is known as the penumbra (a similar naming convention is used for lunar eclipses).

Sunspots usually come in cycles of approximately eleven years (and could actually run anywhere from nine to fourteen years in length). Many more sunspots, often along with solar flares and CMEs, are seen around the peak of the sunspot cycle or Solar Maximum, while many fewer sunspots are seen during the lull portion of the cycle or Solar Minimum. A historical Solar Minimum, known as the Maunder Minimum, occurred from approximately 1645 to 1715, when sunspots were very rare according to solar observers of that time period.

Scientists say the current sunspot cycle, Solar Cycle 24, has reached the Solar Maximum this year, but is one of the lowest Solar Maximums in recent history. However, Sunspot AR-2209 and the 2012 CME are examples of what can happen even during a low Solar Maximum.

Similar "starspots" have been indirectly observed on stars beyond our solar system.

Pittsburgh's original Buhl Planetarium and Institute of Popular Science, which observed its 75th anniversary on October 24, regularly showed sunspots to the public, weather permitting (1941 to 1991), using a rather unique 10-inch Siderostat-type Refractor Telescope. The polar-aligned and horizontally mounted telescope, fed by a first-surface mirror on a sidereal coleostat or siderostat unit driven by a clock-drive motor, projected the solar image on a large projection screen in a heated observing room. Two small circles inscribed on the screen (depicting the size of the Earth) allowed the public to compare the size of sunspots to the size of the Earth, when the telescope used a 65-power or 80-power eyepiece to project the image of the Sun.

More on Sunspots: Link >>> 

More on Solar Flares: Link >>> 

More on Coronal Mass Ejections: Link >>>

More on the Sun: Link >>> 

More on the Carrington Event: Link >>> 

More on the Maunder Minimum: Link >>>

More on Solar Observing at Pittsburgh's original Buhl Planetarium and Institute of Popular Science:
Link >>>

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Colossal Sunspot Growing Fast, Solar Storms Possible (2013 Feb. 21):

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Sunspot AR1654 Getting Bigger w/ Solar Flare (2013 Jan. 12):

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Enormous Sunspot Could Lead to Solar Flares (2012 May 9):

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70th Anniversary: Buhl Planetarium Observatory: (2011 Nov. 19):

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November 21 photograph of  Sunspot AR-2209, the largest sunspot in 24 years!
(Image Source: Alfredo Vidal)

Source: Glenn A. Walsh, Reporting for SpaceWatchtower, a project of Friends of the Zeiss.

2014: 75th Year of Pittsburgh's Buhl Planetarium Historic Zeiss II Planetarium Projector at Pittsburgh's original Buhl Planetarium and Institute of Popular Science.

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