A CARRINGTON-CLASS SUNSPOT: Sunspot AR3664 has grown so large, it now rivals the great Carrington sunspot of 1859. To illustrate their similarity, we've added Carrington's famous sketch (to scale) to a NASA photo of today's sun:
Sprawling almost 200,000 km from end to end, AR3664 is 15 times wider than Earth. You can see it through ordinary eclipse glasses with no magnification at all. Moreover, it is easy to project an image of this sunspot onto the sidewalk or a white screen just as Carrington did in the 19th century.
Carrington's sunspot is famous because in August and Sept. 1859 it emitted a series of intense solar flares and CMEs. The resulting geomagnetic storms set fire to telegraph offices and sparked auroras from Cuba to Hawaii. The "Carrington Event" has since become a touchstone of space weather in pop culture, with recent headlines stoking fears of an "internet apocalypse" if it repeats.
Indeed, it could repeat. Studies suggest that Carrington-class storms occur once every 40 to 60 years, so we're overdue. CMEs currently en route to Earth will not cause a new Carrington Event; they are puny compared to the CMEs of 1859. Nevertheless, it would be wise to keep an eye on this growing active region while Earth is in its strike zone.
GEOMAGNETIC STORM WATCH--UPGRADED: This weekend's geomagnetic storm watch has been upgraded from G2 (Moderate) to G3 (Strong). Why? Because giant sunspot AR3664 keeps hurling CMEs toward Earth. There are now at least 3 storm clouds heading our way. See how many you can count in this 24-hour movie from the Solar and Heliospheric Observatory:
A NOAA forecast model predicts the first CME will reach Earth late on May 10th. Additional CMEs will arrive on May 11th and possibly 12th. Minor to strong geomagnetic storms could occur on all three days, with auroras potentially visible at mid-latitudes in Europe and the USA.
The video below explains the situation in about 3 minutes:
