NASA’s Solar Dynamics Observatory has spotted a huge hole in the sun’s outer atmosphere, appearing as a dark shadow across the surface. While it might seem alarming, the phenomenon in this case is no cause for worry; according to NASA, this particular coronal hole was likely to blame for the breathtaking auroras seen earlier this month.
SDO observed the huge hole from November 7-9, during which the opening sent high-speed solar wind streaming toward Earth. In the striking ultraviolet image, the hole is immediately clear – it stretches along the top and sides of the sun like a dark inkblot.
‘Coronal holes are magnetically open areas on the Sun that allow high-speed solar wind to gush out into space,’ NASA explains. ‘They always appear darker in extreme ultraviolet. This one was likely the source of bright aurora that shimmered for numerous observers, with some reaching down even to Nebraska.’
While these holes can appear at any time and place on the sun, they’re more common around solar minimum, according to the NOAA’s Space Weather Prediction Center. And, scientists say solar minimum is approaching.
During this time, certain types of activity such as sunspots and solar flares will drop – but, it’s also expected to bring the development of long-lived phenomena including coronal holes.
According to NASA, solar minimum could also enhance the effects of space weather, potentially disrupting communications and navigation systems, and even causing space junk to ‘hang around.’ The sun follows roughly an 11-year cycle. While sunspots were relatively high back in 2014, they’re now heading toward a low point expected in 2019-2020, according to NASA.
‘This is called solar minimum,’ said Dean Pesnell of NASA’s Goddard Space Flight Center in Greenbelt, MD, earlier this year. ‘And it’s a regular part of the sunspot cycle.’
 |
| In this time, certain types of activity, such as sunspots and solar flares will drop – but, it’s also expected to bring the development of long-lived phenomena including coronal holes |
The change, however, doesn’t mean that activity ceases altogether, the expert explains. Instead, different types of events tend to take hold. For instance, ‘during solar minimum we can see the development of long-lived coronal holes,’ Pesnell says. ‘We see these holes throughout the solar cycle, but during solar minimum, they can last for a long time – six months or more.’
These are areas in the sun’s atmosphere where the magnetic field opens up, sending streams of solar particles into space. When the resulting solar wind hits Earth’s magnetic field, it can cause space weather events including geomagnetic storms, auroras, and disruptions to communications and even satellites.
According to NASA, it can even effect the space debris floating around Earth. The drag experienced as objects circle Earth helps to keep low-Earth orbit clean, the space agency explains.
This is the result of heating by ultraviolet radiation from the sun. When solar minimum occurs, the upper atmosphere cools down, reducing the drag. And, NASA explains, this means space junk is more likely to linger.
‘During solar minimum, the sun’s magnetic field weakens and provides less shielding from these cosmic rays,’ Pesnell says. ‘This can pose an increased threat to astronauts travelling through space.’
Via DailyMail