On July 5, 2017, NASA’s Solar Dynamics Observatory
watched an active region — an area of intense and complex magnetic fields —
rotate into view on the Sun. The satellite continued to track the region as it
grew and eventually rotated across the Sun and out of view on July 17.
With their complex magnetic fields, sunspots are often
the source of interesting solar activity:
During its 13-day trip across the face of the Sun, the
active region — dubbed AR12665 — put on a show for NASA’s Sun-watching
satellites, producing several solar flares, a coronal mass ejection and a solar
energetic particle event. Watch the video below to learn how NASA’s satellites
tracked the sunspot over the course of these two weeks.
Such sunspots are a common occurrence on the Sun, but
less frequent at the moment, as the Sun is moving steadily toward a period of
lower solar activity called solar minimum — a regular occurrence during its
approximately 11-year cycle. Scientists track such spots because they can help
provide information about the Sun’s inner workings. Space weather centers, such
as NOAA’s Space Weather Prediction Center, also monitor these spots to provide
advance warning, if needed, of the radiation bursts being sent toward Earth,
which can impact our satellites and radio communications.
On July 9, a medium-sized flare burst from the sunspot,
peaking at 11:18 a.m. EDT. Solar flares are explosions on the Sun that send
energy, light and high-speed particles out into space — much like how
earthquakes have a Richter scale to describe their strength, solar flares are
also categorized according to their intensity. This flare was categorized as an
M1. M-class flares are a tenth the size of the most intense flares, the X-class
flares. The number provides more information about its strength: An M2 is twice
as intense as an M1, an M3 is three times as intense and so on.
Days later, on July 14, a second medium-sized, M2 flare
erupted from the Sun. The second flare was long-lived, peaking at 10:09 a.m. EDT
and lasting over two hours.
This was accompanied by another kind of solar explosion
called a coronal mass ejection, or CME. Solar flares are often associated with
CMEs — giant clouds of solar material and energy. NASA’s Solar and Heliospheric
Observatory, or SOHO, saw the CME at 9:36 a.m. EDT leaving the Sun at speeds of
620 miles per second and eventually slowing to 466 miles per second.
Following the CME, the turbulent active region also
emitted a flurry of high-speed protons, known as a solar energetic particle
event, at 12:45 p.m. EDT.
Research scientists at the Community Coordinated
Modeling Center — located at NASA’s Goddard Space Flight Center in Greenbelt,
Maryland — used these spacecraft observations as input for their simulations of
space weather throughout the solar system. Using a model called ENLIL, they are
able to map out and predict whether the solar storm will impact our instruments
and spacecraft, and send alerts to NASA mission operators if
By the time the CME made contact with Earth’s magnetic
field on July 16, the sunspot’s journey across the Sun was almost complete. As
for the solar storm, it took this massive cloud of solar material two days to
travel 93 million miles to Earth, where it caused charged particles to stream
down Earth’s magnetic poles, sparking enhanced aurora.