On August 1st, the sun emitted a C-class solar flare that spawned what scientists call a coronal mass ejection, or CME, headed toward Earth. The CME impacted Earth's magnetic field August 3rd. CMEs occasionally hit Earth. This CME will have few noticeable consequences beyond producing an aurorae.
The CME hit Earth's magnetic field on August 3rd at 1740 UT. The impact sparked a G2-class geomagnetic storm that lasted nearly 12 hours time enough for auroras to spread all the way from Europe to North America. The possible arrival of a second CME on August 4th might provide even better spectacular auroral displays.
CMEs are large clouds of charged particles that are ejected from the sun over the course of several hours and can carry up to ten billion tons of plasma. They expand away from the sun at speeds as high as a million miles an hour. A CME can make the 93 million mile journey to Earth in just two to four days. Stronger solar storms could cause adverse impacts to space based assets and technological infrastructure on Earth.
The sun goes through a regular activity cycle about 11 years long. The last solar maximum occurred in 2001 and its recent extreme solar minimum was particularly weak and long lasting. These kinds of eruptions are one of the first signs that the sun is waking up and heading toward another solar maximum expected in the 2013 time frame.