<p>As Earth's magnetic field weathered a strong solar shock wave this week, the sun unleashed another powerful flare that could herald more geomagnetic storms on Thursday.</p>
<p>"It's like the Earth is looking right down the barrel of a giant gun pointed at us by the sun...and it's taken two big shots at us," said John Kohl of the Harvard-Smithsonian Center for Astrophysics.</p>