Spectacular Northern Lights may be visible tonight across the northern hemisphere, following a solar eruption on Sunday night.
In the early hours of Sunday morning, the Sun's surface erupted in what's called called a coronal mass ejection, blasting tons of ionized atoms into space.
This plasma is headed straight for the Earth, and when it arrives, could create a spectacular light show.
"This eruption is directed right at us, and is expected to get here early in the day on August 4th," said astronomer Leon Golub of the Harvard-Smithsonian Center for Astrophysics (CfA). "It's the first major Earth-directed eruption in quite some time."
The eruption itself was caught on camera by NASA's Solar Dynamics Observatory (SDO), launched in February.
"We got a beautiful view of this eruption," said Golub. "And there might be more beautiful views to come, if it triggers aurorae."
When a coronal mass ejection reaches Earth, it interacts with the planet's magnetic field, potentially creating a geomagnetic storm. Solar particles stream down the field lines toward Earth's poles and collide with atoms of nitrogen and oxygen in the atmosphere, causing them to light up like little neon signs.
Aurorae can usually only be seen at high latitudes - but a geomagnetic storm can make them visible much further south. Sky watchers in the Northern US and Europe should look for rippling 'curtains' of green and red light to the north.
The Sun goes through a regular activity cycle lasting around 11 years. The last solar maximum occurred in 2001, and the latest minimum has been particularly weak and long lasting.
This eruption looks like one of the first signs that the Sun is waking up again and heading toward another maximum.