How would we recognise a CME heading for Earth?
Fortunately the answer is fairly simple. If a CME shows up in a LASCO image as a bright ring around the Sun, we can be sure it's not shooting out from the Sun sideways, but is likely to be heading straight for SOHO. Since SOHO is almost directly between the Sun and the Earth, the CME must also be heading straight for us! This kind of CME is called 'halo CME', because, when it first forms, it looks like halo around the Sun.
This is what happens when a CME hits SOHO.
It's not all bad news though. CMEs can produce beautiful effects too, like the aurora or Northern Lights seen in these images.
It’s important that we know when large CMEs are going to hit. LASCO acts as an early warning system.
We can use data from LASCO to make space weather forecasts. This will help operators of satellites. If the space weather forecast is bad, they can prevent damage to their satellites by, for example, shutting them down until the storm has passed.
Find out more about this in the space weather section.