Quote from BBC \"A strong solar storm is expected to hit Earth shortly, and expe
ID: 1373293 • Letter: Q
Question
Quote from BBC "A strong solar storm is expected to hit Earth shortly, and experts warn it could disrupt power grids, satellite navigation and plane routes."
How is it that we are aware of a massive solar activity that will hit us before it actually does? Isn't that activity all electromagnetic and therefore travelling at the same speed towards us (light speed)?
Or are there separate elements to a solar storm, some light speed waves and some physical particles slower than light speed?
A
http://www.bbc.co.uk/news/science-environment-17295337
Explanation / Answer
Coronal Mass Ejection is indeed a stream of particles that moves at velocities significantly lower than the speed of light. The speed of CME varies between 20km/s to 3200km/s with average velocity around 489km/s.
Thus, observations of the Sun can notice changes in Solar activity hours or even days before CME hits Earth (85 hours for average speed of 489km/s, 13 hours for the extreme velocity of 3200km/s).
More importantly, SOHO spacecraft located at L1 (around 1.5 million kms from Earth on the Sun-Earth line) can detect an incoming CME minutes to hours before it hits Earth. The stream of particles travelling at 489km/s takes around 51 minutes to travel 1.5 million kms, while the radio signal from SOHO only needs around 5 seconds. In the extreme case of CME travelling at 3200km/s, SOHO's warning is only 7 minutes ahead, though
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