There is an article in the newspaper today entitled "Northern lights predicted in US and UK on Monday night in wake of solar storms".

I assume that the reason that someone can make this prediction is because 2 different things are ejected by the sun:

  1. The first thing to arrive at the earth must be travelling more quickly and it is our observation of this that enables us to make the prediction i.e. this is our "early warning". I think that this is "Light travelling at light speed" but I'm not sure.

  2. The second thing to arrive at the earth must be travelling more slowly and it is this which creates the northern lights / aurora borealis. I think that this is the solar wind but again I'm not sure.

What are the waves / particles involved in 1 and 2 above and how fast are they travelling? (I just want to work out the times involved.)

(The Aurora Tutorial cites a height of around 300km which means that once the light of the aurora is created, it will travel from the point of creation to our eyes in approximately 0.001 seconds (ignoring zenith angle / it not being a vacuum etc.)

Am I even vaguely on the right track here? Is my understanding correct?


1 Answer 1


You are roughly correct, although the first thing isn't really a material thing that is "ejected" by the Sun. The prediction is usually first done by satellites directly observing the Sun (indeed "light travelling at light speed"), most notably the SOHO which uses a coronagraph. From this, information such as the strength of the solar flare and whether there's an Earth-directed CME can be determined. The CME, which consists of charged particles, is the second thing you are talking about and takes a couple of days to reach Earth, causing aurora. The charged particles travel anywhere between $100$ and $3000 \;\text{km/s}$, although speeds are most typically a few hundred $\text{km/s}$.

Instruments closer to Earth detect when the CME actually arrives. For example, the DSCOVR and ACE satellites, which measure the interplanetary magnetic field and solar wind, are located at the Sun-Earth L1 point which gives about 30 minutes of advance warning. Finally, magnetometers on Earth detect when it actually hits Earth.

More information can be found here.

There are dedicated websites that track such data, such as https://solarham.net and https://www.spaceweatherlive.com.


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