In order to develop the physics of the interstellar journey, we need theoretical foundations. Especially we are interested in the motion of an electron in a homogeneous constant magnetic field. We assume a nonzero velocity of the electron, oriented not parallel to the magnetic field lines.
The difference between the acceleration of an electron by an electric field and by a magnetic field simply is: A homogeneous constant electric field can set in motion a resting electron - a magnetic one cannot.

Let us start our excursion with the Lorentz-force _L - don't be afraid, we will explain every term in it step by step.
(1a.01)
The Lorentz-force is the sum of an electric force,
_E = Q ,
and a magnetic force,
_B = Q .
In our case Q is the charge of the electron,

(please don't confuse the elementary charge, |e|, and the electron charge, e); is the electric field strength, is the electron velocity, is the vector of the magnetic induction, and is the vector product of the vectors and .
In the following sections we set:

Perhaps this was a bit too much at once for you, who heard about the vector product the first time. For not having any complications in future, in the next section we give you a small introduction to this part of vector calculus.

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Chapter One