Waves that need no medium

Radio telescopes pick up radio waves from stars very far away, and the information in them helps us understand the history of the universe. Radio waves are one kind of electromagnetic wave.

Figure to be added

A radio telescope: a large dish antenna pointed at the sky.

Electromagnetic waves do not need the particles of a medium to take part. That is how they cross the empty space between the stars and the earth.

Important properties

They are not affected by external electric and magnetic fields.
They need no medium to travel.
In a vacuum they travel at 3 × 10⁸ m s^-1.