David Butler

This channel by David Butler hosts his “How Far Away Is It” video books. Since 2013 he has produced long series of introductory astronomy and physics videos, pitched at around sixth form and first year university level. A companion website gives notes for each video, and it is used by science teachers.

The main series explains how we know the distance to objects in space, from the back garden to the most distant galaxies. It builds up step by step using triangulation, parallax, standard candles and red shift. Further series cover how fast and how old things are, including gravitational waves and the early universe. Videos are long and use images from Hubble, Euclid and other telescopes.

Some highlights include:

A chapter on gravitational waves, how they are produced and how they are detected.

An explanation of the epoch of reionisation, a key stage in the early history of the universe.

A look at the evidence for how long life has existed on Earth.

The channel has around 189,000 subscribers.

The video books follow a clear logical path, much like a well-planned course. They suit students studying A level physics who want to see where the subject leads. They connect to astrophysics, space science and the measurement techniques used across engineering. Because the videos build on each other, they are best watched in order, like chapters of a book.