Planck was a European Space Agency space-based observatory observing the Universe at wavelengths between 0.3 mm and 11.1 mm (corresponding to frequencies between 27 GHz and 1 THz), broadly covering the far-infrared, microwave, and high frequency radio domains. The mission's main goal was to study the cosmic microwave background – the relic radiation left over from the Big Bang – across the whole sky at greater sensitivity and resolution than ever before. Planck was therefore like a time machine, giving astronomers insight into the evolution since the birth of our Universe, nearly 14 billion years ago.