People across the western hemisphere may be surprised to see a rust-coloured Moon in the sky on 21 February. Early that morning (the evening of the 20 February for observers in North and South America) will be this year’s first and only total eclipse of the Moon. In a total lunar eclipse, the Earth, Sun and Moon are almost exactly in line and the Moon is on the opposite side of the Earth from the Sun. The Moon is full, moves into the shadow of the Earth and dims dramatically but usually remains visible, lit by sunlight that passes through the Earth’s atmosphere. Stronger atmospheric scattering of blue light means that the light that reaches the lunar surface is predominantly red in colour so observers on Earth see a Moon that may be brick-coloured, rusty, blood red or sometimes dark grey, depending on terrestrial conditions.