Figure 3 The scale of the Universe from atoms to galaxies. Each image is representative of the unit indicated. Each stage is 1000 times larger than the previous one. The smallest shown, femtometres (fm), is depicted by the nucleus of an oxygen atom. The next microscopic scale (pm) is still too small to show a whole atom. The next two scales (nm and µm) are represented by the diameter of deoxyribonucleic acid (DNA) and a bacterial cell respectively. You will be familiar with the scales millimetres (mm) to megametres (Mm). The Sun is at the scale of a gigametre (Gm). Moving outwards are the inner Solar System (Tm), Oort cloud (Pm), a nebula (Em), galaxy (Zm) and cluster of galaxies (Ym).