Convert nanometer to parsec

The astronomical unit is the mean Earth–Sun distance, fixed at exactly 149,597,870.7 km: Mars orbits at 1.5 au, Neptune at 30. The light-year is the distance light travels in a Julian year, 9.46 trillion km, and the light-second 299,792 km, about three quarters of the way to the Moon. The parsec, 3.26 light-years, is the distance at which the Earth's orbit spans one second of arc, and is what astronomers actually use: the nearest star is 1.3 pc (4.2 ly) away, the centre of the Milky Way about 8 kpc.

Atoms and molecules are measured in ångströms, 0.1 nm: the Bohr radius of hydrogen is 0.53 Å, a carbon–carbon bond 1.54 Å, and X-rays have wavelengths of about 1 Å, which is why crystallographers keep the unit although it is not part of the SI (chemistry tables give the same radii in picometres, 53 pm). The nanometre is the scale of the DNA double helix (2 nm across), of viruses (20–300 nm) and of visible light (380–750 nm); a chip's '3 nm' process is a marketing name, its transistors are really tens of nanometres apart. Bacteria, red blood cells (7 µm) and hair (50–100 µm) belong to the micrometre, and the femtometre, or fermi, to the atomic nucleus: a proton is 1.7 fm across.