| Ångströms (Å) | Nautical miles (nmi) |
|---|---|
| 1 Ångström | 5.39956803456 × 10-14 nmi |
| 2 Ångströms | 1.07991360691 × 10-13 nmi |
| 3 Ångströms | 1.61987041037 × 10-13 nmi |
| 4 Ångströms | 2.15982721382 × 10-13 nmi |
| 5 Ångströms | 2.69978401728 × 10-13 nmi |
| 10 Ångströms | 5.39956803456 × 10-13 nmi |
| 20 Ångströms | 1.07991360691 × 10-12 nmi |
| 25 Ångströms | 1.34989200864 × 10-12 nmi |
| 50 Ångströms | 2.69978401728 × 10-12 nmi |
| 100 Ångströms | 5.39956803456 × 10-12 nmi |
| Reference | Ångströms (Å) | Nautical miles (nmi) |
|---|---|---|
| A sheet of A4 paper (long side) | 2.97 × 109 Å | 0.000160367 nmi |
| Average adult human height | 1.7 × 1010 Å | 0.000917927 nmi |
| A football pitch (length) | 1.05 × 1012 Å | 0.0566955 nmi |
| A marathon | 4.2195 × 1014 Å | 22.7835 nmi |
| Height of Mount Everest | 8.849 × 1013 Å | 4.77808 nmi |
The ångström is a unit of length equal to one ten-billionth of a metre, or 0.1 nanometres. It takes its name from Anders Jonas Ångström, the Swedish physicist who used it in his 1868 map of the solar spectrum. The symbol is Å, a letter borrowed from the Swedish alphabet.
The ångström survives because it matches the scale of atoms. A hydrogen atom has a radius of about 0.5 Å. A carbon-carbon single bond measures roughly 1.5 Å. Expressing these figures in nanometres produces awkward decimals, so crystallographers, spectroscopists and structural biologists continue to prefer the older unit. Protein structures deposited in public databases are still described by their resolution in ångströms, and a structure resolved to better than 2 Å is considered high quality.
Wavelengths of visible light also fall in a convenient range. Red light sits near 7000 Å and violet near 4000 Å. X-ray wavelengths cluster around 1 Å, which is precisely why X-ray diffraction reveals atomic spacing: the probe and the target are the same size.
The ångström is not part of the International System of Units. The BIPM lists it among units that are accepted for use with SI but discourages new applications, preferring the nanometre or picometre. That guidance has had limited effect in the fields where the unit is entrenched. Semiconductor manufacturing offers a clear illustration. Process nodes were named in nanometres for decades, but as features shrank the industry began quoting gate oxide thicknesses in ångströms, and Intel named a generation of its technology the Angstrom era.
Reading older scientific literature requires care. Before the ångström was tied to the metre it was defined against a specific spectral line of cadmium, and figures published in the early twentieth century may differ slightly from modern values. The International Astronomical Union adopted that spectroscopic definition in 1907, and it stood until the metre itself was redefined against krypton in 1960. The discrepancy is small, but it is real, and it matters when comparing historical spectral measurements against current ones.
Converting is straightforward. One ångström equals 10-10 metres, 0.1 nanometres, or 100 picometres. Ten ångströms make a nanometre.
The nautical mile is a unit of length equal to exactly 1852 metres. The symbol is nmi, though NM and M also appear in maritime and aviation practice. It is longer than the statute mile by about 15 per cent.
Its definition is geographical rather than arbitrary. One nautical mile corresponds to one minute of latitude, so sixty nautical miles span one degree. This makes navigation on a chart remarkably direct: a navigator can measure a distance against the latitude scale printed on the chart's edge without any conversion, because the two are the same thing. No other length unit has this property, which is why the nautical mile has resisted metrication where almost every other traditional unit has given way.
Because the Earth is slightly flattened, a minute of latitude is not constant, varying from about 1843 metres at the equator to 1862 metres at the poles. The First International Extraordinary Hydrographic Conference in Monaco adopted the round figure of 1852 metres in 1929 to settle the discrepancy. The United States accepted this value in 1954 and the United Kingdom in 1970, both having previously used slightly different definitions.
Speed at sea and in the air is measured in knots, one knot being one nautical mile per hour. The name records the method: a log line knotted at regular intervals was paid out behind a ship and the knots counted against a sand glass. Aviation adopted both units from maritime practice, and aircraft airspeed indicators worldwide read in knots.
Maritime law is written in the same unit. Territorial waters extend twelve nautical miles from the baseline and exclusive economic zones two hundred, figures set by the United Nations Convention on the Law of the Sea.
A related unit occasionally appears in older texts. The geographical mile is one minute of arc along the equator, about 1855 metres, and differs slightly from the nautical mile because it is measured on a great circle rather than a meridian. The distinction rarely matters in practice but explains small discrepancies between historical sources.
One nautical mile equals 1852 metres, about 1.15078 statute miles, or 6076.12 feet.