How to use it
- Look at the orange line on the globe: the Tropic of Cancer. The dashed grey line is the Equator.
- Type a place or press My location to see how far you are from it.
- Read the countries it crosses and the facts.
5 practical uses
- Find the northern limit of the tropics for a climate or a plant.
- Plan a visit to a tropic marker in Mexico, Taiwan or India.
- Teach the solstices and the overhead sun.
- Check how far a place is from the tropics.
- See which countries the line crosses.
The maths behind it
The tropic is the parallel at φ = ε, the obliquity of the ecliptic, 23.4365° in 2026, decreasing by about 0.47″ a year. Its length is 2πR cos ε = 36,788 km. The distance from a place to it along the meridian is R·|φ − ε|. The countries crossed are found by testing every edge of every outline for a crossing of that latitude.
What it is
The Tropic of Cancer is the parallel at the latitude of the Earth's axial tilt, about 23°26′N. It is the farthest north the sun ever stands directly overhead, which it does once a year, at noon on the June solstice. North of it the sun is always to the south at midday; between it and the Tropic of Capricorn lie the tropics, where the sun passes overhead twice a year.
The name comes from the constellation the sun was in at the June solstice two thousand years ago; the precession of the Earth's axis has since moved that point into Taurus, but the name stayed.
It moves
The Earth's tilt wobbles slowly between 22.1° and 24.5° over 41,000 years and is currently decreasing, so the line creeps south by about 14 m a year. The marker monuments along it in Mexico, Taiwan and elsewhere are re-sited from time to time.
Where it runs
Through Mexico, the Bahamas, Western Sahara, Mauritania, Mali, Algeria, Niger, Libya, Egypt, Saudi Arabia, the United Arab Emirates, Oman, India, Bangladesh, Myanmar, China and Taiwan, and just north of Hawaii.