Tropic of Cancer

The sun on the Tropic of Cancer

How to use it

1. The line is drawn in orange across the whole map as soon as the page opens.
2. Pan and zoom to follow it. On the web map's Mercator projection, parallels are straight horizontal lines and meridians straight vertical ones.
3. Under the map, read the list of countries whose land the line crosses and the notes about the line.
4. Use the other line pages linked below to compare positions, or the miles per degree calculator for the length of a degree at this latitude.

Why the Tropic of Cancer is where it is

The Tropic of Cancer is the northernmost latitude where the sun can be straight overhead. That happens at noon on the June solstice, when the sun's declination equals the tilt of the Earth's axis. North of the line, the noon sun is always somewhat to the south.

The tilt is not fixed. It changes slowly over tens of thousands of years, so the tropic drifts too. This page uses the IAU mean obliquity for the J2000 epoch, 23.4394°. The present value is slightly smaller, so the real line sits a little closer to the equator.

How long the line is

A parallel is a circle whose radius is the distance from the Earth's axis. On the WGS84 ellipsoid that radius is N · cos φ, where N is the prime vertical radius of curvature, which at 23.4394° N is 6,381,518 m. The circumference 2π · N · cos φ comes to 36,787.6 km.

One degree of longitude along it is 102.19 km, or 63.50 miles. The miles per degree calculator gives the same figure for any latitude.

Countries on the line

Testing a point every 0.02° along the line against the Natural Earth 1:50m outlines finds land in 17 countries: Mexico, Bahamas, Western Sahara, Mauritania, Mali, Algeria, Niger, Libya, Egypt, Saudi Arabia, United Arab Emirates, Oman, India, Bangladesh, Myanmar, China, Taiwan. At that scale small islands drop out, so the list covers the mainland and larger islands.

• The tropic migrates slowly as Earth's axial tilt changes.
• This page uses the IAU mean obliquity for J2000 (23.4394°).
• The 1:50m outlines also touch the edges of Chad and of the area mapped as Morocco. This list leaves out those two edge cases.

The United States and this line

Of the 50 state capitals, only Honolulu, at 21.307° N, lies south of the Tropic of Cancer, 147 miles from it along a meridian. So Honolulu is the only capital where the noon sun passes straight overhead, twice a year. The other 49 state capitals and Washington, DC are north of the tropics.