Tropic of Cancer: Where It Is and Why It Matters
The Tropic of Cancer sits at roughly 23.5 degrees north latitude. It is the farthest north the Sun ever appears directly overhead, which happens once a year around 21 June. This article covers its exact position, the countries and Indian states it passes through, why the latitude is slowly moving, and how it shapes climate.
The Tropic of Cancer sits at roughly 23.5 degrees north latitude. It is the farthest north the Sun ever appears directly overhead, which happens once a year around 21 June. This article covers its exact position, the countries and Indian states it passes through, why the latitude is slowly moving, and how it shapes climate.
Where the Tropic of Cancer is
The Tropic of Cancer is the line of latitude at 23 degrees 26 minutes north of the equator, usually rounded to 23.5 degrees N. It marks the northernmost point where the Sun can be directly overhead, at the zenith, with vertical objects casting no shadow at local noon. That moment happens once a year, on or around 21 June, the June solstice.
North of this line, the Sun is never straight overhead. Not in June, not ever. In London or New York, the Sun at midday is always at least a little to the south, which is why north-facing walls in those cities get so little direct light.
The line exists because Earth is tilted. Our axis leans about 23.4 degrees from the vertical relative to our orbit, and that tilt is the whole reason we have seasons. The Tropic of Cancer is simply that tilt drawn onto the map.
Why it is named after a crab
The name is a leftover from Greek astronomy, roughly 2,000 years old. When the term was coined, the Sun at the June solstice sat in front of the constellation Cancer, the crab. Astronomers called that turning point the tropic, from the Greek tropos, meaning turn, because the Sun appears to stop climbing north and turn back south.
The name stuck. The astronomy did not. Because of axial precession, a slow 26,000 year wobble of Earth's axis, the June solstice Sun now sits in Taurus, near the border with Gemini. So the Tropic of Cancer has nothing to do with Cancer any more. Nobody renamed it.
The countries it crosses
The line runs through roughly 16 countries, plus a lot of ocean. Mexico, the Bahamas, Western Sahara, Mauritania, Mali, Algeria, Niger, Libya, Egypt, Saudi Arabia, the UAE, Oman, India, Bangladesh, Myanmar, China and Taiwan all sit on or across it, depending on how you count small territorial slices.
Look at that list and something jumps out. The Sahara, the Arabian Desert, the Thar. Deserts cluster along this latitude because of the Hadley circulation: air rises at the equator, dumps its rain there, then sinks around 20 to 30 degrees north, dry and warm. Sinking air does not make clouds. That is the subtropical high pressure belt, and it is why Cairo gets around 25 millimetres of rain a year.
India is the exception that proves the rule. The same latitude that gives Libya sand gives Kolkata a monsoon, because the Asian landmass and the Himalaya rewire the wind pattern every summer.
The eight Indian states it passes through
This one gets asked constantly in Indian exams, so here it is straight. The Tropic of Cancer crosses eight states, running west to east. A common memory trick is the phrase MRMCJWTM, or just remember it enters at the Rann of Kachchh and exits into the hills of Mizoram.
Roughly half of India lies north of the line and half south, which is why the country is described as both tropical and subtropical. Ranchi, Bhopal, Ujjain, Gandhinagar and Kolkata all sit close to it. Ujjain's old observatory was built there for exactly that reason.
| # | State | Notes |
|---|---|---|
| 1 | Gujarat | Enters India near the Rann of Kachchh |
| 2 | Rajasthan | Southern Rajasthan, near Banswara |
| 3 | Madhya Pradesh | Longest stretch, passes near Bhopal |
| 4 | Chhattisgarh | Northern part of the state |
| 5 | Jharkhand | Passes very close to Ranchi |
| 6 | West Bengal | Crosses near Krishnanagar, north of Kolkata |
| 7 | Tripura | Northern Tripura |
| 8 | Mizoram | Exits India towards Myanmar |
The line is moving, slowly
The Tropic of Cancer is not fixed. Earth's axial tilt oscillates between about 22.1 and 24.5 degrees over a 41,000 year cycle, and right now the tilt is decreasing. The line is drifting south at roughly 15 metres a year, about half a metre every twelve days.
That has practical consequences for monuments. Taiwan and Mexico have both built markers on the line, and some now sit measurably north of where the Sun actually stands overhead. Taiwan's marker at Hualien has been rebuilt more than once.
If you want to see the effect for yourself, you do not need to travel. Stand outside at local solar noon on 21 June and measure your shadow. Do it again on 21 December. The difference in the Sun's angle between those two dates is 47 degrees, twice the tilt, and that single number explains the Tropic of Cancer, the Tropic of Capricorn, and every season you have ever lived through.
FAQs
What is the difference between the Tropic of Cancer and the Tropic of Capricorn?
They are mirror images. The Tropic of Cancer is at 23.5 degrees north and gets the overhead Sun around 21 June; the Tropic of Capricorn is at 23.5 degrees south and gets it around 22 December. The zone between them is the tropics.
Does the Tropic of Cancer pass through Delhi or Mumbai?
No. Delhi is at about 28.6 degrees north and Mumbai at about 19 degrees north, so both are off the line, Delhi to the north and Mumbai to the south. The Indian cities closest to it are Ranchi, Bhopal and Ujjain.
What happens on the Tropic of Cancer on 21 June?
The Sun passes directly overhead at local solar noon, so a vertical pole casts almost no shadow. It is the longest day of the year in the Northern Hemisphere and the only day the Sun reaches the zenith at that latitude.
How many times does the Sun cross the Tropic of Cancer in a year?
Once. The Sun reaches 23.5 degrees north on the June solstice and immediately turns back south. Places between the two tropics get an overhead Sun twice a year, but the tropics themselves get it only once.
Why are so many deserts on the Tropic of Cancer?
Air that rises and rains at the equator sinks back down near 20 to 30 degrees latitude, warm and dry. Sinking air suppresses cloud formation, creating the subtropical high pressure belt that holds the Sahara, the Arabian Desert and the Thar.
What is the exact latitude of the Tropic of Cancer today?
About 23 degrees 26 minutes 9 seconds north, and slowly decreasing. Earth's tilt is shrinking on a 41,000 year cycle, so the line moves south by roughly 15 metres a year.