Last updated: October 2026 · Method: built from published site information and recurring traveller reports; figures approximate, verify on site.
The Jantar Mantar holds nineteen instruments, each explained below.
The key yantras
- Samrat Yantra: the giant sundial, accurate to two seconds and the largest stone sundial in the world.
- Jai Prakash: two concave hemispheres that map the sky onto the ground, though they pose a real photography challenge.
- Ram Yantra and others: the instruments measuring star positions, altitudes and the astronomical calendar.
One tip covers the visit: hire the guide, as the heritage-walk guides recommend, because the instruments are meaningless without interpretation.
How long it takes
- The honest arithmetic repeated by guides is thirty minutes to walk through and ninety to actually understand, and the difference is entirely interpretation.
The Samrat Yantra is the anchor: a giant sundial accurate to seconds by its builders’ claims, its shadow reading time at a scale that finally makes astronomy physical. Jai Prakash follows, two concave hemispheres that map the sky onto the ground so you walk inside the instrument. Hire the guide or take the audio set, because the nineteen yantras are meaningless without their purpose explained, and the site is flat, easy walking with shade scarce, so mornings suit it best.