Travel - India

Our group at the Jai Prakash Yantra

This instrument is a kind of armillary sphere. It measures altitudes, azimuths, hour angles, and declinations of the sun, other stars, or any light in the night sky.

There is a wire strung across the top holding a round sighting target above the center of the bowl. To take a measurement of the sun during the day, you simply find the target's shadow on the marble below. Engraved markings in the curved stone specify the equatorial coordinates.

To take a measurement at night, you would climb down into the instrument to the point where the sighting target lines up with your selected star. Then you can read the coordinates on the marble. Gaps in the bowl offer a place to stand while you're inside.

In my photo, our Road Scholar group is standing between the two halves of the instrument. The far bowl is the complement of the near one. Where one has empty gaps, the other has engraved marble, and vice-versa.

When the sun's shadow creeps into a gap, you simply walk over to the other bowl to find the coordinates.