The Hindu : New Delhi News : When the sun "stands still"

Online edition of India's National Newspaper
Tuesday, Jun 20, 2006

New Delhi

New Delhi

When the sun "stands still"

Staff Reporter

NEW DELHI: Every year around June 21 the Northern Hemisphere experiences the summer solstice. This is marked by the sun seeming higher in the sky and the day being longer than at other times of the year.

As summer progresses, the sun appears to move northward, reaches its maximum northern swing on a particular day, and then starts its southward journey. The days the sun appears to change direction are termed "solstices'', a word that essentially means that the sun stands still. For the Northern Hemisphere, summer solstice is the longest day of the year.

Summer solstice on Wednesday

Officials at Delhi's good old Nehru Planetarium have announced that this year's summer solstice will fall on this Wednesday. As seen from Delhi, the sun will rise that day at 5-24 a.m. and set at 7-22 p.m.

Though Delhiites will not see an absence of shadows on the day of the summer solstice -- a distinctive feature of the solstice -- they can appreciate the day by visiting Jantar Mantar. Nearly 300 years old, the historic astronomical observatory in the Capital has large masonry instruments, some of which have special constructions meant precisely to appreciate the summer solstice.

The most celebrated instrument at Jantar Mantar is the Misra Yantra. Come summer solstice and all eyes will be on the Misra Yantra's back wall -- the Karka Rasi Valaya.

On the day of the solstice, the sun shines exactly over this wall for a considerable part of the day. The wall itself was used to indicate the entry of the sun into the Tropic of Cancer. However, the dial markings on the instrument seem to indicate that it was meant for more detailed observations.

The Karka Rasi Valaya is equipped with a small straight rod, which acts as a gnomon, centred in the East-West direction.

On the day of the solstice, the shadow of this rod swings along the wall giving the impression of a giant hand of a clock moving with the movement of the sun across the sky. But the instrument is meant for measurement of certain celestial coordinates and not really for measuring time.

On June 22 last year, a small group of students from Delhi University along with Nehru Planetarium staff marked the shadow locations of the rod on the Karka Rasi Valaya throughout the solstice day.

This was part of the ongoing work at the Nehru Planetarium to fully understand the usage of all the instruments at Jantar Mantar.

The work of trying to understand and calibrate the Karka Rasi Valaya will be kept up this Wednesday by the team from the Nehru Planetarium and the Amateur Astronomers' Association, Delhi. Those interested can join in these observations and get a feel of the usage of this unique instrument.

Nehru Planetarium Director N. Rathanasree will also treat visitors to a presentation about the use of the Misra Yantra at 5 p.m.

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