Thiruvananthapuram (or Trivandrum) has a rich history in astronomy and is arguably one of the most important cities in the history of modern astronomical research in India. At the epicentre of this research has been the Astronomical Observatory which is now located in the University of Kerala. This was commissioned by the then Maharaja of Travancore, His Highness Swati Thirunal in 1836. This is a short write up about the pleasant surprise that awaited us when we visited this observatory, unannounced, one fine evening in October 2024
Firstly, dont confuse this with the other public telescope which is at the Priyadarsini Planetarium, a couple of kilometres away.
To be honest, we had very little expectation from our visit. We have visited many government outreach offices before, and the experience has, unfortunately, always been underwhelming. So, when we reached the gate of the Astronomical observatory, we were fully expecting to be shooed away, with contempt.
The security guard stopped us and enquired where we were heading to. I turned my palm into a circle of sorts and held it to my eye. He told we could proceed. This was very good sign. The road leading up the hill is not well lit, and a short 2-minute ride had us stop near a flight of stairs.
Picture courtesy google images @Abhishek Ajayakumar
We went up the stairs and were greeted by Dr Jayakrishnan Ramakrishnan, Honorary Director of the Observatory. What followed was an interaction that could only be had with someone who is very passionate about astronomy. Dr Jayakrishnan is a Associate Professor at the department of Physics, University of Kerala.
Ridhi and I, introduced ourselves and explained what we do back in Bangalore. We also said that we had just come to check the place out, knowing well that the skies weren’t clear.
Dr Jayakrishnan explained about the history of the place. They have a 14-inch telescope and an 8-inch telescope for public viewing. After exchanging pleasantries, we headed into the office located on the ground floor.
Dr Jayakrishnan is very enthusiastic about astronomy and if you are in Trivandrum, you must visit the place on any weekday between 630 PM to 830 PM. He has put in a lot of effort to display information related to the history of the place. This is unlike any other government outreach building. Not only do you feel welcome, but you also learn a lot of things from a knowledgeable physics professor, who is enthusiastic about public outreach.
For Visiting the Observatory/Research Activities, Contact
Honorary Director
Astronomical Observatory
University of Kerala
Observatory Hills, Thiruvananthapuram-695033
Ph: 0471-2303732
Please read on if you are interested in some technical information related to the instruments on display.
We were led to a second room that had a huge Transit Telescope at its centre.
This telescope is aligned the pole star through a window (in picture) in the north side of the room. The telescope can move on one axis along the imaginary north pole - south pole line, also called as the meridian. The roof would have been open above the window, right across to the south side. Perhaps it had a rolling roof?
Dr Jayakrishnan explaining the mechanism.
This telescope, also from the 19th century, has a bench, on which an observer would lie down and wait patiently for the target star to come into the center of the field of view of the telescope.
This would signify that the target star had crossed the meridian or midway from its journey from rising in the east, to setting in the west. This is also known as a transit event for your local area. With a synchronized, reliable clock, an astronomer would record the exact time of the event. Now, you could use this as a base to log future meridian crossings and derive the exact time of the day with each passing. This observatory was also used to commission religious yearly almanacs (Panchangam) back in the day. This instrument would be useful for such an endeavour.
As a side note, we take time for granted today. A flick of the wrist or a glance at the phone, and we know the right time. You can appreciate how difficult your life would be if not for clocks. But what would one do when the clock stopped? This is where a meridian crossing of a target star would have been useful.
Also, if you were out at sea, knowing your longitude would be easy if you had a transit telescope and a reliable clock that tracked a known anchor time like the Greenwich Mean time (GMT), for instance. A calm sea would help! You would also need an almanac that contained the transit timings at GMT longitude for some bright celestial objects/stars.
Now, you would measure the transit time of the target star at your location at sea, using your clock which tracked the time at GMT. The rate of earth's rotation is about 15 degrees an hour. So, if the target star transited 3 hours later than what the GMT based Almanac suggests, it means you are about 45 degrees ahead (or east) of the GMT line. That was not complicated, was it?
We also noticed that there were several antique eye pieces, a radiometer with a quartz dome to measure solar radiance.
There were still many rolls of strip chart recorders stacked neatly in the room! These would have been used back in the day to record the electrical signals generated by the radiometers, making continuous recordings of solar irradiance through the day. I could not help but imagine a typical day in the life of an astronomer here about a century ago!
We also were able to see the personal 2 inch refractors of John Allan Broun, who was one of the early British astronomers who headed the observatory.
One odd thing about the design was that the focusser moved the primary lens forward and backward, rather than move the eyepiece or diaganol.
They also have 3 sidereal clocks from 1841, and they still work!
Now, usually, a day is defined as the period taken for the sun to return to the same position in the sky, as long as the observer has taken the measurement from the same location on earth. It takes 24 hours and the clock hanging on our wall, is synced to this
A second way to measure time would be to see how much time does the earth take to do one rotation, in relation to the stars other than the sun. This would give us the actual rotational period of the earth. It is slightly lesser than the solar day, taking only 23 hours 56 minutes and 4.1 seconds. Solar days are longer only because the earth has moved along the revolutionary orbit. If earth did not revolve around the sun, solar and sidereal time would be the same.
This video can help visualize
A sidereal clock would be useful if you are measuring the transit of stars. It would help you keep a more accurate record of the transit. I was wondering what calculations, gearing etc would need to be different for such a clock. Dr Jayakrishnan explained the formula for calculating the length of the pendulam. He said all it would need is a simple but precise shortening of the radius of the pendulam. Interesting!
He also wound up the clock for us. It was mesmerizing watching this relic from the past, still tick!
He has also authored a research article, published in the Indian Journal of History of Science. It is about a second modern observatory that was commissioned in nearby Agastiar hills, which operated from 1855 to 1859 and then briefly from 1864 to 1865. It was setup by John Allan Broun, supported by the Maharaja of Travancore, Sri Swati Thirunal. This observatory made significant contributions to global geomagnetic research. Two unfortunate things are highlighted in the article - 1) No global recognition has been recieved for the observatory and its contribution to science and 2) After it was eventually closed down due to logistical challenges, traces of this observatory have still not been found. There is only speculation of its exact location.
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