With the plethora of satellites orbiting the Earth and imaging the cosmos, do Earth-based astronomical observatories have any significance in this age of remote and robotic astronomical imaging? The demonstration of astronomy to the common person as a means of universalization of the structure of the cosmos is the most fundamental aspect of ground-based observatories and the major reason why they remain relevant in this era.

All ground-based observatories open their facilities to the public on days of special celestial events or on specific weekdays, providing the opportunity to view celestial objects using the state-of-the-art instruments available at the facility. The Department of Physics at the University of Kerala, India, has control of the historical Trivandrum Observatory and began opening it to the public on a daily basis in 2018. This change has helped connect the local populace with the science of astronomy. Access to the night sky in the city of Thiruvananthapuram in Kerala is challenged by light pollution, but the observatory’s two modern optical telescopes have allowed visitors to see a transit of Io across Jupiter and a recent comet — C/2022 E3 (ZTF). The comet was tracked by the observatory for five successive days, starting from 13 February 2023, and was shown in real time to the visitors1. Different to a routine research task, public discourse on such occasions leads to exciting questions for the observatory staff from the visitors.

Historical activities

The history of Thiruvananthapuram (Trivandrum) Astronomical Observatory extends back to 1837, when it was established at a latitude of 8 degrees, 30 minutes, 35 seconds north and a longitude of 76 degrees, 59 minutes, 45 seconds east by the then-King Swathi Thirunal Rama Varma of the Travancore kingdom2. He envisioned it as a means of scientific exchange between established schools of mathematics and astrology in the princely state of Travancore and the Western science of astronomy. Englishman John Caldecott was the founding director (1837–1851) of the observatory and furnished the observatory with his personal optical telescopes3,4,5. By 1841, a transit instrument, two mural circles, an altitude and azimuth instrument, a 7-foot equatorial telescope, chronometers, and magnetic and meteorological instruments were installed with help from the British Association for the Advancement of Science. Caldecott communicated the sightings of comets from Trivandrum Observatory in 1843 and 1844 to the Royal Astronomical Society in the United Kingdom3,4,5.

Caldecott was succeeded as director by John Allan Broun (1852–1869), who established a twin observatory for magnetic studies to the east of Trivandrum Observatory on a hilltop called Agasthiyar, 6,200 feet above sea level and deep inside a forest in the western Ghats of the Indian subcontinent6. The Agasthiyar Observatory had a clock with a mercurial pendulum and a barometer, thermometers and an anemometer, which were kept on the tower roof. Thus, the direction and force of the wind, species of clouds and amount of cloud surface, evaporation of salt water, temperature of water, rainfall and so on were regularly observed. The diurnal variation of atmospheric pressure and its dependence on altitude was also documented by Broun. Broun discovered that disturbances on the surface of the Sun were connected to the state of Earth’s magnetism and he proved that they had a periodicity of about 27 days. He also showed that there exists a lunar-diurnal effect that varies with the position of the Sun. Broun was awarded the Keith Medal from the Royal Society of Edinburgh for the period 1859–1861 and the Royal Medal from the Royal Society of London in 1878 for his work7,8,9,10. The Trivandrum Observatory thus was transformed into a meteorological and magnetic observatory under the tenure of Broun, moving away from the subject of astronomy.

In 1890, Alexander Crichton Mitchell, a professor of mathematics and physics at the University College of Travancore, volunteered to take charge of the observatory. Under his directorship (1892–1910), the main activity of the observatory became the signalling of time to the Nair brigade, the official army of the Travancore government. Mitchell also introduced a scheme of rainfall mapping for the kingdom of Travancore by setting up a chain of meteorological stations spread across the princely state. In 1910, J. Stephenson, professor of physics at the University College of Travancore, succeeded Mitchell as the director (1911–1920) of the observatory. He continued the work started by Mitchell. During the latter part of Stephenson’s time, he had an assistant director, M. Rama Varma Raja, who was a highly enthusiastic worker in the field of astronomy. For the years 1916 to 1919, Raja published an astronomical ephemeris11. In 1920, K. R. Ramanathan succeeded Stephenson as director (1920–1921). He arranged for the normals of a large number of meteorological elements to be brought up to date (1920–1922) and he studied the thunderstorm activity in Trivandrum11. In 1922, Ramanathan left the Travancore service to join the India Meteorological Department in the Government of India service11,12.

Sivaramakrishna Iyer was confirmed as honorary director (1921–1926) when Ramanathan left the observatory12. Self-recording instruments for meteorological measurements were set up in 1922 and the institution was recognized as a first-class meteorological observatory by the India Meteorological Department. In 1927, the work of the observatory was divided into two independent sections, astronomical and meteorological, under the charge of the government astronomer H. Subramania Iyer (1927–1941) and the government meteorologist Sivaramakrishna Iyer, both of whom were named directors12. With the creation of an astronomical department, a weekly publication of astronomical notes giving the position of the Sun, Moon and the planets for Trivandrum and details of other important celestial phenomena began12.

Subramania Iyer sighted a new comet, 1941-C, at the observatory on the morning of 23 January 1941 and communicated it to the Royal Observatory in Greenwich. By the time his cable arrived, the sighting was already being reported from other observatories around the world. For his 23 January observation of the comet, Subramania Iyer was named as an independent discoverer, alongside J. S. Paraskevopoulos and R. Grandon13. The comet was kept under observation for a month using the 5-foot telescope and the orbit of the comet was computed by P. K. Kuttan Nair, who was working as an assistant at the observatory.

In 1937, the University of Travancore was established by the Maharaja of Travancore Sri Chithirathirunal Balarama Varma. On 17 August 1939, the observatory was transferred to the control of this university and it functioned as a unit of the Central Institute of Research14. In 1940, the meteorological and astronomical sections were amalgamated. In 1951, the meteorology section of the observatory was taken over by the Government of India and the astronomical section was taken over by the Kerala state government. On 1 January 1976, the Government of Kerala decided to transfer the observatory back to the control of the University of Kerala and since then it has been under the aegis of the Department of Physics and has been known as the Trivandrum Astronomical Observatory. The arrival of Halley’s comet in 1985, the transit of the planet Mercury across the solar disk on 13 November 1986 and the total lunar eclipse of 17 October 1986 gave the observatory an onus towards augmentation of its facilities. The arrival of comet Ikeya-Zhang in February 2002, the rare planetary alignment in the western sky during May 2002, and other astronomical events such as eclipses, occultations and transits have continued to revive the activities of the observatory and received wide coverage in newspapers and television networks.

Modern-day activities

The establishment of the Indian Institute of Space Science and Technology (IIST) in Thiruvananthapuram in 2007 was seen an opportunity for the observatory to become scientifically relevant in modern times. The need to implement a policy change was felt by the University of Kerala whereby the observatory could serve as a corridor for academicians, science practitioners, researchers and industries interlinking the academic and research activities in the University of Kerala with the research and development activities of Vikram Sarabhai Space Centre (VSSC) and with the programmes of IIST.

In recent years, the Trivandrum Astronomical Observatory has been revitalized with the initiative of establishing a centre of excellence in astronomy and astrophysics by the Government of Kerala. The observatory now houses 14-foot and 8-foot Schmidt–Cassegrain telescopes (SCTs) with motorized domes. The 14-foot telescope has a focal ratio of f/11 and an equatorial GOTO-type mount. The telescope is mounted inside a motorized dome with opening from 0° to 90°. The telescope is equipped with a cooled charge-coupled device with a resolution of 2,592 × 1,944 pixels. The 5-megapixel colour sensor reduces image noise levels significantly. There is also a filter wheel for the telescope with the typical UBVRI Johnson photometry set of red, green and blue filters. The 14-foot and 8-foot telescopes were recently made operational for the monitoring of planetary motion. First-light images from these ground-based telescopes located in the Trivandrum Astronomical Observatory are shown in Fig. 1. Figure 1a shows the satellite Io in transit across Jupiter, recorded using the 8-foot telescope. The shadow of the satellite creates the black spot on the surface. Figure 1b shows an image of Jupiter recorded using the 14-foot telescope. The image shows the great red spot and the alternate white and red bands representing the cold zones and hot belts of Jupiter respectively. Figure 1c is a direct image recorded of comet C/2022 E3 (ZTF) as visible using the telescope without any image processing algorithms and represents what was shown to the enthusiastic public. The inset in Fig. 1c is a processed and magnified image of the comet, which shows the greenish head and tail of the comet with a whitish coma. A much better image can be constructed by further processing the data by stacking the recorded frames, subtracting the dark, flat and bias frames, and using professional image processing software to render colours and enhance the contrast and sharpness. This is a work in progress.

Fig. 1: First-light images from the Schmidt–Cassegrain telescopes at Thiruvananthapuram Astronomical Observatory.
figure 1

a, Image of Io’s transit of Jupiter recorded using the 8-foot SCT. b, Image of Jupiter recorded using the 14-foot SCT. c, Raw image of the comet C/2022 E3 (ZTF), recorded using the 8-foot SCT on 13 February 2023. Inset: a filtered and scaled image of the same comet.

As part of the 2018 project on developing the observatory as a scientific tourist destination, the observatory began to be kept open to the public daily from 6:30 pm to 8:30 pm as an opportunity for inquisitive minds. The vintage class 5-foot refractive telescope installed in 1841 is still in operational condition and could qualify to be the oldest working telescope of its class in India. Of the three sidereal clocks imported from London in 1841, one is still working and could possibly be one of the oldest working mechanical clocks in India. The observatory is open to the public on all weekdays for sky-watchers using the modern telescopes, and on special occasions open houses are conducted for schools, colleges, community welfare groups and residence associations. The public are allowed to use the 5-foot vintage telescope under the guidance of the observatory staff on occasions of special celestial events. Figure 2a shows the footfall in the observatory over the past 5 years, with the impact of COVID-19 restrictions during 2020–2022 evident. Jupiter’s opposition of 26 September 2022 provided an impetus to the observatory when there was public interest in the possibility of seeing the celestial event using our telescopes. Public interest increases when the news of a celestial event spreads through media such as television channels, newspapers, the Internet and so on. After September’s Jupiter opposition was broadcast live on television, the observatory saw a considerable increase in the number of visitors. However, Thiruvananthapuram is on the southern tip of the Indian subcontinent, so it receives rain through an extended period from June to January, making a limited number of nights available for any kind of serious astronomy. Compounded with that, the observatory, once located on the highest mountain in the city, now has a city grown all around it with trees overarching the horizontal line of vision and skyscrapers polluting the night light.

Fig. 2: Footfall in the observatory.
figure 2

a, Yearly account for 2018–2023. b, Monthly account for the 2022–2023.

The arrival of comet C/2022 E3 (ZTF) further stimulated public attention. The sky did not allow any observations during the days the comet was predicted to be nearest to Earth, with a depression in the Bay of Bengal spoiling the viewing conditions in January/February 2023. Fig. 2b shows the monthly footfall in the observatory over the past year, showing the effect of the arrival of the comet. The comet C/2022 E3 (ZTF) was visible from 13 February 2023 to 18 February 2023 and the public were sensitized on the possibility of viewing it using the observatory telescopes. The whitish comet as shown in Fig. 1c was what the public could see through the telescopes, and they were curious to know why the observatory telescopes were not showing them the green-headed comet as widely reported on the Internet and in newspapers. This has helped the observatory to be sought after for genuine scientific discourse on celestial observations.

With the occurrences of visible celestial events getting attention in the media and the opportunity to visualize them at Thiruvananthapuram, the observatory is nurturing a generation of knowledgeable society. An exciting phase is starting for the post-graduate and research students in the state of Kerala who have been waiting eagerly for this first light from the Thiruvananthapuram Astronomical Observatory.