Skip to main content

100 years with our closest star, the sun (hindu)

Indian Institute of Astrophysics releases digitised images of the sun for researchers and science enthusiasts

Every day, since 1904, staff at the Kodaikanal Solar Observatory in Tamil Nadu have aimed their telescope at the sun, freezing the images of its disc. This data, spanning a hundred years and more, has now been digitised by astrophysicists from the Indian Institute of Astrophysics, Bengaluru, and made available to the public.

Apart from use in academic studies of long term behaviour of the sun, the data can be used to better understand sunspot activity which impacts climate and affects telecommunication systems. It also throws light on major events in the past which had an impact on the earth’s magnetic field. “From that knowledge we may understand the current and future events with greater precision. This also allows us to predict future [sunspot] activity levels with better accuracy,” says Dipankar Banerjee, IIAP, the Principal Investigator.

While ‘spectroheliograms’ were taken at the Kodai observatory since 1902, it was in 1909 that the data was used to discover the Evershed effect – that gases in the sunspots flowed radially outwards. The discovery by John Evershed put the KSO at par with the best observatories in the world. But its importance eventually declined as it was not upgraded or maintained. In a backhanded way, though, this turned out to be beneficial, because “the pictures had all been taken with the same instrument over the years, and this made it much easier to calibrate and digitise,” says Sudip Mandal, a Ph.D student who has worked on the project.

The data is unique not only in that it spans a hundred years, but that there are three sets of images, taken using different filters – White light, H-alpha and Calcium-K. It is known that the sun has a layered structure, and each of these data sets exposes a different layer.

Under white light filtering, the sun’s photosphere and the sunspots are visible, while the Calcium-K light can show layers some 2,000 km above this, in the chromosphere. The H-alpha images show up layers a little above the Calcium-K images. Features called “filaments” which are related to large expulsions of material from the sun’s surface can be viewed in the sets.

Opening up the digitised data has attracted international attention: Max Planck Institute, Gottingen; National Astronomical Observatories of China, Beijing and Big Bear Solar Observatory, US are interested in studying the way the sun’s luminosity changes. Though the sun appears to have a steady brightness, its luminosity actually undergoes changes over time. Some of the groups. The Big Bear Solar Observatory and the Beijing teams are interested in the H-alpha data in order to study the filaments that can be observed in those shots. Within India, groups from IUCAA, Pune; Physical Research Laboratory, Ahmedabad; and IISER, Kolkata, want to make studies.

A movie that the scientists made out of a sequence of hundreds of white light images shows how the sunspots appear and disappear periodically over an eleven-year cycle. Such movies offer immense possibilities for developing educational software, as classes of students can visually experience how the sun and the sunspots behave over the years. Just like CERN offers its data to science hobbyists, for analysis that does not require much training and yet cannot be carried out without human intervention, this data, too, could be used by science fora in India to build citizen science projects.

The data was historically archived in photographic plates and film. After the digitisation, the images are preserved in high-resolution digital format. “We store it in FITS [flexible image transport system] which is the most commonly used digital file format,” clarifies Dr Banerjee.

Digitising this has been a challenging task wthat involves not just reading and displaying the image but also extracting information – for instance differentiating a sunspot from artefacts such as a scratch or a fungal streak. “It can only be done using a lot of sophisticated mathematical tools. Some are available some we have had to develop to handle these challenges,” says Dr Banerjee.

This data can be freely downloaded from and wis also available on request through the contact details given on this website.

The project which was initiated about six years ago by S.S. Hasan, then the director of IIAP, has succeeded in converting to digitised format some sixty-seventy thousand images previously stored in photographic plates. The team includes scientists and the big team of research assistants at the Kodaikanal lab.

At the moment, the group has released the “lowest level” or raw data and plans are on to eventually release the processed ones, too.


Popular posts from this blog

Cloud seeding

Demonstrating the function of the flare rack that carries silver iodide for cloud-seeding through an aircraft. 
Water is essential for life on the earth. Precipitation from the skies is the only source for it. India and the rest of Asia are dependent on the monsoons for rains. While the South West Monsoon is the main source for India as a whole, Tamil Nadu and coastal areas of South Andhra Pradesh get the benefit of the North East Monsoon, which is just a less dependable beat on the reversal of the South West Monsoon winds.

SC asks Centre to strike a balance on Rohingya issue (.hindu)

Supreme Court orally indicates that the government should not deport Rohingya “now” as the Centre prevails over it to not record any such views in its formal order, citing “international ramifications”.

The Supreme Court on Friday came close to ordering the government not to deport the Rohingya.

It finally settled on merely observing that a balance should be struck between humanitarian concern for the community and the country's national security and economic interests.

The court was hearing a bunch of petitions, one filed by persons within the Rohingya community, against a proposed move to deport over 40,000 Rohingya refugees. A three-judge Bench, led by Chief Justice of India Dipak Misra, began by orally indicating that the government should not deport Rohingya “now”, but the government prevailed on the court to not pass any formal order, citing “international ramifications”. With this, the status quo continues even though the court gave the community liberty to approach it in …

India’s criminal wastage: over 10 million works under MGNREGA incomplete or abandoned (hindu)

In the last three and half years, the rate of work completion under the Mahatma Gandhi National Rural Employment Guarantee Act (MGNREGA) has drastically declined, leading to wastage of public money and leaving villages more prone to drought. This could also be a reason for people moving out of the programme.

At a time when more than one-third of India’s districts are reeling under a drought-like situation due to deficit rainfall, here comes another bad news. The works started under the MGNREGA—close to 80 per cent related to water conservation, irrigation and land development—are increasingly not being completed or in practice, abandoned.

Going by the data (as on October 12) in the Ministry of Rural Development’s website, which tracks progress of MGNREGA through a comprehensive MIS, 10.4 million works have not been completed since April 2014. In the last three and half years, 39.7 million works were started under the programme. Going by the stipulation under the programme, close to 7…