New technology is set to pave the way in predicting solar flares
The Swedish 1-m Solar Telescope (SST) on the Spanish island of La Palma has undergone a significant upgrade. Operated by Stockholm University, this telescope now has a larger field of view, whilst critically maintaining sharpness. Additionally, it has gained the ability to measure light polarisation in a new range of wavelengths.
“The new technology gives us completely new opportunities to map the Sun's magnetic field,” says Dan Kiselman, assistant director of the Institute for Solar Physics at Stockholm University’s Department of Astronomy. “This is an important step towards being able to predict the kind of solar flares that can cause problems for us on Earth.”
Making magnetic fields visible
The telescope works by directing sunlight through a lens at the top of a tall tower down into a basement, where the light is divided between various scientific instruments. The updated system features the replacement of the CRISP instrument which operated in red light, with the new CRISP2 instrument, revealing a substantial increase in the field of view: 120 arc seconds, corresponding to 86,000 km on the Sun's surface. CHROMIS, which observes blue light, has new detectors providing a larger field of view and it has also been supplemented with a polarimeter to measure the polarisation of light, i.e. its plane of oscillation.
“This will enable us to measure magnetic fields by observing the H and K spectral lines, hopefully at higher altitudes in the solar atmosphere than has previously been possible,” says Dan Kiselman.
Maps of the Solar Atmosphere
Spectral lines are formed in the solar atmosphere when atoms absorb or emit light at specific wavelengths, or colours. By observing certain spectral lines, information can be obtained about different layers of the Sun’s atmosphere, and phenomena that propagate vertically can be tracked.
“One of our goals is to create reliable maps of the solar atmosphere’s structure and magnetic field, so that we can follow what is going on and in the future even learn to predict what will happen based on the data we collect,” says Dan Kiselman.
Northern Lights and magnetic storms
The Sun experiences bursts of energy so powerful that they can affect Earth. One such example is solar flares, which can be likened to magnetic short circuits initiated at high altitudes above the sun’s surface, where unfortunately, it is difficult to take measurements. Another example is ‘coronal mass ejections’, which are clouds of plasma thrown off by the sun. These take a couple of days to reach Earth, where they collide with the magnetosphere.
“This creates auroras and magnetic storms, which can cause problems for our technological systems,” says Dan Kiselman.
We need to stay one step ahead
Most of the time, ordinary people on Earth do not notice solar eruptions, but there are risks when they become particularly strong. For example, there is a risk of high levels of X-ray radiation in the upper atmosphere, which can affect radio communication. An additional risk is that a large solar flare could disrupt or even pose damage to electrical installations on Earth, and in the worst case, entire power grids. To prevent these risks, further knowledge about solar flares is required, such as how they are triggered. In the future this will enable us to predict them based on observations.
“To achieve that goal, we need to be able to map the physical conditions higher up in the solar atmosphere. We also need a wide field of view to increase our chances of covering an eruption in real time when it occurs,” says Dan Kiselman.
The atmosphere sets limits
Once the technical conditions are in place, constant readiness is required. Even though the conditions at La Palma are perhaps the best on Earth, it is usually the atmosphere that sets limits on how good the data will be.
“It's like when you see air above hot asphalt on a very hot day. The air shimmers and the images through the telescope become blurred and distorted. We can correct for some of these effects, but ultimately it is when conditions are almost perfect that you get really useful data. A lot of time is therefore spent waiting for the right conditions and stable air”, says Dan Kiselman.
But every now and then it happens. When the Earth’s atmosphere is stable and an important event occurs on the Sun, such as a large solar flare, unique data is collected.
“We can't let a single day go to waste because you never know when that moment will come. Then everything has to work,” says Dan Kiselman.
About the SST
The Swedish 1-m Solar Telescope (SST) is one of the world’s highest-resolution solar telescopes.
The SST is considered a research infrastructure of national importance. It is operated by the Institute for Solar Physics, a part of the Department of Astronomy at Stockholm University, which receives support from the Swedish Research Council.
Commissioned in 2002, the SST is still one of the world’s most advanced solar telescopes despite its twenty-three years of service. Located 2,400 metres above sea level on the island of La Palma in the Canary Islands, the SST benefits from ideal atmospheric conditions. The new technical upgrade therefore consolidates the SST’s position as a world leader in the field. Its combination of image quality, field of view size, and advanced instruments that can all work in parallel, is unique.
The two instruments that have recently been upgraded are:
CHROMIS, an imaging spectrometer for blue light. Its field of view has increased from 60x40 to 80x80 arc seconds (approximately 57,000 km on the Sun). CHROMIS is now also equipped with a polarimeter, enabling measurements of the polarisation (direction of oscillation) of light in spectral lines. This can be used to estimate the strength and direction of magnetic fields.
CRISP2 is an imaging spectropolarimeter that operates in red light and replaces the previous CRISP. Its circular field of view has grown from 80 to 120 arc seconds (approximately 86,000 km on the Sun).
Both CHROMIS and CRISP2 are double Fabry–Pérot interferometers. They function as narrow-band optical filters that can rapidly scan in wavelength through spectral lines in the solar spectrum.
Funding
The upgrade of the instrumentation and the research it enables is funded by Stockholm University, as well as by grants from the Swedish Research Council and the European Research Council.
Last updated: September 22, 2025
Source: Communications Office