Inouye Solar Telescope activates powerful new spectro polarimeter for detailed Sun studies

Inouye Solar Telescope activates powerful new spectro polarimeter for detailed Sun studies
by Robert Schreiber
Berlin, Germany (SPX) Apr 30, 2025

The Inouye Solar Telescope, the world's largest solar observatory, has reached a critical milestone with the activation of its most advanced instrument to date: the Visible Tunable Filter (VTF), a massive spectro-polarimeter now operational atop Hawaii's Haleakala volcano. With a four-meter primary mirror, the telescope has delivered remarkable solar images since 2022, and the VTF dramatically expands its capabilities.

Researchers refer to the event as a "technical first light" for VTF. This 5.6-ton, two-floor instrument is designed to dissect sunlight with exceptional precision. Developed over 15 years by the Institute for Solar Physics in Freiburg, Germany, it uses two custom Fabry-Perot interferometers to isolate specific wavelengths of light and polarization states, enabling researchers to extract detailed solar data with spatial resolutions of 10 kilometers per pixel and temporal capture rates of hundreds of frames per second.

"The Inouye Solar Telescope was designed to study the underlying physics of the Sun as the driver of space weather. In pursuing this goal, the Inouye is an ideal platform for an unprecedented and pioneering instrument like the VTF," said Christoph Keller, Director of the National Solar Observatory.

The VTF allows scientists to explore the Sun's dynamic photosphere and chromosphere in unparalleled detail, capturing critical measurements such as plasma flow velocity, magnetic field strength, temperature, and pressure. This level of insight is essential for decoding the origins of solar eruptions that can affect Earth's magnetosphere and satellites.

"The commissioning of VTF represents a significant technological advance for the Inouye Solar Telescope. The instrument is, so to speak, the heart of the solar telescope, which is now finally beating at its final destination," explained Matthias Schubert, VTF project scientist at the Kiepenheuer Institute for Solar Physics (KIS).

In a demonstration of its imaging power, VTF captured a high-resolution image at 588.9 nanometers wavelength showing a sunspot and its finely detailed penumbra spanning a 25,000-kilometer square region of the solar surface. These sunspots are zones of intense magnetic activity that block the ascent of hot plasma, a key phenomenon in space weather research.

"VTF enables images of unprecedented quality and thus heralds a new era in ground-based solar observation," noted Sami K. Solanki, director at the Max Planck Institute for Solar System Research.