The NSF Daniel K. Inouye Solar Telescope, located on Haleakalā volcano in Maui, Hawaii, has achieved a major milestone by reaching 'first light' with its new Visible Tunable Filter (VTF), the world's largest imaging spectro-polarimeter.

The VTF, developed over 15 years by the Leibniz Institute for Solar Physics in Germany, is designed to capture high-resolution spectral, spatial, and temporal images of the sun, enabling detailed studies of solar phenomena and their effects on Earth.

The VTF is the fourth instrument added to the Inouye Solar Telescope, which has been operational since 2022, with four out of five planned instruments already in use.

Researchers celebrated the first successful images from the VTF, marking a significant technical milestone, as these images illustrate the dynamic nature of the sun's surface and its magnetic activity.

The VTF will undergo further science verification and commissioning, with full operational capabilities expected to begin in 2026, promising to advance our understanding of solar physics and its impact on space weather.

Christoph Keller, Director of the National Solar Observatory, emphasized the importance of DKIST in studying solar physics to better understand space weather, which can disrupt communications and affect infrastructure on Earth.

The VTF's debut coincides with the solar maximum phase of the 11-year solar cycle, characterized by heightened magnetic activity, which began peaking in late 2024.

This advanced instrument, weighing 5.6 tons and occupying two floors at the National Solar Observatory, showcases its capabilities by capturing images of sunspots with a spatial resolution of 10 kilometers per pixel.

The telescope's first observations were made possible after extensive calibration and integration of the VTF, completing the original suite of five first-generation instruments.

Despite still being in the testing phase, the VTF has already revealed very small structures on the sun, and further data processing is expected to enhance resolution when it enters regular scientific operation.

The VTF's ability to measure attributes such as magnetic field strength, temperature, and plasma flow velocity makes it a crucial addition to the DKIST's observational capabilities.