Most astronomical objects can be studied with a wide variety of telescopes, but the Sun is a different matter; even a brief peek would destroy the sensitive instruments on most professional telescopes. The National Solar Observatory exists to build and operate telescopes across America suited to observing our local light source. Its most powerful instrument yet, the Daniel K. Inouye Solar Telescope on Maui, Hawaii is now in operation and has released its first images. These are the first images of the chromosphere, the Sun's atmosphere.
The telescope was officially commissioned on August 31, but the images that have now been released were taken in June when the Sun was almost directly above the telescope’s location at Mount Haleakalā.
“NSF’s Inouye Solar Telescope is the world’s most powerful solar telescope that will forever change the way we explore and understand our sun,” said National Science Foundation Director Sethuraman Panchanathan in a statement. “Its insights will transform how our nation, and the planet, predict and prepare for events like solar storms.”
One of the newly released images is of the Sun’s “surface”, the other of its chromosphere, or middle atmospheric layer. Since the Sun is made of gas there is no solid surface, but there are major differences between what is considered the Sun proper and its atmosphere, and both need plenty of study.
Haleakalā has a long history as a site for solar research – the Mees Solar Observatory opened there in 1964, but the Inouye Telescope, with a 4-meter (13-foot) diameter mirror, is a whole new level of power. It’s been in planning for 25 years, and under construction for almost a decade.
Instruments this big take a lot of time to reach full operation, and that is particularly the case for a solar telescope, which needs to disperse all the heat its giant mirror concentrates. In 2020, test images of cells on the Sun and a sunspot looking like a close-up of an eye were released from the telescope.
Back then Thomas Rimmele boasted in a statement, “The sunspot image achieves a spatial resolution about 2.5 times higher than ever previously achieved, showing magnetic structures as small as 20 kilometers on the surface of the Sun.” The resolution of the images exceeded that managed even by the European Solar Orbiter, although the satellite can also see in wavelengths obscured for land-based telescopes by our atmosphere.
The Sun was still in a minimum of its 11-year cycle when the test images were made, with most days having not a single sunspot. There was little sign of associated activity such as solar flares and coronal mass ejections. The Inouye Telescope reaches full operations as the Sun climbs to peak activity, with five groups of sunspots visible today, and a spot on the far side so immense it is affecting the Sun’s vibrations.
All this activity has set off a burst of auroras near the Earth’s poles, but so far we have been spared anything powerful enough to do serious damage. On the other hand, Venus has been hit by two solar storms so large that if they had been pointed at Earth the costs could be high. The Inouye Solar Telescope may allow us to understand this peak in solar activity and prepare for the next one.