World's largest solar telescope

 The Daniel K. Inouye Solar Telescope revealing breath taking image of a continent-size sunspot  

The Daniel K. Inouye Solar Telescope, the world's largest solar telescope, can see the sun in unprecedented detail. The National Science Foundation’s (NSF) Daniel K. Inouye Solar Telescope is a four-meter solar telescope on the island of Maui, Hawai’i. It’s currently the largest solar telescope in the world. With a focus on understanding the Sun’s explosive behaviour, observations of magnetic fields are at the forefront of this innovative telescope. A combination of an off-axis design, to reduce scattered light, and cutting edge polarimetery produces the first on-going measurements of the magnetic fields in the Sun’s corona. The Inouye’s 4-meter mirror provides views of the solar atmosphere like we’ve never seen before. Focusing on small observing changes, the cutting-edge instrument suite gathers unprecedented images from the Sun’s surface to the lower solar atmosphere. The Inouye Solar Telescope reveals features three times smaller than anything we can see on the Sun today, and does so multiple times a second. Not only do the world-class instruments and optical assembly allow spectacular imagery, but also have incredible spectroscopic capabilities. Observing the specific fingerprints of hundreds of atoms and ions throughout the solar surface and atmosphere will help us explain the dynamic nature of the Sun’s behaviour. Weather on Earth can be wild, but it's not the only kind of weather we have to deal with. Space weather, all the winds and particles streaming off the sun, can have major impacts on Earth and human infrastructure. In the worst cases, this can mean dangerous disruption to our power grids and communications satellites.

To help us predict these space storms, astronomers have a newly improved space weatherman, and it's the best one to date. The Daniel K. Inouye Solar Telescope (DKIST), perched atop the Hawaiian mountain of Haleakalā, is the world's largest telescope used for studying the sun and predicting these storms. The team behind this technological marvel recently hit a major milestone, finally turning on one of DKIST's most powerful cameras, known as the Visible Tunable Filter, or VTF, after more than a decade working on its creation. This camera is the final piece of the puzzle for DKIST, and the VTF's addition "will complete its initial arsenal of scientific instruments," Carrie Black, director of the National Solar Observatory, said. DKIST will be a four-meter off-axis reflecting telescope, which will have the spatial, temporal, spectral resolution and dynamic range which is needed to see and measure the basic magnetic structures (magnetic fibrils) at the solar surface and into the outer atmosphere. Currently much of the magnetic field is invisible. We therefore will depend on the DKIST for quantifying, understanding, and predicting the consequences of such magnetism on solar-terrestrial and astrophysical plasmas.

"The significance of the technological achievement is such that one could easily argue the VTF is the Inouye Solar Telescope's heart, and it is finally beating at its forever place," Matthias Schubert, project scientist for the VTF, said. The debut image from the Inouye telescope's Visible Tunable Filter (VTF) camera shows a sunspot cluster many times larger than the continental US. VTF's first image shows a major clump of sunspots, dark blobs on the sun's surface caused by its intense magnetic field, each blob measuring wider than the continental US. This impressive camera can see details down to a resolution of about 6.2 miles (10 km's) per pixel on the solar surface, an absolutely wild resolution given that the sun is tens of millions of miles away from us. With DKIST we will have the ability to zoom in to observe fundamental magnetic and plasma processes occurring at their natural, and finally gain an understanding of the role magnetic fields and their interaction with the embedding plasma plays in solar activity. With the new spatial scales that DKIST will allow us to resolve, and the new spectral windows it will make available to us, we will also have new opportunities for discoveries of processes we had no idea existed before.

VTF provides more than just a simple snapshot. It captures images at multiple wavelengths of light to measure a spectrum, while also gathering information on how the light's electric field is oriented (known as polarization). These extra perspectives on the sun help reveal details of the solar surface, magnetic field and plasma which are otherwise invisible, informing our predictions for space weather and solar flares. During just one observation of the sun, this instrument can collect more than 10 million spectra, graphs of the light's intensity over different wavelengths, which help scientists determine how hot the solar atmosphere is, how strong the sun's magnetic field is and more. The main driver for a large aperture is the need to spatially resolve the fundamental length scales in the solar atmosphere: the photon mean-free path and the pressure scale height. To resolve both fundamental length scales, a resolution of 70 km or 0.1 arcsec is required in the photosphere. In addition, simulations have shown that some magnetic structures might be as small as 35 km (0.05 arcsec) in cross section. Current solar telescopes cannot resolve such scales because of their limited aperture. The near-infrared spectrum around 1.5 µm has many advantages, particularly for magnetic field studies; an aperture of 4 m is needed to clearly resolve features at 0.1 arcsec in the near infrared. Access to even longer wavelengths in the thermal infrared requires an open-air telescope design. It is only the beginning for the VTF and DKIST. The incredibly complex instrument still requires more testing and set-up, which is expected to be completed by next year.

In addition to the diffraction limit, time resolution is also a major driver for a large aperture. The number of photons per angstrom per second is independent of aperture size at the diffraction limit. Photospheric structures can move with surface speeds of 7 km/s, so for 0.1 arcsec or smaller features one must collect photons for only a few seconds to avoid spatial smearing. Thus, the total number of available photons collected with diffraction-limited spatial resolution actually decreases with increasing aperture. To obtain the necessary signal-to-noise ratio at a given spatial resolution, the required aperture is larger than required by diffraction alone. An accurate measurement in the visible of the vector magnetic field at 0.1-arcsec resolution and 5-second integration time requires a 4-m aperture. The newly released first images show great promise for how much we can learn about the sun, our nearest star. These images are "something no other instrument in the telescope can achieve in the same way," said National Solar Observatory optical engineer Stacey Sueoka. "I'm excited to see what's possible as we complete the system." DKIST will be the ideal tool for magnetic remote sensing in future ahead.