Telescope on IRIS sees first light

The observatory has produced its first images of a little understood region of the Sun.
By | Published: July 26, 2013 | Last updated on May 18, 2023
Region around two sunspots
This image from NASA’s IRIS spacecraft shows the region around two sunspots – the dark areas at upper left and lower right. It shows emission from ionized silicon (Si IV) in the transition region at a temperature of about 116,000° Fahrenheit (64,000° Celsius), plus ultraviolet continuum from the chromosphere at a temperature of about 17,000°F (9,000°C). The bright dots are short-lived intense patches of Si IV emission. The role that these dynamic events have in heating the solar atmosphere is currently unknown. // NASA
NASA’s Interface Region Imaging Spectrograph (IRIS) observatory has produced its first images and spectra of a little understood region of the Sun, through which the energy that supports the Sun’s hot corona is transported. IRIS was launched June 27, 2013, and the front cover of the IRIS telescope was opened July 17.

“Already, we’re finding that IRIS has the capability to reveal a very dynamic and highly structured chromosphere and transition region,” said Hui Tian of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts. “Thin and elongated structures are clearly present in these first-light images, and they evolve quickly in time.”

Important goals of the IRIS mission are to understand how the Sun’s million-degree corona is heated and to reveal the genesis of the solar wind. By tracing the flow of energy and plasma through the transition region — between the solar surface and the solar corona — where most of the Sun’s ultraviolet emissions are generated, IRIS data will allow scientists to study and model a region of the Sun that has yet to reveal its secrets. Ultimately, such understanding could enable scientists to provide forecasts for the Sun’s destructive behavior, which can disable satellites, cause power grid failures, and disrupt GPS services. IRIS will deliver near-continuous solar observations throughout its two-year mission.

IRIS takes images with four different filters in the ultraviolet wavelength range. It is the first time that images in these wavelengths have been taken with high resolution — about 150 miles (240 kilometers) — and at a cadence that can capture the rapid evolution of the chromosphere (every 10 seconds).

IRIS also takes very high-resolution spectra in three ultraviolet wavelength ranges. The spectra are critical for providing physical measurements underlying the dynamics seen in the images. Through the analysis of high-spatial-resolution spectra, scientists can measure flow speeds, energy deposition, and wave properties and densities of the atmospheric plasma.