On June 27, 2013, NASA's newest solar observatory was launched into orbit around Earth. The Interface Region Imaging Spectrograph, or IRIS, observes the low level of the sun's atmosphere -- a constantly moving area called the interface region -- in better detail than has ever been done before. Unlike most orbiting observatories, IRIS has a very small images that only sees solar surface details within a small ‘window’ that is about 1/10 the diameter of the sun (3 arcminutes). This is a perfect size to study small details on the surface of the sun. It was also used in 2016 to observe the Transit of Mercury.
On May 9, 2016, IRIS focused on Mercury as it passed across the face of the sun in order to help calibrate its telescope. By observing the planet — a region that ideally should appear completely dark — the team could determine just how the optics focus incoming light. IRIS can then be recalibrated to accommodate any changes that may have happened during launch into space.
Mercury transits sun 2016
Credits: IRIS, LMSAL/NASA, Wei Liu and Bart De Pontieu
This movie shows a composite of the IRIS imagery, in the inset, and imagery from NASA's Solar Dynamics Observatory, or SDO, as the golden background with a view of Mercury's transit moving from left to right across the bottom.
IRIS was able to track Mercury for 50-minute chunks of time after which the telescope was repointed. Repointing takes about 10 minutes during which time no data can be gathered, so IRIS was not able to see Mercury during its whole transit. The inset shows a blend of IRIS observations with SDO filling in the gaps while IRIS was repointing.
During the August 21, 2017 total solar eclipse, IRIS will not be able to capture an image of the sun the way that Hinode or SDO will, but through its small observing window, it will be able to study the limb of the moon and the Baily’s Beads phenomenon among other high-resolution studies.
Images will be presented on this page as IRIS scientists release them after the eclipse.