A "current sheet" is a very fast and flat flow of electrically-charged material, defined in part by its extreme thinness compared to its length and width.
"Current sheets" form when two oppositely-aligned magnetic fields come in close contact, creating very high magnetic pressure.
The multi-faceted view of the December 2013 flare was made possible by three solar-watching missions: Nasa's Solar Dynamics Observatory (SDO), Nasa's Solar and Terrestrial Relations Observatory (STEREO) and Hinode, a collaboration between the space agencies of Japan, the US, Britain and Europe.
Solar flares are intense bursts of light from the sun. They are created when complicated magnetic fields suddenly and explosively rearrange themselves, converting magnetic energy into light.
"The existence of a 'current sheet' is crucial in all our models of solar flares," said James McAteer, astrophysicist at New Mexico State University.
"These observations make us much more comfortable that our models are good," he added.
The strongest solar flares can impact the Earth's atmosphere and interfere with our communications systems and also disrupt onboard satellite electronics.
Unlike other space weather events, solar flares travel at the speed of light, meaning we get no warning that they are coming.
Better models lead to better forecasting, said Michael Kirk, space scientist at Nasa's Goddard Space Flight Center in Greenbelt, Maryland.
"These complementary observations allowed unprecedented measurements of magnetic reconnection in three dimensions. This will help refine how we model and predict the evolution of solar flares," Kirk added.
Because "current sheets" are so closely associated with magnetic reconnection, observing a "current sheet" in such detail backs up the idea that magnetic reconnection is the force behind solar flares.
"You have to be watching at the right time, at the right angle, with the right instruments to see a current sheet," said McAteer in the study published in the Astrophysical Journal Letters.
The new study is unique in that several measurements of the current sheet - such as speed, temperature, density and size - were observed from more than one angle or derived from more than one method.