Sun Surface Cooler Than Previously Thought
February 4, 2013

Why Surface Of Sun Isn’t As Hot As You’d Think

Lee Rannals for — Your Universe Online

One who didn't know better would think that the closer you get to the sun, the warmer you are. However, it is actually the outer edge of the sun that you would find to be scorching, compared to the surface, and one study sought to find out why.

Scientists from Northumbria University wrote in the journal Nature Communications that they used solar-imaging technology to observe the Sun's chromosphere, which is a region of the Sun's atmosphere sitting between its surface (photosphere) and outer layer (corona).

Astronomers have been looking into what causes some stars to have a corona that is nearly 200 times hotter than their photosphere, despite being further away from the heat source. They believed the cause of the increased temperature is due to magnetohydrodynamic (MHD) waves, which distribute energy generated below the star's surface to the outer layers of the sun's atmosphere.

The team looked at the MDH waves using the Rapid Oscillations in the Solar Atmosphere (ROSA) solar-imaging telescope to look at the chromosphere. This tool allowed some of the highest resolution images of the chromosphere to be obtained, which in turn allowed scientists to study the speed and power of the waves, and then determine the amount of energy they transport.

Dr. Richard Morton and his colleagues confirmed through their study that MHD waves could be responsible for transporting energy from below the solar surface, through the chromosphere, and into the corona, leading to the heating of the outer layers in excess of a million degrees.

"The Sun is our closest star and provides a unique opportunity to study the properties of stars in detail," Morton said in a statement. "Stars generate heat through thermonuclear reactions in their core and the temperature decreases towards the star´s surface."

However, Morton said, a large number of stars have higher temperatures at the outer edges of their atmospheres than on their surface.

“Our observations have permitted us to estimate the amount of energy transported by the magnetic waves, and these estimates reveal that the waves´ energy meets the energy requirement for the unexplained temperature increase in the corona," Morton explained.

The Northumbria researchers aren't the only group of scientists looking to gain a better understanding of the sun. NASA recently announced that its scientists have witnessed the first flux rope, which will inevitably help them to get a better start on predicting space weather.

Flux ropes are a series of loops that lie at the heart of coronal mass ejections on the sun, and images taken by NASA's Solar Dynamics Observatory helped capture this event, which scientists say looked exactly like the theorized cartoon sketches that had previously been drawn up of it.

Knowing when and why these flux ropes occur with CMEs will help scientists know when to look for the eruptions on the sun, and whether we can expect any adverse effects from it here on Earth.