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The Transition Region

THE SUN 

Why We Study the Sun 
The Big Questions 
Magnetism - The Key 

SOLAR STRUCTURE 

The Interior 
The Photosphere 
The Chromosphere 
The Transition Region 
The Corona 
The Solar Wind 
The Heliosphere 

SOLAR FEATURES 

Photospheric Features 
Chromospheric Features 
Coronal Features 
Solar Wind Features 

THE SUN IN ACTION 

The Sunspot Cycle 
Solar Flares 
Post Flare Loops 
Coronal Mass Ejections 
Surface and Interior Flows 
Waves and Helioseismology 

RESEARCH AREAS 

Flare Mechanisms 
3D Magnetic Fields 
The Solar Dynamo 
Sunspot Cycle Predictions 
Solar Wind Dynamics 

sumer_C_IV_sm.jpg (18800 bytes)

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The transition region is a thin and very irregular layer of the Sun's atmosphere that separates the hot corona from the much cooler chromosphere. Heat flows down from the corona into the chromosphere and in the process produces this thin region where the temperature changes rapidly from 1,000,000ºC (1,800,000ºF) down to about 20,000ºC (40,000ºF). Hydrogen is ionized (stripped of its electron) at these temperatures and is therefore difficult to see. Instead of hydrogen, the light emitted by the transition region is dominated by such ions as C IV, O IV, and Si IV (carbon, oxygen, and silicon each with three electrons stripped off). These ions emit light in the ultraviolet region of the solar spectrum that is only accessible from space.

sumer_S_VI_sm.jpg (12900 bytes)

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The transition region has been studied from space using instruments on several spacecraft including the Solar Maximum Mission and the Solar and Heliospheric Observatory. The Transition Region and Coronal Explorer (TRACE) mission is now actively acquiring data on the structure and dynamics of the transition region. The images to the left are from the SUMER instrument on the SOHO Mission. The top image is emission from Carbon IV at temperatures of about 100,000ºC. The bottom image is emission from Sulfur VI at temperatures of about 200,000ºC.

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Author: David H. Hathaway, david.hathaway@msfc.nasa.gov, (256) 544-7610
Mail Code SD50, NASA/Marshall Space Flight Center, Huntsville, AL 35812

 

Responsible Official: John M. Davis, john.m.davis@msfc.nasa.gov, (256) 544-7600
Mail Code SD50, NASA/Marshall Space Flight Center, Huntsville, AL 35812

 

Curator
Last revised 2000 February 04 - D. H. Hathaway


Reproduced from http://science.nasa.gov