TRACE, pictured above, is the first U.S. led solar research satellite since the Solar Maximum Mission and the first transition region and coronal satellite to observe the Sun during the rise to solar maximum. TRACE was launched on April 2, 1998 in Universal Time. Its launch was scheduled to allow joint observations with the Solar and Heliospheric Observatory (SOHO) during the rise to the maximum of solar activity. Using TRACE, solar physicists are able to observe the solar surface (photosphere), through the transition region into the corona. They are able to make these observations with as little a delay as a few seconds per image between the various wavelengths and with one arc second spatial resolution, corresponding to about 725 kilometers at the Earth-Sun distance. TRACE explores the connections between the different layers of the solar atmosphere, tracing the magnetic field from the photosphere, where it is buffeted by flows, into the corona, where it shapes and channels the plasma.
The composite image above was produced using three different instruments on board SOHO. The solar disk (the innermost image) was taken by the Extreme Ultraviolet Imaging Telescope (EIT) in a spectral line emitted by an iron atom with fourteen electrons missing (284 Angstroms). The Sun's lower corona (the next annular image out) was taken in a line of oxygen with 5 electrons missing (O VI), by the Ultraviolet Coronagraph Spectrometer (UVCS). The outer most annular image was taken by the Large Angle Spectroscopic Coronagraph (LASCO). While SOHO has the capability to produce images out to 32 solar radii (solar radius = 6.96 * 10^5 km), a significant fraction of the Earth-Sun distance (1.496 * 10^8 km), TRACE can produce images of high spatial resolution and temporal cadence. Together they allow scientists to obtain simultaneous digital measurements of all the temperature regimes of the solar atmosphere.
Using TRACE in conjuction with various other solar missions, scientists hope to solve the mystery of how the corona is heated to over a million degrees and how the magnetic field and ionized gases interact. The Michelson Doppler Imager (MDI), an instrument on board SOHO, provides scientists with a history of how, when, and where the magnetic field emerges from or sinks below the solar surface. It shows how the magnetic field curves into an essentially horizontal direction which escapes detection or sometimes grows to make strong concentrations of magnetic field which can then produce flares. This history is invaluable for understanding TRACE observations and data. A typical full disk magnetogram is shown at the start of this paragraph. One magnetic polarity is represented by black, while the other polarity is represented by white.
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