Header image

Images of the Sun taken by the
Transition Region and Coronal Explorer

The TRACE images may be used without restrictions in publications of any kind. We appreciate an acknowledgement indicating that the Transition Region and Coronal Explorer, TRACE, is a mission of the Stanford-Lockheed Institute for Space Research, and part of the NASA Small Explorer program. More information on TRACE and other TRACE images can be found here.

A quiet day on the Sun. No spectacular flares or mass ejections, no odd filaments moving, and nevertheless the image of AR 9169, with the much smaller AR 9167 just ahead of it, is very pretty. This image was taken with TRACE in the 171Å passband, showing the bright emission of the gas at about 1 million degrees, with the cooler material around 10,000 degrees showing up as dark, absorbing structures.
AR9154 in 171Å
AR9154 in 1216Å
These images of AR9154 were observed on 12 September 2000, around 11:41UT. They show a system of coronal loops at 1 million degrees (top) and at about 10,000 degrees (bottom). These loops are cooling down following what was probably a a C4.6 flare in the region that occurred at 08:55UT. Note the filament that runs from the active region to the left (south); it shows up clearly in the Lyman alpha (1216) image, even obscuring some of the active-region loops behind it, but is seen in the 171Å image only as dark whisps gliding erratically through the corona, suspended in the magnetic field. The images have been rotated, so that north is to the left.
A composite of solar images
Looking through the solar atmosphere. The central image is a three-color composite of the solar corona, observed with the Transition Region and Coronal Explorer (a NASA Small Explorer mission). This mosaic is made up of 3 exposures at each of 23 pointings; the green, blue, and red color tables in this ``true color'' image represent the 171Å (1 MK), 195Å (1.5 MK), and 284Å (2 MK) channels, respectively. The surrounding images are, clockwise starting from the top: SOHO/MDI magnetic map, white light, TRACE 1700A continuum,TRACE Lyman alpha, TRACE 171Å, TRACE 195Å, TRACE 284Å, YOHKOH/SXT X-ray image. The composite was prepared by Joe Covington (Lockheed-Martin Missiles and Space, Palo Alto).
AR 9143 again

Coronal mass ejection

This is a snapshot of Active Region 9143 observed with TRACE in the 171Å passband, showing bright material around 1 million degrees. This image, taken at 17:07UT on August 28, 2000, shows the corona during a C3.3 flare, associated with a mass ejection (towards the upper left of the image). The associated 3.3MB

AVI movie (Cinepak compressed)

shows the flare and mass ejection as a difference movie: where the image turns bright, the solar corona has become brighter after 16UT, and where it turns black it has dimmed. This shows the ejected material very well, first flying upward at several hundred kilometers per second. Later, some of it is seen to fall back as a dark cloud.
AR 9149/9147 (171Å) AR 9149/.9147 (white light)

Magnetic X point

These are snapshots of Active Regions 9149 (north) and 9147 (south) observed with TRACE in the 171Å passband (top), showing bright material around 1 million degrees, and in the white-light passband (using a smaller field of view). The 171Å image, taken at 10:17UT on 4 September 2000, shows the corona between two sunspots of equal polarity (look at the SOHO/MDI magnetogram here; the two regions are at the rightmost edge of the square on the full-disk magnetogram). Between the spots, the loops meet and are deflected sideways, forming a so-called X point in the magnetic field. The leftmost half of the field shows up clearly, but the rightmost half has a different temperature and is only vaguely visible.
An unstable filament
This is a still image in 171 Angstroms of a filament that is partially erupting. A filament is a structure in the corona consisting of relatively cool plasma supported by magnetic fields; the material is dense enough to absorb extreme ultraviolet light emitted by regions of the hot corona behind them. This image was taken by TRACE on 30 August 2000, at 22:33UT. Courtesy: Dawn Myers.
AR 9143

Flare shakes the corona!

This is a snapshot of Active Region 9143 observed with TRACE in the 171Å passband, showing bright material around 1 million degrees. This image, taken at 15:25UT on August 25, 2000, shows the corona exactly one hour after an M1.4 flare rocked the field. In 1999, TRACE discovered loop oscillations following flares. Since then, only very few of these have been observed. This time we were lucky: high over the region, diagonally towards the upper-left corner from the flare site, there are some loop bundles that oscillate about two periods before the motions disappear again. The associated 1.9MB

Quicktime movie (Cinepak compressed)

shows that in half resolution (showing only every 2nd exposure in our database). The high loops are so faint, that a normal intensity scale would not have shown them; the contrast in the images had to be reduced considerably to bring out these oscillating loops.
AR 9139
This is a snapshot of Active Region 9139 observed with TRACE in the 1600Å passband, showing bright material around 100,000 degrees. The associated 7MB

Quicktime movie (AVI compressed)

shows three days in the life of the region (from 11:20 UT on 23 August 2000 until 04:10 UT on 25 August 2000). The movie (with one frame every 7.5 minutes - showing 1/4 of all frames available) shows the field in the relatively compact active region shifting around in response to the convective flows. Note the continuous streaming of bright elements in the perimeter of the large sunspot on the right: although it appears that things are streaming away from the spot, the spot does not noticeably decrease in size, nor is there an accumulation of field in at the outer perimeter of the region where the streaming is seen. What exactly is going on here (a common feature of most sunspots) is still under study. Note also the faint flickering of the entire field of view: this is caused by sound waves that make the Sun ring like a bell (listen to it here) and are used in helioseismology.
High solar loops (1)
High solar loops (2)
On the left (top) is a TRACE image taken on 9 August 1999, around 23:00 UT, in the 171Å passband (characteristic of 1 million degree gas; shown as the square root of the measure intensity). High-arching loops stand out, to a height of appriximately 120,000 km, visible along their entire length. The image on the right is a ratio of 195Å to 171Å, and serves as a measure of temperature. This image shows the loops as green along most of their length, demonstrating that the temperature varies little along them (which is why they can be seen in the 171Å image in the first place). The fact that the temperature is so nearly constant along the length requires that most of the heating is concentrated low down, in the bottom 15,000 km or so.

If the temperature does not vary much along aloop, and lies around 1 million degrees along most of its length, the gas should sag into the bottom of the loops under the influence of gravity. Consequently, the gas density should decrease by a factor of almost three every 50,000 km; the emission (which scales as the square of the density) should drop by that factor every 25,000 km. The right-hand bar in the lower image on the left shows how radidly the emission should have dropped off in the case of such simple gravitational stratification; the observed situation is closer to the intensity profile in the left-hand bar, for which the scale height has been doubled. Clearly, the emission drops off much more slowly than expected from a simple static model. The assumptions that are generally made that solar coronal loops are essentially stationary (evolving slow compared to the time they can adjust to a new situation) and that they are uniformly heated have been demonstrated to be fundamentally untenable: many loops evolve very rapidly, and none of them is heated uniformly!

Temperature (filter ratio)

Arches and open fields
A comparison of an image of the solar corona and of the magnetic field direction at the solar surface (the thumbnail on the right, rotated version of the original, is too small to show enough details: click on it to see the large version). The image on the left is a full-disk mosaic of TRACE images (made up of 3 exposures at each of 23 pointings; the green, blue, and red color tables in this ``true color'' image represent the 171 A (1 million degrees), 195 A (1.5 million degrees), and 284 A (2 million degrees) channels, respectively). The white lines show where the magnetic field at the surface are magnetic neutral lines where the surface field vanishes. The image on the right is based on magnetograms observed with the 150-foot solar tower at Mount Wilson. It shows the same neutral field lines, while the colors indicate the direction of the magnetic field (as estimated by comparing measurements taken days apart, using the solar rotation to get a different view of the field): blue means that the field at the surface is tilted towards the right (West on the Sun), and red that the field is pointed towards the left (East). Wherever blue is to the left of a neutral line and red to the left, the field is expected to arch over the neutral line, and indeed we find arcades of loops in the TRACE image (as near ``a''). Where the colors adjacent to the neutral line are either reversed or the same on both sides, the field is more open and no coronal arcade is seen (as near ``b''). Image courtesy of Roger Ulrich (UCLA).

Other TRACE images in this collection: Set 1, 2, 3, 4, 5, 6. 7.

See also a collection of images related to the Sun, other cool stars, and solar-terrestrial effects


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