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.

Exhibit on the web Go to `Arts in the Academy'	Most people don't give the Sun, the nearest of all stars, a second thought. Neither its presence nor its apparent stability is questioned. If it were, it would quickly become clear that the Sun is a star whose variability affects us in many ways. It impacts Earth's climate with effects that are yet to be fully understood. It also affects our technology, as eruptions on the Sun interrupt communications, play havoc with navigation systems, generate radiation that is harmful to astronauts and airline passengers, and occasionally push power grids to failure. The cause of this variability is the Sun's magnetic field. The magnetic field of the Sun shapes its atmosphere from the surface to well beyond the orbit of the Earth. It heats the atmospheric gases to temperatures that are nearly a thousand times higher than the temperature of the surface. This atmosphere glows at many different colors (wavelengths), depending on the temperature of the gas. Special optical systems and detectors allow us to image this mysteriously glowing Sun, with "false" colors added, giving visual form to things our unaided eyes could never see. An exhibit, on view at the National Academy of Sciences from February 19 to August 15, 2002, presents recent research and pictures of the sun. The exhibition encompasses images from the NASA Transition Region and Coronal Explorer (TRACE), the Extreme Ultraviolet Imaging Telescope (EIT), the Large Area Solar Coronal Observatory (LASCO), and the Michelson Doppler Imager (MDI) telescopes on the ESA/NASA Solar and Heliospheric Observatory (SOHO).
	From early November through the end of February the orbit of TRACE puts the Earth between the spacecraft and the Sun for a fraction of the time, thus obscuring our view of the Sun. This ``eclipse season'' is generally a period of simpler observing, often in the visible and ultraviolet wavelengths rather than in the EUV, and with substantial gaps in our otherwise continuous viewing of the Sun. This ``picture of the day'' site will not be updated during that period (but we'll save the interesting images for the spring of next year!). As a parting gift for the year, we put together a collage of some of the many images shown at this site in a one-page calendar for the year 2002. You're welcome to download a (6.6MB) postscript version of it.
	This image shows an eruption in progress in Active Region 9682 (observed in the 171Å pass band, most sensitive to emission at 1 million degrees). The event started shortly after 11.30. The (QuickTime/JPEG; 5.6MB) movie in 171Å shows the evolution of the eruption for an hour. Notice the apparent twisting of the field, and the intricate fine structure in the emission that suggest blobs of material moving along and distorting the magnetic field. Compare the H alpha image obtained at Big Bear Solar Observatory.
	The top image of Active Region 9678 was taken with TRACE on 28 October 2001 at 11:02 UT in the 171Å passband, showing emission from gas at approximately 1 million degrees (the area is 512 by 512 arcseconds, binned 2x2 relative to the usual resolution). The image is centered on the sunspots in the western side of the bipolar magnetic region. A fan of cool loops radiates away from this cluster of magnetic flux, in part reaching over the active region to connect to the field in the eastern side, in part to other nearby field clusters. The twist in the coronal loop fan as one looks further and further away from the region is indicative of large electrical currents through spot and overlying corona. These add their own field component to what otherwise would have been much more like the simple field lines over a horseshoe magnet. The lower image is a hydrogen alpha image taken at Big Bear Solar Observatory, on the same day at 15:54 UT (the alignment and image scale are approximate, and the image was high-pass filtered). Notice that a similar spiraling of the field can be seen even in the chromosphere close to the solar surface. (TRACE image courtesy Dawn Myers)
	The magnetic field in the solar atmosphere shapes the structures that we see, as the emitting gas can generally only move along the field. Sometimes, however, packets of gas are accelerated so much that they can shoot through the magnetic field almost in a straight line. This (QuickTime/JPEG; 5.0MB) movie in 171Å of a surge (and some loop brightenings) at the east limb of the Sun shows an example of that. But despite the large initial speed it has difficulty escaping the Sun: much of the material in this event slows down, being pulled back by the solar gravitational field, and - as it cools and darkens - slides back to the surface. Courtesy Charles Kankelborg.
	Active regions 9628 and 9632 are rotating over the southwest limb of the Sun in this image, making a nice display of thin loops arching above them. This image was taken in the Fe IX/X 171Å channel at 23:59 UT on the first day of the new fiscal year, 01 10 01. North is to the left, west to the top. The field of view is 512 arc sec N/S and 384 arc sec E/W. These active regions produced several M and X flares during their disk passage, including the M1.2 flare at 23:40 UT that is seen in this image. Courtesy Dick Shine.
	On 3 October 2001 TRACE observed a small filament eruption (C6.1 flare, not obviously associated with a coronal mass ejection) from Active Region 9636. The event started around 06:38 UT when a compact filament started to rise. At 06:40 UT a compact brightening occurred in the 171Å channel (most sensitive to emission from gas at 1 million degrees), and within 2 minutes of that, the eruption had started, with material moving upward with velocities in excess of 600 km/s. From about 06:46 UT onward cool, dark material could be seen moving up surrounded by bright, hot material. At 07:02, TRACE moved into a high-radiation SAA zone. By the time it came out, at 07:21 UT, the erupting material had disappeared, and only a cooling set of loops was left at the site of the eruption. The composite image on the left is shown at half the resolution. Here are the four panels at full resolution of one pixel for each 375 km: 1, 2, 3, 4.
	Filaments are complex, dynamic magnetic structures, in which cool, chromospheric material is suspended in the otherwise hot corona. The top image to the left is a snapshot (at 11:30:53) out of this (QuickTime/JPEG; 6.7MB) movie in 171Å, which shows 4h 20m in the life of the filament. Notice how the cool material, which shows up because it absorbs EUV light emitted by hot gas behind it, seems to slosh back and forth as field and gas pressures evolve. The lower image shows the filament in the Halpha line of hydrogen, characteristic of gas around 10,000 to 20,000 degrees. That image was taken at Big Bear Solar Observatory at 16:05 UT on that day.
	Not only big filaments erupt. In the image to the left, we see an eruption in progress from a small magnetic bipole emerging to the northwest of AR9636, right next to a fan of relatively cool loops emanating from a cluster of magnetic field in the quiet Sun (this image was taken at 02:28 UT on 3 October 2001 in the 171Å channel, sensitive to emission from about 1 million degrees; expanded by a factor of two compared to the usual scale). The (QuickTime/JPEG; 8.5MB) movie in 171Å shows the evolution of the emergence and eruption. The emergence started around 0 UT on 2 October. There are some small eruptive events along the way, for example at 14:00 UT, 16:05 UT, 17:25 UT, and 22:18 UT. But around 02:22 UT on 3 October a much larger event occurs with bright and dark material being lifted up through a cusp-like magnetic field structure. Much of the cool material can be seen to slide down again after about half an hour, absorbing light from the underlying brighter loops. After that, the region's activity decreases, and the loops evolve smoothly.
	An M9.1 flare (see the GOES X-ray plot) went off in Active Region 9632 around 04:41 UT. This TRACE image (left), taken in the 171Å passband (1 million degrees) shows the event developing into a mass ejection around 05:20UT, at about the time of maximum X-ray brightness. The animated gif on the right shows the coronal mass ejection as observed with SOHO's LASCO.