Comet ISON

In the early hours of Nov. 27, 2013, Comet ISON entered the field of view of the European Space Agency/NASA Solar and Heliospheric Observatory. In this picture, called a coronagraph, the bright light of the sun itself is blocked so the structures around it are visible. The comet is seen in the lower right; a giant cloud of solar material, called a coronal mass ejection or CME, is seen billowing out under the sun.

During the last week of its inbound trip, ISON will enter the fields of view of several NASA Heliophysics observatories. Comet ISON will be viewed first by the broad field of view seen by NASA's Heliospheric Imager instrument aboard its Solar Terrestrial Relations Observatory, or STEREO, Next the comet will be seen in what's called coronagraphs, images that block the brighter view of the sun itself in order to focus on the solar atmosphere, the corona. Such images will come both from STEREO and the joint European Space Agency/NASA Solar and Heliospheric Observatory, or SOHO. Then, NASA's Solar Dynamics Observatory, or SDO, will view the comet for a few hours during its closest approach to the sun, known as perihelion. The X-Ray Telescope on the JAXA/NASA Hinode mission will also be looking at Comet ISON for about 55 minutes during perihelion.

All of these observatories will have different views. STEREO-B will be the only one that sees the comet transit across the face of the sun. In SDO's view, the comet will appear to travel above the sun, and the SDO instruments will point away from the center of the sun to get a better view for three hours on Nov. 28. In addition to learning more about the comet itself, these observations can make use of the comet as a tracer to show movement in the solar wind and solar atmosphere.