Welcome to the STEREO Learning Center

Image artifacts - Stars, planets, and comets

Stars are always present in the STEREO COR2, HI1, and HI2 images, and can sometimes be seen in COR1. Stars drift slowly from left-to-right with time, caused by the spacecraft orbiting around the Sun. Twice a year the Milky Way will drift through the field-of-view, as in this example from the HI1 on STEREO Ahead.

The Milky Way passing through the field-of-view of the STEREO Ahead HI1 telescope on October 12, 2009. Click on any image for a higher resolution version.

Often, planets can also be seen passing through the telescope fields-of-view. The STEREO Planet Finder page shows what planets are currently visible in the STEREO telescopes, while the STEREO Orbit Tool shows the positions of the planets in the solar system for any given date during the mission. Most planets are too bright for the sensitive optics in the STEREO coronagraphs, causing them to appear overly large and distorted. Note the "butterfly" shape of Venus in the COR2 image below, caused by diffraction off the occulter stem. In the HI1 and HI2 images, planet images and particularly bright stars will also be accompanied by vertical streaks (either white or black), which is due to the shutterless readout of the cameras on these telescopes. Most planets will move from left to right, but the inner planets Mercury and Venus often are seen moving from right to left.

The planets Venus (left) and Mercury (right) as seen by the STEREO Behind COR2 telescope on October 13, 2009		Jupiter as seen by the STEREO Ahead HI1 telescope on September 1, 2008

Occasionally, even bright comets can cause vertical streaks in the data. Here is an image of Comet McNaught as it appears in HI1-B on the SSC website. Note the large dark vertical dark streak, and the smeared brightness toward the bottom of the image, both effects caused by the high brightness of this particular comet. Advanced techniques exist for removing some of these effects from the images, but these are not applied routinely on the SSC website. Better images of Comet McNaught are available on the STEREO Gallery. Additional information about comets seen by STEREO can be found on the Sungrazer website.

Comet McNaught as seen by the STEREO Behind COR2 telescope on January 12, 2007

Back to image artifacts page.