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Gegenschein in Leo/Cancer with tracking telescope in foreground. The Gegenschein is caused by the reflection of the Sun's light by dust lying in the plane of the Solar System. The dust acts like a mirror, forming a faint image of the Sun at the anti-solar point. Occasionally a faint band of light, known as the Zodiacal Band, is also visible, stretching around the ecliptic (the projection of the plane of the Solar System on the sky). The dust also causes a halo around the Sun, elongated along the ecliptic & visible just after sunset, known as zodiacal light. Although all of these effects are permanent, they are extremely faint and so only visible from very dark sites. See back of print 01 for technical details. (KEYSTONE/SCIENCE PHOTO LIBRARY/JOHN SANFORD/SCIENCE PHOTO LIBRARY)