Science & Nature - Space jellyfish: glowing rocket plumes in the twilight sky

A space jellyfish is a glowing atmospheric display produced during rocket launches at morning or evening twilight. While an observer on the ground is immersed in darkness, high-altitude exhaust gases emitted by the rising rocket are struck by direct sunlight. This illuminates the expanding plume, creating a glowing shape reminiscent of a jellyfish floating in the sky. Because of its unusual luminescence, sightings of this rocket phenomenon have occasionally caused public alarm, missile strike scares, and reports of unidentified flying objects.

Source: Wikipedia