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A spike-like jet in the upper chromosphere of the Sun, visible especially in Hα light. Spicules rise upwards into the corona at velocities of about 30 km/s, reaching altitudes of 9000 km in about 90 s. They last about 15 min, ending their lives by fading rather than descending. They tend to be clustered, giving the appearance of porcupine quills on the solar limb. Seen against the disk, in Hα light, they seem to be identifiable as fine mottles, light or dark depending on their height (although they always appear dark when observed in the red line wing of the Hα line). Fine mottles form clusters with their bases in the coarse mottles which outline the chromospheric network. At the centre of the Sun's disk, clumps of spicules form radiating patterns called rosettes.

Subjects: Astronomy and Astrophysics.

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