  Solar spicules are chromospheric fibrils that appear everywhere on the Sun,
yet their origin is not understood. Using high resolution observations of
spicules obtained with the Swedish 1-m Solar Telescope, we aim to understand
how spicules appear in filtergrams and Dopplergrams, how they compare in Ca II
H and H-alpha, and what can make them appear and disappear. We find
thatspicules display a rich and detailed spatial structure, and show a
distribution of transverse velocities that when aligned with the line of sight
can make them appear at different H-alpha wing positions. They become more
abundant at positions closer to the line core, reflecting a distribution of
Doppler shifts and widths. In H-alpha width maps they stand out as bright
features both on disk and off limb, reflecting their large Doppler motions and
possibly higher temperatures than in the typical H-alpha formation region.
Spicule lifetimes measured from narrowband images at only a few positions will
be an underestimate because Doppler shifts can make them disappear prematurely
from such images; for such cases, width maps are a more robust tool. In H-alpha
and Ca II H filtergrams, off limb spicules essentially have the same
properties, appearance, and evolution. We find that the sudden appearance of
spicules can be explained by Doppler shifts from their transverse motions, and
does not require other convoluted explanations.
