skyeye
The Ghostly Tail of Comet SWAN

What causes the structure in Comet SWAN's tail? Comet SWAN, which unexpectedly flared up
to naked-eye brightness last week, has been showing detail in its ion tail that might be
described as ghostly. The ion tail is made of ionized gas, energized by ultraviolet light
from the Sun and pushed outward by the solar wind. The solar wind itself is quite structured
and sculpted by the Sun's complex and ever changing magnetic field. Following the wind,
structure in Comet SWAN's tail can be seen to move outward from the Sun even alter its
wavy appearance over time. The blue color of the ion tail is dominated by recombining
carbon monoxide atoms. The color of the coma surrounding the head of the comet is tinged
green by slight amounts of the molecule cyanogen. The above image was taken last week
from California, USA. This week may be the best remaining chance for northern hemisphere
observers to see the fading interplanetary snowball. SWAN has now past both the Earth and
the Sun and will fade as it moves away from the Earth and heads out into the vast space
between the stars.