http://www.skyandtelescope.com.au 67surrounding zones and accentuating bright features
within the belts like ovals and rifts.
The blue festoons that protrude into the light-
toned Equatorial Zone from the edges of the
adjoining equatorial belts and many features at
high latitudes darken dramatically through yellow
(Wratten 8, 12 and 15), orange (Wratten 21) and red
(Wratten 23A) filters. Yellow-green (Wratten 11) and
light-green (Wratten 56) filters often give the most
pleasing overall views.
Due to its greater distance from the Sun, Saturn
has a colder upper atmosphere, and consequently
the hues of its cloudtops are muted by an overlying
murky haze of photochemical smog. The planet’s belts
typically appear a pale greyish brown, while its dusky
polar regions feature a cool palette of colours ranging
from olive green to teal, aquamarine and azure blue.
With an apparent surface brightness only 30% that
of Jupiter, Saturn is too feebly illuminated to permit
the use of dense colour filters. Yellow (Wratten 8 and
12) filters invariably improve contrast and definition,
while many observers prefer the Wratten 11 yellow-
green filter to further selectively darken the warm
tint of Saturn’s belts. Use the Wratten 82A very-light-
blue filter for sharpening the boundaries between
belts and zones.
Filters won’t result in startling revelations at the
eyepiece, but few accessories offer more ‘bang for the
buck’. A comparatively modest investment in a well-
chosen set of half a dozen colour filters will pay rich
dividends by allowing you to coax the best possible
performance from your telescope. ✦
Jupiter’s Great Red Spot
nearly disappears in red
light, but it becomes
increasingly prominent
at shorter wavelengths.
Conversely, the blue festoon
on the North Equatorial
Belt’s southern edge darkens
dramatically in red light.Saturn’s azure polar
hood is sharply
delineated in red light
but subdued in blue. A
green filter brings out
belt structure in the
planet’s tropical and
temperate latitudes.S&T: SEAN WALKER (2)