Jupiter · Saturn · Mars · Venus · The Moon

Planetary filters: color contrast for each planet

A color filter darkens features of the opposite color, so a blue filter makes Jupiter's reddish belts stand out and a red one darkens the dusky markings of Mars. The effect is subtle; good seeing and the right magnification matter far more.

Jupiter #80A blue Saturn #11 yellow-green Mars #21 orange, #23A red Venus #47 violet Moon Neutral density or polarizer

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The planets in the order readers ask about them, with the filter that helps most. Filters are named by their old Kodak Wratten numbers, which most makers still use.
Jupiter
#80Alight blue
Saturn
#11yellow-green
Mars
#21 or #23Aorange or red
Venus
#47violet, bright planet only
Moon
ND 0.9or a variable polarizer

Jupiter: a light blue #80A filter darkens the red belts and the Great Red Spot

Jupiter's cloud belts and the Great Red Spot are reddish brown against cream zones. A light blue filter (#80A or #82A) absorbs red, so the belts and spot turn darker and stand out. A yellow #12 or yellow-green #11 brings out blue festoons at the belt edges. Jupiter is bright enough for any of these in a 4-inch or larger telescope at about 1 mm exit pupil (see eyepieces).

Saturn: a yellow-green #11 or yellow #8 filter sharpens the belts and ring edges

Saturn is fainter and lower in contrast than Jupiter, so use pale filters: yellow #8 or yellow-green #11 lift the belts and the Cassini Division in the rings. A light blue #80A helps with the ring shading. The rings are opening again after appearing edge-on in 2025, so the ring divisions will become easier through the late 2020s.

Mars: orange #21 or red #23A for surface markings, blue for clouds and polar caps

The dark markings on Mars are areas of rock where dust has blown away. Orange #21 and red #23A filters cut the blue scattering in its thin atmosphere and darken them. Blue #80A or violet #47 does the reverse, bringing out high clouds and polar hoods; dust storms show best in orange or yellow. Mars only shows detail for a few months around opposition. The next opposition, in February 2027, is a small one: Mars reaches about 14 arcseconds, so expect polar caps and the largest markings in an 8-inch.

Venus: a violet #47 filter shows faint cloud bands; a red one cuts the glare

Venus is covered in cloud and shows a phase, not a surface. Its cloud bands absorb ultraviolet, so a violet #47 filter, which passes the deepest blue the eye sees, sometimes shows faint shadings; it needs a 6-inch or larger telescope because it passes little light. A red #25 or a polarizer cuts the glare, and observing in twilight or daylight, with Venus higher in steadier air, helps more than any filter. See planets in daylight.

The Moon: a neutral density or variable polarizing filter cuts glare without color

The full Moon is bright enough to leave an afterimage in a large telescope. A neutral density filter (ND 0.9 passes about 13 percent of the light) or a variable polarizer, which is two polarizing filters you can twist to adjust brightness, makes it comfortable. The best lunar views come away from full Moon anyway, along the terminator where shadows are long.

Uranus and Neptune show only a tiny disk, and no filter changes that

Uranus spans about 3.7 arcseconds and Neptune about 2.3. A telescope shows a blue-green disk at 150x or more; filters add nothing for visual observers.

Planetary imagers use infrared-pass and methane filters instead of color filters

Planetary imaging captures thousands of short video frames and stacks the sharpest. Imagers with color cameras such as the ZWO ASI662MC and ASI585MC use an infrared-pass filter (685 nm or longer) to get through turbulence, which disturbs red and infrared light less than blue. A methane-band filter at 889 nm shows Jupiter and Saturn as they look in their deep atmospheres: the Great Red Spot glows bright. Monochrome imagers shoot through separate red, green and blue filters and combine them.