MERCURY
From the perspective of someone standing on Mercury, the Sun would appear three times larger* and seven times brighter than it appears from Earth (on average). However, with the exception of a few whispers of sodium vapor, Mercury has no atmosphere at all. Consequently, the Sun shines with a blindingly bright white color. In fact, were you to approach the Sun in space, it would also appear white from your perspective. Note that the Sun produces radiation along all wavelengths and so the combined effect is to produce a bright white Sun.**

VENUS
Whereas Mercury’s atmosphere is a mere whisper of sodium, Venus’ atmosphere is approximately 90 times thicker than Earth’s. If one were to stand on Venus’ surface, neglecting the 900 degree temperature and crushing atmospheric pressure, the Sun wouldn’t be visible at all through its thick, pervasive carbon dioxide cloud cover. However, based on probe images from the region, if the Sun were visible, it would appear orangish.

MARS
The Sun appears only about 60% as large and 40% as bright from the perspective of a Martian as it would from an Earthling’s perspective. While the sky around the Sun would appear a faint rosy color when the Sun is away from the horizon, due to the Purkinje Effect, which causes the eye’s peak light sensitivity to shift toward the blue end of the spectrum in regions of low illumination (reds appear darker, blues brighter), the area around the Sun at sunrise and sunset appears bluish.

Sunset on Mars as photographed by the Opportunity Rover in 2015.

JUPITER

Now we enter the gas giant region: Jupiter, Saturn, Uranus and Neptune. We have no way of actually knowing how the Sun would appear from their interiors as they are all shrouded by immensely thick atmospheres. Moreover, these ‘atmospheres’ are distinctly different from the comparatively thin terrestrial planet atmospheres. As we can see from the graphic below, Jupiter’s atmosphere is not only gaseous, but also contains dense regions of liquid metallic hydrogen and helium. The Sun is not visible from Jupiter’s surface, if we define the surface to be the core’s outer layer.

However, let’s assume we venture down through Jupiter’s turbulent upper cloud layer until we reach a depth at which Jupiter vanishes from sight. First, at this distance, the Sun would appear about 16 times fainter and 25% as large as it does from Earth. During our descent through the upper atmosphere, the Sun would likely appear as a bright white disc with a bluish tint, owing, again, to the above mentioned Purkinje Effect.

SATURN

The Sun would appear 100 times smaller and 10 times dimmer than it does from Earth. Here we should mention that Saturn’s average distance from the Sun is about twice that of Jupiter’s. As was true with Jupiter, the Sun would not be visible from the surface of Saturn’s core, but would instead look like a faint whitish disc with perhaps a subtle bluish-tinge. Even from this distance, the Sun would still be the most prominent feature in the sky, apart, perhaps, from the ring system. It would also not look just like another star.

URANUS

From Uranus, the Sun appears 20 times smaller and 1/400th as bright*** as it appears from Earth. The Sun would appear like a bright white disc from Uranus. Remember that from space the Sun would appear white. From this distance, the Sun would still appear whitish, but much fainter than it does on Earth. However, the Sun would still be easy to find as it remains hundreds of times brighter than the full moon.

NEPTUNE
Neptune is thirty times farther away from the Sun than Earth and consequently about 1/900th as bright.
Again, the Sun would appear as a whitish disk. Were we to descend into the upper cloud layers, the Sun would rapidly disappear, as it also would from Uranus.

PLUTO
We’re including Pluto because I still consider it a planet and we finally have a world where the surface is not covered by unfathomably thick, impenetrable atmospheres. On average, the Sun would be about 35 times smaller and 1/1,225 times dimmer than it does from Earth. (At perihelion, Pluto is about 2.7 billion miles from the Sun; at aphelion, its distance increases to 4.5 billion.) From Pluto’s surface, the Sun would appear only slightly larger than the other stars. However, it would still appear 400 times brighter than the full moon. Amazingly, it would still be painful to view it directly.

Pluto’s tenuous atmosphere consists primarily of molecular nitrogen with lesser amounts of methane and carbon monoxide. Through this atmosphere, the Sun would again appear as a small white disk with a bluish tint. The atmospheric layers, themselves, exhibit a faint blue hue, as seen in the below image captured by the New Horizons craft.

I hope this answer proves helpful.

*The Sun’s apparent size from the surface of any given planet changes as the planet’s distance from the Sun vacillates from its nearest point (perihelion) to its most distant location (aphelion). The sizes mentioned in the above paragraphs are averages. The graphic below shows the apparent sizes of the Sun from the different planets. It also includes the apparent sizes at aphelion and perihelion for the planets. One will notice, for instance, that the Sun angular size from Mercury varies considerably from perihelion to aphelion. Mercury’s perihelion distance from the Sun approximately equals 28.5 million miles. The aphelion distance is nearly 43.2 million miles. One observes variations on other planets, but to a lesser extent.

The Sun’s apparent size from the other planets. (Pay no attention to the color)

[Image credit: Larry McNish]

**The Sun’s peak wavelength is around 500 nm, within the blue-green region of the EM spectrum. However, the Sun will not appear green because the radiation emission along the other visible light wavelengths will be almost as strong.

***No, it is not a coincidence that the brightness diminishment seems to be the square of the size reduction. Light intensity, like that of sound, diminishes with the square of the distance.

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