Our View from Neptune

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Our View from Neptune

Postby david48 » Mon Jan 02, 2017 10:42 pm

Suppose we were intelligent beings, on an outer planet such as Neptune. And we were looking inwards at the Solar System. What kind of Astronomy would we arrive at, and what questions would we ask.

Such as:

1. How big would the Sun look - what would be its apparent diameter, would it be a perceptible disk, or just an intensely brilliant star-like point?

2. Could we see Uranus and its rings and satellites

3. Could we see Saturn and its rings, and Jupiter, with its cloud-belts, and Great Red spot

4. About the inner planets: Mars, Earth, Venus, and Mercury - would they be visible?
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Re: Our View from Neptune

Postby Gfamily2 » Tue Jan 03, 2017 2:53 pm

An interesting question, and one that you could spend some useful time working out the answers.

Mostly the responses will depend on the relative distances between the the various planets and Neptune vs Earth when making the observations. There is also the issue that when observing Jupiter and Saturn, the phase will make a huge difference.

So, for starters:
Neptune's orbit is 30AU, compared to 1AU for the Earth, so the Sun's disc will be about 1 arcminute across. This is only a little more than the eye's limit of resolution, so the Sun will be very barely distinguishable as a disc.

As for the other planets, only Uranus will ever be closer to Neptune than the Earth, but only when the phase is very small, so in general, we're better placed for observing here than we would be out there.

It would be an interesting exercise to work out profiles of how the brightness and size varies as they orbit when seen from Neptune
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Re: Our View from Neptune

Postby The Man with the Corrugated Iron Roof » Sun Mar 05, 2017 6:22 pm

The inner planets will be invisible from Neptune, as they will be less than 4 degrees from the Sun at maximum elongation. Jupiter will be 10 degrees from the Sun at maximum elongation: tricky.

Even Uranus would probably be a binocular object.
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Re: Our View from Neptune

Postby Aratus » Thu Mar 09, 2017 7:42 pm

david48 wrote:1. How big would the Sun look - what would be its apparent diameter, would it be a perceptible disk, or just an intensely brilliant star-like point?

2. Could we see Uranus and its rings and satellites

3. Could we see Saturn and its rings, and Jupiter, with its cloud-belts, and Great Red spot

4. About the inner planets: Mars, Earth, Venus, and Mercury - would they be visible?


Not a good place for solar system observing, I'm afraid.
The sun would be a very small disc. About the size of a big crater on the moon.
Saturn and Jupiter would be quite a bit smaller than as seen from Earth, About the size of Mars as seen from the Earth at the moment. One compensation is that you would see phases, like you do the moon, or Venus. Mars would be too faint to see with the eye. Seeing the Earth would be very difficult because of its nearness to the sun. If you could see it, it would be 4th magnitude, the moon, 7th magnitude. Uranus is so far away from Neptune at the moment it is bearly 6th magnitude.

Neptune's moon, Triton, is about the same apparant size as our moon in the sky, but very pale looking.
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