APOD: Crescent Neptune and Triton (2023 May 27)

[APOD Robot]

Crescent Neptune and Triton

Explanation: Gliding through the outer Solar System, in 1989 the Voyager 2 spacecraft looked toward the Sun to find this view of most distant planet Neptune and its moon Triton together in a crescent phase. The elegant image of ice-giant planet and largest moon was taken from behind just after Voyager's closest approach. It could not have been taken from Earth because the most distant planet never shows a crescent phase to sunward eyes. Heading for the heliopause and beyond, the spacecraft's parting vantage point also robs Neptune of its familiar blue hue.

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[Rauf]

Crescent Neptune and Triton

Explanation: Gliding through the outer Solar System, in 1989 the Voyager 2 spacecraft looked toward the Sun to find this view of most distant planet Neptune and its moon Triton together in a crescent phase. The elegant image of ice-giant planet and largest moon was taken from behind just after Voyager's closest approach. It could not have been taken from Earth because the most distant planet never shows a crescent phase to sunward eyes. Heading for the heliopause and beyond, the spacecraft's parting vantage point also robs Neptune of its familiar blue hue.

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Do Voyager pictures of Uranus and Neptune show these planets as bright as a human eye could see if they were close to them? Since they are so far, I think not much sunlight reaches those planets, but in famous pictures of Voyager of Neptune and Uranus, They look really bright. Are they like this because those pictures area composition of multiple pictures stacked together? Or are they enhanced in a way so we could see them more easily?

[Chris Peterson]

Crescent Neptune and Triton

Explanation: Gliding through the outer Solar System, in 1989 the Voyager 2 spacecraft looked toward the Sun to find this view of most distant planet Neptune and its moon Triton together in a crescent phase. The elegant image of ice-giant planet and largest moon was taken from behind just after Voyager's closest approach. It could not have been taken from Earth because the most distant planet never shows a crescent phase to sunward eyes. Heading for the heliopause and beyond, the spacecraft's parting vantage point also robs Neptune of its familiar blue hue.

<< Previous APOD

This Day in APOD

Next APOD >>

Do Voyager pictures of Uranus and Neptune show these planets as bright as a human eye could see if they were close to them? Since they are so far, I think not much sunlight reaches those planets, but in famous pictures of Voyager of Neptune and Uranus, They look really bright. Are they like this because those pictures area composition of multiple pictures stacked together? Or are they enhanced in a way so we could see them more easily?

The light level at Neptune is about the same as in a well lit room, which means you could easily see it. And it wouldn't look much different to you than Earth does when you're at Earth. Because that's how our eyes and brain work. It's the same reason that an object in your hand when you're standing in sunlight looks about the same as it does when you're in your well lit living room at night, despite the ambient brightness differing by a factor of 1000 (which is the same as the difference between sunlight at Earth and at Neptune). Our eyes basically scale things so that the brightest neutral color appears white. We do the same thing with images (something Ansel Adams developed with his Zone System). Most images are processed so that the lightest pixels are scaled to white, and the darkest to black, which maximizes the dynamic range.

Of course, if we could somehow see the Earth and Neptune together, lit as they are, we'd barely see Neptune at all. (This is why we don't see stars in images of the planets.)

If you look at Neptune through a telescope (which yields exactly the same brightness as if you were much closer to it) you'll see a white (or bluish) disk. To your eye it will be bright.

[De58te]

Another question about the light from Neptune. From the https://apod.nasa.gov/apod/ap091213.html it says that Neptune emits more light than it receives from the Sun. Here today that statement has been edited out. Has that been debunked? If Neptune does emit more Neptune light than it receives from the Sun, shouldn't we see some light in the night areas beyond the crescent. I suppose both light should combine in the crescent but there should still be this Neptune light visible in the night sky.

[Chris Peterson]

Another question about the light from Neptune. From the https://apod.nasa.gov/apod/ap091213.html it says that Neptune emits more light than it receives from the Sun. Here today that statement has been edited out. Has that been debunked? If Neptune does emit more Neptune light than it receives from the Sun, shouldn't we see some light in the night areas beyond the crescent. I suppose both light should combine in the crescent but there should still be this Neptune light visible in the night sky.

Neptune emits 2-3 times more energy than it receives from the Sun. This is seen at longer wavelengths, from IR to radio, but not in the visible spectrum. While it is common to refer to any part of the EM spectrum as "light", perhaps it was felt this would confuse too many people, so it was removed from the caption.

[Rauf]

Crescent Neptune and Triton

Explanation: Gliding through the outer Solar System, in 1989 the Voyager 2 spacecraft looked toward the Sun to find this view of most distant planet Neptune and its moon Triton together in a crescent phase. The elegant image of ice-giant planet and largest moon was taken from behind just after Voyager's closest approach. It could not have been taken from Earth because the most distant planet never shows a crescent phase to sunward eyes. Heading for the heliopause and beyond, the spacecraft's parting vantage point also robs Neptune of its familiar blue hue.

<< Previous APOD

This Day in APOD

Next APOD >>

Do Voyager pictures of Uranus and Neptune show these planets as bright as a human eye could see if they were close to them? Since they are so far, I think not much sunlight reaches those planets, but in famous pictures of Voyager of Neptune and Uranus, They look really bright. Are they like this because those pictures area composition of multiple pictures stacked together? Or are they enhanced in a way so we could see them more easily?

The light level at Neptune is about the same as in a well lit room, which means you could easily see it. And it wouldn't look much different to you than Earth does when you're at Earth. Because that's how our eyes and brain work. It's the same reason that an object in your hand when you're standing in sunlight looks about the same as it does when you're in your well lit living room at night, despite the ambient brightness differing by a factor of 1000 (which is the same as the difference between sunlight at Earth and at Neptune). Our eyes basically scale things so that the brightest neutral color appears white. We do the same thing with images (something Ansel Adams developed with his Zone System). Most images are processed so that the lightest pixels are scaled to white, and the darkest to black, which maximizes the dynamic range.

Of course, if we could somehow see the Earth and Neptune together, lit as they are, we'd barely see Neptune at all. (This is why we don't see stars in images of the planets.)

If you look at Neptune through a telescope (which yields exactly the same brightness as if you were much closer to it) you'll see a white (or bluish) disk. To your eye it will be bright.

I understand now. Thanks for answering!

[orin stepanek]

neptunetriton_voyager_960.jpg

Triton is a bit smaller than Luna!