APOD: Crescent Neptune and Triton (2021 Jul 25)

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APOD: Crescent Neptune and Triton (2021 Jul 25)

Post by APOD Robot » Sun Jul 25, 2021 4:06 am

Image Crescent Neptune and Triton

Explanation: Gliding silently through the outer Solar System, the Voyager 2 spacecraft camera captured Neptune and Triton together in crescent phase. The elegant picture of the gas giant planet and its cloudy moon was taken from behind just after closest approach in 1989. It could not have been taken from Earth because Neptune never shows a crescent phase to sunward Earth. The unusual vantage point also robs Neptune of its familiar blue hue, as sunlight seen from here is scattered forward, and so is reddened like the setting Sun. Neptune is smaller but more massive than Uranus, has several dark rings, and emits more light than it receives from the Sun.

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Re: APOD: Crescent Neptune and Triton (2021 Jul 25)

Post by De58te » Sun Jul 25, 2021 8:05 am

Another fun fact. Neptune has the fastest winds in the Solar System. They can whip past you at twice the speed of sound! Which means if you happen to be on Neptune you'll never hear the wind blowing before it tears you apart like if you fell into a tornado. At least on Earth you can hear the tornado coming.

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Re: APOD: Crescent Neptune and Triton (2021 Jul 25)

Post by Chris Peterson » Sun Jul 25, 2021 12:39 pm

De58te wrote:
Sun Jul 25, 2021 8:05 am
Another fun fact. Neptune has the fastest winds in the Solar System. They can whip past you at twice the speed of sound! Which means if you happen to be on Neptune you'll never hear the wind blowing before it tears you apart like if you fell into a tornado. At least on Earth you can hear the tornado coming.
Bulk air movement in the upper atmosphere may exceed the speed of sound on Earth (but not necessarily the local speed of sound). If there's a tornado on Neptune, you'll hear it coming.
Chris

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Re: APOD: Crescent Neptune and Triton (2021 Jul 25)

Post by orin stepanek » Sun Jul 25, 2021 12:55 pm

Interesting feature of Neptune;
APOD , and emits more light than it receives from the Sun.
What causes this?

neptunetriton_voyager_960.jpg
Probably the only time see this kind of view of Neptune & Triton 8-)
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Re: APOD: Crescent Neptune and Triton (2021 Jul 25)

Post by Chris Peterson » Sun Jul 25, 2021 1:05 pm

orin stepanek wrote:
Sun Jul 25, 2021 12:55 pm
Interesting feature of Neptune;
APOD , and emits more light than it receives from the Sun.
What causes this?
Internal heating. The excess "light" is infrared. And this effect is true for all of the gas giants.
Chris

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Re: APOD: Crescent Neptune and Triton (2021 Jul 25)

Post by Fred the Cat » Sun Jul 25, 2021 2:30 pm

Even X-rays!
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Re: APOD: Crescent Neptune and Triton (2021 Jul 25)

Post by E Fish » Sun Jul 25, 2021 3:07 pm

I keep hoping that one of the space agencies will announce a mission to Neptune and/or Uranus. They're the only planets that haven't had a dedicated mission and there's so much out there that we need to know more about. Heck, a moon is getting a dedicated mission ahead of Neptune and Uranus.

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Re: APOD: Crescent Neptune and Triton (2021 Jul 25)

Post by RJN » Sun Jul 25, 2021 8:09 pm

After receiving email from a Neptune ice-giant expert, the term "gas giant" has now been changed to "ice-giant" on the main NASA APOD. The term "gas-giant" is now somewhat outdated when applied to Uranus or Neptune. - RJN

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Re: APOD: Crescent Neptune and Triton (2021 Jul 25)

Post by Ann » Sun Jul 25, 2021 8:39 pm

I note that the crescent of Triton appears bluer - or at least more intensely cyan-colored - than the crescent of Neptune, which looks relatively gray.

How can this be?

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Re: APOD: Crescent Neptune and Triton (2021 Jul 25)

Post by neufer » Sun Jul 25, 2021 9:36 pm

Ann wrote:
Sun Jul 25, 2021 8:39 pm

I note that the crescent of Triton appears bluer - or at least more intensely cyan-colored
- than the crescent of Neptune, which looks relatively gray. How can this be?
  • Ask Triton's near twin: the red & white dwarf planet Pluto:
https://en.wikipedia.org/wiki/Atmosphere_of_Pluto#Haze wrote: <<New Horizons discovered in the atmosphere of Pluto a multi-layered haze, which covers the entirety of the dwarf planet and reaches altitude over 200 km. The best images show about 20 layers of the haze. Horizontal extent of the layers is no less than 1000 km. The thickness of the layers varies from 1 to >10 km, and vertical distance between them is about 10 km. In northern regions the haze is 2-3 times denser than near the equator. Despite the very low density of the atmosphere, the haze is rather appreciable: it even scatters enough light to allow photographing some details of Pluto's night side. Somewhere long shadows from mountains are seen on the haze. Scale height of the haze is 45–55 km; it approximately coincides with scale height of pressure in the middle atmosphere. On the heights of 100–200 km it diminishes to 30 km. The layers show the presence of atmospheric waves (presence of which is also suggested by observations of occultations), and such waves can be created by wind blowing over Pluto's rough surface.

Size of the haze particles is unclear. Its blue color points to a particle radius near 10 nm, but the ratio of brightnesses at different phase angles indicates a radius exceeding 100 nm. This can be explained by aggregation of small (tens of nm) particles into larger (hundreds of nm) clusters. The haze probably consists of particles of non-volatile compounds, which are synthesized from atmospheric gases under influence of cosmic high-energy radiation.>>
Art Neuendorffer

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Re: APOD: Crescent Neptune and Triton (2021 Jul 25)

Post by Gord Seifert » Sun Jul 25, 2021 10:07 pm

According to wikipedia Neptune emits more energy than it receives: "Neptune radiates about 2.61 times as much energy as it receives from the Sun." Using the term 'light' is misleading even though infrared is a form of light. Light, in common usage, is more than likely to be taken as a reference to light that we might be able to see, :lol2: or that an ordinary camera might record.

Gord Seifert

Re: APOD: Crescent Neptune and Triton (2021 Jul 25)

Post by Gord Seifert » Sun Jul 25, 2021 10:15 pm

Gord Seifert wrote:
Sun Jul 25, 2021 10:07 pm
According to wikipedia Neptune emits more energy than it receives: "Neptune radiates about 2.61 times as much energy as it receives from the Sun." Using the term 'light' is misleading even though infrared is a form of light. Light, in common usage, is more than likely to be taken as a reference to light that we might be able to see, :lol2: or that an ordinary camera might record.
Sorry about the lol2 smilie in my previous post. That was a finger check, certainly not intended!

Regards,
Gord

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Re: APOD: Crescent Neptune and Triton (2021 Jul 25)

Post by orin stepanek » Mon Jul 26, 2021 1:07 am

Gord Seifert wrote:
Sun Jul 25, 2021 10:15 pm
Gord Seifert wrote:
Sun Jul 25, 2021 10:07 pm
According to wikipedia Neptune emits more energy than it receives: "Neptune radiates about 2.61 times as much energy as it receives from the Sun." Using the term 'light' is misleading even though infrared is a form of light. Light, in common usage, is more than likely to be taken as a reference to light that we might be able to see, :lol2: or that an ordinary camera might record.
Sorry about the lol2 smilie in my previous post. That was a finger check, certainly not intended!

Regards,
Gord
Well; if you feel you don't want something in your post; you can edit it!
Personally; I don't see anything wrong with your laughing face! 8-)
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Re: APOD: Crescent Neptune and Triton (2021 Jul 25)

Post by neufer » Mon Jul 26, 2021 3:03 pm

Chris Peterson wrote:
Sun Jul 25, 2021 12:39 pm
De58te wrote:
Sun Jul 25, 2021 8:05 am

Another fun fact. Neptune has the fastest winds in the Solar System. They can whip past you at twice the speed of sound! Which means if you happen to be on Neptune you'll never hear the wind blowing before it tears you apart like if you fell into a tornado. At least on Earth you can hear the tornado coming.
Bulk air movement in the upper atmosphere may exceed the speed of sound on Earth (but not necessarily the local speed of sound). If there's a tornado on Neptune, you'll hear it coming.
Bulk air movement can NEVER exceed the local speed of sound because it is the air, itself, that carries the sound waves.

If you are downstream of a tornado (or a dark spot hurricane), you'll hear it coming; however, the storms may not be able to "hear" you. (And if you are upstream you have nothing to worry about).

In any event, the retrograde equatorial winds nearly reach supersonic velocity only with respect to Neptune's fixed magnetic field lines which the winds presumably ignore.
https://en.wikipedia.org/wiki/Neptune#Climate wrote:
<<Because Neptune is not a solid body, its atmosphere undergoes differential rotation. The wide equatorial zone rotates with a period of about 18 hours (2,400 m/s), which is slower than the 16.1-hour rotation of the planet's magnetic field (2,685 m/s). By contrast, the reverse is true for the polar regions where the rotation period is 12 hours. This differential rotation is the most pronounced of any planet in the Solar System, and it results in strong latitudinal wind shear.

Neptune's weather is characterised by extremely dynamic storm systems, with winds reaching speeds of almost 600 m/s—nearly reaching supersonic flow [with respect to Neptune's fixed magnetic field lines]. Most of the winds on Neptune move in a direction opposite the planet's rotation. The general pattern of winds showed prograde rotation at high latitudes vs. retrograde rotation at lower latitudes. The difference in flow direction is thought to be a "skin effect" and not due to any deeper atmospheric processes.

The abundance of methane, ethane and acetylene at Neptune's equator is 10–100 times greater than at the poles. This is interpreted as evidence for upwelling at the equator and subsidence near the poles because photochemistry cannot account for the distribution without meridional circulation.>>
Art Neuendorffer

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Re: APOD: Crescent Neptune and Triton (2021 Jul 25)

Post by Chris Peterson » Mon Jul 26, 2021 3:07 pm

neufer wrote:
Mon Jul 26, 2021 3:03 pm
Chris Peterson wrote:
Sun Jul 25, 2021 12:39 pm
De58te wrote:
Sun Jul 25, 2021 8:05 am

Another fun fact. Neptune has the fastest winds in the Solar System. They can whip past you at twice the speed of sound! Which means if you happen to be on Neptune you'll never hear the wind blowing before it tears you apart like if you fell into a tornado. At least on Earth you can hear the tornado coming.
Bulk air movement in the upper atmosphere may exceed the speed of sound on Earth (but not necessarily the local speed of sound). If there's a tornado on Neptune, you'll hear it coming.
Bulk air movement can NEVER exceed the local speed of sound because it is the air, itself, that carries the sound waves.

If you are downstream of a tornado (or a dark spot hurricane), you'll hear it coming; however, the storms may not be able to "hear" you. (And if you are upstream you have nothing to worry about).

In any event, the retrograde equatorial winds nearly reach supersonic velocity only with respect to Neptune's fixed magnetic field lines which the winds presumably ignore.
https://en.wikipedia.org/wiki/Neptune#Climate wrote:
<<Because Neptune is not a solid body, its atmosphere undergoes differential rotation. The wide equatorial zone rotates with a period of about 18 hours (2,400 m/s), which is slower than the 16.1-hour rotation of the planet's magnetic field (2,685 m/s). By contrast, the reverse is true for the polar regions where the rotation period is 12 hours. This differential rotation is the most pronounced of any planet in the Solar System, and it results in strong latitudinal wind shear.

Neptune's weather is characterised by extremely dynamic storm systems, with winds reaching speeds of almost 600 m/s—nearly reaching supersonic flow [with respect to Neptune's fixed magnetic field lines]. Most of the winds on Neptune move in a direction opposite the planet's rotation. The general pattern of winds showed prograde rotation at high latitudes vs. retrograde rotation at lower latitudes. The difference in flow direction is thought to be a "skin effect" and not due to any deeper atmospheric processes.

The abundance of methane, ethane and acetylene at Neptune's equator is 10–100 times greater than at the poles. This is interpreted as evidence for upwelling at the equator and subsidence near the poles because photochemistry cannot account for the distribution without meridional circulation.>>
By "local" I meant Neptune. Not Earth.
Chris

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