APOD: Aurora around Saturn's North Pole (2018 Sep 03)

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APOD: Aurora around Saturn's North Pole (2018 Sep 03)

Post by APOD Robot » Mon Sep 03, 2018 4:05 am

Image Aurora around Saturn's North Pole

Explanation: Are Saturn's auroras like Earth's? To help answer this question, the Hubble Space Telescope and the Cassini spacecraft monitored Saturn's North Pole simultaneously during Cassini's final orbits around the gas giant in September 2017. During this time, Saturn's tilt caused its North Pole to be clearly visible from Earth. The featured image is a composite of ultraviolet images of aurora and optical images of Saturn's clouds and rings, all taken recently by Hubble. Like on Earth, Saturn's northern auroras can make total or partial rings around the pole. Unlike on Earth, however, Saturn's auroras are frequently spirals -- and more likely to peak in brightness just before midnight and dawn. In contrast to Jupiter's auroras, Saturn's auroras appear better related to connecting Saturn's internal magnetic field to the nearby, variable, solar wind. Saturn's southern auroras were similarly imaged back in 2004 when the planet's South Pole was clearly visible to Earth.

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Re: APOD: Aurora around Saturn's North Pole (2018 Sep 03)

Post by Boomer12k » Mon Sep 03, 2018 4:57 am

I don't have a space telescope nor ultraviolet cameras....but I still get some good shots...
Unfortunately my Celestron Evolution 6 has a boot error, and need to be reflashed or something... I hope to get out with the 8" Meade LX-90...for a shot at Mars...

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Re: APOD: Aurora around Saturn's North Pole (2018 Sep 03)

Post by Chris Peterson » Mon Sep 03, 2018 2:27 pm

APOD Robot wrote:
Mon Sep 03, 2018 4:05 am
Unlike on Earth, however, Saturn's auroras are frequently spirals -- and more likely to peak in brightness just before midnight and dawn.
Also unlike Earth- Saturn's magnetic axis is almost perfectly aligned with its rotational axis, so we see the auroral ovals centered on the poles, not offset as on Earth (and Jupiter).

And on Earth, too, auroras commonly peak a bit before midnight.
Chris

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Re: APOD: Aurora around Saturn's North Pole (2018 Sep 03)

Post by bystander » Mon Sep 03, 2018 2:56 pm

Chris Peterson wrote:
Mon Sep 03, 2018 2:27 pm
And on Earth, too, auroras commonly peak a bit before midnight.
:? Does the peak move geographically with time?
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Re: APOD: Aurora around Saturn's North Pole (2018 Sep 03)

Post by Chris Peterson » Mon Sep 03, 2018 3:03 pm

bystander wrote:
Mon Sep 03, 2018 2:56 pm
Chris Peterson wrote:
Mon Sep 03, 2018 2:27 pm
And on Earth, too, auroras commonly peak a bit before midnight.
:? Does the peak move geographically with time?
Yes. Because local midnight moves geographically with time. The most active region of the auroral oval is commonly opposite the Sun. But there are a lot of factors that can change that, so while it's a good rule of thumb, you can't count on it if you're hoping to see an aurora.
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Re: APOD: Aurora around Saturn's North Pole (2018 Sep 03)

Post by bystander » Mon Sep 03, 2018 3:16 pm

Chris Peterson wrote:
Mon Sep 03, 2018 3:03 pm
bystander wrote:
Mon Sep 03, 2018 2:56 pm
Chris Peterson wrote:
Mon Sep 03, 2018 2:27 pm
And on Earth, too, auroras commonly peak a bit before midnight.
:? Does the peak move geographically with time?
Yes. Because local midnight moves geographically with time. The most active region of the auroral oval is commonly opposite the Sun. But there are a lot of factors that can change that, so while it's a good rule of thumb, you can't count on it if you're hoping to see an aurora.
Ok, I guess that makes sense. I just assumed the peak was more related to the timing and intensity of the geomagnetic storm produced by the solar wind.
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
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Re: APOD: Aurora around Saturn's North Pole (2018 Sep 03)

Post by Chris Peterson » Mon Sep 03, 2018 3:28 pm

bystander wrote:
Mon Sep 03, 2018 3:16 pm
Chris Peterson wrote:
Mon Sep 03, 2018 3:03 pm
bystander wrote:
Mon Sep 03, 2018 2:56 pm

:? Does the peak move geographically with time?
Yes. Because local midnight moves geographically with time. The most active region of the auroral oval is commonly opposite the Sun. But there are a lot of factors that can change that, so while it's a good rule of thumb, you can't count on it if you're hoping to see an aurora.
Ok, I guess that makes sense. I just assumed the peak was more related to the timing and intensity of the geomagnetic storm produced by the solar wind.
Sure, if there's a short burst of high energy particles, that can create an intense aurora at any time. If you want to see an aurora, you need to keep your eyes on the spaceweather reports. It takes a lot more than just going outside for a few minutes around midnight and checking the sky.
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Re: APOD: Aurora around Saturn's North Pole (2018 Sep 03)

Post by neufer » Mon Sep 03, 2018 5:20 pm

Chris Peterson wrote:
Mon Sep 03, 2018 2:27 pm
APOD Robot wrote:
Mon Sep 03, 2018 4:05 am

Unlike on Earth, however, Saturn's auroras are frequently spirals -- and more likely to peak in brightness just before midnight and dawn.
Also unlike Earth- Saturn's magnetic axis is almost perfectly aligned with its rotational axis, so we see the auroral ovals centered on the poles, not offset as on Earth (and Jupiter).
  • And Uranus:
https://en.wikipedia.org/wiki/Uranus#Magnetosphere wrote:
<<Before the arrival of Voyager 2, no measurements of the Uranian magnetosphere had been taken, so its nature remained a mystery. Before 1986, scientists had expected the magnetic field of Uranus to be in line with the solar wind, because it would then align with Uranus's poles that lie in the ecliptic.

Voyager's observations revealed that Uranus's magnetic field is peculiar, both because it does not originate from its geometric centre, and because it is tilted at 59° from the axis of rotation. In fact the magnetic dipole is shifted from the Uranus's centre towards the south rotational pole by as much as one third of the planetary radius. This unusual geometry results in a highly asymmetric magnetosphere, where the magnetic field strength on the surface in the southern hemisphere can be as low as 0.1 gauss, whereas in the northern hemisphere it can be as high as 1.1 gauss. Studies of Voyager 2 data in 2017 suggest that this asymmetry causes Uranus's magnetosphere to connect with the solar wind once a Uranian day, opening the planet to the Sun's particles. In comparison, the magnetic field of Earth is roughly as strong at either pole, and its "magnetic equator" is roughly parallel with its geographical equator. The dipole moment of Uranus is 50 times that of Earth. Neptune has a similarly displaced and tilted magnetic field, suggesting that this may be a common feature of ice giants. One hypothesis is that, unlike the magnetic fields of the terrestrial and gas giants, which are generated within their cores, the ice giants' magnetic fields are generated by motion at relatively shallow depths, for instance, in the water–ammonia ocean. Another possible explanation for the magnetosphere's alignment is that there are oceans of liquid diamond in Uranus's interior that would deter the magnetic field.

Despite its curious alignment, in other respects the Uranian magnetosphere is like those of other planets: it has a bow shock at about 23 Uranian radii ahead of it, a magnetopause at 18 Uranian radii, a fully developed magnetotail, and radiation belts. Overall, the structure of Uranus's magnetosphere is different from Jupiter's and more similar to Saturn's. Uranus's magnetotail trails behind it into space for millions of kilometres and is twisted by its sideways rotation into a long corkscrew.

Uranus's magnetosphere contains charged particles: mainly protons and electrons, with a small amount of H2+ ions. No heavier ions have been detected. Many of these particles probably derive from the thermosphere. The ion and electron energies can be as high as 4 and 1.2 MeV, respectively. The density of low-energy (below 1 keV) ions in the inner magnetosphere is about 2 cm−3. The particle population is strongly affected by the Uranian moons, which sweep through the magnetosphere, leaving noticeable gaps. The particle flux is high enough to cause darkening or space weathering of their surfaces on an astronomically rapid timescale of 100,000 years. This may be the cause of the uniformly dark colouration of the Uranian satellites and rings.>>
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Re: APOD: Aurora around Saturn's North Pole (2018 Sep 03)

Post by Chris Peterson » Mon Sep 03, 2018 5:28 pm

neufer wrote:
Mon Sep 03, 2018 5:20 pm
Chris Peterson wrote:
Mon Sep 03, 2018 2:27 pm
APOD Robot wrote:
Mon Sep 03, 2018 4:05 am

Unlike on Earth, however, Saturn's auroras are frequently spirals -- and more likely to peak in brightness just before midnight and dawn.
Also unlike Earth- Saturn's magnetic axis is almost perfectly aligned with its rotational axis, so we see the auroral ovals centered on the poles, not offset as on Earth (and Jupiter).
  • And Uranus:
I think Saturn is the only planet that has a magnetic field closely aligned to its rotational axis.
Chris

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Re: APOD: Aurora around Saturn's North Pole (2018 Sep 03)

Post by neufer » Mon Sep 03, 2018 5:52 pm

Chris Peterson wrote:
Mon Sep 03, 2018 5:28 pm

I think Saturn is the only planet that has a magnetic field closely aligned to its rotational axis.
https://www.ifa.hawaii.edu/~barnes/ast110_06/gphah.html#[14] wrote:


<<Further evidence that the outer solar system has two types of planets comes from magnetic fields. Jupiter and Saturn have well-aligned fields generated by convection and rotation in metallic hydrogen deep within their interiors. Uranus and Neptune, in contrast, have off-center fields, suggesting more localized sources in the mantles of these planets.>>
Art Neuendorffer

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Re: APOD: Aurora around Saturn's North Pole (2018 Sep 03)

Post by Chris Peterson » Mon Sep 03, 2018 5:58 pm

neufer wrote:
Mon Sep 03, 2018 5:52 pm
Chris Peterson wrote:
Mon Sep 03, 2018 5:28 pm

I think Saturn is the only planet that has a magnetic field closely aligned to its rotational axis.
https://www.ifa.hawaii.edu/~barnes/ast110_06/gphah.html#[14] wrote:


<<Further evidence that the outer solar system has two types of planets comes from magnetic fields. Jupiter and Saturn have well-aligned fields generated by convection and rotation in metallic hydrogen deep within their interiors. Uranus and Neptune, in contrast, have off-center fields, suggesting more localized sources in the mantles of these planets.>>
I think that's referencing whether the magnetic axis passes through the planetary center. That's a separate issue than alignment with the rotation axis. Jupiter's magnetic axis is similar to Earth's in that respect- not well aligned at all.
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Re: APOD: Aurora around Saturn's North Pole (2018 Sep 03)

Post by Fred the Cat » Mon Sep 03, 2018 6:25 pm

Chris Peterson wrote:
Mon Sep 03, 2018 5:28 pm
neufer wrote:
Mon Sep 03, 2018 5:20 pm
Chris Peterson wrote:
Mon Sep 03, 2018 2:27 pm


Also unlike Earth- Saturn's magnetic axis is almost perfectly aligned with its rotational axis, so we see the auroral ovals centered on the poles, not offset as on Earth (and Jupiter).
  • And Uranus:
I think Saturn is the only planet that has a magnetic field closely aligned to its rotational axis.
Makes you wonder if it has anything to do with the relatively large rings :?:
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Re: APOD: Aurora around Saturn's North Pole (2018 Sep 03)

Post by neufer » Mon Sep 03, 2018 8:48 pm

Fred the Cat wrote:
Mon Sep 03, 2018 6:25 pm
Chris Peterson wrote:
Mon Sep 03, 2018 5:28 pm

I think Saturn is the only planet that has a magnetic field closely aligned to its rotational axis.
Makes you wonder if it has anything to do with the relatively large rings :?:
  • Are you their spokes person?
https://en.wikipedia.org/wiki/Rings_of_Saturn#Spokes wrote:
Click to play embedded YouTube video.
<<Until 1980, the structure of the rings of Saturn was explained as being caused exclusively by the action of gravitational forces. Then images from the Voyager spacecraft showed radial features in the B Ring, known as spokes, which could not be explained in this manner, as their persistence and rotation around the rings was not consistent with gravitational orbital mechanics. The spokes appear dark in backscattered light, and bright in forward-scattered light; the transition occurs at a phase angle near 60°. The leading theory regarding the spokes' composition is that they consist of microscopic dust particles suspended away from the main ring by electrostatic repulsion, as they rotate almost synchronously with the magnetosphere of Saturn. The precise mechanism generating the spokes is still unknown, although it has been suggested that the electrical disturbances might be caused by either lightning bolts in Saturn's atmosphere or micrometeoroid impacts on the rings.

The spokes were not observed again until some twenty-five years later, this time by the Cassini space probe. The spokes were not visible when Cassini arrived at Saturn in early 2004. Some scientists speculated that the spokes would not be visible again until 2007, based on models attempting to describe their formation. Nevertheless, the Cassini imaging team kept looking for spokes in images of the rings, and they were next seen in images taken on 5 September 2005.

The spokes appear to be a seasonal phenomenon, disappearing in the Saturnian midwinter and midsummer and reappearing as Saturn comes closer to equinox. Suggestions that the spokes may be a seasonal effect, varying with Saturn's 29.7-year orbit, were supported by their gradual reappearance in the later years of the Cassini mission.>>
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Re: APOD: Aurora around Saturn's North Pole (2018 Sep 03)

Post by saturno2 » Mon Sep 03, 2018 10:48 pm

It seems to me that Chris Peterson is right.
Saturn is the only planet whose magnetic axis
Is almost aligned with the axis of rotation

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Re: APOD: Aurora around Saturn's North Pole (2018 Sep 03)

Post by Fred the Cat » Mon Sep 03, 2018 11:03 pm

neufer wrote:
Mon Sep 03, 2018 8:48 pm
Fred the Cat wrote:
Mon Sep 03, 2018 6:25 pm
Chris Peterson wrote:
Mon Sep 03, 2018 5:28 pm

I think Saturn is the only planet that has a magnetic field closely aligned to its rotational axis.
Makes you wonder if ( Saturn's magnetic field alignment) has anything to do with (its) relatively large rings :?:
  • Are you their spokes person?
Only in my dreams :wink:
Freddy's Felicity "Only ascertain as a cat box survivor"

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Re: APOD: Aurora around Saturn's North Pole (2018 Sep 03)

Post by MarkBour » Tue Sep 04, 2018 10:49 pm

Very fine images, Boomer!
----------------------------------
Fred the Cat wrote:
Mon Sep 03, 2018 11:03 pm
neufer wrote:
Mon Sep 03, 2018 8:48 pm
Fred the Cat wrote:
Mon Sep 03, 2018 6:25 pm

Makes you wonder if ( Saturn's magnetic field alignment) has anything to do with (its) relatively large rings :?:
  • Are you their spokes person?
Only in my dreams :wink:

From "Five Amazing Women In Space", article at: https://spacecentre.co.uk/blog-post/fiv ... men-space/
Carolyn Porco - planetary scientist
Carolyn Porco - planetary scientist Carolyn Porco. Credit: Elliot Severn
Carolyn Porco (1953 – ) has shaped our understanding of the Solar System, thanks to her key discoveries from the Voyager and Cassini-Huygens mission data.

In 1983, after completing her PhD at Caltech, Carolyn became a member of the Voyager Imaging Team and tasked with the job of studying the images from the two Voyager probes. These probes visited the outer Solar System for the first time; Voyager 1 flew by Jupiter and Saturn and Voyager 2 flew by Jupiter, Saturn, Uranus and Neptune. Carolyn was key to the discovery of brand new features in Saturn’s rings, including eccentric ringlets and spokes. These ringlets and spokes are connected to Saturn’s magnetic field, a connection which Carolyn discovered.

As Voyager 2 swung by Uranus and Neptune, Carolyn was heavily involved in the study of their thin rings. Until recently, she led the imaging science team on the Cassini-Huygens mission at Saturn.
I vote for Carolyn as their spokesperson. She is a regular speaker in all sorts of media.
Mark Goldfain