Starship Asterisk*

Rings and Seasons of Saturn

Explanation: On Saturn, the rings tell you the season. On Earth, today marks a solstice, the time when the Earth's spin axis tilts directly toward the Sun. On Earth's northern hemisphere, today is the Summer Solstice, the day of maximum daylight. Since Saturn's grand rings orbit along the planet's equator, these rings appear most prominent -- from the direction of the Sun -- when the Saturn's spin axis points toward the Sun. Conversely, when Saturn's spin axis points to the side, an equinox occurs and the edge-on rings are hard to see. In the featured montage, images of Saturn over the past 11 years have been superposed to show the giant planet passing from southern summer toward northern summer. Although Saturn will only reach its northern summer solstice in 2017 May, the image of Saturn most analogous to today's Earth solstice is the bottommost one.

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You've been at this for a long time, Damian...

...and it's a Peach of a picture.

Wow.....both for the great "illustration" of the changing seasons and for the time involved in developing this image.
Awesome!

Great shot but interesting that no mention is made of the shifting cloud patterns, specifically the large blue one on the Saturn just below centre.......

If some nasty monster told us he was going to make all of the planets vanish forever except for Earth, plus one other planet of our choice, and so a vote had to be held; well, we would vote to keep Saturn, I am sure! Those rings are terrific!

PhilT wrote:Great shot but interesting that no mention is made of the shifting cloud patterns, specifically the large blue one on the Saturn just below centre.......

That was a famous storm and it made headlines in 2011. It has also been featured in several APODs over the years. Read all about it!
http://apod.nasa.gov/apod/ap110119.html
http://apod.nasa.gov/apod/ap110317.html
http://apod.nasa.gov/apod/ap111226.html

How about nobody has yet mentioned it is visibly flattened due to its fast rotation. Almost 10%.

Last I heard the concept of a toroidal planet was still, though highly theoretical, not impossible.

Damien Peach is a legendary planetary imager and to think he does all this from mostly cloudy UK!!
For some reason, my favourite planet fluctuates between Saturn and Jupiter.

Craine wrote:Last I heard the concept of a toroidal planet was still, though highly theoretical, not impossible.

What mechanism could produce a toroidal structure in a planet massive enough to in hydrostatic equilibrium? As it spins faster, it simply becomes more oblate, until the outer surface can no longer be maintained by self-gravitation.

Chris Peterson wrote:

Craine wrote:Last I heard the concept of a toroidal planet was still, though highly theoretical, not impossible.

What mechanism could produce a toroidal structure in a planet massive enough to in hydrostatic equilibrium? As it spins faster, it simply becomes more oblate, until the outer surface can no longer be maintained by self-gravitation.

No idea how it may come to be.
This article has an interesting discussion on planet formation, including the possibility of a toroidal planet (the author concludes it won't happen naturally):
http://www.thephysicsmill.com/2014/06/01/planets-form/
But once it exists, apparently it can be stable. With some very peculiar properties though. See here for instance:
https://physicshrocks.wordpress.com/201 ... -possible/

Then again, it is a very large universe....

Fellow astronomer wannabes:
I have a bone to pick with today's discussion of the APOD.
Actually, Earth's axis of rotation is NOT pointed directly at the sun today (or on any day for that matter). A better description would be to say Earth's axis of rotation on the summer solstice is perpendicular to the plane of its revolution around the sun.
I believe I am correct on this despite the fact that I am a geologist, not an astronomer.
I love APOD though, and look at it virtually every day. Thanks for posting it.
Jim Shea

JimShea wrote:I have a bone to pick with today's discussion of the APOD.
Actually, Earth's axis of rotation is NOT pointed directly at the sun today (or on any day for that matter). A better description would be to say Earth's axis of rotation on the summer solstice is perpendicular to the plane of its revolution around the sun.

On either solstice, the Earth's axis of rotation "tilts directly toward the Sun" in the sense that it lies on the same plane as a line between the Earth and the Sun. The Earth's axis of rotation is never perpendicular to the plane of its revolution around the Sun. The angle between the two is called obliquity, and is about 23°, which doesn't change with the time of year.

Chris Peterson wrote:

JimShea wrote:I have a bone to pick with today's discussion of the APOD.
Actually, Earth's axis of rotation is NOT pointed directly at the sun today (or on any day for that matter). A better description would be to say Earth's axis of rotation on the summer solstice is perpendicular to the plane of its revolution around the sun.

On either solstice, the Earth's axis of rotation "tilts directly toward the Sun" in the sense that it lies on the same plane as a line between the Earth and the Sun. The Earth's axis of rotation is never perpendicular to the plane of its revolution around the Sun. The angle between the two is called obliquity, and is about 23°, which doesn't change with the time of year.

Someone else on the Facebook page had a gripe about this, too. Personally, I did not find the explanation confusing at all because I am quite familiar with Earth's axial tilt and its relationship to the sun and I know better than to think it means anything but what Chris has elaborated on, here. It was ambiguously worded, but I would give most people the benefit of the doubt and presume that, like myself, they also figured it out.

geckzilla wrote:

Chris Peterson wrote:On either solstice, the Earth's axis of rotation "tilts directly toward the Sun" in the sense that it lies on the same plane as a line between the Earth and the Sun. The Earth's axis of rotation is never perpendicular to the plane of its revolution around the Sun. The angle between the two is called obliquity, and is about 23°, which doesn't change with the time of year.

Someone else on the Facebook page had a gripe about this, too. Personally, I did not find the explanation confusing at all because I am quite familiar with Earth's axial tilt and its relationship to the sun and I know better than to think it means anything but what Chris has elaborated on, here. It was ambiguously worded, but I would give most people the benefit of the doubt and presume that, like myself, they also figured it out.

"Tips directly toward the Sun" doesn't mean "points directly toward the Sun" (which is where I presume some people find confusion). I don't think the wording is ambiguous, although it could possibly be clearer.

Chris Peterson wrote:

geckzilla wrote:

Chris Peterson wrote:On either solstice, the Earth's axis of rotation "tilts directly toward the Sun" in the sense that it lies on the same plane as a line between the Earth and the Sun. The Earth's axis of rotation is never perpendicular to the plane of its revolution around the Sun. The angle between the two is called obliquity, and is about 23°, which doesn't change with the time of year.

Someone else on the Facebook page had a gripe about this, too. Personally, I did not find the explanation confusing at all because I am quite familiar with Earth's axial tilt and its relationship to the sun and I know better than to think it means anything but what Chris has elaborated on, here. It was ambiguously worded, but I would give most people the benefit of the doubt and presume that, like myself, they also figured it out.

"Tips directly toward the Sun" doesn't mean "points directly toward the Sun" (which is where I presume some people find confusion). I don't think the wording is ambiguous, although it could possibly be clearer.

If the word "directly" were removed, it would remove the ambiguity of "tilt" which is where the ambiguity is. How far does it tilt? If you know what Earth's axial tilt is, then you know how far and the ambiguity doesn't exist. If you don't already know and haven't already worked out that the pole never actually points directly at the sun, then it is ambiguous. This would be more important if the subject was an unfamiliar planet with unknown characteristics.

geckzilla wrote:

Chris Peterson wrote:"Tips directly toward the Sun" doesn't mean "points directly toward the Sun" (which is where I presume some people find confusion). I don't think the wording is ambiguous, although it could possibly be clearer.

If the word "directly" were removed, it would remove the ambiguity of "tilt" which is where the ambiguity is.

But the Earth's axis is always tipped towards the Sun, except at the instant of the two equinoxes. So I think the work "directly" is important in the context of the solstices.

Chris Peterson wrote:

JimShea wrote:I have a bone to pick with today's discussion of the APOD.
Actually, Earth's axis of rotation is NOT pointed directly at the sun today (or on any day for that matter). A better description would be to say Earth's axis of rotation on the summer solstice is perpendicular to the plane of its revolution around the sun.

On either solstice, the Earth's axis of rotation "tilts directly toward the Sun" in the sense that it lies on the same plane as a line between the Earth and the Sun. The Earth's axis of rotation is never perpendicular to the plane of its revolution around the Sun. The angle between the two is called obliquity, and is about 23°, which doesn't change with the time of year.

The axis "tilts directly toward the Sun" at a solstice. This does not mean that the axis "points directly at the sun". (I might lean to the left, but not so far that I'm lying down.) Perhaps the confusion has arisen because the "tilt" was not expressly stated in the explanation as the obliquity, which as Chris stated, is the angle between the spin axis and the orbital plane axis (or the angle between the equatorial and orbital planes). Not only does the obliquity stay constant, but the direction of tilt, relative to the "fixed" stars, hardly moves over a human lifetime -- it must therefore tilt directly towards the Sun, exactly twice per year.

Edit: IMHO, this bit could have been improved with "tilts" instead of "points":

APOD Robot wrote:... Since Saturn's grand rings orbit along the planet's equator, these rings appear most prominent -- from the direction of the Sun -- when the Saturn's spin axis points toward the Sun. Conversely, when Saturn's spin axis points to the side, an equinox occurs and the edge-on rings are hard to see. ...

(Super impressive APOD by the way. Doubleplus drool.)

It is not a static universe...everything is moving somehow....

Really nice sequence....
:---[===] *

I am confused about the images of Saturn in the APOD and would appreciate any help. The "images of Saturn" link brings up images of Saturn ( ) that vary in the angle of the rings, but the images in the APOD all show the rings at the same angle. I wonder if they have been arranged like that so as to perhaps make a more picturesque montage? In any event though the images of Saturn are superb.

To Chris Peterson and others:
Whoopppsss! I was wrong. Sorry about that. I should have remembered the old axiom: Better to keep silent and be thought a fool
than to speak and remove all doubt.
Jim shea

DavidLeodis wrote:I am confused about the images of Saturn in the APOD and would appreciate any help. The "images of Saturn" link brings up images of Saturn ( ) that vary in the angle of the rings, but the images in the APOD all show the rings at the same angle. I wonder if they have been arranged like that so as to perhaps make a more picturesque montage? In any event though the images of Saturn are superb.

The "angle" in question is the angle that the ring plane (and Saturn's equator) is inclined to our line of sight. So, the angle does vary in the APOD. From top to bottom, we progressively see less of the South pole and more of the North pole of Saturn.

You could rotate any one of these images of Saturn by any angle, and it would be a natural, "horizontal" representation of how Saturn would have appeared to an observer from some place on Earth, at some time of the night. From most places on Earth, Saturn will appear to rotate through the sky each day (by about 180 degrees) from it rising, through its culmination, to its setting. But the "angle" under discussion in this APOD, varies very slowly, over Saturn's orbital period of ~29.5 years.

JimShea wrote:To Chris Peterson and others:
Whoopppsss! I was wrong. Sorry about that. I should have remembered the old axiom: Better to keep silent and be thought a fool
than to speak and remove all doubt.
Jim shea

The geometry isn't all that easy to visualize. It's never foolish to ask questions. When it comes to scientific knowledge, the only way to advance is to question. Remain silent and you remain ignorant, and that's what's foolish! And your comment stimulated an interesting discussion.

Nitpicker wrote:

DavidLeodis wrote:I am confused about the images of Saturn in the APOD and would appreciate any help. The "images of Saturn" link brings up images of Saturn ( ) that vary in the angle of the rings, but the images in the APOD all show the rings at the same angle. I wonder if they have been arranged like that so as to perhaps make a more picturesque montage? In any event though the images of Saturn are superb.

The "angle" in question is the angle that the ring plane (and Saturn's equator) is inclined to our line of sight. So, the angle does vary in the APOD. From top to bottom, we progressively see less of the South pole and more of the North pole of Saturn.

You could rotate any one of these images of Saturn by any angle, and it would be a natural, "horizontal" representation of how Saturn would have appeared to an observer from some place on Earth, at some time of the night. From most places on Earth, Saturn will appear to rotate through the sky each day (by about 180 degrees) from it rising, through its culmination, to its setting. But the "angle" under discussion in this APOD, varies very slowly, over Saturn's orbital period of ~29.5 years.

Thanks for your help nitpicker .

If I had a sudden thought about Saturn could I say that Saturn rings a bell (wink and an embarrassed smilie here so as not to have exceeded the maximum of 3 in a thread!).

It's 3-smilies per post, David. Same as the quotes.