APOD: Saturn at Night (2019 Sep 20)

[APOD Robot]

Saturn at Night

Explanation: Still bright in planet Earth's night skies, good telescopic views of Saturn and its beautiful rings often make it a star at star parties. But this stunning view of Saturn's rings and night side just isn't possible from telescopes closer to the Sun than the outer planet. They can only bring Saturn's day into view. In fact, this image of Saturn's slender sunlit crescent with night's shadow cast across its broad and complex ring system was captured by the Cassini spacecraft. A robot spacecraft from planet Earth, Cassini called Saturn orbit home for 13 years before it was directed to dive into the atmosphere of the gas giant on September 15, 2017. This magnificent mosaic is composed of frames recorded by Cassini's wide-angle camera only two days before its grand final plunge. Saturn's night will not be seen again until another spaceship from Earth calls.

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[Ann]

Click to view full size image

Crescent Venus (left) and the crescent Moon in the daytime sky. Source:
https://earthsky.org/space/how-to-see-t ... aytime-sky

I couldn't help giggling a little when I read the "title" of this APOD. Saturn at night? Hey, I only know about Venus by day!

Joking aside, the picture of Saturn's night side is stunning indeed. What a sight that would have been through an Earth telescope! On the other hand, we are lucky that we can't see Saturn that way, because we would be in deep trouble indeed if we could!!!!

Ann

[FLPhotoCatcher]

The write-up says, "this stunning view of Saturn's rings and night side just isn't possible from telescopes closer to the Sun than the outer planet." The outer planet is Neptune (or the unconfirmed Planet Nine), so the statement isn't correct. Not a big deal though.

[heehaw]

How I remember my first view of Saturn through my new SkyScope, so many decades ago! Shocked awe!

[orin stepanek]

Beautiful pic; Makes a good wallpaper!

[Tszabeau]

The “grand finale” link takes you to a very interesting link that states “Throughout the mission, Cassini has primarily relied upon its reaction wheels for fine adjustments to its orientation, especially during science observations.”
So... I’m left wondering what Cassini’s “reaction wheels” are.

[Chris Peterson]

The write-up says, "this stunning view of Saturn's rings and night side just isn't possible from telescopes closer to the Sun than the outer planet." The outer planet is Neptune (or the unconfirmed Planet Nine), so the statement isn't correct. Not a big deal though.

All planets with orbits larger than Earth's are called "outer planets".

[Chris Peterson]

The “grand finale” link takes you to a very interesting link that states “Throughout the mission, Cassini has primarily relied upon its reaction wheels for fine adjustments to its orientation, especially during science observations.”
So... I’m left wondering what Cassini’s “reaction wheels” are.

Reaction wheels. Google is your friend.

[TheOtherBruce]

The “grand finale” link takes you to a very interesting link that states “Throughout the mission, Cassini has primarily relied upon its reaction wheels for fine adjustments to its orientation, especially during science observations.”
So... I’m left wondering what Cassini’s “reaction wheels” are.

They're like gyroscopes; the wheel spins one way, Cassini spins (much more slowly) the opposite way. I think the Hubble telescope uses them as well. One big advantage reaction wheels have over attitude thrusters is that they don't need fuel, only electricity from solar panels or an RTG.

[neufer]

Click to play embedded YouTube video.

The “grand finale” link takes you to a very interesting link that states “Throughout the mission, Cassini has primarily relied upon its reaction wheels for fine adjustments to its orientation, especially during science observations.”
So... I’m left wondering what Cassini’s “reaction wheels” are.

They're like gyroscopes; the wheel spins one way, Cassini spins (much more slowly) the opposite way. I think the Hubble telescope uses them as well. One big advantage reaction wheels have over attitude thrusters is that they don't need fuel, only electricity from solar panels or an RTG.

[DL MARTIN]

Outside of the Moon landing, I hold Cassini as the 'best bang for the buck' undertaking in inter-planetary exploration. Perfection in every way.

[Chris Peterson]

Outside of the Moon landing, I hold Cassini as the 'best bang for the buck' undertaking in inter-planetary exploration. Perfection in every way.

I'm not sure we got very much for our money by landing on the Moon. Not much compared with Cassini. Or Voyager. Or the Mars landers. Or Rosetta. Or New Horizons.

[FLPhotoCatcher]

The write-up says, "this stunning view of Saturn's rings and night side just isn't possible from telescopes closer to the Sun than the outer planet." The outer planet is Neptune (or the unconfirmed Planet Nine), so the statement isn't correct. Not a big deal though.

All planets with orbits larger than Earth's are called "outer planets".

Indeed. But saying "the outer planet", narrows it to ONE.

[Chris Peterson]

The write-up says, "this stunning view of Saturn's rings and night side just isn't possible from telescopes closer to the Sun than the outer planet." The outer planet is Neptune (or the unconfirmed Planet Nine), so the statement isn't correct. Not a big deal though.

All planets with orbits larger than Earth's are called "outer planets".

Indeed. But saying "the outer planet", narrows it to ONE.

I sure don't read it that way. In this case, "the" simply refers to "the" planet under discussion. Saturn. The caption could read "the pretty planet" or "the gas giant" or any number of other qualifiers, and the context makes it absolutely clear what is meant.

[DL MARTIN]

If Chris Peterson thinks any astronomical activity surpasses the Moon landing, then he fails to see the vicarious nature of his work.

[Chris Peterson]

If Chris Peterson thinks any astronomical activity surpasses the Moon landing, then he fails to see the vicarious nature of his work.

Depends what you mean by "surpasses". I was talking about scientific return on investment.

[Tszabeau]

I’m a little surprised/disappointed that I don’t see any lightning.

[De58te]

The write-up says, "this stunning view of Saturn's rings and night side just isn't possible from telescopes closer to the Sun than the outer planet." The outer planet is Neptune (or the unconfirmed Planet Nine), so the statement isn't correct. Not a big deal though.

All planets with orbits larger than Earth's are called "outer planets".

Saturn is also an outer planet as well as Jupiter. But I beg to differ with Chris. I was taught that Mars is also an inner planet because it is a rocky planet. Outer planets were gaseous. With the exception of Pluto, at the time considered a planet, but then they said it is not known what Pluto is, it could be made out of ice not rocks. In addition even if you were an observer around Neptune, that view is not possible now. For one thing Saturn is not aligned to Neptune currently, or is the word conjunction, so Saturn would appear like a quarter phase now to Neptune. Checking up on fourmilab, what the planets positions are, Saturn would only appear like that to Neptune around the year 2024, when it comes between the Sun and Neptune. But then the Neptune observer would need a bigger telescope since Saturn is farther away from Neptune than Saturn is from Earth. As the crow flies Saturn is about 8.5 AU away from the Earth, yet Saturn is about 20 AU away from Neptune at closest approach. It would appear much smaller than what we see.

[geckzilla]

Huh, I always thought the outer planets were the ones past the asteroid belt, and the inner planets were within it.

[Chris Peterson]

The write-up says, "this stunning view of Saturn's rings and night side just isn't possible from telescopes closer to the Sun than the outer planet." The outer planet is Neptune (or the unconfirmed Planet Nine), so the statement isn't correct. Not a big deal though.

All planets with orbits larger than Earth's are called "outer planets".

Saturn is also an outer planet as well as Jupiter. But I beg to differ with Chris. I was taught that Mars is also an inner planet because it is a rocky planet. Outer planets were gaseous. With the exception of Pluto, at the time considered a planet, but then they said it is not known what Pluto is, it could be made out of ice not rocks. In addition even if you were an observer around Neptune, that view is not possible now. For one thing Saturn is not aligned to Neptune currently, or is the word conjunction, so Saturn would appear like a quarter phase now to Neptune. Checking up on fourmilab, what the planets positions are, Saturn would only appear like that to Neptune around the year 2024, when it comes between the Sun and Neptune. But then the Neptune observer would need a bigger telescope since Saturn is farther away from Neptune than Saturn is from Earth. As the crow flies Saturn is about 8.5 AU away from the Earth, yet Saturn is about 20 AU away from Neptune at closest approach. It would appear much smaller than what we see.

Again, context matters. When we consider how the Sun illuminates planets as seen from the Earth, it's common for the "superior planets" to be referred to as the "outer planets", which in that case includes Mars.

[Ann]

The write-up says, "this stunning view of Saturn's rings and night side just isn't possible from telescopes closer to the Sun than the outer planet." The outer planet is Neptune (or the unconfirmed Planet Nine), so the statement isn't correct. Not a big deal though.

All planets with orbits larger than Earth's are called "outer planets".

Saturn is also an outer planet as well as Jupiter. But I beg to differ with Chris. I was taught that Mars is also an inner planet because it is a rocky planet. Outer planets were gaseous. With the exception of Pluto, at the time considered a planet, but then they said it is not known what Pluto is, it could be made out of ice not rocks.

Wow, the discussion of semantics here.

My own greatest mathematical achievement by far was when I built a model of what I decided was the inner Solar system. It consisted of the Sun, Mercury, Venus, the Earth and Moon and Mars. I made a reasonable job of making the Sun and the planets moderately accurate in relative size, and I also managed to place them at moderately accurate distances from one another. (I was inordinately proud of myself.)

Anyway, to me, "the inner Solar system" comprises the Sun, Mercury, Venus, the Earth-Moon system and Mars.

Ann

[neufer]

Outside of the Moon landing, I hold Cassini as the 'best bang for the buck' undertaking in inter-planetary exploration.

I'm not sure we got very much for our money by landing on the Moon.

Not much compared with Cassini. Or Voyager. Or the Mars landers. Or Rosetta. Or New Horizons.

And Cassini included its own moon lander... paid for by others:

https://en.wikipedia.org/wiki/Cassini%E ... s#Overview

[neufer]

All planets with orbits larger than Earth's are called "outer planets".

Saturn is also an outer planet as well as Jupiter. But I beg to differ with Chris. I was taught that Mars is also an inner planet because it is a rocky planet. Outer planets were gaseous. With the exception of Pluto, at the time considered a planet, but then they said it is not known what Pluto is, it could be made out of ice not rocks.

Wow, the discussion of semantics here.

My own greatest mathematical achievement by far was when I built a model of what I decided was the inner Solar system. It consisted of the Sun, Mercury, Venus, the Earth and Moon and Mars. I made a reasonable job of making the Sun and the planets moderately accurate in relative size, and I also managed to place them at moderately accurate distances from one another. (I was inordinately proud of myself.)

Ah...but was it "spread out" enough vs-a-vi the size of your Sun

<<planet (n.) late Old English planete, from Old French planete (Modern French planète), from Late Latin planeta, from Greek planetes, from (asteres) planetai "wandering (stars)," from planasthai "to wander," a word of uncertain etymology. Perhaps from a nasalized form of PIE root *pele- (2) "flat; to spread," on the notion of "spread out...but the semantics are highly problematic," according to Beekes, who notes the similarity of meaning to Greek plazein "to make devious, repel, dissuade from the right path, bewilder," but adds, "it is hard to think of a formal connection.">>

Anyway, to me, "the inner Solar system" comprises the Sun, Mercury, Venus, the Earth-Moon system and Mars.

I think we need a big debate on which planets are innies and which are outies.

<<Innie belly buttons are said to comprise 90% of the belly button population, with outies making up the remaining 10%. The exact reason for this innie/outie belly button discrepancy remains a medical mystery, although there are some interesting theories floating around the Internet.

The belly button, also called the navel, is actually the body's first scar. The umbilical cord, which supplied nutrients to the unborn baby, is routinely clamped off shortly after the placenta has been expelled. Two clamps are placed a few inches away from the baby's body, and the cord is severed between them. The remaining vestiges of the umbilical cord eventually wither and fall off, leaving a small scar we know as the belly button. For many people, the scar is concave, meaning it recedes into the body. For others, the remaining scar tissue protrudes slightly from the body.

One theory holds that the innie belly button is the norm, while an outie is the result of a genetic aberration. Needless to say, this theory of natural selection does not enjoy widespread popularity among the outie belly button set. There is no scientific evidence to suggest that an outie is genetically preordained, or that an innie is the default setting once the umbilical cord falls off.

While we're on the subject, there are a few factoids concerning the formation of belly button lint that I feel compelled to share. The most common color of belly button lint is blue, primarily due to the prevalence of blue fibers in modern clothing. Belly buttons also attract more lint from below than from above. It's likely that more personal belly button lint came from your underwear and pants than from your shirt. I don't know what to do with this information personally, but you never know what might show up on a game show some day.>>

<<Omphaloskepsis or navel-gazing is contemplation of one's navel. The word derives from the Ancient Greek words ὀμφᾰλός (omphalós, lit. 'navel') and σκέψῐς (sképsis, lit. 'viewing, examination, speculation'). Actual use of the practice as an aid to contemplation of basic principles of the cosmos and human nature is found in the practice of yoga of Hinduism and sometimes in the Eastern Orthodox Church. In yoga, the navel is the site of the manipura (also called nabhi) chakra, which yogis consider "a powerful chakra of the body". The monks of Mount Athos, Greece, were described as Omphalopsychians by J.G. Minningen, writing in the 1830s, who says they "...pretended or fancied that they experienced celestial joys when gazing on their umbilical region, in converse with the Deity". However, phrases such as "contemplating one's navel" or "navel-gazing" are frequently used, usually in jocular fashion, to refer to self-absorbed pursuits>>

[Ann]

Saturn is also an outer planet as well as Jupiter. But I beg to differ with Chris. I was taught that Mars is also an inner planet because it is a rocky planet. Outer planets were gaseous. With the exception of Pluto, at the time considered a planet, but then they said it is not known what Pluto is, it could be made out of ice not rocks.

Wow, the discussion of semantics here.

My own greatest mathematical achievement by far was when I built a model of what I decided was the inner Solar system. It consisted of the Sun, Mercury, Venus, the Earth and Moon and Mars. I made a reasonable job of making the Sun and the planets moderately accurate in relative size, and I also managed to place them at moderately accurate distances from one another. (I was inordinately proud of myself.)

Ah...but was it "spread out" enough vs-a-vi the size of your Sun

<<planet (n.) late Old English planete, from Old French planete (Modern French planète), from Late Latin planeta, from Greek planetes, from (asteres) planetai "wandering (stars)," from planasthai "to wander," a word of uncertain etymology. Perhaps from a nasalized form of PIE root *pele- (2) "flat; to spread," on the notion of "spread out...but the semantics are highly problematic," according to Beekes, who notes the similarity of meaning to Greek plazein "to make devious, repel, dissuade from the right path, bewilder," but adds, "it is hard to think of a formal connection.">>

Anyway, to me, "the inner Solar system" comprises the Sun, Mercury, Venus, the Earth-Moon system and Mars.

I think we need a big debate on which planets are innies and which are outies.

<<Innie belly buttons are said to comprise 90% of the belly button population, with outies making up the remaining 10%. The exact reason for this innie/outie belly button discrepancy remains a medical mystery, although there are some interesting theories floating around the Internet.

The belly button, also called the navel, is actually the body's first scar. The umbilical cord, which supplied nutrients to the unborn baby, is routinely clamped off shortly after the placenta has been expelled. Two clamps are placed a few inches away from the baby's body, and the cord is severed between them. The remaining vestiges of the umbilical cord eventually wither and fall off, leaving a small scar we know as the belly button. For many people, the scar is concave, meaning it recedes into the body. For others, the remaining scar tissue protrudes slightly from the body.

One theory holds that the innie belly button is the norm, while an outie is the result of a genetic aberration. Needless to say, this theory of natural selection does not enjoy widespread popularity among the outie belly button set. There is no scientific evidence to suggest that an outie is genetically preordained, or that an innie is the default setting once the umbilical cord falls off.

While we're on the subject, there are a few factoids concerning the formation of belly button lint that I feel compelled to share. The most common color of belly button lint is blue, primarily due to the prevalence of blue fibers in modern clothing. Belly buttons also attract more lint from below than from above. It's likely that more personal belly button lint came from your underwear and pants than from your shirt. I don't know what to do with this information personally, but you never know what might show up on a game show some day.>>

<<Omphaloskepsis or navel-gazing is contemplation of one's navel. The word derives from the Ancient Greek words ὀμφᾰλός (omphalós, lit. 'navel') and σκέψῐς (sképsis, lit. 'viewing, examination, speculation'). Actual use of the practice as an aid to contemplation of basic principles of the cosmos and human nature is found in the practice of yoga of Hinduism and sometimes in the Eastern Orthodox Church. In yoga, the navel is the site of the manipura (also called nabhi) chakra, which yogis consider "a powerful chakra of the body". The monks of Mount Athos, Greece, were described as Omphalopsychians by J.G. Minningen, writing in the 1830s, who says they "...pretended or fancied that they experienced celestial joys when gazing on their umbilical region, in converse with the Deity". However, phrases such as "contemplating one's navel" or "navel-gazing" are frequently used, usually in jocular fashion, to refer to self-absorbed pursuits>>

My Sun was a table cloth, two meters in diameter. My inner planets were cotton balls, 2 centimeters in diameter, except the Moon and Mercury, which were small yellow peas. I placed my Earth 200 meters from the Sun, and Mars 300 meters from the Sun. If I remember correctly, I placed the Moon 60 centimeters from the Earth.

Perfectly accurate? Heck no! Good enough? I thought so.

Ann

[neufer]

My Sun was a table cloth, two meters in diameter. My inner planets were cotton balls, 2 centimeters in diameter, except the Moon and Mercury, which were small yellow peas. I placed my Earth 200 meters from the Sun, and Mars 300 meters from the Sun. If I remember correctly, I placed the Moon 60 centimeters from the Earth.

Perfectly accurate? Heck no! Good enough? I thought so.

• Oh when those cotton balls get rotten
  You can't pick you very much cotton
  In them old cotton fields back home
  
  It was down in Louisiana
  Just a mile [~8 AU] from Texarkana
  In them old cotton fields back home