APOD: Jupiter and the Moons (2020 Sep 02)

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APOD: Jupiter and the Moons (2020 Sep 02)

Post by APOD Robot » Wed Sep 02, 2020 4:05 am

Image Jupiter and the Moons

Explanation: How many moons do you see? Many people would say one, referring to the Earth's Moon, prominent on the lower left. But take a closer look at the object on the upper right. That seeming-star is actually the planet Jupiter, and your closer look might reveal that it is not alone - it is surrounded by some of its largest moons. From left to right these Galilean Moons are Io, Ganymede, Europa and Callisto. These moons orbit the Jovian world just like the planets of our Solar System orbit the Sun, in a line when seen from the side. The featured single shot was captured from Cancun, Mexico last week as Luna, in its orbit around the Earth, glided past the distant planet. Even better views of Jupiter are currently being captured by NASA's Juno spacecraft, now in a looping orbit around the Solar System's largest planet. Earth's Moon will continue to pass nearly in front of both Jupiter and Saturn once a month (moon-th) as the two giant planets approach their own great conjunction in December.

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Ann
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Re: APOD: Jupiter and the Moons (2020 Sep 02)

Post by Ann » Wed Sep 02, 2020 6:06 am

Great picture. A caption that leaves something to be desired.
APOD robot wrote:

(Jupiter) is surrounded by some of its largest moons. From left to right these Galilean Moons are Io, Ganymende, Europa and Callisto.

Some of its largest moons? Does that mean that when we Earthlings look at dear old Luna in the sky, we are actually watching one of the Earth's largest moons? As if Jupiter and Earth had other large moons too, apart from the Galilean moons and Luna? Maybe the wording of the caption could be corrected.

I would also have liked to see a comment on the bright flashes of colored light between the Moon and Jupiter in the APOD. What are they, and what caused them?

Could they be a Moon halo? These halos can be quite colorful. On the other hand, I expect them to be very round in shape, not "tattered and torn" like that flashes of light in today's APOD.

Well, I really like the APOD anyway!

Ann
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Re: APOD: Jupiter and the Moons (2020 Sep 02)

Post by XgeoX » Wed Sep 02, 2020 11:25 am

Since it was taken in Cancun I imagine the rainbow is from the modern day scourge of light pollution (I wonder how much greenhouse gas is needlessly pumped into the air on wasteful lighting) plus it’s overlapping the moon which rules out a moonbow.
I can’t wait for that incredible conjunction, I even splurged on a new eyepiece! 🪐🔭👁

Eric

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Re: APOD: Jupiter and the Moons (2020 Sep 02)

Post by jc1742 » Wed Sep 02, 2020 11:56 am

So when did "Ganymende" get its second 'n'? I've never noticed that spelling before. ;-)

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Re: APOD: Jupiter and the Moons (2020 Sep 02)

Post by neufer » Wed Sep 02, 2020 12:19 pm

https://www.quora.com/We-grew-up-with-American-Indians-speaking-of-the-past-as-many-moons-Is-this-Hollywood-or-did-native-Americans-judge-time-in-this-way wrote:
Click to play embedded YouTube video.

<<The following excerpt is from A New Voyage and Description of the Jsthmus of America, first published in 1695 in London; the author Lionel Wafer was a ship surgeon, explorer and buccaneer who was stranded on the Isthmus of Panama. Wikipedia claims the Welshman spent four years, 1680-1684, in Panama, but according to a second source, he spent only four months. Wafer cohabited with the Cuna Indians, and became friends with their king named Lacenta. On his return home, the Welsh ‘pirate’ wrote about their culture, their shamanism and a short vocabulary of their language.
  • The Indians, when they travel, guide themselves either by the Sun, when it shines, or by steering towards such a determinate Point, observing the bending of the Trees, according as the Wind is. If they are at a loss this way, they notch the Barks of Trees, to see which side is thickest; which is always the South, or the Sunny Side; and their way lies generally through Woods. […]

    I observ'd among them no distinction of Weeks, or particular Days, no parting the Day into Hours, or any Portions, otherwise than by this Pointing: And when they use this, or any other Sign, yet they speak at the same time, and express their Meaning in their own Language, tho' to Europeans who understand it not. They reckon Times past by no Revolutions of the Heavenly Bodies, but the Moons: For Lacenta speaking of the Havock the Spaniards had made to the Westward, intimated 'twas a great many Moons ago.
Art Neuendorffer

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Re: APOD: Jupiter and the Moons (2020 Sep 02)

Post by Cousin Ricky » Wed Sep 02, 2020 12:47 pm

Ann wrote:
Wed Sep 02, 2020 6:06 am
I would also have liked to see a comment on the bright flashes of colored light between the Moon and Jupiter in the APOD. What are they, and what caused them?

Could they be a Moon halo? These halos can be quite colorful. On the other hand, I expect them to be very round in shape, not "tattered and torn" like that flashes of light in today's APOD.
The photographer link has this comment:
Es una imagen con cierto grado de dificultad, en la que el mérito principal ha sido la paciencia, esperar la nube correcta.
which translates as
It’s a picture with some degree of difficulty, in which the main merit has been patience, waiting for the right cloud.
So, I’m guessing that they are clouds interacting with the moon halo. It also seems some exposure gradient or editing was done; the Moon appears much too dim compared to the other elements of the scene.

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Re: APOD: Jupiter and the Moons (2020 Sep 02)

Post by Ann » Wed Sep 02, 2020 1:27 pm

jc1742 wrote:
Wed Sep 02, 2020 11:56 am
So when did "Ganymende" get its second 'n'? I've never noticed that spelling before. ;-)
Good point. I should have noted. [groan-n]😣[/groan-n]

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Re: APOD: Jupiter and the Moons (2020 Sep 02)

Post by orin stepanek » Wed Sep 02, 2020 1:27 pm

JupiterAndMoons_Fedez_1080.jpg
I remember a similar photo of Jupiter & its moons! I can't recall it that photo included Earth's moon or if this picture is a repeat! 🧐
JupiterAndMoons_Fedez_1080.jpg
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Re: APOD: Jupiter and the Moons (2020 Sep 02)

Post by neufer » Wed Sep 02, 2020 2:59 pm

APOD Robot wrote:
Wed Sep 02, 2020 4:05 am

Explanation: These moons orbit the Jovian world just like the planets of our Solar System orbit the Sun,
in a line when seen from the side.
  • Except, perhaps, for one screwball planet (i.e., the third from the Sun):
https://en.wikipedia.org/wiki/Orbital_inclination wrote:

Code: Select all

		Inclination
------------------------------------------
Moon  		Jupiter's equator
..................................
Io 		0.050°
Europa		0.471°
Ganymede	0.204°
Callisto	0.205°
-------------------------------------------------------------
Planet 	 	Sun's equator 	Invariable plane
.................................................
Mercury 	3.38° 		6.34°
Venus 	 	3.86° 		2.19°
Earth 		7.155° 		1.57°
Mars 	 	5.65° 		1.67°
Jupiter 	6.09° 		0.32°
Saturn 	 	5.51° 		0.93°
Uranus 	 	6.48° 		1.02°
Neptune 	6.43° 		0.72°
Art Neuendorffer

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Re: APOD: Jupiter and the Moons (2020 Sep 02)

Post by ccsawyer » Wed Sep 02, 2020 7:17 pm

Shakespeare was so prescient. From King John (4.2):
My lord, they say five moons were seen to-night; Four fixed, and the fifth did whirl about the other four in wondrous motion.

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Re: APOD: Jupiter and the Moons (2020 Sep 02)

Post by neufer » Wed Sep 02, 2020 7:39 pm

ccsawyer wrote:
Wed Sep 02, 2020 7:17 pm

Shakespeare was so prescient. From King John (4.2):

My lord, they say five moons were seen to-night;
Four fixed, and the fifth did whirl about the other four in wondrous motion.
https://www.etymonline.com/search?q=prescient wrote:
<<prescient (adj.)"having knowledge of events before they take place," 1620s, from Middle French prescient (15c.) and directly from Latin praescientem (nominative praesciens), present participle of praescire "to know in advance," from Latin prae "before" (see pre-) + scire "to know" (see science).>>
  • Shakespeare was so post-science:
https://en.wikipedia.org/wiki/Galilean_moons wrote:
<<The Galilean moons are the four largest moons of Jupiter—Io, Europa, Ganymede, and Callisto. They were first seen by Galileo Galilei in December 1609 or January 1610, and recognized by him as satellites of Jupiter in March 1610. Galileo initially named his discovery the Cosmica Sidera ("Cosimo's stars"), but the names that eventually prevailed were chosen by Simon Marius. Marius discovered the moons independently at nearly the same time as Galileo, 8 January 1610, and gave them their present names, derived from the lovers of Zeus, which were suggested by Johannes Kepler, in his Mundus Jovialis, published in 1614.>>
https://en.wikipedia.org/wiki/King_John_(play) wrote:
<<The Life and Death of King John, a history play by William Shakespeare, dramatises the reign of John, King of England (ruled 1199–1216), son of Henry II of England and Eleanor of Aquitaine and father of Henry III of England. It is believed to have been written in the mid-1590s but was not published until it appeared in the First Folio in 1623.>>
https://groups.google.com/forum/#!msg/humanities.lit.authors.shakespeare/4SbFaZg0vso/0fjmtZjrwGMJ wrote:
  • So there are the five moons, and it is presumably Arthur,
    at present believed dead (and soon to be dead accidentally
    anyway) who is the moon whirling about in wonder.
Art Neuendorffer

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Re: APOD: Jupiter and the Moons (2020 Sep 02)

Post by 4mipre@gmailcom » Wed Sep 02, 2020 8:13 pm

It is important to note that when accurate clocks that could be taken on ships were made that an accurate longitudinal position could be made from the positions of Jupiters moons and the GMT it indicated. You could calculate how far around the world you had traveled.

Although I will need to look up just how it was done.

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Re: APOD: Jupiter and the Moons (2020 Sep 02)

Post by neufer » Thu Sep 03, 2020 2:30 am

4mipre@gmailcom wrote:
Wed Sep 02, 2020 8:13 pm

It is important to note that when accurate clocks that could be taken on ships were made that an accurate longitudinal position could be made from the positions of Jupiters moons and the GMT it indicated. You could calculate how far around the world you had traveled. Although I will need to look up just how it was done.
https://en.wikipedia.org/wiki/History_of_longitude#Satellites_of_Jupiter wrote:
<<In 1612, having determined the orbital periods of Jupiter's four brightest satellites (Io, Europa, Ganymede and Callisto), Galileo proposed that with sufficiently accurate knowledge of their orbits one could use their positions as a universal clock, which would make possible the determination of longitude. He worked on this problem from time to time during the remainder of his life.

The method required a telescope, as the moons are not visible to the naked eye. For use in marine navigation, Galileo proposed the celatone, a device in the form of a helmet with a telescope mounted so as to accommodate the motion of the observer on the ship. This was later replaced with the idea of a pair of nested hemispheric shells separated by a bath of oil. This would provide a platform that would allow the observer to remain stationary as the ship rolled beneath him, in the manner of a gimballed platform. To provide for the determination of time from the observed moons' positions, a Jovilabe was offered — this was an analogue computer that calculated time from the positions and that got its name from its similarities to an astrolabe. The practical problems were severe and the method was never used at sea.

On land, this method proved useful and accurate. An early example was the measurement of the longitude of the site of Tycho Brahe's former observatory on the Island of Hven. Jean Picard on Hven and Cassini in Paris made observations during 1671 and 1672, and obtained a value of 42 minutes 10 seconds (time) east of Paris, corresponding to 10° 32' 30", about 12 minute of arc higher than the modern value.

Two proposed methods depend on the relative motions of the moon and a star or planet. An appulse is the least apparent distance between the two objects, an occultation occurs when the star or planet passes behind the moon — essentially a type of eclipse. The times of either of these events can be used as the measure of absolute time in the same way as with a lunar eclipse. Edmond Halley described the use of this method to determine the longitude of Balasore, using observations of the star Aldebaran (the Bull's Eye) in 1680, with an error of just over half a degree. A longitude determination using the occultation of a planet, Jupiter, was described by James Pound in 1714.

The first to suggest travelling with a clock to determine longitude, in 1530, was Gemma Frisius, a physician, mathematician, cartographer, philosopher, and instrument maker from the Netherlands. The clock would be set to the local time of a starting point whose longitude was known, and the longitude of any other place could be determined by comparing its local time with the clock time. While the method is perfectly sound, and was partly stimulated by recent improvements in the accuracy of mechanical clocks, it still requires far more accurate time-keeping than was available in Frisius's day. The term chronometer was not used until the following century, and it would be over two centuries before this became the standard method for determining longitude at sea.>>
Art Neuendorffer