APOD: Triple Transit and Mutual Events (2021 Aug 21)

[APOD Robot]

Triple Transit and Mutual Events

Explanation: These three panels feature the Solar System's ruling gas giant Jupiter on August 15 as seen from Cebu City, Phillipines, planet Earth. On that date the well-timed telescopic views detail some remarkable performances, transits and mutual events, by Jupiter's Galilean moons. In the top panel, Io is just disappearing into Jupiter's shadow at the far right, but the three other large Jovian moons appear against the planet's banded disk. Brighter Europa and darker Ganymede are at the far left, also casting their two shadows on the gas giant's cloud tops. Callisto is below and right near the planet's edge, the three moons in a triple transit across the face of Jupiter. Moving to the middle panel, shadows of Europa and Ganymede are still visible near center but Ganymede has occulted or passed in front of Europa. The bottom panel captures a rare view of Jovian moons in eclipse while transiting Jupiter, Ganymede's shadow falling on Europa itself. From planet Earth's perspective, similar mutual events, when Galilean moons occult and eclipse each other, can be seen every six years or so when Jupiter is near its own equinox.

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[jks]

In the '70's, I loved watching transits of the Jovian moons' shadows, and transits of the moons themselves on Jupiter's disk but for some reason I was never able to see a moon eclipse another, much less on Jupiter's disk, as seen from Earth. But I was able to see one moon occult another on more than one occasion.

Here's to the Criterion Dynascope 6 (circa 1975)* !

* I'm pretty sure that I am not violating Rule #8, or if I am, I'm 46 years too late ).

[De58te]

This is very interesting because usually you would see a still picture of just one moon's shadow transiting. Science can easily be learned here. Europa's shadow seems to start behind and overtake Ganymede's shadow. We can assume Europa is orbiting faster and therefore be closer to the planet. But what I never knew before is that Ganymede's shadow seems to keep exact pace with the red spot above and the white oval below. So that means that Ganymede's shadow transit is at the same speed as the winds blowing the clouds. Now the timer on the clock says that just under 3 hours had passed. But since the final picture didn't end right at the terminator We should say just over 3 hours passed. Now the circumference is diameter times pi, so we can say that the winds blow the clouds around the entire circumference of Jupiter in about 9 and a half hours.

[neufer]

Click to play embedded YouTube video.

[orin stepanek]

The moons and their shadows; very interesting!

[johnnydeep]

Deciphering the description to determine what's what (moon, shadow, "mutual event") in each panel pains me. Who wants to annotate it?

[Joe Stieber]

Deciphering the description to determine what's what (moon, shadow, "mutual event") in each panel pains me. Who wants to annotate it?

Okay, here's my annotated version. I labeled the satellites as I, E, G and C for Io, Europa, Ganymede and Callisto respectively. When followed by an S, it's that satellite's shadow. I used FastStone to do the labeling and WinJUPOS as my satellite/shadow position reference. This is a remarkable set of images showing some rare configurations!

Joe

[johnnydeep]

Deciphering the description to determine what's what (moon, shadow, "mutual event") in each panel pains me. Who wants to annotate it?

Okay, here's my annotated version. I labeled the satellites as I, E, G and C for Io, Europa, Ganymede and Callisto respectively. When followed by an S, it's that satellite's shadow. I used FastStone to do the labeling and WinJUPOS as my satellite/shadow position reference. This is a remarkable set of images showing some rare configurations!
J20210815a_cgo-label.jpg
Joe

Thanks! In the fourth pic of Jupiter, GS points to two shadows. It should only point to the larger one, right?

[Joe Stieber]

Deciphering the description to determine what's what (moon, shadow, "mutual event") in each panel pains me. Who wants to annotate it?

Okay, here's my annotated version. I labeled the satellites as I, E, G and C for Io, Europa, Ganymede and Callisto respectively. When followed by an S, it's that satellite's shadow. I used FastStone to do the labeling and WinJUPOS as my satellite/shadow position reference. This is a remarkable set of images showing some rare configurations!
J20210815a_cgo-label.jpg
Joe

Thanks! In the fourth pic of Jupiter, GS points to two shadows. It should only point to the larger one, right?

No -- the two arrows are correct. The top of Europa intercepts the bottom of Ganymede's shadow (a partial eclipse), then the rest of shadow continues to the Jovian surface where it mingles with Europa's shadow. Here's a close-up clip of the WinJUPOS synthetic image for Aug 15 @ 17:25 UT. Pretty amazing!

Joe

P.S. -- The dashed line in the WinJUPOS clip represents Jupiter's equator.

[Avalon]

Thank you for the clear annotation. Now I understand what all of the dots are!

[VictorBorun]

Okay, here's my annotated version. I labeled the satellites as I, E, G and C for Io, Europa, Ganymede and Callisto respectively. When followed by an S, it's that satellite's shadow. I used FastStone to do the labeling and WinJUPOS as my satellite/shadow position reference. This is a remarkable set of images showing some rare configurations!
J20210815a_cgo-label.jpg
Joe

Thanks!
I can see that the velocity of the Ganymede's & Europa's shadows are similar to the velocity of the Jupiter's surface.
This does not mean that the satellites are almost stationary in Jupiter's sky though.
This only means that the satellites move slowly in relataion to Sun in Jupiter's sky.

equatorial rotation velocity of Jupiter is 12.6 km/s. It is in-between:
orbital velocity of Europa is 13.7 km/s; that is faster by 1.1 km/s
orbital velocity of Ganymede is 10.880 km/s; that is slower by 1.72 km/s

We are more lucky with Moon-Sun dance:
equatorial rotation velocity of Earth is 0.46 km/s
orbital velocity of Moon is 0.970 to 1.082 km/s in plane at 5.145° to the equatorial plane of Earth;
that is faster just by 0.51…0.622 km/s, and can be outrun by a supersonic plane

[johnnydeep]

Okay, here's my annotated version. I labeled the satellites as I, E, G and C for Io, Europa, Ganymede and Callisto respectively. When followed by an S, it's that satellite's shadow. I used FastStone to do the labeling and WinJUPOS as my satellite/shadow position reference. This is a remarkable set of images showing some rare configurations!
J20210815a_cgo-label.jpg
Joe

Thanks! In the fourth pic of Jupiter, GS points to two shadows. It should only point to the larger one, right?

No -- the two arrows are correct. The top of Europa intercepts the bottom of Ganymede's shadow (a partial eclipse), then the rest of shadow continues to the Jovian surface where it mingles with Europa's shadow. Here's a close-up clip of the WinJUPOS synthetic image for Aug 15 @ 17:25 UT. Pretty amazing!
2021-08-15-1725.0-Jupiter-NR.png
Joe

P.S. -- The dashed line in the WinJUPOS clip represents Jupiter's equator.

Thanks again. Now I understand. Indeed, this is pretty amazing and quite subtle as well.

[XgeoX]

In the '70's, I loved watching transits of the Jovian moons' shadows, and transits of the moons themselves on Jupiter's disk but for some reason I was never able to see a moon eclipse another, much less on Jupiter's disk, as seen from Earth. But I was able to see one moon occult another on more than one occasion.

Here's to the Criterion Dynascope 6 (circa 1975)* !

* I'm pretty sure that I am not violating Rule #8, or if I am, I'm 46 years too late ).

Don’t forget the Prime Directive, which they broke about every episode!

Eric

[neufer]

I can see that the velocity of the Ganymede's & Europa's shadows are similar to the velocity of the Jupiter's surface.

This does not mean that the satellites are almost stationary in Jupiter's sky though.
This only means that the satellites move slowly in relataion to Sun in Jupiter's sky.

equatorial rotation velocity of Jupiter is 12.6 km/s. It is in-between:
orbital velocity of Europa is 13.7 km/s; that is faster by 1.1 km/s
orbital velocity of Ganymede is 10.880 km/s; that is slower by 1.72 km/s

We are more lucky with Moon-Sun dance:

equatorial rotation velocity of Earth is 0.46 km/s
orbital velocity of Moon is 0.970 to 1.082 km/s in plane at 5.145° to the equatorial plane of Earth;
that is faster just by 0.51…0.622 km/s, and can be outrun by a supersonic plane

Solar eclipse of June 30, 1973

---

<<A total solar eclipse occurred at the Moon's descending node of the orbit on June 30, 1973. With a maximum eclipse of 7 minutes and 3.55 seconds, this was the last total solar eclipse that exceeds 7 minutes in this series. The last total eclipse over 7 minutes was on July 1, 1098 which lasted 7 minutes and 5 seconds. There will not be a longer total solar eclipse until June 25, 2150. The greatest eclipse occurred in the Agadez area in the northwest of Niger not far from Algeria inside the Sahara Desert somewhat 40 km east of the small mountain of Ebenenanoua at 18.8 N and 5.6 E and occurred at 11:38 UTC.

This eclipse was observed by a group of scientists, which included Donald Liebenberg, from the Los Alamos National Laboratory. They used two airplanes to extend the apparent time of totality by flying along the eclipse path in the same direction as the Moon's shadow as it passed over Africa.

One of the planes was a prototype of what was later to become the Concorde, which has a top speed of almost 0.606 km/s. This enabled scientists from Los Alamos, the Paris Observatory, the Kitt Peak National Observatory, Queen Mary University of London, the University of Aberdeen and CNRS to extend totality to more than 74 minutes; nearly 10 times longer than is possible when viewing a total solar eclipse from a stationary location. That Concorde was specially modified with rooftop portholes for the mission, and is currently on display with the Solar Eclipse mission livery at Musée de l’air et de l’espace. The data gathered resulted in three papers published in Nature and a book.

A separate observation opportunity was provided on a specialized commercial cruise by the S.S. Canberra, which traveled from New York City to the Canary Islands and Dakar, Senegal, observing 5 minutes and 44 seconds of totality out in the Atlantic between those two stops in Africa. That cruise's passengers included notables in the scientific community such as Neil Armstrong, Scott Carpenter, Isaac Asimov, Walter Sullivan, and the then 15-years old Neil deGrasse Tyson.>>

[VictorBorun]

One of the planes was a prototype of what was later to become the Concorde, which has a top speed of almost 0.606 km/s. This enabled scientists from Los Alamos, the Paris Observatory, the Kitt Peak National Observatory, Queen Mary University of London, the University of Aberdeen and CNRS to extend totality to more than 74 minutes; nearly 10 times longer than is possible when viewing a total solar eclipse from a stationary location.

I wonder is it a chance configuration.
At its starting moment there was a synestia, so Earth's equatorial velocity must have been almost equal to the low orbit velocity about 7 km/s, and Moon was in an almost low orbit. Then the tidal interaction stopped Moon's spin down to the tidal lock and slowed Earth's spin down to the period of 24 hours and the equatorial velocity of 0.46 km/s; the total spin is preserved by Moon's escaping to a high orbit where Moon's orbital radius is longer and, though Moon's orbital velocity is slower, still Moon's orbital spin is higher.
This today's configuration is many times slower and, though the two velocities (Moon's orbital and Earth's equatorial) are not like each other any more they both are now so slow that we can get on a plane and freeze Moon against the superlunar sky.

[neufer]

At its starting moment there was a synestia, so Earth's equatorial velocity must have been almost equal to the low orbit velocity about 7 km/s, and Moon was in an almost low orbit. Then the tidal interaction stopped Moon's spin down to the tidal lock and slowed Earth's spin down to the period of 24 hours and the equatorial velocity of 0.46 km/s; the total spin is preserved by Moon's escaping to a high orbit where Moon's orbital radius is longer and, though Moon's orbital velocity is slower, still Moon's orbital spin is higher.

This today's configuration is many times slower and, though the two velocities (Moon's orbital and Earth's equatorial) are not like each other any more they both are now so slow that we can get on a plane and freeze Moon against the superlunar sky.

Way back when I was a kid I could even pop in the back of our old Plymouth & would note that
no matter how far my father drove... the Moon would always be able to follow the car