APOD: Planetary Alignment over Italy (2021 Dec 19)

[APOD Robot]

Planetary Alignment over Italy

Explanation: It is not a coincidence that planets line up. That's because all of the planets orbit the Sun in (nearly) a single sheet called the plane of the ecliptic. When viewed from inside that plane -- as Earth dwellers are likely to do -- the planets all appear confined to a single band. It is a coincidence, though, when three of the brightest planets all appear in nearly the same direction. Such a coincidence was captured earlier this month. Featured above (right to left), Venus, Saturn, and Jupiter were all imaged together in a line just after sunset, from the San Fermo Hills, Bergamo, Italy. Joining the alignment are Earth's Moon, and the position of the more distant Uranus. Bands of clouds streak across the sky toward the setting Sun. As Comet Leonard fades, this planetary alignment -- absent the Moon -- should persist for the rest of the month.

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[heehaw]

Hey, just wait til the year 2492: https://henry.pha.jhu.edu/2492.png

[rj rl]

Looks like noctilucent clouds also made an appearance. Isn't Italy a bit too southern to see them? They're also towards the south

[Sa Ji Tario]

I estimate that it was in the 60s of the last century that something similar happened and led to the launch of the two Voyagers with the results that are known, the new discoveries led to new explorations and today there are innumerable probes roaming the cosmic neighborhood in search news .-
I understand that on average every 160 years planetary alignments will occur, although some will be in opposition, this achieved a diffusion of the science of Astronomy as it was never known

[Chris Peterson]

Not apparent in this image, but present all the same... Neptune lies on a line almost exactly between the Moon and Jupiter, and Pluto is in conjunction with Venus, lying just a half a degree below it. (Mercury is just below the horizon, and could theoretically have been captured had the image been made a few minutes earlier... although that would have been so shortly after sunset that the sky might have been too bright to see either it or Uranus, and maybe even Saturn. Jupiter and Venus can both be seen while the Sun is still above the horizon, if you look carefully.)

[orin stepanek]

I had trouble spotting Saturn; and Uranus I couldn't spot!

Cute critter; even has a telephone dial nose!

Aw! Good doggie giving tired kitty a lift!

[johnnydeep]

Hey, just wait til the year 2492: https://henry.pha.jhu.edu/2492.png

Wait - why don't the planets shown there appear nearly in a straight line?

Click to view full size image

[neufer]

Hey, just wait til the year 2492: https://henry.pha.jhu.edu/2492.png

Wait - why don't the planets shown there appear nearly in a straight line?

Click to view full size image

• All (seven planets?) in the same 180° wide path of the sky
  
  This is not my understanding of the true significance of May 6, 2492:

<<May 6, 2492 : Belgian astronomer Jean Meeus asserts that the orbits of all eight planets and Pluto will be within the same 90° arc (i.e., heliocentric longitude) of the Solar System.

The last time this is believed to have occurred was on February 1, 949.>>

[johnnydeep]

Hey, just wait til the year 2492: https://henry.pha.jhu.edu/2492.png

Wait - why don't the planets shown there appear nearly in a straight line?

Click to view full size image

• All (seven planets?) in the same 180° wide path of the sky
  
  This is not my understanding of the true significance of May 6, 2492:

<<May 6, 2492 : Belgian astronomer Jean Meeus asserts that the orbits of all eight planets and Pluto will be within the same 90° arc (i.e., heliocentric longitude) of the Solar System.

The last time this is believed to have occurred was on February 1, 949.>>

Ok, but you didn't address my "not in the same line" question. So, I looked up the orbital inclinations of the planets and only Pluto (17 degrees) and Mercury (7 degrees) are the odd men out, with the other planets all under 3.5 degrees orbital plane inclination. So, I guess that jives with the image.

EDIT: I used this chart:

Click to view full size image

[Chris Peterson]

Hey, just wait til the year 2492: https://henry.pha.jhu.edu/2492.png

Wait - why don't the planets shown there appear nearly in a straight line?

Click to view full size image

They look pretty darn straight to me!

[neufer]

Wait - why don't the planets shown there appear nearly in a straight line?

Click to view full size image

• All (seven planets?) in the same 180° wide path of the sky
  
  This is not my understanding of the true significance of May 6, 2492:

<<May 6, 2492 : Belgian astronomer Jean Meeus asserts that the orbits of all eight planets and Pluto will be within the same 90° arc (i.e., heliocentric longitude) of the Solar System.

The last time this is believed to have occurred was on February 1, 949.>>

Ok, but you didn't address my "not in the same line" question. So, I looked up the orbital inclinations of the planets and only Pluto (17 degrees) and Mercury (7 degrees) are the odd men out, with the other planets all under 3.5 degrees orbital plane inclination. So, I guess that jives with the image.

Pluto isn't even shown in the https://henry.pha.jhu.edu/2492.png image ...
while Mars (1.9°) & Neptune (1.8°) are the most obvious planets "not in the same line."

I went to: http://www.faustweb.net/solaris/ and put
in the dates: 6-5-2492 & 1-2-949 which shows:

• 1) agreement with the https://henry.pha.jhu.edu/2492.png image and
  2) agreement with all eight planets being within the same 90° arc (i.e., heliocentric longitude) of the Solar System.

However,

• All (seven planets?) are NOT in the same 180° wide path of the sky on February 1, 949.
  
  This type of alignment is much easier when ONLY the seven shown planets are within the same 90° arc
  (i.e., heliocentric longitude) of the Solar System while a (non-aligned) Earth observes them from afar.
  
  (6-5-2492 & 1-2-949 (eight planet) alignments are rarer birds... especially if Pluto is included )

[johnnydeep]

Neufer wrote "while Mars (1.9°) & Neptune (1.8°) are the most obvious planets "not in the same line."

Yeah, I overlooked that Pluto isn't shown, but from a purely line-fitting POV, depending on the line you choose, it looks like either Mercury and Jupiter are off it, or maybe Mercury and Venus. How are you picking Mars and Neptune?

[neufer]

Neufer wrote "while Mars (1.9°) & Neptune (1.8°) are the most obvious planets "not in the same line."

Yeah, I overlooked that Pluto isn't shown, but from a purely line-fitting POV, depending on the line you choose, it looks like either Mercury and Jupiter are off it, or maybe Mercury and Venus. How are you picking Mars and Neptune?

They are adjacent to each other and, hence, most obviously out of ( great circle) alignment.

[alter-ego]

Neufer wrote "while Mars (1.9°) & Neptune (1.8°) are the most obvious planets "not in the same line."

Yeah, I overlooked that Pluto isn't shown, but from a purely line-fitting POV, depending on the line you choose, it looks like either Mercury and Jupiter are off it, or maybe Mercury and Venus. How are you picking Mars and Neptune?

They are adjacent to each other and, hence, most obviously out of ( great circle) alignment.

The Stellarium views show the two planetary configurations discussed. I'm showing only the planets, sun and moon with the best eyeball-fit for a great circle. Also, atmosphere and ground removed. For both cases, the "line" is a great-circle arc, and the planets line up quite well to this arc. Relatively speaking, Pluto is the most off. With regard to planetary alignment, image creation (image projection to the sensor plane and FoV) matters. For the Stellarium simulations, finding the best alignment sweet spot was straight forward.
 
• Today's APOD - Surprise! Neptune is also present and fits well on the line. It's just not visible. It is 2+ magnitudes fainter, and the clouds don't help. It doesn't matter here, but I did set the view from in or around Italy on Dec 12. (Note, I did not weight Ceres in the fit.)
 

Planetary Alignment Dec 12, 2021

 
• May 6, 2492 - Here too, the planets align well, except for Pluto which is really off by about 12°.
 

Planetary Alignment May 6, 2492

[Ann]

Neufer wrote "while Mars (1.9°) & Neptune (1.8°) are the most obvious planets "not in the same line."

Yeah, I overlooked that Pluto isn't shown, but from a purely line-fitting POV, depending on the line you choose, it looks like either Mercury and Jupiter are off it, or maybe Mercury and Venus. How are you picking Mars and Neptune?

They are adjacent to each other and, hence, most obviously out of ( great circle) alignment.

The Stellarium views show the two planetary configurations discussed. I'm showing only the planets, sun and moon with the best eyeball-fit for a great circle. Also, atmosphere and ground removed. For both cases, the "line" is a great-circle arc, and the planets line up quite well to this arc. Relatively speaking, Pluto is the most off. With regard to planetary alignment, image creation (image projection to the sensor plane and FoV) matters. For the Stellarium simulations, finding the best alignment sweet spot was straight forward.
 
• Today's APOD - Surprise! Neptune is also present and fits well on the line. It's just not visible. It is 2+ magnitudes fainter, and the clouds don't help. It doesn't matter here, but I did set the view from in or around Italy on Dec 12. (Note, I did not weight Ceres in the fit.)
 

Click to view full size image

 
• May 6, 2492 - Here too, the planets align well, except for Pluto which is really off by about 12°.
 

Click to view full size image

Impressive, alter-ego! Does that mean that today's alignment is extremely rare?

Ann

[alter-ego]

...

Impressive, alter-ego! Does that mean that today's alignment is extremely rare?

Ann

Well, thanks, Ann
Yes! Extremely rare!!

Below, Pluto is designated by the red cursor (also surrounding Venus!). Yes, at 13:00UT, Pluto reaches minimum separation from Venus < 4 arc minutes 8.5 hours later than the simulation time.!
This simulation also shows mars on the other side of the sun, but none the less, the 7 planets + Pluto are lined up within 180°.
Mars wasn't visible at the same time since it's on the other side of the sun, and Pluto extremely close to Venus.
 

7 Planet Alignment + Pluto Conjuction with Venus, Dec 12, 2021

Edit: I just saw I missed Chris' earlier post (twice!!) on both Neptune and Pluto. I couldn't believe that these hadn't come up! Indeed, I found they had. No matter, seeing / verifying the line-ups is still interesting. (I still can't believe I missed that )

[johnnydeep]

Alright, alter-ego's exacting work above notwithstanding, why again don't the planets appear to be in a straight line in the image neufer posted showing the alignment in year 2492. Is it merely an artifact of the perhaps panoramic view?

Click to view full size image

[Chris Peterson]

Alright, alter-ego's exacting work above notwithstanding, why again don't the planets appear to be in a straight line in the image neufer posted showing the alignment in year 2492. Is it merely an artifact of the perhaps panoramic view?

Click to view full size image

The planets are not in a line. They lie on the same plane (or nearly so). Similarly, the horizon isn't a line, but represents a plane. And those two planes are not the same- they are tilted with respect to each other. Project the image so the planets are in a line, and the horizon will be curved (as we see in the APOD image). Project the image so the horizon is a line, and the ecliptic will be curved (as we see in the simulation). You can't have both.

[neufer]

Alright, alter-ego's exacting work above notwithstanding, why again don't the planets appear to be in a straight line in the image neufer posted showing the alignment in year 2492. Is it merely an artifact of the perhaps panoramic view?

In today's APOD "the planets appear to be in a straight line" because the horizon is curved.

In the 2492 simulation "the planets appear to be in a curved line" because the horizon is set as straight.

The non-Euclidean geometry of the celestial sphere requires all "parallel lines" to intersect.

However, the Euclidean geometry of your video screen allows "parallel lines" to intersect
if and ONLY if one or more of them appear to be in a curved.

[Chris Peterson]

Impressive, alter-ego! Does that mean that today's alignment is extremely rare?

As the positions of the planets never have and never will repeat, every single instant of time represents an extremely rare alignment! They are all the same as far as the Universe is concerned- of no importance. So it all comes down to the significance we, as humans, choose to put on the patterns our brains try to detect.

[johnnydeep]

Alright, alter-ego's exacting work above notwithstanding, why again don't the planets appear to be in a straight line in the image neufer posted showing the alignment in year 2492. Is it merely an artifact of the perhaps panoramic view?

In today's APOD "the planets appear to be in a straight line" because the horizon is curved.

In the 2492 simulation "the planets appear to be in a curved line" because the horizon is set as straight.

The non-Euclidean geometry of the celestial sphere requires all "parallel lines" to intersect.

However, the Euclidean geometry of your video screen allows "parallel lines" to intersect
if and ONLY if one or more of them appear to be in a curved.

Thanks neufer (and Chris). I think I understand now.

[alter-ego]

One interesting side note. You might think the ecliptic (a great circle) should be the best-fit curve for planets. Logically, it would be for heliocentric coordinates, but from Earth, the planets' appearance against the stars is complicated by the Earth's orbit. For the 2492 planet grouping, I added the ecliptic-of-date (which intersects the sun). It's clear the magenta curve is the better fit.
 

2492 Planet grouping - Added Ecliptic of Date

 
You can see the ecliptic appears curved. Within this wide-field view, only one (either one) of these two curves can "straight". Only in the limit as the FoV → 0°, i.e. arc -lengths → 0°will Euclidean geometry apply, and both arc segments will become straight.

[alter-ego]

... You might think the ecliptic (a great circle) should be the best-fit curve for planets. Logically, it would be for heliocentric coordinates, but from Earth, the planets' appearance against the stars is complicated by the Earth's orbit.
...

Ok, below is the view from the Sun's equator-of-date. This version of Stellarium happens not to plot the ecliptic, but the equator-of-date is shown. It is the same as the ecliptic-of-date. In this case Mercury joins Pluto being way off from the great circle, but Earth is now part of the orderly group. Excluding Mercury and Pluto, the best-fit great circle for the 7 remaining planets does appear to be the Solar equator (ecliptic). At least it's a better fit than as viewed from Earth. From the sun, this grouping extends <100°
 

2492 planet grouping from the Sun