2020 A Great Conjunction - and a Galilean Connection

 

Patience pays. Or is it persistence. Finally got a glimpse of the "Great Conjunction" of Jupiter and Saturn on the evening of Dec 23, two days after its closest approach (on the 21st). After a major snowstorm in New Jersey the prior week, dense clouds and fog that hung over the US east coast persisting for five days relented for a few hours enough for this capture from my front porch.  

The angular separation at peak conjunction on the evening of the 21st was about 6 arc minutes. In this image from 2 days later, they’re slightly wider apart* but still close enough for both to fit in a single eyepiece view of a medium size telescope.  Jupiter's four largest moons are visible in the picture left to right are Io, Europa, Callisto and Ganymede with an orbital plane inclined at an angle to the ecliptic.

Some argue that a celestial conjunction such as this is loosely defined and over hyped. There is perhaps some truth to this since many celestial bodies can get reasonably close from time to time. But the fact is, for Jupiter and Saturn, a closeness of under 10 minutes of arc is rare. These were expected to happen only 5 times between 1200 and 2400 CE, of which this was the penultimate instance.  The last time they were this close (~5 arc minutes apart) was in July of 1623. At the time, Galileo was alive, more on that later. Since 1623, the two planets have danced between 2 to 10 times this separation as seen from the earth. The next great conjunction of the under 10 arc minutes variety will be in 2080, the last of its kind until at least 2400 CE. 

A message in the brightness.  

In the image Saturn appears much fainter than Jupiter. That is a function of its greater distance. At this point in its orbit, Saturn is a billion miles from us, twice as far as Jupiter. Since they are both illuminated only by sunlight, the inverse square law predicts that Saturn at twice the distance should be four times fainter than Jupiter. In fact astronomers use this principle for computing unknown distances to objects based on a known distance.   

In processing the image, I kept the relative brightness difference of Jupiter and Saturn constant. The image however did not start off as a single snapshot. The original capture format is a short video clip of over 500 frames which is processed by software to align the images per frame, and another to stack them into a single image followed by sharpening and retouching brightness. This long winded method of going from video to still image helps minimize blurring in individual stills due to earth's atmospheric turbulence. Our present day digital camera sensors, still suffer from a limited range of brightness compared to the human eye. So tradeoffs are needed. The overall image brightness was tweaked to a sweet spot so that Saturn's rings are not lost in darkness and yet the hint of  Jupiter‘s cloud bands aren’t blown to white. Of course individually adjusting their brightness of each planet would yield a clearer picture, but then the relative difference would not be preserved. 

Jupiter's four moons have however received targeted brightness adjustment, as they would not be visible otherwise.  They are seen here on an inclined orbital plane at angle to the ecliptic, apparently defying gravity as they appear to "float" around Jupiter.

A Christmas star?

The popular media narrative was that on Christmas day the duo will appear as a single “Christmas star” to the naked eye. Below is a wide angle view of the same scene with a red box enclosing the pair. One certainly needs worse than average eyesight for such a  “merger” to happen. 

1 second exposure of wide angle view of conjunction on Dec 23, 2020

Heavy fog. 1 second exposure of the same scene, on Dec 21st, the day of conjunction

Galileo's inquisition and a semicolon

The Great Conjunction last happened in 1623, when Galileo was alive. In fact 13 years had passed since he had discovered the four moons of Jupiter and made the startling proposition that they orbited Jupiter (not the earth). In fact he computed their orbital periods by observing how they changed position over 18 months. His findings upset the belief of the day that all celestial bodies must revolve around the earth. At the time, Copernican heliocentrism had already been tried by the Roman Inquisition in 1616 and found "formally heretical" and "foolish and absurd in philosophy".  But it was not until 1633 that  Galileo would be tried by the Roman inquisition and found guilty of heresy and placed under house arrest for the rest of his life.  The original assessment document from the inquisition of 1616 has been paraphrased and translated from Italian in more than one way. The variations present an interesting problem due to placement of a semicolon. 

One translation (p. 10 of the above document) goes as follows:

"All said that this proposition is foolish and absurd in philosophy and formally heretical, since it explicitly contradicts in many places the sense of Holy Scripture."

This translation suggests that the philosophical absurdity arises purely from contradicting the scriptures. However in another translation, there is a semicolon after the word "philosophy": 

"All said that this proposition is foolish and absurd in philosophy; and formally heretical, since it explicitly contradicts in many places the sense of Holy Scripture."

The second translation suggests that the philosophical absurdity is separate from heretical nature. Which is perhaps more palatable since the absurdity hopefully evoked due to a different reason than just contradicting scriptures

Regardless of the reason for him being held guilty, Galileo did pay a price sacrificing his freedom. Today, 400 years later, has the epic battle between prevalent belief and informed rationality become any easier? I'll let the reader decide.  

Technical Information:

• Celestron 127 SLT with Celestron 8-24 zoom eyepiece at 24 mm
• Canon 70D in eyepiece projection, 30 fps, 1/100th second 
• Planetary Image pre-Processor (PIPP) for video pre-processing and alignment
• Registax for stacking and wavelet processing
• Photos (Windows) / Photoshop retouching

*around 15 arc minutes in azimuth and 8 arc minutes in altitude