The Night of January 23, 2015

By David Nakamoto

The Setting

Three of the moons of Jupiter would cast shadows on its disk. Such a thing has not happened for more than a decade, since 2004 March 27th to be exact. Back then, we were at the Griffith satellite station, south of the Los Angeles Zoo parking lot. It was also a much more inconvenient time for a public star party, since we had to stay up until after midnight to see the event on that date. This time, it would occurred much earlier, at 10:25pm.

But it was the day BEFORE our regularly scheduled public star party at Griffith Observatory. But thanks to the author's efforts to bring this up to everyone's awareness, the preparatory work to make it happen went through, and so Griffith Observatory, the LAAS, and the public were going to be treated to a show.
Or they would have, if it weren't for . . .

The Beginning

Sunset had occurred, but Jupiter was still about an hour and a half away from rising over the distant eastern mountains, so in the meantime some of us amused ourselves by looking at Venus . . . and quit being amused.
Venus was twinkling with the unaided eye! Planets aren't supposed to twinkle. In fact, this is one way you can tell if a "star" is really a star or a planet. The twinkling was a sign of VERY bad Seeing.
For those new to our hobby, Seeing is the amount of turbulence in the air. The turbulence can begin at ground level and extend to high up in the atmosphere. It determines what you can see. Seeing is rated on a scale from 1 to 5, with 1 being perfect with no distortions, and 5 being the worst. Stars are the most affected by seeing since they're basically pinpoints of light. Planets aren't supposed to be affected by it, at least to the unaided eye, since they're actually small disks. So if planets start twinkling, the atmosphere is very turbulent.
By all accounts, the Seeing on the 23rd was the worst anyone can remember, and all across the greater LA area. LAAS member Barry Megdal at Mt Wilson reported as such, and the images taken with the Mt Wilson 60-inch confirmed this. From La Verne another LAAS member, Jeff Schroeder, texted me with the same report. And the reports from Garvey Ranch Park were the same.
This meant that faint or fine objects could not be seen, so the chance of seeing all three shadows on Jupiter was somewhere between slim and none. And the turbulence was high in the atmosphere, since Mt Wilson was higher than anyone else. Everything in the sky with the exception of the Moon was twinkling, and the Moon was a blurred object through telescopes.
Yup, one bad evening just got started.

Cresting the Horizon

At around 7pm, Jupiter rose above the distant eastern mountains. I got on it right away, since Callisto's shadow should have started its passage across the Jovian disk. Such a passage is generally called a transit.
But Jupiter was not even a disk! It was an ever-morphing blob in constant turmoil. I couldn't see the bands on Jupiter, let alone the smaller shadow of Callisto.
As time wore on, Jupiter got higher in the sky, and the Seeing VERY gradually got better, but . . .
While I saw the three satellites that were going to produce the shadow show off to the right of Jupiter, they bounced around like little butterflies.
The edge of the disk of Jupiter never did become anything resembling a steady distinct edge.
And I didn't see the bands at all, except for one or two seconds out of every minute.

The Io Show Got Cancelled

At about 9:50pm, Io should have been in the middle of passing into Callisto's shadow. This would have darkened it a lot, briefly producing what looked like another shadow on Jupiter. But no one saw this to my knowledge. And unfortunately, I forgot to take video around that time.
Around 10:00pm or so, the atmosphere finally steadied enough to where I could see the bands of Jupiter more often than not, but Callisto's shadow remained elusive.
Then around 10:20pm, Io should have passed in front of Callisto's shadow. Since it is a brightly lit disk, it should have changed Callisto's shadow to a black ring. Also, Callisto should have been on the edge of Jupiter starting its transit. Again, no one saw anything, including the video feeds from my setup, Mt Wilson's, and Griffith's.

The Main Show

Then, around 10:30pm or so, Europa's shadow should have been completely on the disk of Jupiter . . . and again, nothing was seen, despite the fact that Jupiter was 50 degrees up in the sky, more than halfway to maximum height. Sadly, the only things visible on the Jovian disk were the two bands and Callisto's shadow, and those not all the time, regardless of what telescope you looked through or on any of the three videos available to the public that night.
And then around 10:55pm, the show was over, when Io's shadow left the Jovian disk and the triple shadow event was finished. I had collected lots of videos of a terribly blurred and distorted Jupiter, with little hope that I had recorded anything but two bands and one spot.

And That's All Folks, Except . . .

I keep taking video more or less continuously from 8pm through to the end, around 10:55pm. Good thing I had.
Naturally, the best videos came near the end of the event when the atmosphere was less turbulent, so I processed the videos from the last towards the first. However, I found that only 40 to 90 frames out of over 3,000 in each three minute video were steady enough to warrant stacking, so I didn't hold out much hope that something would filter through the computer.
Last video, nothing. Same for the next two. But on the fourth to the last video, in a stack of about 90 frames, I saw more than just the bands and one shadow:


This was good enough to take a chance at further processing. Although that image never appeared too clear, I hoped that one of the others might show things clearer. Sure enough, two videos earlier, this appeared after stacking and processing.


From left to right, Europa's shadow is the darker of the two on the left edge. Callisto is above it, lighter and a lot fuzzier. Callisto's shadow is the darkest mark, halfway from the center of the disk of Jupiter to the right edge. Near the right edge, the gray spot there is Io's shadow. If you look carefully, there is a pale yellowish spot just off of Callisto's shadow 3:30 o'clock. I believe that is Io. Europa is off the left edge of Jupiter's disk, invisible due to the short exposure time of needed to capture features on the bright Jovian disk.

And no, that isn't the Red Spot just above center. The Red Spot is in the Southern Temperate band, the same band Europa's shadow lies in.

Initially, the videos from around 10:20pm did not appear to show anything. But persistence, plus an adjustment of the processing parameters, produced an image that seemed to show Callisto's shadow as a ring. I had imaged Io passing in front of that shadow! In the image below, Callisto's shadow is the ring just right of the center of Jupiter's disk. The interior of the ring is yellowish, not white, indicating it is Io. Io's shadow is the fainter dark disk to the right of Callisto's. It also appears as a ring but this is an effect of the aggressive image processing I had to use to bring out the superposition of Io in front of Callisto's shadow.


So the night was successful after all, although none of my images looked sharp due to the seeing, and no one to my knowledge saw the triple shadows visually or on live video. But the public were enthused, entertained, and educated, so while Los Angeles based amateur astronomers might have been disappointed, it was a good public event.

The Next Big Thing?

Towards the end of this year, a former near-earth asteroid turned Very Long Period comet, C/2013 US10 (Catalina), might make it to 3rd mag, visible to the unaided eye. It also goes circumpolar for us beginning next year. But this comet is apparently coming from the Oort cloud. The orbit so far has an eccentricity of over 1, meaning hyperbolic, meaning even if it really is elliptical, its aphelion is WAY out there. Such comets are unpredictable since they're making their first trip to the inner Solar System. Remember comet ISON? So we'll have to see.

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