Category: Astronomy

Speculating on Applications of the Hypothetical Interstellar Origin of the Zodiacal Dust Cloud

I had read part of Brian May’s thesis, A Survey of Radial Velocities in the Zodiacal Dust Cloud, a week or so ago, and one section of it had stuck in my mind. Here I quote it below (ellipses mine).

It is remarkable that so few earlier records are available, since…the mysterious Light of the Zodiac ought to have been very conspicuous in the dark skies of earlier civilisations, comparable in dimensions with the Milky Way, and at its brightest, more luminous. … Could it be that our view of the Zodiacal Light is highly variable? Cassini was convinced that it disappeared completely between 1665 and 1681, and this man was certainly no casual observer. I have no solution to the puzzle. In the light of Cassini’s reports, along with Jones’s observations detailed below, and the curious dearth of references pre-Cassini, I am convinced that, despite the lack of any recent confirmation, we must admit the possibility that the Zodiacal Light has not always been what it is today.

The passage in full is worth reading, but the salient detail is that the zodiacal light may be a relatively recent phenomenon.

Later in the same chapter, another note got my attention, here quoted.

One of the great ‘surprises’ in space observations, as noted by Sykes et al (2004), was that the detectors on board the space vehicle Ulysses, once past the orbit of Jupiter, began to register particle impacts from the opposite direction to that expected from interplanetary dust particles, and at high velocities, clearly indicating an interstellar component to the dust cloud, which predominates at these distances from the Sun, but has been now detected, by the Hiten detector, even at 1 AU (Grün et al 1993).

Here we see that the dust particles are interstellar, as well, meaning from outside the solar system.

My mind returned to these two details today, and it occurred to me that the latter detail easily accounts for the former if I posit the explanation that the zodiacal dust cloud originates from interstellar dust through which the solar system has moved during its galactic orbit, encountering it in much the same way the Earth encounters cometary dust during its orbit, giving rise to meteor showers.

In fact, the zodiacal dust cloud’s interplanetary dust particles (IDPs) are located asymmetrically with respect to both the ecliptic and to the circumstellar disc, and I speculate it is for this very reason. (That is to say, in reading Brian May’s summarizations of other surveys’ findings of the locations of the IDPs in our solar system, they tend to be located in particular areas, not in a smooth ring.)

When I turned to chapter four of his thesis, Brian May’s interpretations of his results already include hypotheses about IDPs flowing in from the interstellar medium, both as the solar system moves through it and as the IDPs flow inward. These were vindicated by more recent observations.

The novelty of my speculations, which I’m sharing here, lies in the recency and asymmetrical nature of the zodiacal dust cloud, and the implications it has on understanding the nature of the galaxy.

By this, I mean that although the interstellar dust throughout the galaxy cannot be observed directly, we can extrapolate from our knowledge of the zodiacal dust cloud—our knowledge of the velocities and positions of the IDPs within our solar system—to use our sun’s past as a kind of lantern to shine a light on the dark, dusty path through which we have passed over the past centuries or millennia. In other words, if the spatial distributions of unseen interstellar dust in our galaxy are uneven, we can gain insight into these distributions.

If this is possible, I foresee implications in dark matter physics because it would help refine our knowledge of the mass of the galaxy, which would in turn help narrow the parameters of dark matter.

I’ve also wondered if this has climate science implications. I’ve read about hypotheses involving climate cycles tied to phenomena from the interstellar medium, and clouds of dust may be one such phenomenon.

Jupiter on 29 March

Jupiter as seen on the evening of 29 March. Video taken using a Sony α6300 camera attached to a Celestron 11-inch Cassegrain-Schmidt telescope, viewed through a 25 mm eyepiece.

Beginning Astrophotography: Jupiter Ascending

Since I got my first telescope, I quickly discovered its abilities and limits, and I knew I wanted more. In fact, I wanted to be able to show other people what I saw, even if they couldn’t be there themselves. That meant learning how to do astrophotography.

I learned from reading online—and by using it myself—that my first telescope wasn’t suitable for astrophotography for a number of reasons. It was too light (being a large, empty tube for the most part), shifted too easily, not mechanized in any fashion, the Dobsonian mount was too simple, and I lacked any adapters to allow me to connect my camera to it. Taking a photo through it meant getting an adapter which would overweight the end, and so I’d have to constantly hold the whole thing still and counterbalance the weight, manually find and track to objects, and somehow manually follow the motion of things in the sky—with an altazimuth mount not designed for tracking, which didn’t have measurements, markings, or indices. To be honest, I was having trouble even finding objects in the first place, needing sometimes several minutes to track in on naked-eye objects (which would then flit out of view in seconds).

So I had to get a new telescope. I wanted something slightly more compact so I could carry it out to sites more easily, so I chose a Schmidt-Cassegrain telescope, which combines lenses and mirrors into a relatively compact body. I wanted to increase my aperture even more, so I looked for eleven-inch options and settled on a set from Celestron which combines the telescope I want with a computerized mount that can automatically find and track objects.

Celestron 11-inch Schmidt-Cassegrain telescope on an Advanced VX computerized mount

Celestron 11-inch Schmidt-Cassegrain telescope on an Advanced VX computerized mount

Putting all this together and learning how to use it has been a trial, but I’m getting better. It’s been cloudy here for weeks, so I’ve been messing around with it indoors learning how to align it and get it ready. A few nights ago, it finally cleared up enough to try it out.

Outside my backdoor, between the house and a nearby fence, there’s a sliver of sky through which the ecliptic passes, meaning I can watch planets rise and pass overhead. Recently, Jupiter has been rising early at night, right around the time the moon rises.

I took the pieces outside to the back walkway—tripod, mount, eyepieces, tube—and set up, switched on the mount, and did a quick alignment. Jupiter was low on the horizon to the east, climbing, visible as an unmistakably bright point. Once the tube was lined up close enough to see through the finderscope sitting on top of the main tube, Jupiter was obvious, a brilliant point surrounded by four smaller points.

I started with my largest (and least magnifying) eyepiece, the forty-millimeter one (giving me seventy-times magnification). It’s the one visible in the photo of the telescope above. Jupiter was clearly in view but out of focus, so I saw it as a large, diffuse disc with a large hole in the middle, the way light looks through a telescope which happens to have a large obstruction. In this case, the obstruction is built into the telescope, the center corrector mirror in the middle of the tube. I began focusing, and Jupiter came into view, no longer a point but a disc which was obviously wider than tall, with four points of light scattered in a line along the bulge. The shapes shifted and scintillated slightly as the air moved around.

This was my first time using computerized tracking, and I was so happy that the planet stayed in view rather than drifting just off out of view in a matter of moments. I found that I had to make adjustments after fifteen minutes or so, but these were pretty minor, likely because I didn’t do a proper alignment. When this happened, I could make them as fine adjustments with the handheld controller pretty easily, so it was so much less exhausting than my last experience. This automatic help made it easier to work on getting the best view I could.

Focusing in on a tiny object like a planet is a little frustrating because it’s plain to see there’s more detail there, but when you try to focus on it, you find yourself hitting a point beyond which it only gets blurrier again. Some of this is attributable to the limits of my optics, but most of it is due to the turbulence of the atmosphere, called seeing. From the ground, unless the circumstances are exceptional, atmospheric seeing limits the detail available to telescopes, meaning that more magnification usually doesn’t help.

Still, I tried. I brought out my twenty-five millimeter eyepiece, a shorter eyepiece with higher magnification (around 112 times). To my surprise, that gave me more detail this time. This proved to me that the tube itself was of higher quality than my previous telescope—or maybe just better seeing than last time. With careful focusing, I make out the cloud bands with my eye, and I thought I could even glimpse the Great Red Spot if I squinted. What I saw was a lot like the video I posted at the top of this entry (only brighter with more obvious moons).

I’ve never tried photographing a planet before, so I decided it was time to try now. I had found an adapter kit for my camera (a Sony NEX-6), so I took out the eyepiece and used the prime focus attachment, which essentially uses the telescope tube itself as a massive zoom lens, but without attaching any additional eyepieces. This meant no magnification beyond the tube’s own field of view, meaning that all the light the mirror was gathering was pulled into a small disc which shone too brightly to see any detail. Below is a picture showing roughly what this looks like.

Jupiter and moons

Jupiter and moons

After recording some pictures and video in this setup, I tried using an adapter that lets me use an eyepiece, getting me a lot closer to what I was seeing. I used the twenty-five millimeter eyepiece and the adapter to attach to the telescope, and after some careful focusing, I got several shots like the following one.

Jupiter at 112-times magnification

Jupiter magnified 112 times

To get this shot, I had to fool around with the camera a bit, speeding up its shutter speed to cut down on the light that was obscuring details. This one was exposed for only 250th of a second. The moons are no longer bright enough to show up except as pale specks seen on zooming in. I applied some minor processing to improve the clarity, but that’s all. Otherwise, this is just a single snapshot of exactly what I saw that night.

What’s next? My current Jupiter shots impressed me more than I’d hoped for, but because of seeing, it’ll take some tricks to get more detail and more impressive photos. I’m looking into image stacking software which will let me combine many individual pictures into a single, more detailed shot. I’ll need it if I want to photograph deep-sky objects like nebulae or galaxies. And I’ll need to improve at aligning my telescope so it can track more accurately. It might take until summer, but I’ll update here when I try again.

© 2017 Emily St*

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