As NASA's Cassini spacecraft continues its weekly ring-grazing orbits, diving just past the outside of Saturn's F ring, it is tracking several small, persistent objects there.
These images show two such objects that Cassini originally detected in spring 2016, as the spacecraft transitioned from more equatorial orbits to orbits at increasingly high inclination about the planet's equator.
Imaging team members studying these objects gave them the informal designations F16QA (right image) and F16QB (left image). The researchers have observed that objects such as these occasionally crash through the F ring's bright core, producing spectacular collisional structures (see PIA08863), similar to those created in 2006 and 2007 by the object designated S/2004 S 6 (see PIA07716).
While these objects may be mostly loose agglomerations of tiny ring particles, scientists suspect that small, fairly solid bodies lurk within each object, given that they have survived several collisions with the ring since their discovery. The faint retinue of dust around them is likely the result of the most recent collision each underwent before these images were obtained.
The researchers think these objects originally form as loose clumps in the F ring core as a result of perturbations triggered by Saturn's moon Prometheus (see PIA08397 and PIA08947). If they survive subsequent encounters with Prometheus, their orbits can evolve, eventually leading to core-crossing clumps that produce spectacular features, even though they collide with the ring at low speeds.
Image Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA
Explanation: The Cassini spacecraft's Grand Finale at Saturn has begun. The Grand Finale will allow Cassini to explore Saturn and some of Saturn's moons and rings in unprecedented detail. The first phase started two weeks ago when a close flyby of Titan changed Cassini's orbit into one that passes near Saturn's poles and just outside of Saturn's outermost F-ring. Featured here is an image taken during the first of Cassini's 20 week-long F-ring orbits around Saturn. Visible are the central polar vortex on the upper left, a hexagonal cloud boundary through the image center, and numerous light-colored turbulent storm systems. In 2017 April, Cassini will again use the gravity of Titan to begin a new series of 22 Proximal orbits -- trajectories that will take Cassini inside of Saturn's rings for the first time. Cassini's new science adventure is scheduled to end on 2017 September 17, though, when the robotic spacecraft will be directed into a dramatic mission-ending dive into Saturn's atmosphere.
Taken from NASA's Astronomy Picture of the Day
Space--Bot is a computer program that searches for space images.
Saturn’s rings were named alphabetically in the order they were discovered. The narrow F-ring marks the outer boundary of the main ring system. Image & Caption Credit: NASA/JPL-Caltech/Space Science Institute
NASA’s robotic Cassini spacecraft will begin a grand tour of Saturn’s ring system starting this week as the mission enters into its final stages. (more…)
Minimaantjes in F-ring van Saturnus leven niet lang
Uit onderzoek blijkt dat de minimaantjes in de F-ring van Saturnus geen lang leven beschoren zijn. Onderzoekers hebben hiertoe een vergelijking gemaakt tussen foto’s die gemaakt zijn door de Cassini-ruimtesonde en foto’s die dertig jaar eerder gemaakt zijn door de Voyager-ruimtesondes. Hieruit is gebleken dat het aantal minimaantjes enorm is afgenomen.
De F-ring is sowieso een geval apart, aangezien de ring nooit een gladde structuur heeft, maar vol zit met klonters en gebiedjes met een hogere en lagere helderheid. Astronomen vermoeden dat minimaantjes van een kilometer of vijf groot hiervoor verantwoordelijk zijn. Deze maantjes verstoren dan het omringende materiaal.
Uit het onderzoek blijkt dat de F-ring ten tijde van de Voyagers veel meer onregelmatige klonters bevatte dan vandaag de dag. Deze klonters zijn vermoedelijk het gevolg van minimaantjes die met hun zwaartekracht het omringende materiaal op elkaar doen knallen en verpulveren. Blijkbaar zijn er nu minder minimaantjes dan dertig jaar geleden, vandaar de afname in het aantal klonters. Maar hoe komt dat?
Wel, je kunt Prometheus de schuld geven. De F-ring bevindt zich namelijk op een bijzonder punt, de zogenaamde Roche-limiet. Alle manen die dichter bij Saturnus staan dan deze limiet, zullen uiteen getrokken worden door de getijdenkrachten van de planeet. Aangezien de F-ring precies op de grens ligt, kan het materiaal uit de ring niet beslissen of het een maan wil gaan vormen, of een ring wil blijven.
Prometheus bevindt zich vlakbij de F-ring en zorgt voor verstoringen. Iedere 17 jaar heeft deze maan een speciale baanresonantie met de F-ring, waardoor het een grotere invloed uitoefent dan gewoonlijk. Als dat klopt, dan zou Cassini de komende jaren weer meer verdichtingen en klonters moeten vinden.
So I bought myself a little present the other day. One of the main problems that a filmmaker faces is focusing issues, and especially when shooting DSLR with photography lenses it can be pretty impossible to pull focus accurately without a follow focus of some kind. But with these systems costing maybe hundreds of pounds it can be a bit annoying for someone just starting out who hasn’t got much money to spare.
Then by accident I spotted a possible solution. I was looking through one of my granddad’s copies of EOS Magazine (which he has a lot of, all unopened) and found their shop (www.eos-magazine-shop.com) where they had a small section for “Movies” which obviously piqued my interest. They didn’t have much to offer since other than their range of Cine Lenses and their movie cameras, Canon don’t offer any filming accessories. So I didn’t have many expectations while browsing, they had some standard LED Video lights which I don’t really need and an on camera mic which cost more than my current RØDE one for less quality (although they did have a couple of loupe’s and external monitors I may look into) so I wasn’t too impressed.
They come in different sizes between 50mm and 85mm so should cover most lenses. Quick note if anyone decides they want one, the sizes they offer are not relative to the filter size usually found on the front of your lens. You’ll have to measure the diameter of your focusing (or zoom) ring with a calliper, either that or with a tape measure, some maths and a bit of Pi (not the yummy kind unfortunately).
So now, after all that build up comes the actual product. It comes in a plastic pack, with a ring, a short lever, a long lever and a bit of paper with a product description on it.
There’s no instructions, but to be honest it is pretty straight forward. You place the ring around the area of your lens you want to use it on, and squeeze the jaws into each other until the teeth lock in place and it stays nice and snug on your lens. If you’re going to be using your camera with any sort of stabilisation (tripods, rigs etc.) you’ll want to make sure that the range of movement of the ring doesn’t get restricted.
You then choose which lever you want to use, personally I decided to test out the long lever first as it seemed the most practical to use.
There are two places you can fit the lever, there’s one hole where you can fit it facing forward or back and to be honest I see no point or use for that, it’s more in the way than anything. Or you can have it pointing directly out, which is kind of the point. It’s a little tricky to fit as the rubbery material doesn’t offer much grip and the hole is quite small and tight, but once it’s in place it’s nice and solid.
I tried just pulling focus on some random objects in my room and switching between different focus points and it was sooooooooo much easier than using the lens directly. As you have the lever to hold you are able to fine tune the focus a lot quicker and easier. Also the idea of “up is far and down is near” is a lot simpler to remember than trying to think which way that lense's ring needs to be turned. I found that when I was just using my camera quickly to try it out handheld, that I could control the lever with my pinky and still have the rest of my hand supporting the lens and controlling the zoom. If I had my camera on a set of sticks it would be just as easy to use my index finger to do the same thing so really how you use this thing is totally up to you and the size of your hands. (Also it’s quite fun to turn on the autofocus and watch the lever wave around as the lens adjusts)
Probably if you stuck some tape to the ring and found a mark on your lens body you could probably mark out focus points, but I think it’s easier to just remember which direction the lever is pointing as the ring is a little bit narrow.
Ones other thing is that you could fit the ring to your zoom and use it like that. But I think that’s a bit pointless unless you’re doing a lot of complicated zooms in one shot.
After I tested out the long lever I the thought it’d obviously be best to test the little one too. I doubt I’ll use it again the though, it was more trouble than anything. It was even my more awkward to fit than the previous one and the small size just didn’t seem worth the hassle. I think the only time I’d ever use this is if something like a matt box was in the way, but then again I’d probably have some sort of follow focus set up by then.
The worst thing was that when I went to remove the small lever, after realising I wouldn’t need it, was the fact that the instead of unscrewing from the ring as designed, the thread stayed in the ring and came out of the lever section instead. Because of the size of this threaded rod, it was now extremely difficult to remove it without damaging the threads. Thankfully it was removed eventually and I’m unlikely to use it again. I’ll stick with the bigger lever!!
So all in all it’s a pretty simple solution to a big problem. Is it worth the £15 I paid? For the build quality, not really. But for its purpose and how well it does it’s job I’ll have to wait and see. But I do have high hopes for how effective it’s going to be!
(NASA) What's causing those strange dark streaks in the rings of Saturn? Prometheus. Specifically, an orbital dance involving Saturn's moon Prometheus keeps creating unusual light and dark streamers in the F-Ring of Saturn. Now Prometheus orbits Saturn just inside the thin F-ring, but ventures into its inner edge about every 15 hours. Prometheus' gravity then pulls the closest ring particles toward the 80-km moon. The result is not only a stream of bright ring particles but also a dark ribbon where ring particles used to be. Since Prometheus orbits faster than the ring particles, the icy moon pulls out a new streamer every pass. Above, several streamers or kinks are visible at once. The above photograph was taken in June by the robotic Cassini Spacecraft orbiting Saturn. The oblong moon Prometheus is visible on the far left.
(NASA/JPL et al., via WiredScience) A single jet feature appears to leap from the F ring of Saturn in this image from the Cassini spacecraft. A closer inspection suggests that in reality there are a few smaller jets that make up this feature, suggesting a slightly more complex origin process. These "jets," like much of the dynamic and changing F ring, are believed by scientists to be caused by the ring's particles interacting with small moons orbiting nearby.
This view looks toward the unilluminated side of the rings from about 45 degrees below the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on June 20, 2013. The view was obtained at a distance of approximately 870,000 miles (1.4 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 77 degrees. Image scale is 5 miles (8 kilometers) per pixel.
Color global view of Prometheus casting shadow on the F ring
Cassini captured the three images for this true-color view of the inner F-ring shepherd Prometheus on December 27, 2009. This view was composed of archive data by Gordan Ugarkovic. Prometheus is 119 × 87 × 61 kilometers in diameter.
Credit: NASA / JPL / SSI / color composite by Gordan Ugarkovic
