Raw image of Saturn with two moons acquired by Cassini on March 11, 2014 (NASA/JPL-Caltech/SSI)
On March 11, NASA’s Cassini spacecraft was acquiring some images of Saturn’s back-lit limb when two of its moons decided to make an entrance. Like stage hands in a darkened theatre the moons quickly passed across the scene, moving between Saturn and the spacecraft and, because of exposure time and spacecraft motion, getting a bit blurred in the process.
In the image above the silhouette of one moon can be seen at bottom right — Mimas, perhaps — while another’s crescent can be made out at upper left… possibly Enceladus. Very cool!
Watch an animation of the moons below:
Two of Saturn’s moons drift into the scene on March 11, 2014 (NASA/JPL-Caltech/SSI. Animation by Jason Major.)
While I admit I’m not 100% sure which moons these are, based on their apparent shapes, positions, and relative sizes I’d make my guess that these are 318-mile (511-km) -wide Enceladus and the 246-mile (395-km) -wide Mimas.
Possible location of icy spray, if Enceladus is in fact this moon’s real name
Cassini was 843,762 miles (1,357,903 km) from Saturn when the images were acquired. And, if the larger moon at left is Enceladus, I’m thinking south in these images is up based on the barely-perceptible presence of a lighter area along its top edge that could be icy spray from its southern geysers. (See enlarged detail at right.)
Saturn, of course, is on the right. A small segment of the bright arc of its backlit limb is what’s running diagonally down across the image.
These images have not yet been calibrated or cataloged by NASA or the Cassini team.
See the latest raw images from Cassini on JPL’s mission page here.
*I say “dark moons” but actually Enceladus and Mimas are pretty bright, both being composed of a lot of ice. Enceladus is actually the most reflective world in the Solar System!
Synthetic view of the waxing Moon as viewed from Earth on 2013-10-15 17:00:00 UTC [NASA/GSFC/Arizona State University].
Take a look around the Moon… no, really, take a good look AROUND the Moon! This is a fantastic animation of our planetary partner in space made by the folks on the Lunar Reconnaissance Orbiter team at Arizona State University. Assembled from reflectance maps and digital terrain models created from data gathered by LRO’s wide-angle camera, this full 360-degree portrait of the Moon shows its surface as if it were receiving direct top-down sunlight on all points — a physical impossibility, yes, but it gives us a great view of pretty much everything (including the far side, which for obvious reasons most of us never get a good look at.)
In addition to shining a light on the lunar landscape (pun intended) the vast amounts of data used to create the view above can also be used to calculate the type of illumination that would be found on any point on the Moon, at any time, allowing for better targeted observation planning with LRO’s narrow-angle camera.
Read more about how this process was engineered here, and see a more recent result of these new capabilities below:
While the image above wouldn’t have been visible from anywhere on North America on October 15, 2013 at 2 p.m. EDT, it’s what would have been seen in the night sky above Mumbai — but no international calls to India were needed, as the view could simply be generated from the LRO WAC data and a ray-tracing algorithm that plots the angles of light and shadow across the lunar terrain. Voilà — it’s Insta-Moon*!
*Some assembly required.
Read more on the Arizona State University LROC site here (and to really blow your mind, watch the high-resolution version here.)
The Solar System: it’s our home in space, the neighborhood that we all grew up in and where — unless we figure out a way to get somewhere else — all of our kids and grandkids and great-great-great-great-times-infinity-great-grandkids will grow up too. That is, of course, until the Sun swells up and roasts Earth and all the other inner planets to a dry crunchy crisp before going into a multi-billion year retirement as a white dwarf.
But until then it’s a pretty nice place to call home, if I may say so myself.
Edu-film designer Philipp Dettmer and his team have put together a wonderful little animation explaining the basic structure of the Solar System using bright, colorful graphics and simple shapes to illustrate the key points of our cosmic neighborhood. It won’t teach you everything you’ll ever need to know about the planets and it’s not advisable to use it as a navigation guide, but it is fun to watch and well-constructed, with nice animation by Stephan Rether and narration by Steve Taylor.
Check out the full video below:
“Through information design, concepts can be made easy and accessible when presented in a short, understandable edu-film or perhaps an infographic. Whether explaining the vastness of the universe or the tiniest building blocks of life – all information can be presented in a way that everyone understands. Regardless of prior knowledge.”
– Philipp Dettmer
(And come on, admit it… you learned something new from this!)
Animation of Iapetus briefly blocking a distant bright object. (NASA/JPL-Caltech/SSI. Assembled by Jason Major.)
It’s a cosmic cover-up! No, don’t put your tinfoil* hats on, this isn’t a conspiracy — it’s just Saturn’s moon Iapetus drifting in front of the bright star Gamma Orionis (aka Bellatrix) captured on Cassini’s narrow-angle camera on August 10, 2013.
Such an event is called an occultation, a term used in astronomy whenever light from one object is blocked by another — specifically when something visually larger moves in front of something apparently smaller. (The word occult means to hide or conceal… nothing mystical implied!)
The animation above was assembled from 19 raw images publicly available on the JPL Cassini mission site, stacked in Photoshop and exported as a gif. They’ve been rotated 90º from the originals but otherwise they’re right from Cassini’s camera.
Iapetus, seen above as just a thin crescent, is best known for its two-toned appearance. One half of the 914-mile-wide moon is bright and icy, the other coated with a layer of dark reddish material, giving it a real “yin-yang” appearance. (Ok, I guess that’s a little mystical. But purely coincidental.)
The Tao of Iapetus (NASA/JPL-Caltech/SSI)
It’s thought that the dark material originates from a more distant moon, Phoebe, which is being pelted by micrometeorites and shedding its surface out into orbit around Saturn, which eventually gets scooped up by the backwards-orbiting Iapetus.
The difference in albedo affects how Iapetus absorbs solar radiation too, causing the water ice beneath the darker material to evaporate over the course of its 79-Earth-day rotation and migrate around its surface, creating a sort of positive feedback loop.
While neat to look at, occultations are important to science because they provide a way to briefly peer into a world’s atmosphere (or in a small moon’s case, exosphere). Watching how light behaves as it passes behind the limb of a planet or moon lets researchers learn details of the air around it — however tenuous — pretty much for free… no probes or flybys needed!
The occulted star above is Bellatrix, the 1.6-magnitude star that marks Orion’s left shoulder.
Iapetus orbits Saturn at the considerable distance of 2,212,889 miles (3,561,300 km). Learn more about Iapetus here, and as always you can find more fantastic Cassini images from Carolyn Porco’s team at the Space Science Institute in Boulder, Colorado at the CICLOPS site here.
Radar images of asteroid 1998 QE2 and its satellite on June 7. Each frame in the animation is a sum of 4 images, spaced apart by about 10 minutes. (Arecibo Observatory/NASA/Ellen Howell)
On the last day of May 2013 asteroid 1998 QE2 passed relatively closely by our planet, coming within 6 million kilometers… about 15 times the distance to the Moon. While there was never any chance of an impact by the 3 km-wide asteroid and its surprise 750 meter satellite, astronomers didn’t miss out on the chance to observe the visiting duo as they soared past as it was a prime opportunity to learn more about two unfamiliar members of the Solar System.
By bouncing radar waves off 1998 QE2 from the giant dish at the Arecibo Observatory in Puerto Rico, researchers were able to construct visible images of the asteroid and its ocean-liner-sized moon, as well as obtain spectrum data from NASA’s infrared telescope in Hawaii. What they discovered was quite surprising: QE2 is nothing like any asteroid ever seen near Earth.
The 305-meter dish at Arecibo Observatory in Puerto Rico (Image courtesy of the NAIC – Arecibo Observatory, a facility of the NSF)
Both Arecibo Observatory and NASA’s Goldstone Deep Space Communications Complex in California are unique among telescopes on Earth for their ability to resolve features on asteroids when optical telescopes on the ground merely see them as simple points of light. Sensitive radio receivers collect radio signals reflected from the asteroids, and computers turn the radio echoes into images that show features such as craters and, in 1998 QE2’s case, a small orbiting moon.
QE2’s moon appears brighter than the asteroid as it is rotating more slowly; thus its Doppler echoes compress along the Doppler axis of the image and appear stronger.
Of the asteroids that come close to Earth approximately one out of six have moons. Dr. Patrick Taylor, a USRA research astronomer at Arecibo, remarked that “QE2’s moon is roughly one-quarter the size of the main asteroid,” which itself is a lumpy, battered world.
Dr. Taylor also noted that our own Moon is a quarter the size of Earth.
QE2’s moon will help scientists determine the mass of the main asteroid and what minerals make up the asteroid-moon system. “Being able to determine its mass from the moon helps us understand better the asteroid’s material,” said Dr. Ellen Howell, a USRA research astronomer at Arecibo Observatory who took both radar images of the asteroid at Arecibo and optical and infrared images using the Infrared Telescope Facility in Hawaii. While the optical images do not show detail of the asteroid’s surface, like the radar images do, instead they allow for measurements of what it is made of.
“What makes this asteroid so interesting, aside from being an excellent target for radar imaging,” Howell said, “is the color and small moon.”
Radar images of asteroid 1998 QE2 and its satellite (top) on June 6. (Arecibo Observatory/NASA/Ellen Howell)
“Asteroid QE2 is dark, red, and primitive – that is, it hasn’t been heated or melted as much as other asteroids,” continued Howell. “QE2 is nothing like any asteroid we’ve visited with a spacecraft, or plan to, or that we have meteorites from. It’s an entirely new beast in the menagerie of asteroids near Earth.”
Spectrum of 1998 QE2 taken May 30 at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea was “red sloped and linear,” indicating a primitive composition not matching any meteorites currently in their collection.
For more radar images of 1998 QE2, visit the Arecibo planetary radar page here.
Source: Universities Space Research Association press release.
Do you live in the southern hemisphere? Are you tired of all those views of the Moon that favor celestial north as up? Well here’s a video just for you from the good folks at the GSFC Scientific Visualization Center — it shows the full 2013 year of lunar phases and libration as seen from Earth’s southern half using data gathered by NASA’s Lunar Reconnaissance Orbiter. (Because what’s so great about north, anyway?)
Each frame represents one hour. Side graphs indicate the Moon’s orbit position, sub-Earth and subsolar points, and distance from the Earth at true scale. Awesome! Um, I mean… bonzer!
And what’s up with all that wobbling around? Find out more below:
The Moon always keeps the same face to us, but not exactly the same face. Because of the tilt and shape of its orbit, we see the Moon from slightly different angles over the course of a month. When a month is compressed into 24 seconds, as it is in this animation, our changing view of the Moon makes it look like it’s wobbling. This wobble is called libration.
The word comes from the Latin for “balance scale” and refers to the way such a scale tips up and down on alternating sides.
The Moon is subject to other motions as well. It appears to roll back and forth around the sub-Earth point (the location on the Moon’s surface where the Earth appears directly overhead, at the zenith.) The roll angle is given by the position angle of the axis, which is the angle of the Moon’s north pole relative to celestial north. The Moon also approaches and recedes from us, appearing to grow and shrink. The two extremes, called perigee (near) and apogee (far), differ by more than 10%.
Read more and see the current phase of the Moon (bottom up) on the GSFC Dial-a-Moon page here.
How old is the Earth, how long did it take for life to appear, and how long would it take for your hair to grow to the Moon? Find out in this video from MinuteEarth (a new project by MinutePhysics’ Henry Reich):
(Because you always wanted to know how long it would take for your hair to grow to the Moon — admit it.)
And be sure to check out MinuteEarth’s newest video Why Are Leaves Green?Part 1 and Part 2.
1/3 the distance from the Sun than Earth, it should be no surprise that a day on Mercury is a real scorcher with temperatures soaring over 400 ºC. But in addition to its solar proximity it also has an extremely slow rotation: a single day on Mercury is 58.6 Earth days long… and you thought your Mondays lasted forever!
To be even more precise, for every 2 Mercury years, 3 Mercury days pass — a 3:2 spin-orbit resonance, caused by the planet’s varying elliptical orbit. (This also makes for some interesting motions of the Sun in Mercury’s sky.)
To illustrate this, UK’s The Open University has published a new video in their 60 Second Adventures in Astronomy series… check it out above (and see more of their excellent and amusing animations here.)
Video: The Open University. Narrated by David Mitchell.
Raw wide-angle Cassini image of Saturn’s rings (NASA/JPL/SSI)
Recently I posted an image of two of Saturn’s shepherd moons, Pandora and Prometheus, captured by Cassini in a face-off across the spindly F ring. Now here’s a much wider-angle view of the gas giant’s rings, seen by Cassini two days later on December 20, and the same two moons can still be seen staring each other down… two tiny points of light visible across the wavering line of the F ring at lower center.
This is just one raw image in a series of 56 that Cassini captured on the 20th, and I’ve combined them together to make a GIF animation — click below to watch:
Animation of Saturn’s rings made from raw images acquired by Cassini on Dec. 20, 2012 (NASA/JPL/SSI. Animation by J. Major)
In the animation you can see Pandora and Prometheus promenade around Saturn (detail at right) as well as a “spoke” of light material moving within the inner dark edge of the A ring. Also many clumps are visible in the thin F ring — caused by embedded moonlets and the gravitational influence of the shepherd moons.
Saturn’s enormous shadow engulfs the entire ring system at the top of the scene.
Cassini was moving relative to Saturn while these images were captured so some background stars make brief appearances, as well as a couple of pixel flares and a cosmic ray hit. These are common in Cassini images.
See more news and images from the Cassini mission here.
