After meeting the major milestone of aligning the telescope to NIRCam, the Webb team is starting to extend the telescope alignment to the guider (the Fine Guidance Sensor, or FGS) and the other three science instruments. This six-week-long process is called multi-instrument multi-field (MIMF) alignment.
When a ground-based telescope switches between cameras, sometimes the instrument is physically taken off the telescope, and a new one is installed during the daytime when the telescope is not in use. If the other instrument is already on the telescope, mechanisms are in place to move part of the telescope’s optics (known as a pick-off mirror) into the field of view.
On space telescopes like Webb, all the cameras see the sky at the same time; to switch a target from one camera to another, we repoint the telescope to put the target into the field of view of the other instrument.
After MIMF, Webb’s telescope will provide a good focus and sharp images in all the instruments. In addition, we need to precisely know the relative positions of all the fields of view. Over last weekend, we mapped the positions of the three near-infrared instruments relative to the guider and updated their positions in the software that we use to point the telescope. In another instrument milestone, FGS recently achieved “fine guide” mode for the first time, locking onto a guide star using its highest precision level. We have also been taking “dark” images, to measure the baseline detector response when no light reaches them – an important part of the instrument calibration.
Webb’s mid-infrared instrument, MIRI, will be the last instrument that is aligned, as it is still waiting for the cryogenic cooler to chill it to its final operating temperature, just under 7 degrees above <span class="glossaryLink" aria-describedby="tt" data-cmtooltip="
” data-gt-translate-attributes=”["attribute":"data-cmtooltip", "format":"html"]”>absolute zero. Interspersed within the initial MIMF observations, the two stages of the cooler will be turned on to bring MIRI to its operating temperature. The final stages of MIMF will align the telescope for MIRI.
You might be wondering: If all of the instruments can see the sky at the same time, can we use them simultaneously? The answer is yes! With parallel science exposures, when we point one instrument at a target, we can read out another instrument at the same time. The parallel observations don’t see the same point in the sky, so they provide what is essentially a random sample of the universe. With a lot of parallel data, scientists can determine the statistical properties of the galaxies that are detected. In addition, for programs that want to map a large area, much of the parallel images will overlap, increasing the efficiency of the valuable Webb dataset.
- Jonathan Gardner, Webb deputy senior project scientist, <span class="glossaryLink" aria-describedby="tt" data-cmtooltip="
NASAEstablished in 1958, the National Aeronautics and Space Administration (NASA) is an independent agency of the United States Federal Government that succeeded the National Advisory Committee for Aeronautics (NACA). It is responsible for the civilian space program, as well as aeronautics and aerospace research. It's vision is "To discover and expand knowledge for the benefit of humanity."
” data-gt-translate-attributes=”["attribute":"data-cmtooltip", "format":"html"]”>NASA’s Goddard Space Flight Center
- Stefanie Milam, Webb deputy project scientist for planetary science, NASA Goddard
Why I Hunt for Sidewalk Fossils – The New York Times
These oft-overlooked records invite us to imagine what has been and what might be.
A paleontologist once told me that city sidewalks hold snapshots. If I trained my gaze toward my feet, he said, I would find evidence of all kinds of commutes: traces of hopping birds, the soles of humans’ shoes, restless leaves that fell and sank into wet concrete at just the right moment. I might see a smattering of little paw prints zigging, zagging, doubling back, evidence of important rodent business that didn’t often overlap with mine.
These marks are too recent to pass muster with scientific sticklers, but in all respects except age, they are fossils. There are many ways to make one. Some form when a creature is entombed in sediment: Water percolates through, flush with minerals, and over time the mixture infiltrates the bones, where it settles and forms stone. Other fossils are casts, made, for instance, when a shell dissolves and leaves behind a mold that eventually fills with sediment, which hardens into rock. But not all fossils involve remains; some catalog movements. These are the kind that stipple our sidewalks — nascent trace fossils, records of fleeting contact.
Throughout the pandemic, I turned to nature to track time and step outside myself. I photographed the sweetgum tree outside my Brooklyn window, noting when it leafed into a bushy chlorophylled curtain or when it dropped fruit that fell to the ground like unshattered ornaments. Most afternoons of that first lonely spring, I roamed a cemetery. When magnolia blossoms smudged the scene pink, I stood under the canopies until wind splashed the petals against my shoulders.
I was lucky, of course, to be simply scared and lonely — not dead, not intubated, not choosing between peril and paycheck. But time was slippery, and I felt stuck in my own brain, a foggy, trembling ecosystem I had no interest in studying. By early 2022, I was cocooned in my partner’s Morningside Heights apartment. On weekend mornings, we shuffled around the neighborhood, and each volunteered to notice something new: a startling mushroom, the pale bellies of pigeons waterfalling down a facade before flocking skyward. I became fixated on sidewalk fossils. Fossil-finding outings were a relief — an invitation to crouch, touch, lose myself in evidence of skittering and scrabbling, tethering myself to a past and a future.
Once I started noticing these impressions, it was fun to imagine myself as a paleontologist of the urban present.
Because sidewalk fossils are essentially the same color as the surrounding concrete, they’re most visible when light rakes across them; a fossil that’s elusive at noon might announce itself at dawn or dusk. So I timed a second daily walk for the hour when the light fled. Late afternoons introduced me to tiny forked footprints that marked the scene of, perhaps, an avian skirmish. There were others: a dog’s paws, three-quarters of a shoe. Though ichnologists, who study trace fossils, might discount leaves, I marveled at those too: most of a London plane and a ginkgo, with its corrugated fan. Across from a closed-up snack cart, I knelt until the cold concrete prickled my knees. I wriggled out of my mitten and traced a leaf’s sharp, diagonal veins, its saw-toothed sides.
When scientists encounter a fossil, they often try to puzzle out an explanation of how it got there. Maybe an animal was stranded or washed off its feet or chased by predators. Once I started noticing these impressions, it was fun to imagine myself as a paleontologist of the urban present. A bonanza of bird feet made me wonder if someone had sprinkled seeds or dropped a bagel. How long ago? What kind? When a leaf didn’t seem to match any of the nearby trees, I wondered if it was an interloper, blown in from blocks away or if it testified to an ecological eviction — a tree yanked out and replaced with another species or swapped for sidewalk. The fossils fastened my attention to something tangible but also invited it to wander and to think about city streets as collages of past and present, about how our nonhuman neighbors are architects, too. How we all shed traces of ourselves, whether we know it or not.
Of course, there is more significant proof of the past. Mammoths sometimes turn up in farmers’ fields, their tusks curved like scythes abandoned in the dirt. Parades of dinosaur footprints still march along the banks or beds of some prehistoric rivers and seas. Those are awesome, showy and obvious. I line up to see them; I happily gawk. But it was a tiny thrill to encounter evidence of the past that was subtle and recent, proof that others were out there. The sidewalk fossils felt intimate — the paleontological equivalent of a raft of letters secreted away beneath a floorboard.
Only they’re not actually rare. When sidewalks are repaired, birds and other animals ignore attempts to keep them pristine. Leaves do whatever the wind demands. These fossils are easy to find, and we’re lucky to have them. When I was lingering in the worst parts of my brain, sidewalk fossils dislodged me. Unlike the many fossils that represent stillness, the moment when an animal died and the place it remained unless humans carved it free, sidewalk fossils are often peeks into lives that continued. The birds flew somewhere; the dogs, I hope, went on to wag over many sticks and smells. As the sun sank and I trudged home, the fossils — these little flukes, these interesting accidents — were reminders of small, exhilarating life.
Jessica Leigh Hester is a science journalist whose first book is “Sewer” (Bloomsbury Academic, 2022).
Green comet expected to be visible for first time in 50 millennia – Al Jazeera English
Comet C/2022 E3 (ZTF) is visible with binoculars, telescopes and in some areas, the naked eye – and it will grow brighter.
A green-hued comet is expected to be the most visible to stargazers on Wednesday as it shoots past Earth and the sun for the first time in about 50,000 years.
Discovered less than a year ago, the dirty snowball last passed near Earth during Neanderthal times, according to NASA.
The cosmic visitor will swing by our planet within 42 million kilometres (26 million miles) Wednesday before speeding away again, unlikely to return for millions of years.
This harmless comet already is visible in a clear northern night sky with binoculars and small telescopes, and possibly the naked eye in the darkest corners of the Northern Hemisphere.
It’s expected to brighten as it draws closer and rises higher over the horizon through the end of January, and is best seen in the predawn hours. By February 10, it will be near Mars, a good landmark.
Stargazers in the Southern Hemisphere will have to wait until next month for a glimpse.
Finding a remote location to avoid light pollution in populated areas is key to catching a nice view of the comet as it journeys past our planet heading away from the sun and back toward the solar system’s outer reaches.
While plenty of comets have graced the sky over the past year, “this one seems probably a little bit bigger and therefore a little bit brighter and it’s coming a little bit closer to the Earth’s orbit,” said NASA’s comet-and asteroid-tracking expert, Paul Chodas.
Nicknamed “dirty snowballs” by astronomers, comets are balls of ice, dust and rocks and wander towards the inner solar system when they’re dislodged from various gravitational forces, becoming more visible as they venture closer to the heat given off by the sun.
Fewer than a dozen comets are discovered each year by observatories around the world.
The green comet was discovered on March 2, 2022 by astronomers using the Zwicky Transient Facility, a wide-field camera at Caltech’s Palomar Observatory in Palomar Mountain, California, the United States. That explains its official, cumbersome name: comet C/2022 E3 (ZTF).
Its greenish, emerald hue reflects the comet’s chemical composition – it is the result of a clash between sunlight and carbon-based molecules in the comet’s coma, the cloud around the nucleus that makes the comet appear fuzzy in the sky.
This comet last passed Earth at a time when Neanderthals still inhabited Eurasia, the human species was expanding its reach beyond Africa, big Ice Age mammals including mammoths and saber-toothed cats roamed the landscape, and northern Africa was a wet, fertile and rainy place.
The comet can provide clues about the primordial solar system because it formed during the solar system’s early stages, according to California Institute of Technology physics professor Thomas Prince.
NASA plans to observe the comet with its James Webb Space Telescope, which could provide clues about the solar system’s formation.
The Virtual Telescope Project at the Bellatrix Astronomical Observatory in Ceccano, Italy will have a live feed accessible here.
The comet — a time capsule from the emerging solar system 4.5 billion years ago — came from what’s known as the Oort cloud well beyond Pluto. This deep-freeze haven for comets is believed to stretch more than one-quarter of the way to the next star.
While comet ZTF originated in our solar system, we can’t be sure it will stay there, NASA’s Chodas said. If it gets booted out of the solar system, it will never return, he added.
But don’t fret if you miss it.
“In the comet business, you just wait for the next one because there are dozens of these,” Chodas said. “And the next one might be bigger, might be brighter, might be closer.”
USask researcher and Nobel laureate Herzberg predicted source of comet's green hue in 1939 – USask News
“It’s important to pay attention to celestial events like this because they are often how we learn about our world,” said Dr. Daryl Janzen (PhD), an astronomy expert and instructor in the Department of Physics and Engineering Physics at USask’s College of Arts and Science. “Science itself was essentially invented because people noticed that the planets follow wandering paths through the stars and wanted to explain that.”
Janzen also co-ordinates public outreach activities for the USask Observatory, which is open for public viewing of celestial objects on the first and third Saturdays of each month.
Like many other comets, Comet 2022 E3 (ZTF) gives off a distinct green colour from its bright head as it arcs across the sky. The puzzle of the exact cause of this green coloration has been solved in recent years, thanks in part to Herzberg.
Herzberg, winner of the Nobel Prize in chemistry in 1971 and a groundbreaking researcher who conducted much of his foundational work at USask from 1935-1945, spent his career studying the structure and geometry of molecules using spectroscopy, the study of the absorption and emission of light and radiation by matter. His studies led to innovative understandings of how molecules and atoms function and interact, and formed the basis of many advancements in astronomy, health, chemistry, and physics.
Herzberg began studying the diatomic molecule, C2, as early as 1937 while he was at USask. C2 is formed because carbon (C) is a relatively unstable element and attempts to stabilize itself by bonding itself with a second carbon molecule. His work eventually evolved into an analysis of how C2 may be of interstellar importance. A prediction Herzberg made in analyzing the spectroscopy of C2 laid the foundations for our current understanding of why colours appear in comet comas—the cloud of dust and gas that surrounds a comet’s head.
According to work published in 1939 in The Astrophysical Journal, Herzberg speculated that the cause of a comet’s green hue could be due to sunlight causing C2 to reach a high level of vibration, which causes the two molecules to break their bond and disassociate. It was thought the ripping apart of these molecules released energy emitted as a green colour.
This prediction remained unconfirmed for almost a century due to the difficulty of testing such a scenario. In December 2021, a University of New South Wales team published a research paper in the Proceedings of the National Academy of Sciences that tested Herzberg’s theory for the first time. Through a lab experiment, the research team showed that C2 molecules disassociate at high vibrational levels and cause a green light to emit from a comet’s coma. This discovery provided scientific proof of what Herzberg suspected back in 1939.
“Comet comas are typically green, and as Herzberg predicted, the colour comes from photo-dissociation of diatomic carbon, which is an abundant molecule in comets,” said Janzen. “This recent study confirmed that C2 has a lifetime of roughly two days until sunlight breaks the molecule apart and emits a green photon. It’s not just the colour, but this short timeframe that explains why the green light comes only from the coma and not the comet’s tail.”
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