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Find out what black holes are, who discovered them, how we know they exist and what would happen if you fell into a black hole.
Focus group for submissions to Astronomy Picture of the Day
A key lesson in unintended consequences that would-be #ClimateCrisis heroes may wish to be mindful of as they endeavor to save the planet from us humans. //
NotCoach | August 13, 2023 at 8:49 pm
Typically anything smaller than 25m in diameter will burn up in our atmosphere, depending on density, and considering these rocks were dislodged from the surface they are likely not very dense (mostly rock, little metal).
NotCoach in reply to NotCoach. | August 13, 2023 at 9:05 pm
As an example the Chelyabinsk meteor was estimated to be about 59 feet in diameter. It did not reach the surface of Earth. It exploded over Chelyabinsk Oblast with the force of 26 to 33 Hiroshimas, but the damage to Chelyabinsk Oblast was minimal because the blast was high up in the atmosphere. A 15 foot boulder is not a concern.
paw Ars Tribunus Militum 21y 1,984
dj__jg said:
I guess ESA has a shot at being a role model at de-orbiting stuff, since they sure aren't being a role model at putting stuff into orbit considering the delays and expendable nature of Ariane 6.
Let's not dump on ESA too much re being a role model. Ariane 5's outstanding launch of JWST, doubling its lifetime, should not be overlooked.
Honest question: have any NASA launches exceeded expectations by that much? //
Cloudgazer Ars Tribunus Angusticlavius 8y 15,517
paw said:
Let's not dump on ESA too much re being a role model. Ariane 5's outstanding launch of JWST, doubling its lifetime, should not be overlooked.Honest question: have any NASA launches exceeded expectations by that much?
I'd love to know what the private opinion of the NASA team was about that launch. One way to view it is that ESA doubled the lifespan of JWST. Another is that they came within 30 m/s of disaster. //
Cloudgazer Ars Tribunus Angusticlavius 8y 15,517
Shiranui said:
How do you mean? How do you turn overdelivering on estimates into pessimistic relief?Either I'm missing something about Arianespace having taken unnecessary risks to achieve this feat (which I have not heard of so far), or that's a very "glass half empty" perspective.
NASA had an estimated life based on ESA delivering JWST into the expected trajectory, JWST would then need to use its on board thrusters to get the perfect insertion into L2. There was never any doubt that Ariane had the grunt to get JWST into that orbit, or indeed beyond that orbit, but it was imperative that they not overshoot, because if they did JWST was lost.
The targeted trajectory NASA requested from Ariane left room at the top because of that. ESA ate into that margin which delivered a 'better' outcome, but the final adjustments by the JWST were a mere 23 m/s. Had they 'over delivered' by another 23m/s which they were quite capable of doing there would be no JWST.
Publically this was all praised as a great success, but I can't imagine it was quite the same story behind the scenes.
Think of it like shooting the proverbial apple off your wife's head. More points if you hit lower on the apple. This doesn't mean if you aimed for the middle and hit right at the bottom then your wife is going to be entirely happy, because a little lower and you're not a hero - you're William S Burroughs. //
Cloudgazer Ars Tribunus Angusticlavius 8y 15,517
Dan Homerick said:
While reading this, I was thinking "But couldn't JWST have rotated around and burned retrograde to correct a small overshoot?" And to answer that thought, I presume the answer is no, because then it'd be flying through it's own thruster plume, which would fog up the mirrors.That right?
Kinda, that's half the story ..
More Than You Wanted to Know About Webb’s Mid-Course Corrections! – James Webb Space Telescope
https://blogs.nasa.gov/webb/2021/12/27/more-than-you-wanted-to-know-about-webbs-mid-course-corrections/
Webb has thrusters only on the warm, Sun-facing side of the observatory. We would not want the hot thrusters to contaminate the cold side of the observatory with unwanted heat or with rocket exhaust that could condense on the cold optics
So you're right about not wanting to fly through the plume, and that (along with other considerations) resulted in thrusters only on one side of the vehicle. But as a result of that design decision it's even worse than just contaminating the instrument
Webb’s Journey to L2 Is Nearly Complete – James Webb Space Telescope
https://blogs.nasa.gov/webb/2022/01/21/webbs-journey-to-l2-is-nearly-complete/
“So, why did the Ariane not give Webb more energy and why did Webb need course correction? If the Ariane had given Webb even a little bit too much energy than needed to get it to L2, it would be going too fast when it got there and would overshoot its desired science orbit. Webb would have to do a significant braking maneuver by thrusting toward the Sun to slow down. Not only would that big burn cost a lot of propellant, it would be impossible because it would require Webb to turn 180 degrees in order to thrust toward the Sun, which would have exposed its telescope optics and instruments directly to the Sun, thus overheating their structures and literally melting the glue that holds them together.
Like the enterprise in star trekkin the JWST is always going forwards 'cause they can't find reverse.
Saturn might be the planet in our Solar System best known for its spectacular rings, but the icy giant Uranus also has a system of 13 nested rings. Eleven of those rings—nine main rings and two fainter dusty rings—are clearly visible in the latest spectacular image from NASA's Webb Space Telescope. Future images should reveal the remaining two faint outer rings discovered with the Hubble Space Telescope in 2007.
"Uranus has never looked better. Really," NASA tweeted. "Only Voyager 2 and Keck (with adaptive optics) have imaged the planet's faintest rings before, and never as clearly as Webb’s first glimpse at this ice giant, which also highlights bright atmospheric features."
Webb's First Deep Field
This stunning infrared image was released one year ago as the James Webb Space Telescope began its exploration of the cosmos. The view of the early Universe toward the southern constellation Volans was achieved in 12.5 hours of exposure with Webb's NIRCam instrument.
The thousands of galaxies flooding the field of view are members of the distant galaxy cluster SMACS0723-73, some 4.6 billion light-years away. Luminous arcs that seem to infest the deep field are even more distant galaxies though. Their images are distorted and magnified by the dark matter dominated mass of the galaxy cluster, an effect known as gravitational lensing. Analyzing light from two separate arcs below the bright spiky star, Webb's NIRISS instrument indicates the arcs are both images of the same background galaxy. And that galaxy's light took about 9.5 billion years to reach the James Webb Space Telescope.
Most of us wish we had more than 24 hours in a day to get everything done and actually breathe. What if each day gave us more than double that time? If it wasn’t for a phenomenon that put the lengthening of Earth’s days on pause billions of years ago, that would have probably happened.
Earth has not always had 24-hour days. There were fewer than 10 hours in a day when the Moon first came into being around 4.5 billion years ago, but they have grown longer as lunar tidal forces gradually slowed Earth’s rotation. But there was a long period when days didn’t grow at all. Astrophysicists have now found that, from 2 billion to 600 million years ago, days were about 19.5 hours because several tidal forces canceled each other out and kept Earth rotating at the same speed for over a billion years. If that had never happened, our present days might be over 65 hours long.
“The fact that the day is 24 hours long…is not a coincidence,” the research team said in a study recently published in Science Advances.
The current race to the Moon is opening up opportunities for lunar astronomy.
The observed and predicted Solar Cycle is depicted in Sunspot Number in the top graph and F10.7cm Radio Flux in the bottom graph.
In both plots, the black line represents the monthly averaged data and the purple line represents a 13-month weighted, smoothed version of the monthly averaged data. The slider bars below each plot provide the ability to display the sunspot data back to solar cycle 1 and F10.7 data back to 2004.
The mean forecast for the current solar cycle (Cycle 25) is given by the red line. This is based on an international panel that was convened in 2019 for this purpose. In February, 2023 the plot was modified to show the full range of the 2019 Panel prediction as the gray shaded region (similarly for the F10.7 cm plot). This takes into account expected uncertainties in the cycle start time and amplitude. Use the drop-down menu below each plot to display specific curves within this range.
Note that any city crossed by a rectangular grid can identify days where the setting Sun aligns with their streets. But a closer look at such cities around the world shows them to be less than ideal for this purpose. Beyond the grid you need a clear view to the horizon, as Manhattan has across the Hudson River to New Jersey. And tall buildings that line the streets create a vertical channel to frame the setting Sun, creating a striking photographic opportunity.
True, some municipalities have streets named for the Sun, like Sunrise Highway on Long Island and the Sunset Strip in Los Angeles. But these roads are not perfectly straight. And the few times a year when the Sun aligns with one of their stretches of road, all you get is stalled traffic solar glare temporarily blinds drivers.
So Manhattanhenge may just be a unique urban phenomenon in the world, if not the universe.
Note that several years ago, an article in the The New York Times identified this annual event as the Manhattan Solstice. But of course, the word solstice translates from the Latin solstitium, meaning stopped sun, in reference to the winter and summer solstices where the Sun's daily arc across the sky reaches its extreme southerly and northerly limits. Manhattanhenge comes about because the Sun's arc has not yet reached these limits, and is on route to them, as we catch a brief glimpse of the setting Sun along the canyons of our narrow streets.
While we are on the subject, when viewed from all latitudes north of the Tropic of Cancer (23.5 degrees north latitude), the Sun always rises at an angle up and to the right, and sets and an angle down and to the right. That's how you can spot a faked sunrise in a movie: it moves up and to the left. Filmmakers are not typically awake in the morning hours to film an actual sunrise, so they film a sunset instead, and then time-reverse it, thinking nobody will notice.
Letting the calendar cycle for 45 years gives each planet a chance to complete a synodic cycle. //
"By increasing the calendar length to 20 periods of 819-days a pattern emerges in which the synodic periods of all the visible planets commensurate with station points in the larger 819-day calendar," the researchers wrote.
The math appears to bear that out. NASA reckons Mercury's synodic period is 115.88 days, but if we allow the ancient Mayans some leniency due to their lack of advanced scientific instruments and say it's 117 days, you can get exactly seven periods on the calendar.
The other planets visible from Earth and known to the Mayans – Venus, Mars, Jupiter and Saturn – all have similar mathematical matches when the calendar is allowed to make multiple cycles. Mars, which has the longest synodic period at 780 days, takes 21 periods to fit exactly into 20 cycles, both of which have 16,380 days, just shy of 45 years.
Salat did not immediately realize that he was witnessing a “SpaceX Spiral.” As noted by SpaceWeather, three hours earlier SpaceX launched 51 small satellites on a Falcon 9 rocket from California’s Vandenberg Space Force Base some 3,000 miles (4,828 kilometers) away. //
An all-sky camera at the University of Alaska’s Poker Flat Research Range also captured the strange whirlpool on Saturday evening. //
SpaceX rockets are designed to land back on Earth but the second stage of the Falcon 9 does not parachute down to the ground. Instead, it burns up in the atmosphere but before doing so it vents its unused fuel which will often take the form of a stunning spiral. //
“I will say I loved the wonderment of not knowing what it was. The auroras kept on dancing so it was hours before I had time to research and try figuring out this unique phenomenon I had witnessed.
“Those were the best hours of blissful bewilderment.”
The James Webb Space Telescope discovers enormous distant galaxies that should not exist
By Tereza Pultarova published 4 days ago
Giant, mature galaxies seem to have filled the universe shortly after the Big Bang, and astronomers are puzzled.
Nobody expected them. They were not supposed to be there. And now, nobody can explain how they had formed.
Galaxies nearly as massive as the Milky Way and full of mature red stars seem to be dispersed in deep field images obtained by the James Webb Space Telescope (Webb or JWST) during its early observation campaign, and they are giving astronomers a headache.
These galaxies, described in a new study based on Webb's first data release, are so far away that they appear only as tiny reddish dots to the powerful telescope. By analyzing the light emitted by these galaxies, astronomers established that they were viewing them in our universe's infancy only 500 to 700 million years after the Big Bang.
Dr. Tamitha Skov
@TamithaSkov
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Talk about Polar Vortex! Material from a northern prominence just broke away from the main filament & is now circulating in a massive polar vortex around the north pole of our Star. Implications for understanding the Sun's atmospheric dynamics above 55° here cannot be overstated! //
Our star is ramping up its activity, getting rowdier with sunspot and flare activity. It has flared every day this year so far, and it spat out several X-class and M-class flares in January 2023, the biggest and second-biggest eruptions the Sun is capable of.
This is nothing to be alarmed about. The Sun undergoes activity cycles every 11 or so years, from relatively quiet and peaceful, to absolutely rambunctious.
These cycles coincide with fluctuations in the solar magnetic field. When the magnetic field is at its weakest at the poles, the Sun’s magnetic poles switch places, and the polarity of the magnetic field reverses. This is when the Sun is at its most active, known as solar maximum.
We’re right on the cusp of solar maximum. Because the Sun is so enigmatic and difficult to predict, we don’t know precisely when the polarity reversal will occur (scientists can usually only make a ruling after the event), but we do know a rough ballpark: Our current predictions place it in July 2025. //
georgfelis | February 12, 2023 at 3:41 pm
The last words of humanity will be some solar scientist saying “That looks interesting.”
A frosty Comet ZTF (C/2022 E3) joins snow-covered Mount Etna in Sicily on January 24, 2023. This scene is exactly how photographer Dario Giannobile saw it through a 300-mm focal-length lens, but to make the comet pop he composited the foreground image with 27 tracked time exposures. The mountain is an active volcano as evidenced by smoke billowing from fumaroles. Comet ZTF exhibits both a dust tail (pointing upward) and a fainter antitail extending in the opposite direction.
Dario Giannobile
https://skyandtelescope.org/astronomy-news/understanding-the-tails-of-comet-ztf-c-2022-e3/
We explore Comet ZTF’s remarkable trio of tails and share the latest news and photos.
Images and spectra from the James Webb Space Telescope suggest that the first galaxies in the universe are too many or too bright compared to what astronomers expected. //
Evidence is building that the first galaxies formed earlier than expected, astronomers announced at the 241st meeting of the American Astronomical Society in Seattle, Washington.
As the James Webb Space Telescope views swaths of sky spotted with distant galaxies, multiple teams have found that the earliest stellar metropolises are more mature and more numerous than expected. The results may end up changing what we know about how the first galaxies formed.
After launching on a Falcon 9 rocket in August 2022, the Korean Pathfinder Lunar Orbiter slid into orbit around the Moon last month. This was South Korea's first lunar probe, and among its chief objectives was surveying the polar regions of the Moon for resources such as water ice.
One of the six instruments carried by the half-ton satellite was a hyper-sensitive camera built by NASA called ShadowCam. The camera was designed with maximum sensitivity to light, such that it could provide images of permanently shadowed regions of the poles—which is to say, capture images of things that are inherently very dark.
Earlier this week, the ShadowCam team released its first image, which reveals a wall and the floor of Shackleton Crater near the south pole of the Moon. At first glance, there's nothing remarkable about the photo. It looks a lot like... the Moon.
However, what you're actually looking at is an area of the Moon that lies in total darkness. Here is a photograph taken by NASA's Lunar Reconnaissance Orbiter in 2009, shortly after it reached the Moon. That black area on the left of the photo? That's the region of Shackleton Crater imaged by ShadowCam. Yeah, it's pretty phenomenal. //
According to the imaging team, the camera's ability to capture clear images at high sensitivity is the equivalent of increasing from ISO 100 to greater than 12,800 without increasing grain.