Total solar eclipses are possible on Earth, and occur whenever the Moon aligns with the Earth-Sun … [+] plane during a new Moon phase, and is close enough for its shadow to fall on Earth. This has happened ~3 billion times in Earth’s history, but won’t happen for much longer.
FLICKR USER KEVIN GILL
In our Solar System, there’s one overwhelming source of mass that all the planets orbit around: our Sun. Each planet has its own unique system of natural satellites that exist in stable orbits around it: moons. Some moons, like Saturn’s Phoebe or Neptune’s Triton, are captured objects that were once comets, asteroids, or Kuiper belt objects. Others, like Jupiter’s Ganymede or Uranus’s Titania, formed from an accretion disk at the same time the planets of the Solar System formed. But from the surface of Earth, we have just one Moon — likely formed from an ancient, giant impact — and it just so happens to be practically identical in angular size to the Sun. Is that just a wild coincidence, or is there some reason behind this fact? That’s what Brian Meadows wants to know, asking:
“From a scientific point of view, what are the chances that the Moon and the Sun would appear the same size in the sky?”
It’s a great question, and one that still has great uncertainties surrounding it. Here’s what we know so far.
Voyager 1 took this photo of Jupiter and two of its satellites (Io, left, and Europa) on Feb. 13, … [+] 1979. The four Galilean moons of Jupiter, along with most moons around the gas giants, likely formed from the initial circumplanetary disk that they each possessed in the early Solar System. (Universal History Archive/Universal Images Group via Getty Images)
Universal Images Group via Getty Images
As far as moons of the Solar System go, there are four known ways that they naturally form.
From the initial material that formed the objects of the Solar System; this is where most of the large moons around our gas giant planets come from.
From collisions between a planet and another large body in space that kick up debris, where that material then coalesces into one or more moons around the planet.
From other objects traversing the Solar System that become gravitationally captured by a parent planet.
Or from material in a ring system around a planet that accretes to form a moon all on its own.
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When we examine the moons found in our Solar System, we find strong evidence of all four types.
The planet Neptune and its largest moon Triton, as photographed by the Voyager 2 space probe in … [+] August 1989. Although it requires a very strong telescope to be able to see Neptune’s largest moon, Triton, Neptune itself can be seen with an off-the-shelf pair of binoculars, if you know where to look. With 1846-level technology, discovering its presence was easy and unambiguous, once its location was known. Triton is the largest captured object in the known Solar System.
NASA / Voyager 2
But three of those types of moons — the ones that form from the initial Solar System material, the ones that get gravitationally captured, and the ones that form from accreted ring systems — are only found around the gas giant worlds in our Solar System. The moons that we find around smaller, terrestrial worlds, including Earth, Mars, and even objects like Pluto, Eris, and Haumea, are all consistent with their moons arising from one source and one source alone: ancient impacts between a large, massive, fast-moving body and the major world itself.
We didn’t always think this was the case, but an enormous suite of evidence now exists to support it. The Apollo missions returned samples of the lunar surface to Earth, where analysis confirmed that the material composing the Moon’s and the Earth’s crust have a common origin. Measurements of the composition and orbital parameters of Mars’s moons not only point to their creation from an impact, but indicate that a third, larger, inner moon was created, and has since fallen back to Mars. And most recently, measurements by New Horizons support a picture that Charon, Pluto’s giant moon (and likely the other, outer moons) all originated from a giant impact as well.
Rather than the two Moons we see today, a collision followed by a circumplanetary disk may have … [+] given rise to three moons of Mars, where only two survive today. This hypothetical transient moon of Mars, proposed in a 2016 paper, is now the leading idea in the formation of Mars’s moons.
LABEX UNIVEARTHS / UNIVERSITÉ PARIS DIDEROT
So if you’re asking a question like, “what are the odds that an Earth-like planet would have a Moon that’s approximately the same angular size as the Sun as seen from that same planet,” here are the facts we have to consider.
The only way that we know of, so far, to get a moon around a rocky planet like Earth is to have some sort of giant impact in the planet’s past.
We’ve only ever detected moons around rocky worlds in our Solar System, never around rocky exoplanets, as the technology to do so isn’t there yet.
Of the rocky planets, Mercury and Venus have no moons, Earth has just the one of this “miracle” size, while Mars’s two surviving moons both appear much smaller than the Sun.
And yet, when we consider the parameters of Earth’s moon with respect to how we observe it compared to the Sun, we experience a remarkable set of circumstances that no other known system possesses.
When the Earth, Moon, and Sun perfectly align during the new Moon, a solar eclipse will result. But … [+] whether that’s annular, total, or hybrid depends on the Moon’s distance from Earth.
NASA’S SCIENTIFIC VISUALIZATION STUDIO
Here on Earth, the Moon orbits our planet in almost exactly the same plane that the Earth rotates on its axis: another piece of evidence that points to our Earth and Moon having a common origin from a giant impact. When the Moon happens to pass directly between the Earth and the Sun, and all three bodies are perfectly aligned, we experience a phenomenon known as a solar eclipse. This is common to all worlds with moons that cross the planet-Sun plane, but Earth and our Moon are unique in a very exciting way.
On Earth, we can experience three different types of solar eclipse with a perfect alignment:
Total solar eclipse — where the Moon appears to entirely block out the disk of the Sun.
Annular solar eclipse — where the Moon fails to block out the Sun’s disk, creating an annulus (or ring) of visible Sun circumscribing the eclipsing Moon.
Hybrid solar eclipse — where the Moon fails to block the entire Sun for a portion of the eclipse, but does successfully block the entire Sun for a different portion.
Right now, the largest (perigee) full Moon appears bigger than the Sun at all times of the year. … [+] However, over time, the Moon will migrate away, causing its angular diameter to shrink. When the perigee full Moon is smaller than the aphelion Sun, no total solar eclipses can occur anymore.
EHSAN ROSTAMIZADEH OF ASTROBIN
Earth only experiences all three types of solar eclipse because the Moon, in its elliptical orbit around the Earth, can appear either larger or smaller than the Sun does due to Earth’s elliptical orbit around the Sun. This is no doubt a rarity; neither of Mars’s moons is ever large enough to eclipse the Sun totally, as every eclipse from Mars is annular. Moreover, if Mars did have a third, larger, inner moon at one point, its eclipses would have always been total eclipses; annular or hybrid eclipses would have been impossible.
But there’s another point to consider: these three possibilities weren’t always what Earth experienced, and they won’t always be what Earth experiences, either. The story of our Solar System, as best as we can reconstruct it, tells a tale of an ever-changing relationship between the Earth, Moon, and the Sun. It began some 4.5 billion years ago, where our ancient protoplanetary disk, which gave rise to all the planets, began to fragment into clumps that grew, interacted, and both merged and ejected one another. There were two types of survivors: large, massive planets that held onto hydrogen and helium envelopes, and smaller, less-decisive victors, which become planets and dwarf planets.
The Solar System formed from a cloud of gas, which gave rise to a proto-star, a proto-planetary … [+] disk, and eventually the seeds of what would become planets. The crowning achievement of our own Solar System’s history is the creation and formation of Earth exactly as we have it today, which may not have been as special a cosmic rarity as once thought.
NASA / DANA BERRY
These early planets, planetoids, and planetesimals interact and sometimes collide, and those collisions — when they occur — tend to kick up large amounts of debris that surround the major planet. This shroud of post-impact material around the planet is known as a synestia, and although it’s short-lived, it’s incredibly important. Most of that material winds up falling back to the parent planet, while the rest coalesces into one or more moons. In general, the innermost moon will be the largest and most massive, and then you’ll have smaller, less massive moons that can exist at greater distances.
These moons exert differential forces on the planet: they gravitationally attract the portion of the planet that’s closer to the moon with a greater force than the portion that’s farther away. This not only creates tides on the planet, but it also results in what we call tidal braking, which causes the main planet to slow its rotation and the moon(s) to spiral away from the planet. Of course, there’s a competing effect: the planet’s atmosphere can create a drag force on the moon, drawing it closer to the planet. Depending on how the moons initially form, either effect can win.
A synestia will consist of a mixture of vaporized material from both proto-Earth and the impactor, … [+] which forms a large moon inside of it from the coalescence of moonlets. This is a general scenario capable of creating one single, large moon with the physical and chemical properties we observe ours to have. It is more general that the Giant Impact hypothesis, which involves a collision between Earth and a hypothesized co-orbiting protoplanetary world: Theia.
S. J. Lock et al., J. Geophys Research, 123, 4 (2018), p. 910-951
In the case of Mars, the drag force appears to have won, drawing the innermost moon in; over time, the next moon, Phobos, will eventually fall back onto Mars as well. In the case of Pluto, tidal braking is complete, and the Pluto-Charon system is now a binary planet, where Pluto and Charon are both tidally locked to one another, surrounded by four additional, outer, smaller moons.
But the Earth-Moon system is fascinating. The current thought is that, early on, the Moon was very close to Earth, and there may have been a number of smaller, outer moons beyond our own. Earth, back more than 4 billion years ago, may have been rotating incredibly rapidly, completing a 360° rotation in just 6-to-8 hours. A year, back in Earth’s early history, may have had as many as 1500 “days” in it.
But over time, the tidal friction of the Moon slowed that rotation tremendously, an act which transfers angular momentum from the spinning Earth to the orbit of the Moon. Over time, this causes the Moon to spiral away from the Earth.
The asymmetrical nature of Earth, compounded by the effects of the Moon’s gravitational pull, causes … [+] the length of a day on Earth to lengthen over time. To compensate and conserve angular momentum, the Moon must spiral outwards.
WIKIMEDIA COMMONS USER ANDREWBUCK, MODIFIED BY E. SIEGEL
For billions of years, until only a few hundred million years ago, all of the solar eclipses on Earth were total eclipses; the Moon was close enough that it always blocked out the Sun from our perspective. In 570 million years, Earth will experience its final total solar eclipse, and in another 80 million years, its final hybrid solar eclipse. After that, all of Earth’s solar eclipses will be annular.
This means that when we look from Earth at the Moon today, and compare its angular size to that of the Sun today, we see three different types of solar eclipses, but that this is a temporary situation. The evidence indicates that, early on, the Moon was much larger in angular size than the Sun was, and that there may have been additional moons farther out. Over time, our Moon has spiraled away, and if there were smaller, more distant moons, they’ve been ejected. In the far future, the Moon will spiral out even farther, and will become eternally smaller in our sky than the Sun will ever be, for the remainder of its lifetime.
While approximately half of all eclipses today are annular in nature, the increasing Earth-Moon … [+] distance means that in approximately 600-700 million years, all solar eclipses will be annular in nature.
WIKIMEDIA COMMONS USER KEVIN BAIRD
When you ask the question, “what are the odds that an Earth-like planet will have a Moon that’s comparable in angular size to the Sun,” you’re really asking what the odds are of:
having an Earth-like planet, which is an Earth-sized planet at the right distance from its star for liquid water on its surface,
that experienced a giant impact in its early history, creating a synestia,
where the planet itself winds up rotating rapidly after that collision,
where a large, inner moon gets created but won’t fall back onto the planet,
and then spirals away as angular momentum gets transferred from the planet to the Moon.
It’s remarkable that science, despite only having information about moons around terrestrial planets in our Solar System alone, has uncovered the ingredients necessary to create the situation we have today. If you assume you get an Earth-like planet, our best estimates have enormous uncertainties, but may lead to a total probability in the range of around 1-10%. To really know the answer to this question, however, we’ll need more and better data, and for that, we’ll need to wait for the next generation of astronomical observatories.
The answers are out there, written on the face of the Universe itself. If we want to find them, all we have to do is look.
More than 40 trillion gallons of rain drenched the Southeast United States in the last week from Hurricane Helene and a run-of-the-mill rainstorm that sloshed in ahead of it — an unheard of amount of water that has stunned experts.
That’s enough to fill the Dallas Cowboys’ stadium 51,000 times, or Lake Tahoe just once. If it was concentrated just on the state of North Carolina that much water would be 3.5 feet deep (more than 1 meter). It’s enough to fill more than 60 million Olympic-size swimming pools.
“That’s an astronomical amount of precipitation,” said Ed Clark, head of the National Oceanic and Atmospheric Administration’s National Water Center in Tuscaloosa, Alabama. “I have not seen something in my 25 years of working at the weather service that is this geographically large of an extent and the sheer volume of water that fell from the sky.”
The flood damage from the rain is apocalyptic, meteorologists said. More than 100 people are dead, according to officials.
Private meteorologist Ryan Maue, a former NOAA chief scientist, calculated the amount of rain, using precipitation measurements made in 2.5-mile-by-2.5 mile grids as measured by satellites and ground observations. He came up with 40 trillion gallons through Sunday for the eastern United States, with 20 trillion gallons of that hitting just Georgia, Tennessee, the Carolinas and Florida from Hurricane Helene.
Clark did the calculations independently and said the 40 trillion gallon figure (151 trillion liters) is about right and, if anything, conservative. Maue said maybe 1 to 2 trillion more gallons of rain had fallen, much if it in Virginia, since his calculations.
Clark, who spends much of his work on issues of shrinking western water supplies, said to put the amount of rain in perspective, it’s more than twice the combined amount of water stored by two key Colorado River basin reservoirs: Lake Powell and Lake Mead.
Several meteorologists said this was a combination of two, maybe three storm systems. Before Helene struck, rain had fallen heavily for days because a low pressure system had “cut off” from the jet stream — which moves weather systems along west to east — and stalled over the Southeast. That funneled plenty of warm water from the Gulf of Mexico. And a storm that fell just short of named status parked along North Carolina’s Atlantic coast, dumping as much as 20 inches of rain, said North Carolina state climatologist Kathie Dello.
Then add Helene, one of the largest storms in the last couple decades and one that held plenty of rain because it was young and moved fast before it hit the Appalachians, said University of Albany hurricane expert Kristen Corbosiero.
“It was not just a perfect storm, but it was a combination of multiple storms that that led to the enormous amount of rain,” Maue said. “That collected at high elevation, we’re talking 3,000 to 6000 feet. And when you drop trillions of gallons on a mountain, that has to go down.”
The fact that these storms hit the mountains made everything worse, and not just because of runoff. The interaction between the mountains and the storm systems wrings more moisture out of the air, Clark, Maue and Corbosiero said.
North Carolina weather officials said their top measurement total was 31.33 inches in the tiny town of Busick. Mount Mitchell also got more than 2 feet of rainfall.
Before 2017’s Hurricane Harvey, “I said to our colleagues, you know, I never thought in my career that we would measure rainfall in feet,” Clark said. “And after Harvey, Florence, the more isolated events in eastern Kentucky, portions of South Dakota. We’re seeing events year in and year out where we are measuring rainfall in feet.”
Storms are getting wetter as the climate change s, said Corbosiero and Dello. A basic law of physics says the air holds nearly 4% more moisture for every degree Fahrenheit warmer (7% for every degree Celsius) and the world has warmed more than 2 degrees (1.2 degrees Celsius) since pre-industrial times.
Corbosiero said meteorologists are vigorously debating how much of Helene is due to worsening climate change and how much is random.
For Dello, the “fingerprints of climate change” were clear.
“We’ve seen tropical storm impacts in western North Carolina. But these storms are wetter and these storms are warmer. And there would have been a time when a tropical storm would have been heading toward North Carolina and would have caused some rain and some damage, but not apocalyptic destruction. ”
Associated Press climate and environmental coverage receives support from several private foundations. See more about AP’s climate initiative here. The AP is solely responsible for all content.
It’s a dinosaur that roamed Alberta’s badlands more than 70 million years ago, sporting a big, bumpy, bony head the size of a baby elephant.
On Wednesday, paleontologists near Grande Prairie pulled its 272-kilogram skull from the ground.
They call it “Big Sam.”
The adult Pachyrhinosaurus is the second plant-eating dinosaur to be unearthed from a dense bonebed belonging to a herd that died together on the edge of a valley that now sits 450 kilometres northwest of Edmonton.
It didn’t die alone.
“We have hundreds of juvenile bones in the bonebed, so we know that there are many babies and some adults among all of the big adults,” Emily Bamforth, a paleontologist with the nearby Philip J. Currie Dinosaur Museum, said in an interview on the way to the dig site.
She described the horned Pachyrhinosaurus as “the smaller, older cousin of the triceratops.”
“This species of dinosaur is endemic to the Grand Prairie area, so it’s found here and nowhere else in the world. They are … kind of about the size of an Indian elephant and a rhino,” she added.
The head alone, she said, is about the size of a baby elephant.
The discovery was a long time coming.
The bonebed was first discovered by a high school teacher out for a walk about 50 years ago. It took the teacher a decade to get anyone from southern Alberta to come to take a look.
“At the time, sort of in the ’70s and ’80s, paleontology in northern Alberta was virtually unknown,” said Bamforth.
When paleontogists eventually got to the site, Bamforth said, they learned “it’s actually one of the densest dinosaur bonebeds in North America.”
“It contains about 100 to 300 bones per square metre,” she said.
Paleontologists have been at the site sporadically ever since, combing through bones belonging to turtles, dinosaurs and lizards. Sixteen years ago, they discovered a large skull of an approximately 30-year-old Pachyrhinosaurus, which is now at the museum.
About a year ago, they found the second adult: Big Sam.
Bamforth said both dinosaurs are believed to have been the elders in the herd.
“Their distinguishing feature is that, instead of having a horn on their nose like a triceratops, they had this big, bony bump called a boss. And they have big, bony bumps over their eyes as well,” she said.
“It makes them look a little strange. It’s the one dinosaur that if you find it, it’s the only possible thing it can be.”
The genders of the two adults are unknown.
Bamforth said the extraction was difficult because Big Sam was intertwined in a cluster of about 300 other bones.
The skull was found upside down, “as if the animal was lying on its back,” but was well preserved, she said.
She said the excavation process involved putting plaster on the skull and wooden planks around if for stability. From there, it was lifted out — very carefully — with a crane, and was to be shipped on a trolley to the museum for study.
“I have extracted skulls in the past. This is probably the biggest one I’ve ever done though,” said Bamforth.
“It’s pretty exciting.”
This report by The Canadian Press was first published Sept. 25, 2024.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
