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If the axis of the Earth was through Greenland, what would the north celestial pole be?
If you assume that the shift was due to natural process, it would still point more-or-less towards Polaris. (If the shift is due to magic or advanced technology, all bets are off.)
I think your question may be based on a false premise, that the celestial sphere is fixed relative to the Earth. It isn't at all. Over the timescales we're dealing with it's basically just fixed and unchanging.
The rotating Earth acts like a gyroscope and its axis points in some direction. To a good approximation, that direction is fixed in space due to conservation of angular momentum. So in the absence of external torques, the Earth just sits there and spins like a top.
(To a better approximation, there are some external torques and the gravitational effects of the Sun and Moon causes the Earth's axis to slowly precess. It wobbles (a bit like a top slowing down) once every 26,000 years, actually chaning where it points to in space. I think this is probably an irrelevant detail though, for your question.)
So, if the Earth's axis passed through Greenland, what would happen? (Other than the climate changes due to the polar and equatorial regions moving around, of course.)
We have in fact seen something like this in the Earth's past, and it's called Polar Wandering. We observe that the Earth's north pole has moved relative to the Earth's surface and actually has moved quite a lot. But what happened was that the Earth's axis stayed fixed relative to the stars and the Earth's bulk shifted relative to its axis of rotation.
The True Polar Wander page referred to above has an excellent diagram:
So, the answer is that if the shift occurred because of changes to the Earth's moment of inertia, the axis of rotation would still point towards Polaris. If it happened due to outside influences (a giant impact, aliens, magic) it might wind up pointing most anywhere.
The Earth Has More Than One North Pole
You may think of the North Pole only as the top of the world&mdashits northernmost point and, if you're younger, Santa's home. But it turns out there are a host of "north (and south) poles" on our planet.
First, and most simply, there is a town in Alaska called "North Pole" which isn't near any of the other north poles (but it does get snow and receives a lot of mail addressed to Santa Claus). Then there is the geographic north pole, also known as "true north." This is the spot in the Arctic Ocean where all the man-made lines of longitude converge on a map as well as the conceptual point on the ice-encrusted waters that countless explorers sought to stab with their national banner&ndashbearing flagpoles, beginning in 1827 with British rear admiral, Sir William Edward Parry.
Somewhat related to the geographic north pole is the considerably less famous instantaneous north pole, where Earth's rotational axis meets its surface, as well as the celestial north pole, where the axis spears the night sky (in an imaginary extension kind of way). The instantaneous north pole is not fixed. Rather, it moves in an irregular circle caused by "the Chandler wobble"&mdashnamed for astronomer Seth Carlo Chandler, who discovered in 1891 that our planet wobbles as it rotates. His discovery gives rise to the "north pole of balance," which lies at the center of this circle.
All of this jargon separates into unique, if not pedantic, definitions. So although they all share the term "north pole," each has clearly staked out its own semantic territory. The same cannot be said, however, of the last two "north poles" in this rundown, and both relate to Earth's very real magnetic field, which is generated by fluid motion inside the planet's core. That motion&mdashaffected by Earth's rotation&mdashsets up a naturally occurring electric generator that sustains the magnetic field.
The magnetic pole describes the two locations (north and south) where the planet's magnetic field is vertical. So if you're standing over the north magnetic pole with a compass, the needle would dip and try to point straight down&mdashhence its other name: the magnetic dip pole. Over the south magnetic pole, your compass needle would point upward.
But there is another magnetically based north pole: the north geomagnetic pole. "One thing that's very confusing is the fact that there's a magnetic pole and a geomagnetic pole and that they're different," says Stefan Maus, a geomagnetic field modeler at the National Oceanic & Atmospheric Administration's (NOAA) National Geophysical Data Center. "It's a historical and slightly outdated definition."
The geomagnetic poles are almost an artifact of reducing Earth's complex and varied magnetic field to that of a simple bar magnet, or dipole. "The only thing that we really want to know is where the field is really vertical," Maus says. "This other pole, which is just an approximation, is generally not very useful and often leads to confusion." So while the north dip pole lies in Northern Canada, the northern dipole is roughly off the northwest coast of Greenland.
But the geomagnetic pole is useful, if you're in space, argues Jeffrey J. Love, a U.S. Geological Survey geophysicist. The farther away from Earth you get, the more its magnetic field actually does act like a dipole, or a bar magnet&mdasheven if in reality it is no such thing.
"A space physicist usually thinks in terms of this tilted dipole that the earth has," Love says, "whereas a navigator would probably be more interested in the magnetic dip poles."
To further confuse things the dip poles move around&mdashsometimes with daily frequency. The north magnetic pole in recent years has started shifting quickly toward Siberia. Its annual movement has accelerated from 10 to 50 kilometers (6.2 to 31 miles), says Larry Newitt, an emeritus scientist with the Geological Survey of Canada, who has pegged the pole's location on many expeditions since 1973.
And here's something to add even more confusion to the north magnetic pole (aka dip pole) versus north geomagnetic pole (aka dipole): the magnetic pole in Earth's northern hemisphere acts like the south pole of a bar magnet.
"If you look at the north pole of the bar magnet you have the field lines going from the north pole to the south pole, but for the earth it's exactly opposite," Maus explains. So the north magnetic pole is where the earth's magnetic field lines pull toward the planet, acting like the south pole of a bar magnet.
From a physics standpoint, then, the north needle of a compass (or any magnet) points to what is physically&mdashbut not in name&mdashthe south magnetic pole of the earth, in other words, in the direction of the Arctic.
"The north pole of your bar magnet is attracted to the north [magnetic] pole of the earth," Maus adds, the reverse of the usual situation in which like poles on magnets repel one another. "That is why some people have suggested that to avoid this confusion we should call the north magnetic pole the 'north seeking pole.'"
Whether that would add or subtract from the confusion remains unclear. What is clear is that&mdasheven in Santa Claus&ndashrelated matters&mdashone must be very precise in specifying exactly what one is talking about when referring to the "north pole."
This is why the Earth wobbles as it spins, according to NASA
NASA's Jet Propulsion Lab found three main reasons behind Earth's wobble, and we play a big role in why that happens.
In this Aug. 3, 2017 file photo, icebergs float in a fjord after calving off from glaciers on the Greenland ice sheet in southeastern Greenland. (Photo: AP)
The Earth doesn't just spin while on its axis, it wobbles. And scientists at NASA say they've identified three reasons why it happens.
A study published in the November issue of the journal Earth and Planetary Science Letters said the wobble – scientifically labeled as "polar motion" – is caused by three factors: melting ice in Greenland, land area rising as ice sheets melt, and changes in Earth's mantle, a mostly rocky layer inside Earth between its outer crust and the core.
Rising temperatures during the 20th century have caused ice to melt in Greenland. Researchers say 7,500 gigatons of ice – equal to the weight of more than 20 million Empire State Buildings – melted into the ocean over that time.
The ice melt, combined with Greenland's location on Earth, plays a role in how the Earth wobbles. "There is a geometrical effect that if you have a mass that is 45 degrees from the North Pole – which Greenland is – or from the South Pole, it will have a bigger impact on shifting Earth's spin axis than a mass that is right near the Pole," said Eric Ivins, a researcher at the Jet Propulsion Laboratory and co-author on the study, in a statement.
Several studies have suggested global warming has contributed to an increase in ice melt in Greenland, Antarctica and other parts of the world. A study in February said sea levels could be at least 2 feet higher by the end of the century compared to now because of melting ice.
Another factor noted by researchers is glacial rebound, a process where land once depressed by heavy glaciers begins to rise. Also, the circulation of material inside the Earth's mantle, called mantle convection, plays a role.
Ivins and lead author Surendra Adhikari said all three factors contribute to a significant redistribution of the Earth's mass, leading to the wobble effect.
"The traditional explanation is that one process, glacial rebound, is responsible for this motion of Earth's spin axis," said Adhikari. "But recently, many researchers have speculated that other processes could have potentially large effects on it as well."
The following chart shows reported fireball events for which geographic location data are provided. Each event's calculated total impact energy is indicated by its relative size and by a color. Hover over an event to see its details. In 2019 it was determined that the Geostationary Lightning Mapper (GLM) instruments on GOES weather satellites can detect fireballs and bolides. The GLM Bolides website provides the data for those detections.
The accompanying table provides information on the date and time of each reported fireball event with its approximate total optical radiated energy and its calculated total impact energy. When reported, the event’s geographic location, altitude and velocity at peak brightness are also provided. Note that data are not provided in real-time and not all fireballs are reported. A blank (empty) field in the table indicates the associated value was not reported.
|Peak Brightness |
|Velocity Components |
Use the "Print" button above to print data contained in this table. Use the "CSV" or "Excel" buttons to download the data for use in your spreadsheet program. Allow a few seconds for downloads of large datasets.
On thin ice
Scientists predict that ships will be able to sail directly over the North Pole by the year 2050. In fact, the Arctic ice sheet will be thin enough for ice breakers to carve a straight path between the Pacific and Atlantic oceans, according to a study by researchers at the University of California, Los Angeles (UCLA). Another study found that by the end of the 21st century, the Northern Sea Route could be navigable for more than half the year.
In particular, the Arctic has experienced major ice decline within the last decade. So what is happening? Typically, the ice follows a seasonal cycle. For example, in the spring and summer months, the warmer temperatures cause the ice floating on top of the Arctic Ocean to shrink. Then as the temperatures drop in the fall and winter months, the ice cover grows again until it reaches its yearly maximum extent, typically in March.
In 2017, however, a combination of warmer-than-average temperatures, winds unfavorable to ice expansion, and a series of storms halted sea ice growth in the Arctic. In fact,on March 7, 2017, Arctic sea ice reached a new record low for wintertime maximum extent, according to NASA. Overall, the ice reached just 5.57 million square miles (14.42 million square kilometers), which is 37,000 sq mi (97,00 sq km) smaller than the previous record low set in 2015, and 471,000 sq mi (1.22 million sq km) smaller than the average maximum extent for 1981-2010.
In fact, on Feb. 13, 2017, the combined level of Arctic and Antarctic sea ice was at its lowest point since satellites began measuring polar ice in 1979. According to NASA, the total polar sea ice on this date covered only 6.26 million square miles (16.21 million square km). This number is 790,000 square miles (2 million square km) smaller than the average global minimum extent for 1981-2010. This is equivalent to losing a chunk of sea ice bigger than Mexico.
How Far Is the North Pole from Other Continents?
Even though the two biggest nations of North America, the United States and Canada have some land on the Arctic Circle, the North Pole is not part of North America. North America is 3,036 miles to the south of the North Pole. North America is in the Northern Hemisphere and about 3,184 miles from the Equator.
The European nation which is close to this point is one of Denmark Kingdom’s constituent countries known as Greenland. Denmark itself is 2,349.9 miles to the south of the North Pole. The Kaffeklubben Island, Greenland is about 430 miles from the North Pole. Kaffeklubben Island is on the northern tip of Greenland.
Asia is about 6,223 miles to the southern parts of the North Pole. Russia is the only Asian state with some cities on the Arctic Circle. About 2,100,000 sq miles of Russia is on the northern parts of the Arctic Circle. Russia is on the Northern Hemisphere and about 3,337 miles south of this position.
South America is in the Southern Hemisphere and about 3,657 miles to the south of the North Pole. Australia is on the Southern Hemisphere and about 7,948 miles from the North Pole with Africa being even further south.
Antarctica is on the opposite side of the Arctic and the home to the South Pole. Antarctica is about 12,430 miles to the south of the North Pole, and unlike the Arctic, it is a continent.
Take a little dip in the Little Dipper
We live in an interesting time. Astronomically speaking, I mean. It just so happens that right now, if you draw a line from Earth's south pole, through the Earth's center, up through the north pole, and extend it up into the sky, it points very close to a fair-to-middlin' bright star.
That star has the designation Alpha Ursae Minoris, but you may know it better as Polaris. It's actually named that way because it's the pole star, the north pole of the sky. You can think of the sky as being like the Earth's surface expanded outward to infinity. As the Earth spins we feel motionless, with the sky apparently spinning above us. It has a north celestial pole, a south celestial pole, and even a celestial equator.
More Bad Astronomy
Alpha Ursae Minoris happens to be very close to that north celestial pole. That makes it an important star, because if you can find it you know you're facing north. But that designation of Alpha means it's important in another way: It's the brightest star in the constellation Ursa Minor: The Little Dipper.
That becomes pretty obvious, too, when you gaze upon the simply gorgeous photo master astrophotographer Rogelio Bernal Andreo took of the constellation back in 2011. I mean seriously, look at this!
Ursa Minor — the Little Dipper — is gorgeous in this deep mosaic that shows thousands of stars, faint wisps of dust, and a brief interplanetary visitor. Credit: Rogelio Bernal Andreo
Polaris is the bright star to the left. Funny, it's really only about the 50th brightest star in the sky — it can be hard to see in even mildly light-polluted areas — but it shines like a beacon here. Of course, Rogelio used his fabulous Takahashi FSQ106EDX telescope and SBIG STL 11k CCD camera — if you want to capture big shots of the sky, that's the dream combo right there (and if you detect just a wee bit of jealousy here, well, I won't deny it).
This image is actually a mosaic made up of 20 frames, and each one consisted of six exposures in four filters (what astronomers call LRGB: luminance (unfiltered), red, green, and blue, to create a natural color image). Each exposure was 5 minutes, so the total was a staggering 40 hours of imaging! He took some of the shots in Spain and some in California.
If you're having a hard time seeing the actual dipper, Rogelio has you covered with this annotated version:
Ursa Minor would be just another overlooked constellation if it didn’t hold the top of the sky within its borders. Credit: Rogelio Bernal Andreo
You may notice that Polaris is not exactly on the pole. It would be a huge coincidence if it were! It's right now about 2/3rds of a degree (a bit bigger than the size of the full Moon on the sky) from the actual true pole. And that's only for now. The Earth wobbles, like a top losing energy, so the axis of the Earth makes a slow circle in the sky. And by slow, I mean it takes 26,000 years to make a complete circuit.
We call this precession, and it's a pain: As the pole moves in the sky, the coordinate system we use to measure positions of objects changes. Imagine if the Earth's north pole wandered over the Arctic, we'd have to change our latitude and longitude system! That's an issue astronomers have to deal with to get precise measurements and even to plan our observations.
The pole will move closest to Polaris in March 2100, when it'll be a bit more than half its current distance. After that the pole will pull away, and Polaris will find its grasp on fame more tenuous. It's only really been near the pole for the past millennium or so 2000 years ago it was as close to Kochab on the other side of the Little Dipper as it was to Polaris.
And far be it from me to cast aspersion on a writer with the stature of Shakespeare, but he goofed when he wrote Julius Caesar. In it, the eponymous leader says,
But I am constant as the northern star,
Of whose true fixed and resting quality
There is no fellow in the firmament.
Yeah, oops. For one, Polaris isn't fixed and resting. For another, it's actually a Cepheid variable star, changing its brightness over time. And third, it wasn't even the North Star in Caesar's time! Shakespeare should've read my blog.
If you look again at Rogelio's shot, you’ll see that there appears to be wispy stuff all through it. That's real! It's called galactic cirrus, or integrated flux nebula: very tenuous clouds of dust floating between the stars, and just barely illuminated by them (hence the second name "integrated" means "added up," and it reflects the light of all the stars around it). It's incredibly faint, and Rogelio is really good at teasing it out of the background. You can see it in his photo of the Big Dipper as well.
Also, take a look just above Polaris. See that razor thing streak? That's likely a meteor, a small bit of rock burning up in our atmosphere. In a 40 hour exposure you're bound to see one or two of those! To be honest, it might be a faint satellite in a polar orbit (one that goes mostly north/south instead of east/west), though by the way it starts off faint, gets bright, then just cuts off, it looks far more like a piece of space debris to me.
[Update (March 28, 2018): BA reader Rick Johnson sent me an email making a convincing argument that the trail actually is a satellite and not a meteor. The satellite would have come in from the top, out of Earth's shadow (he says the location for that is correct for this image) and it cuts off to the lower left as the exposure ended in one of the sub-frames making up the images in the mosiac. There are lots of other details, too, but all in all I think he's most likely right. I stand corrected.]
As any (boreal) amateur astronomer will tell you, when you take your 'scope out of the garage and set it up, the first thing you do is polar align it, get it set up to track the motion of the stars as the sky spins overhead. That means aiming it at Polaris to get it as close to the north celestial pole as possible.
And the next time I do that with my own 'scope, I'll be thinking of this image, and remembering that Polaris is more than just a useful guidepost. It benchmarks an area of the sky just as gorgeous as any other you care to pick.
What would happen if the Earth stopped rotating?
The good news is that if the Earth's rotation stopped, we wouldn't fall off. With water pushed to the poles, we could walk on land around the entire equator, but it would be a very inhospitable place, as Dr Karl Kruszelnicki explains.
We know that the rotation of the Earth is gradually slowing down. But what would happen if God, the devil or aliens suddenly and completely stopped our planet from rotating on its axis of spin? Luckily, thanks to improved knowledge about our planet, geographers can now give us the answers.
You could travel around the Earth on the equator and stay entirely on dry land—ignoring the freezing cold on the night side, and the searing heat on the day side.
Of course, if you suddenly stopped the Earth from spinning, most of our planet would rapidly become very inhospitable.
Half of the planet would almost continuously face the heat of the Sun, while half would face the cold of space.
Life could continue in a narrow twilight zone between the hot and cold halves. But this twilight zone would slowly creep around the planet over the period of a year, as the Earth did its annual orbit around the Sun.
To make it easier to work out what would happen, let's pretend the oceans don't freeze on the cold side, or evaporate on the hot side. And let's look only at centrifugal force, which should really be called centripetal force.
Over several billion years, this force, which effectively pushes outwards, has made the planet a bit fatter around the middle. So the diameter of the Earth measured through the equator is today about 21.4 kilometres more than the diameter of the Earth measured through the poles.
But this bulge in the solid Earth took billions of years to slowly develop. This is because the solid matter moved only very slowly in response to the outward force caused by the spin of the planet.
But the liquid water in the oceans is far more mobile and responsive to forces. So the Earth's spin has pushed up this liquid water to an 'abnormal' elevation of about eight kilometres.
In other words, at the equator, thanks to the spinning Earth, the water has been pushed up some eight kilometres higher than in the case of the Earth having no spin.
But today, on the entire equator, the deepest part of the oceans is only about 5.75 kilometres.
So take away the spin and you take away all water at the equator.
If the Earth were to stop spinning on its axis, gradually the oceans would migrate towards the poles from the equator. At first, only small regions of terra firma around the equator would rise out of the retreating waters.
Eventually, there would be a huge mega-continent wrapped continuously around the Earth at the equator. You could travel around the Earth on the equator and stay entirely on dry land—ignoring the freezing cold on the night side, and the searing heat on the day side.
The water that left the equatorial regions would have to go somewhere, and that 'somewhere' would be the poles. There would be two totally disconnected polar oceans on each side of the equatorial mega-continent.
In the north, Canada would be entirely underwater. And roughly following the line of the border of current-day USA and Canada, all of Greenland, as well as the northern plains of Siberia, Asia and Europe would be underwater. But Spain would mostly stay above water.
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On the other side of the equator, the new southern ocean would start roughly on a line running through current-day Canberra. Africa would be joined to Madagascar, while Australia would be joined to New Guinea and Indonesia.
It turns out that the underwater basin around the South Pole is much bigger than the one around the North Pole.
So the new southern ocean would be lower. Because it's a bigger 'bowl' with a greater capacity, its sea level would be about 1.4 kilometres lower than the sea level of the new northern ocean.
Now it's not just the spin of the Earth that has given us today's eight-kilometre-high bulge of water at the equator.
The other factor is gravity. The poles are about 10 kilometres closer to the centre of the Earth than the equator, so the gravity is ever so slightly stronger at the poles.
This would be another factor drawing the water away from the equator.
Our spinning Earth is in fact slowing down. Billions of years in the past, the faster-spinning Earth had a bigger bulge around the equator, and billions of years in the future, the slowed-down Earth will have a smaller bulge, and will be closer to a sphere.
In fact, this slowing of the spin is why we have to add an extra second into our clocks every 500 days or so. I'll talk more about that, next time.
Climate has shifted the axis of the Earth, study finds
Glacial melting due to global warming is likely the cause of a shift in the movement of the poles that occurred in the 1990s.
The locations of the North and South poles aren't static, unchanging spots on our planet. The axis Earth spins around -- or more specifically the surface that invisible line emerges from -- is always moving due to processes scientists don't completely understand. The way water is distributed on Earth's surface is one factor that drives the drift.
Melting glaciers redistributed enough water to cause the direction of polar wander to turn and accelerate eastward during the mid-1990s, according to a new study in Geophysical Research Letters, AGU's journal for high-impact, short-format reports with immediate implications spanning all Earth and space sciences.
"The faster ice melting under global warming was the most likely cause of the directional change of the polar drift in the 1990s," said Shanshan Deng, a researcher at the Institute of Geographic Sciences and Natural Resources Research at the Chinese Academy of Sciences, the University of the Chinese Academy of Sciences and an author of the new study.
The Earth spins around an axis kind of like a top, explains Vincent Humphrey, a climate scientist at the University of Zurich who was not involved in this research. If the weight of a top is moved around, the spinning top would start to lean and wobble as its rotational axis changes. The same thing happens to the Earth as weight is shifted from one area to the other.
Researchers have been able to determine the causes of polar drifts starting from 2002 based on data from the Gravity Recovery and Climate Experiment (GRACE), a joint mission by NASA and the German Aerospace Center, launched with twin satellites that year and a follow up mission in 2018. The mission gathered information on how mass is distributed around the planet by measuring uneven changes in gravity at different points.
Previous studies released on the GRACE mission data revealed some of the reasons for later changes in direction. For example, research has determined more recent movements of the North Pole away from Canada and toward Russia to be caused by factors like molten iron in the Earth's outer core. Other shifts were caused in part by what's called the terrestrial water storage change, the process by which all the water on land -- including frozen water in glaciers and groundwater stored under our continents -- is being lost through melting and groundwater pumping.
The authors of the new study believed that this water loss on land contributed to the shifts in the polar drift in the past two decades by changing the way mass is distributed around the world. In particular, they wanted to see if it could also explain changes that occurred in the mid-1990s.
In 1995, the direction of polar drift shifted from southward to eastward. The average speed of drift from 1995 to 2020 also increased about 17 times from the average speed recorded from 1981 to 1995.
Now researchers have found a way to wind modern pole tracking analysis backward in time to learn why this drift occurred. The new research calculates the total land water loss in the 1990s before the GRACE mission started.
"The findings offer a clue for studying past climate-driven polar motion," said Suxia Liu, a hydrologist at the Institute of Geographic Sciences and Natural Resources Research at the Chinese Academy of Sciences, the University of the Chinese Academy of Sciences and the corresponding author of the new study. "The goal of this project, funded by the Ministry of Science and Technology of China is to explore the relationship between the water and polar motion."
Water loss and polar drift
Using data on glacier loss and estimations of ground water pumping, Liu and her colleagues calculated how the water stored on land changed. They found that the contributions of water loss from the polar regions is the main driver of polar drift, with contributions from water loss in nonpolar regions. Together, all this water loss explained the eastward change in polar drift.
"I think it brings an interesting piece of evidence to this question," said Humphrey. "It tells you how strong this mass change is -- it's so big that it can change the axis of the Earth."
Humphrey said the change to the Earth's axis isn't large enough that it would affect daily life. It could change the length of day we experience, but only by milliseconds.
The faster ice melting couldn't entirely explain the shift, Deng said. While they didn't analyze this specifically, she speculated that the slight gap might be due to activities involving land water storage in non-polar regions, such as unsustainable groundwater pumping for agriculture.
Humphrey said this evidence reveals how much direct human activity can have an impact on changes to the mass of water on land. Their analysis revealed large changes in water mass in areas like California, northern Texas, the region around Beijing and northern India, for example -- all areas that have been pumping large amounts of groundwater for agricultural use.
"The ground water contribution is also an important one," Humphrey said. "Here you have a local water management problem that is picked up by this type of analysis."
Liu said the research has larger implications for our understanding of land water storage earlier in the 20th century. Researchers have 176 years of data on polar drift. By using some of the methods highlighted by her and her colleagues, it could be possible to use those changes in direction and speed to estimate how much land water was lost in past years.