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Ngumi Mirie
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In the Belt

The Kuiper belt is a region of objects beyond the orbit of Neptune. You can think of it as an outer asteroid belt, where the bodies are icy rather than rocky. The dwarf planets Pluto, Haumea and Makemake are part of the belt, as well as about 100,000 other bodies. It’s generally thought that the Kuiper belt likely formed during the great migration, when Jupiter moved farther out from the Sun due to interactions with other outer planets. One of the questions, then, is whether other planetary systems would also have a Kuiper belt. Recently, observations from the Gemini South Telescope in Chile have found a similar belt around a young star.

The team observed a ring around a 10-20 million year old star that’s about 50% more massive than our Sun. The belt lies in a range of 37 – 55 AU from the star, which is a similar range to that of our own Kuiper belt. It’s brightness also indicates a similar composition to the Kuiper belt. What’s particularly striking about the ring is that it isn’t centered on the star, but is offset slightly. This could be explained by gravitational interactions with large planets, similar to the way Jupiter affected the formation of the Kuiper belt.

Paper: Thayne Currie, et al. Direct Imaging and Spectroscopy of a Young Extrasolar Kuiper Belt in the Nearest OB Association. arXiv:1505.06734 [astro-ph.EP] (2015)
A region of material similar to the Kuiper belt of our solar system has been directly observed around another star.
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Yin Yang Moon

Iapetus is a moon of Saturn known for two distinctive features. One is that it has a two-tone coloration, where roughly half of the planet is a dark, reddish-brown color while the other half is white and almost as bright as Jupiter’s moon Europa. It’s not entirely clear what gives Iapetus is yin yang coloring, but the most popular view is that it is cause by sublimation of the moon’s warmer side. Ice evaporates away leaving the dark remnant material. We know, for example, that the dark layer is no more than a foot thick, and has a bright layer underneath it.

Another strange feature is the moon’s large equatorial ridge. It’s about 1,300 km long, and 13 km high. We know that the ridge is old because it is heavily cratered. Again, we aren’t entirely sure how such a ridge could have formed, but generally fall into two camps.  One is that it was produced by some type of internal mechanism such as a convective overturn in its youth, the other is that is was caused an external mechanism such as the accumulation of debris from an ancient ring system. A recent paper in Icarus gives support to the accumulation model.

In this work the team made a detailed model of the ridge system based upon observations from the Cassini probe. They then measured the shapes of the mountain peaks in the ridge, and found that they were within the angle of repose. That is, the angle at which accumulated matter tends to form a peak. Any steeper and the material will tend to collapse to a shallower peak. A geologic upheaval would likely produce a wide range of peak angles, so this suggests the ridge was produced by accumulation. Accumulation from a collapsed ring system would explain why the ridge lies along the equator.

Paper: Erika J. Lopez Garcia, et al. Topographic constraints on the origin of the equatorial ridge on Iapetus. Volume 237, Pages 419–421 (2014)
Saturn's moon Iapetus has a strange yin yang coloring, as well as a mysterious equatorial ridge.
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A Whole New World

Twenty-five years ago the Hubble space telescope took its first image of the heavens. While the first image might not have seemed impressive at first glance, it opened a view of the universe previously unattainable.

The Hubble telescope had several advantages over ground-based telescopes of the time. To begin with, it didn’t suffer from the atmospheric distortions that cause stars to twinkle. Because of such distortions, ground-based telescopes had a limiting resolution of about a second of arc. The Hubble could gather light to about 0.05 arcseconds. Since Hubble’s launch, ground based telescopes have gained greater precision through interferometry and adaptive optics, but these were years away when Hubble’s mission began. Hubble could also observe infrared and ultraviolet wavelengths, much of which are absorbed by Earth’s atmosphere.

The greater range and precision of Hubble has given us a much deeper understanding of the universe. It allowed us to measure Cepheid variable stars with greater precision, which gave us a more accurate cosmic distance ladder. It found protoplanetary disks in the Orion nebula, confirming the basic model of planetary formation. It gave us the Ultra Deep Field, which found that there are thousands of galaxies in a patch of sky no bigger than a grain of sand. It also gave us thousands of beautiful images, from the Pillars of Creation to the starry ocean of the Andromeda galaxy.

But perhaps its most revolutionary discovery came from observations of distant supernovae. By measuring the brightness of these supernovae, we could determine their distance. What we found was that the universe is not only expanding, but that the rate of expansion is increasing. This not only gave us an accurate measure of the age of the universe, it also led to the discovery of dark energy, which we are still trying to understand.

The Hubble telescope was named in honor of Edwin Hubble, who played a central role in demonstrating that the universe extended far beyond our Milky Way galaxy. It is perhaps fitting that the telescope bearing his name has done so much to determine the true age and scale of the cosmos.
The Hubble telescope is 25 years old, and in that time it has revolutionized our understanding of the cosmos.
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Two Worlds, One Sun

There’s an image going around of a blue sunset on Mars. Yes, it’s a real image, and yes, the colors are reasonably true to life. It was taken by the Curiosity rover in April. Given that sunsets on Earth are typically red, how does Mars get a blue sunset? It all has to do with the way light scatters in the atmospheres of Earth and Mars.

Earth has a relatively thick atmosphere, so most of the atmospheric scattering occurs when light strikes a molecule of air, known as Rayleigh scattering. Rayleigh scattering occurs when the object a photon scatters off (the air molecule) is much smaller than the wavelength of the photon. The closer the wavelength is to the size of the molecule, the more likely it is to scatter. This means that red wavelengths (which are the longer wavelengths of visible light) don’t scatter with air molecules much, while blue wavelengths (which are shorter) tend to scatter a lot. In fact blue light is almost 10 times more likely to scatter against air molecules than red light. This is why the sky appears blue, since so much of the blue light is scattered.

When the Sun is low in the sky, it’s light has to travel a long path through the atmosphere to reach you. As the light travels through the atmosphere some of the photons are scattered off the air molecules. When the photons scatter off air molecules, they scatter randomly in all directions, so usually when a photon scatters, it scatters away from your line of sight. Since blue photons scatter much more often than red ones, much of the blue light is scattered away. This leaves red photons to reach your eye. Hence the Sun looks red when low in the sky. When the Sun is overhead, the path it takes to reach you is much shorter, so only a bit of the blue light is scattered. So the Sun looks yellow.

A daytime Martian sky (left) vs a Martian sunset (right). Credit: NASA / JPL-Caltech / MSSS / Damia Bouic
A daytime Martian sky (left) vs a Martian sunset (right). Credit: NASA / JPL-Caltech / MSSS / Damia Bouic
Mars has a much thinner atmosphere, so the amount of Rayleigh scattering is much less. But Mars also has a dry, dusty surface, and a weaker surface gravity, so the atmosphere of Mars is often filled with fine dust particles. These particles are more comparable in size to the wavelengths of visible light, so most of the light is scattered by Mie scattering. One of the main differences between Rayleigh and Mie scattering is that Rayleigh scattering tends to occur in all directions, but Mie scattering varies with scattering angle. What this means is that longer wavelengths (reds) tend to scatter more uniformly, while shorter wavelengths (blues) tend to scatter at slight angles. This means that blue light tends to be deflected less than red light. This means Mars can have a dusty red daytime sky, and a blue sunset.

Mie scattering does occur on Earth as well, but since Mie scattering is less efficient than Rayleigh scattering it’s never strong enough to give us a blue sunset. It can (rarely) produce a blue moon. The most widespread incidence of modern history occurred after the eruption of Krakatoa in 1883, which sent so much ash into the atmosphere it produced brilliantly red sunsets and visibly blue moons all across the globe for nearly two years. As a result, the phrase “once in a blue moon” came to mean a rare occurrence.
While Earth can have lovely red sunsets, Mars can have a sunset that is truly blue.
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Wonder Year

Albert Einstein is perhaps the most famous scientist in history. He was a true “rock star” scientist, known around the world for his theory of general relativity, which revolutionized our understanding of gravity. Not surprisingly, he was awarded the Nobel prize in 1921, but it wasn’t for general relativity. It was for a completely different work he published in 1905, the year known as Einstein’s annus mirabilis, or wonderous year.

Publishing research is a challenge for any scientist. Most of us might publish a few to several papers a year, collaboratively with other scientists. While our work is interesting and innovative, it isn’t typically revolutionary. Publishing a truly revolutionary, groundbreaking paper is rare, and something most scientists won’t achieve in their lifetime. But in 1905 Einstein published four groundbreaking papers. Each one was a revolutionary work that changed our understanding of the universe. None of them where about gravity. Einstein’s most famous work wasn’t published until 1915, and one could argue that it wasn’t nearly as revolutionary as his 1905 papers.

So this week we’ll look at Einstein’s annus mirabilis papers:

Brownian Motion, which settled the debate over the existence of atoms, and laid the foundation for a new field of work known as statistical mechanics.

The Photoelectric Effect, which demonstrated the particle aspects of light, and led to the quantum theory of matter.

Special Relativity, which overturned a model of space and time that had stood for millennia.

Mass-Energy Equivalence, which connected matter and energy, and led us to a true understanding of the stars.

Although the photoelectric effect is specifically noted in his Nobel prize award, one of these papers would have been worthy of note. We’ll find out why starting tomorrow.
In 1905 Einstein published four papers that revolutionized science. For this reason 1905 is sometimes called Einstein's wondrous year.
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The Dark Side

Dark matter remains enigmatic, but we are learning more about it. While much of the observations about dark matter have determined what it’s not, there hasn’t been nearly as much data to determine what it is. So far we know that it is predominantly cold (meaning it isn’t zipping around at near light speeds) and it likely interacts with matter through the weak force and gravity. It’s generally been thought that dark matter should also be self-interacting, but recent observations haven’t shown any such interaction. But new observations of the galaxy cluster Abell 3827 show some evidence of dark matter’s self-interaction.

One of the ways we observe the behavior of dark matter is by looking at colliding galaxy clusters. When two galaxies collide, two things happen. First, the gas and dust in these galaxies collide and interact. When they do, they tend to combine to produce large clouds that can start producing new stars. Because interstellar gas clouds tend to be diffuse and spread across light years, they are fairly likely to interact. The stars in these galaxies, on the other hand, tend to move right past each other. They will interact gravitationally, but the chance of two stars actually colliding with each other is very small. So when we observe galaxies that have collided, we tend to see a central region where the gas and dust interacts, and stars on either side that have simply passed through.

Since dark matter doesn’t interact strongly with regular matter, it tends to pass through the collision just like the stars. As a result, the stars and the dark matter stay together. If dark matter interacts with itself, then during a collision it should clump a bit in the center. Most of the dark might might pass through the collision, but some of it should be left behind. In past observations, we haven’t seen any difference in the distribution of stars and dark matter in colliding galaxies, so we know that dark matter self-interacts with about the same strength as stars, which is tiny on a galactic scale.

But in Abell 3827, a team of astronomers has observed differences between the distribution of stars and that of dark matter. The difference is consistent with a self-interaction of dark matter, and is the first time such an interaction has been observed. While we should be careful not to read too much into just one observation, the result has gotten theorists excited because it hints at a dark matter interaction beyond the fundamental forces we know. For example there may be things such as “dark photons” interacting with dark matter similar to the way two charges interact through electromagnetic fields. Time will tell whether those ideas pan out, and certainly we need more observations to confirm dark matter interactions.

But this may be the first evidence of a dark side of the force.

Paper: Richard Massey, et al. The behaviour of dark matter associated with four bright cluster galaxies in the 10 kpc core of Abell 3827. MNRAS 449 (4): 3393-3406 (2015).
New observations of colliding galaxies shows that dark matter interacts with itself, and may do it through a "dark force."
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Conjunction Junction

In astronomy a conjunction occurs when two bodies have the same right ascension as seen from Earth. In simple terms, this means that they are aligned in the sky. Often the term is applied for planets relative to the Sun, where a planet is either passing between us and the Sun (inferior conjunction) or the Sun is passing between us and the planet (superior conjunction). 

In addition to being an interesting astronomical event, conjunctions do have real consequences. For example, Mars is currently in superior conjunction, which means we can’t get a clear signal from the planet. As a result, the Curiosity is placed in sleep mode until Mars moves out of conjunction. This happens for all the planets, so every now and then we can’t communicate with our space probes.

Another area where conjunctions have an impact is in popular videos, such as the one recently that claimed massive earthquakes will hit California today because of several planets aligning in conjunctions. Needless to say, there’s nothing to worry about. Despite the claims, the planets aren’t that closely aligned, and even if it were the gravitational influence of the planets on Earth is negligible. In fact a person standing a foot away from you exerts a stronger gravitational pull on you than the entire planet Jupiter.
A planet is in conjunction when it has same right ascension as the Sun as seen from Earth.
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Young and Brilliant

Young galaxies typically go through a period of rapid star production. For example, dusty starburst galaxies produce stars so rapidly that it would consume all of its gas and dust in about 10 million years at that rate. But before that early star production period, a galaxy also has a period of rapid formation into a galaxy. In this period the central black hole of the galaxy is particularly active. As a result these galaxies are bright in the infrared, and are known as luminous infrared galaxies (LIRGs).

Recently, analysis of data from the WISE infrared satellite has found dozens of LIRGs, including the brightest galaxy ever discovered, known as WISE J224607.57-052635.0. The light from this particular galaxy has traveled for about 12.5 billion years, which means it comes from a time when the universe was only 1.3 billion years old.  It has a luminosity equivalent to 350 trillion Suns, which is surprising since it is smaller than our own Milky Way.

The reason it is so bright in the infrared is that it is surrounded by a halo of gas and dust. As the central black hole gorges itself it emits light at a range of wavelengths from x-rays to ultraviolet. Most of that light is absorbed by the surrounding halo, which is heated by the light and emits infrared. But given just how bright this galaxy is, the central black hole must be consuming matter at a prodigious rate. So much that it would exceed a theoretical limit known as the Eddington limit. Basically as a black hole consumes matter the light it emits should push back against infalling matter, thus limiting how much can be captured.

There are ways that the Eddington limit can be bypassed, but the fact that this would occur in a young galaxy indicates that supermassive black holes in the centers of galaxies may have formed earlier and faster than we once supposed.

Paper: Chao-Wei Tsai et al. The Most Luminous Galaxies Discovered by WISE. ApJ 805 90. doi:10.1088/0004-637X/805/2/90 (2015)
The most luminous galaxy ever discovered shines brilliantly in infrared. This is likely due to a quickly forming supermassive black hole in its center.
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Red Hot Vacuum

One of the common tropes in astronomy is a comparison of our Sun to other stars. It’s a great way of showing just how tiny we are. Betelgeuse, for example, has a radius more than 1,100 times that of the Sun. In an image comparing stars, our Sun is easily reduced to a tiny pixel among giants. But such an image is also a bit misleading. While the relative sizes of these images are typically accurate, they ignore the more important aspect of a star, which is its mass.

Since Betelgeuse has a radius 1,100 times that of the Sun, it has a volume about 1.3 billion times larger than the Sun. But its mass is only about 8 – 20 times the Sun. This means the density of Betelgeuse is much, much lower than the Sun. The density of a star isn’t uniform, and increases with depth, but very roughly the average density of the Sun is about 1.4 grams/cc, or about 1.4 times the density of water. That might not seem like much, but it’s pretty high for an object that is mostly hydrogen and helium. The average density of Betelgeuse is about 12 billionths of a gram/cc, which is about a million times less dense than Earth’s atmosphere at sea level. That’s about the same as a vacuum found in an insulating Thermos bottle.

Basically, a star like Betelgeuse is a red hot vacuum.

You might think that such a hot, low-density star isn’t sustainable long term, and you’d be right. Betelgeuse is in its red giant stage, where it makes a last ditch effort to fuse heavier elements to keep going. Most of what we see as the star is in fact its outer layers being expanded to near vacuum by the hot core. Eventually it will lose its battle with gravity and explode as a supernova (though it poses no threat to us).

So the next time you see a comparison of stars, keep in mind that most of the largest stars are basically hot vacuums. In terms of mass the largest stars are only about 200 times that of the Sun. If they had the same density as our home star, even the most massive stars would only be about 6 times larger than the Sun.
Giant stars such as Betelgeuse may appear to dwarf our Sun, but their densities are so low that they are basically red hot vacuums.
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Lunchtime Doubly So

We live in a universe of space and time. Events occur at a particular time, and in some location in space. In this way, space and time can be seen as a background against which things happen. Throughout most of human history, this background was seen as absolute. Each event occurs at a unique point in space and time, and in principle everyone can agree what that point is. Intuitively, it makes a lot of sense. In our everyday lives the Earth seems to be an unmoving rock, and acts as a point of reference for everything we do. Sure, we now know the Earth moves around the Sun, but it doesn’t feel that way. When Galileo and others began proposing a more sophisticated view of physics, the intuitive view of spacetime as an immutable background remained. Galileo argued that the motion of objects was relative to each other, but that motion could always be measured relative to the “fixed” space. For Galileo, speed was relative, but spacetime was not. When Newton developed his theories of physics and gravity, he also assumed that spacetime was fixed and absolute.

The success of Newton’s physics seemed to confirm the absolute nature of spacetime, and the assumption remained largely unquestioned for two centuries. But as we came to understand light, the idea became less intuitive. According to Maxwell’s equations, the speed of light is the same for all light. That’s because electromagnetic waves propagate at the same rate. But water waves propagate through water, and sound waves through air, so what do light waves propagate through?

The most popular idea was that light moved through a luminiferous aether. This aether couldn’t be observed directly, but it was thought to be stationary relative to the background of space. Some proposed that this aether could in fact be the absolute frame of reference for the universe. But if that’s the case, then your measurement of the speed of light should depend upon your motion relative to the aether.

Suppose you were on the platform of a train moving at 10 m/s (20 mph). If you measured the speed of sound in the direction you are moving, you would get a speed of 330 m/s. That’s because the sound is traveling through the air at 340 m/s, but you are traveling through the air in the same direction at 10 m/s, so the sound is moving 330 m/s relative to you. In the same way, if you measured the speed of sound in the opposite direction, you would get 350 m/s because of your motion. This is a key feature of waves traveling through a medium: they can be different in different directions because of your motion through the medium.

Then in 1887, Albert Michelson and Edward Morley performed an experiment to measure this difference in the speed of light. But what they found was the speed of light was always the same. No matter what direction light traveled, no matter how they oriented their experiment, the speed of light never changed. This was not only surprising, it violated the fundamental assumption of an absolute reference frame. It seemed the speed of light (and only the speed of light) is absolute, and this made no sense at all.

This is the puzzle Einstein sought to resolve in his paper “On the Electrodynamics of Moving Bodies.” In this paper Einstein noted that in order for the speed of light to be an absolute constant, either Maxwell’s equations or Newton’s concept of space and time had to be wrong. Somewhat surprisingly, Einstein argued for the latter. Specifically, he argued that the “grid” of space and time was relative to the observer. He demonstrated this by looking at a property known as simultaneity. In Newton’s view, two events seen to occur at the same time will be seen to be simultaneous for all observers. But Einstein showed that the constancy of light required this concept of “now” to be relative. Different observers moving at different speeds will disagree on the order of events.

Rather than a fixed background, space and time is a relation between events that depends upon where and when the observer is. This relativity of space and time led to strange predictions, such as time dilation, which were later found to be true. It’s a concept that’s still difficult to fully understand, but is absolutely necessary for modern devices such as GPS.

Tomorrow: Einstein looks at the connection between matter and energy, and finds that relativity could explain the light of the stars.

Paper:  Einstein, Albert. Zur Elektrodynamik bewegter Körper. Annalen der Physik 17 (10): 891–921 (1905)
How Einstein used the invariant speed of light to overturn a view of space and time that had stood for centuries.
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It's Just That Simple

In general relativity a black hole is a relatively simple object.  It can be described by three basic quantities: its mass, its rotation (angular momentum), and its charge. No matter what type of material collapses into a black hole, in the end it’s reduced to mass, rotation and net charge. This property is known as the no-hair theorem, because unlike other astronomical objects like stars and planets, black holes should have no features (hair). But is the theorem too simplistic?

One of the criticisms of the no-hair theorem is that it’s only been formally proven in the case of isolated black holes. The problem is that black holes tend to do things like build up disks of matter around them, or orbit with other black holes and the like. Does the no-hair theorem apply then, or is it just for lonely black holes? A new paper in Physical Review Letters argues that the no-hair theorem does apply even for black holes surrounded by matter, at least for a broad class of physically reasonable cases.

The paper looks at an aspect of gravity known as multipoles. A perfectly spherical mass would have a gravitational field that is the same in all directions. But an object like the Earth isn’t perfectly spherical, so the Earth’s gravitational field is slightly distorted. But the Earth is approximately spherical, so one can approximate Earth’s gravitational field as a series of perturbations from perfectly spherical. The spherical part is sometimes called the monopole, and the deviation along its axis the dipole, then the quadrupole, octopole, etc. With each successive multipole your model of the gravitational field better approximates the actual field. This is often done in relativity because after a few terms the deviations are so small that you can basically ignore them.  It’s like saying the value of pi is 3.14159. For most applications that’s close enough.

According to the no-hair theorem, the gravitational field of a stationary black hole should be a monopole. Other multipole terms would be due to deviations from a spherical shape, and thus be “hair.” In this new work the author showed that the gravitational field of stationary black hole is just a monopole, even if there is matter surrounding it.

This is rather surprising. Suppose there were a black hole with a dense accretion disk surrounding it (which is actually rather common). The mass of the accretion disk would exert a gravitational force on the black hole, and the event horizon of the black hole should distort accordingly. This would mean the black hole isn’t perfectly spherical, and so should have multipole gravity terms. But it turns out that in general relativity the distortion of the event horizon actually cancels out the multipole gravity terms due to the non-spherical shape of the black hole. So even when a stationary black hole isn’t spherical, its gravity only has a monopole term.

This is a nice bit of theoretical work, but it could also have observational consequences. Monopole gravity doesn’t produce gravitational waves, for example, so any gravitational waves produced by such a black hole would be due to the surrounding matter, not the black hole itself. There are also alternatives to general relativity where the no-hair theorem doesn’t apply, so there might be a way to use this to distinguish general relativity from other models.

For now, though, we know that for black holes it really is that simple.

Paper: Norman Gürlebeck. No-Hair Theorem for Black Holes in Astrophysical Environments. Phys. Rev. Lett. 114, 151102 (2015)
The no hair theorem for black holes is found to apply even when they are surrounded by matter.
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From Heaven to Earth

No matter where you go, there you are. Determining where “there” is, however, is another matter.

On Earth we can define our position by three parameters: latitude, longitude, and elevation. Latitude is the angular position that defines how far north or south you are from the equator. Elevation is your height above or below the average level of the oceans. Longitude is your angular position along the equator, relative to some point, which is now Greenwich, England. If you’re navigating at some point along the surface the world, latitude and longitude are the most important things to know.

Latitude is fairly straightforward to determine. As the Earth rotates on its axis, the stars in the night sky appear to revolve around a fixed point in the sky, known as the celestial poles. In the northern hemisphere that point is fairly close (off by only 1°) to the second magnitude star Polaris, so by measuring the angle of Polaris relative to the horizon, you can get a good idea of your latitude. In the southern hemisphere there isn’t a bright star nearby, but you can use the Magellanic clouds to triangulate the south celestial pole.

While careful measurement of the stars can give a very accurate measure of latitude, it isn’t something easily done at sea. So instead, latitude was determined using a sextant to measure the angular position of the Sun at local noon, when it is highest in the sky. As long as it is a clear day, measuring the angle of the Sun is quite easy. The catch is that unlike the celestial poles, the angular height of the Sun at noon varies with the seasons. So you also need to know the date and have a table (or do the trigonometric calculation) that tells you the latitude at which the Sun would pass directly overhead that day. By taking this into account, you can then determine your latitude.

Longitude, however, is another matter. For one, unlike latitude it is reckoned relative to an arbitray point. We use Greenwich, England, but we could just as easily use Poughkeepsie, New York. For another, there is no simple way to use the Sun or stars to determine longitude. Given the importance of longitude, lots of methods have been proposed over the years, but until recently one of the more accurate methods was to use the moons of Jupiter.

When Galileo discovered four moons of Jupiter in the early 1600s, he noticed that their motions followed Kepler’s laws. This clockwork precision meant that the Jovian system could be used as a “heavenly clock” to determine the time. One way this could be done was by observing when the moons entered-or-exited the shadow of Jupiter as they passed behind the giant planet. Even with a small telescope, one could observe a moon fade to darkness over the course of a few minutes as it entered the shadow, or gradually brighten as it left the shadow on the other side.

With a table listing the predicted times of these eclipses as seen from a particular observatory, one could know the exact local time at that observatory. By comparing that with the time that you measured your local noon to be, you could then determine the time difference between your location and the observatory. Knowing that the Earth rotates 360 degrees in a day, you could then determine your longitude relative to the observatory.

Galileo went so far as to calculate time tables for these eclipses, but they weren’t accurate enough to be very useful. Then in 1668 Giovanni Domenico Cassini published the first truly accurate table of Galilean eclipses. Cassini’s tables were so accurate that they redefined the shape of Europe. The distances between cities as given since the Roman Empire were found to be hundreds of kilometers off. You can see this in the maps of Europe before and after Cassini’s tables.

Despite its accuracy, the Galilean method of longitude had some serious drawbacks. There are times when Jupiter is too close to the Sun for the moons to be observed, and the method was completely useless while at sea. By the late 1700s John Harrison’s marine chronometer became the preferred method for calculating longitude at sea, but well into the 1800s Galileo’s method was preferred for land explorers. Chronometers were both expensive and fragile, so a small telescope was the preferred tool.

Modern methods have now replaced Galileo’s moons as a method of calculating longitude, but the moons of Jupiter were a huge step forward that quite literally changed the face of the world.
Determining your position on Earth used to be an astronomical problem, and the discovery of Jupiter's moons made that task much easier.
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Origin.The ancient Egyptian name,Meri-Amun,meaning "beloved of the sun god Amun"when adopted by the Isralites was recorded in the bible as Miriam.The sister of the famous Moses who led the Isralites to the promised land of Canaan was called Miriam.The Latin adopted the name as Maria which form appears in most Western European languages.Mary is the English Bible Version.The Ethiopia versions Maryam and Mariam unlike in Europe where it is a female baptisimal name have been used as patronymics/surnames for ages.Some examples of well known Ethiopians with the patronymic are;Emporor Takla Maryam(1430-1433) of the Solomonic Dynasty,Emporor Baeda Maryam (1468-1478) and more recently Mengistu Haile Mariam who was head of state between 1977 and 1991.And the current Ethiopian Prime Minister HailleMariam Desalegn.The introduction of the name to giküyüland(Central Kenya)came about either in the late 1700s or early 1800s during the period in Ethiopian history reffered to as Zamana Masafint or" Era of the Prince" when there was protracted conflicts between the many claimants of the seat of the emporor populary known as the king of kings(Nègusa Nagäst)Among the group of royals who escaped the terror of Ras Sehul the powerful Tigrean Warlord were several women with the title Waizero.One of the women,escorted by some men among them Kassa and Tefere reached an area now known as Dagorreti and settled there.The woman was carrying a boy whose name was Mariam which the Agiküyü adopted as Miríí.Though Waizero was a title(Married Woman or the equivalent of Dame in the court titles of Ethiopian Nobility) the Agiküyü were not to know that and they called her Waithera,so,the boy grew up to be known as Miríí wa Waithera and is the originator of the family by the name Mbari ya Mirie.The boy is my anscestor and it is partly the reason why I have a fairer skin color than most kikiyus.
Bragging rights
Able to relate to matters of science while lifting weights.I know a thing or two about the origin of the universe and at my weight of 152lbs(70 Kgs) My PB deadlift is 330lbs(150 Kgs) and I am aiming a bit higher than that.
Basic Information
Gender
Male