Why did the last 8 glacial periods only end when the earth's orbit around the sun reached maximum eccentricity ? This is the real unsolved mystery of the Ice Ages as discussed in previous posts and recently on The Science of Doom.

1. Phenomenology of Ice Ages
2. What causes interglacials - part 1
3. Part 2: The real cause of interglacials - Resonant dust clouds

With the last of these posts I finally thought there could be a solution to this mystery based on resonant interplanetary dust, but alas I could find no evidence whatsoever in TSI data and dismissed the idea. However I now realise that perhaps there is another solution which may have been looking us in the face all the time. The Earth already has a large resonant interplanetary body - the moon. There is no need to invent some hypothetical resonant dust. The trigger for interglacials is not changes in insolation but instead changes in tidal forces acting on the oceans and cryosphere. Every 100,000 years super-tides must occur whenever the decreased perihelion distance of the earth from the sun and the moon coincide and are synchronised with maximum eccentricity. These tidal forces combined with already known increases in insolation could well be the trigger that initiates the rapid break up and melting of the northern glaciers.

The 100,000 and 400,000 year cycles in the ellipticity of the Earth's orbit are caused by regular gravitational effects of the other planets as they orbit the sun, particularly those of Jupiter and Saturn. Every 100,000 years the orbits of Jupiter and Saturn align themselves so that their net gravity perturbs the Earth's orbit causing it to elongate and become more elliptical. This cycle reaches a maximum every 400,000 years in regular fashion.

The moon also is effected by the same regular (Milankovitz) induced variation in its orbit around the sun. This also causes an increased elliptical orbit of the moon around the Earth. Tidal forces vary as 1/r^3 so small changes in distance can have large effects on tides.

The gravitational force of the sun on the moon is more than twice that of the Earth. For an observer in outer space the moon appears to orbit the sun just like any other planet. It's orbit is perturbed by the Earth's gravity making it slightly concave. It is only from Earth that it appears to us to be in an elliptical orbit around the Earth.

Scientists searched a corner of the Internet for evidence of time travel into the past. They found no evidence that this fantastical form of travel exists.

Time travel into the future is physically possible: Einstein's theory of special relativity predicts that the time between two events is slower for faster-moving objects. This has been experimentally proven by measuring clocks on commercial planes. But time travel into the past is trickier.

Although many scientists have proposed the possibility of time travel into the past using the equations and concepts of Einstein's subsequent theory of general relativity, few scientists have conducted experiments to test these theories.

This is because the theories include mysterious concepts like wormholes and cosmic strings. Scientists have yet to confirm these things exist at all, let alone prove that they enable time travel into the past. But this is not for lack of trying.

One of the few experimental studies that has searched for evidence of time travelers from the future includes a party hosted by the famous physicist Stephen Hawking.

Finally, some good news for men, as a new study in PLOS Genetics has found that the human race may not be losing the Y chromosome after all. Some popular theories have posited that the male sex chromosome is destined to diminish and disappear.

"The Y chromosome has lost 90 percent of the genes it once shared with the X chromosome, and some scientists have speculated that the Y chromosome will disappear in less than 5 million years," said study author Melissa A. Wilson Sayres, a post-doctoral evolutionary biologist at the University of California, Berkeley.

Some mammal species have lost their Y chromosome, yet still have the ability to sexually reproduce viable offspring - fueling suspicions that the chromosome may not be essential in humans.

"Our study demonstrates that the genes that have been maintained, and those that migrated from the X to the Y, are important, and the human Y is going to stick around for a long while," Wilson Sayres said.

Based the Y chromosome analysis of 16 men, researchers found genetic evidence of natural selection maintaining the chromosome's content, which has been shown to mostly play a role in male fertility. The researchers said the Y chromosome's diminutive size is a sign that it is stripped down to its 27 essential genes.

In 2009, a biologist named Daniel Gluesenkamp was driving through San Francisco when he saw a ghost. Draped over a bluff by the side of the road was a twenty-foot wide shrub festooned with cream-colored flowers. Gluesenkamp immediately recognized the plant as Franciscan manzanita, or Arctostaphylos hookeri franciscana. He was astonished, because it had been considered extinct in the wild for decades. The last known wild Franciscan manzanita had been bulldozed in a graveyard in 1947.

Before 1947, a few clippings of Franciscan manzanita had ended up in nurseries. Today you can buy the plant online. But the nursery form is the result of hybridization and extreme breeding; it's now about as much like wild Franciscan manzanita as a German shepherd is like a wolf. It's unlikely it could survive in the wild anymore. For thousands of years, wild Franciscan manzanita had grown luxuriantly in the prairies that carpeted much of the California coast. Now the wild plants were all gone - or almost, it turned out.

Before Gluesenkamp's discovery, the U.S. government officially listed Franciscan manzanita as extinct in the wild. But then three organizations - the Wild Equity Institute, Center for Biological Diversity, and California Native Plant Society - petitioned the U.S. government to change its status. In 2012, the Fish and Wildlife Service agreed to the request and reclassified Franciscan manzanita from extinct to endangered. Its known wild population was precisely one.

This wasn't exactly the original plan for the Endangered Species Act when it was enacted in 1973. It was intended to protect species that were moving in the other direction, from healthy populations towards extinction. But once the single wild Franciscan manzanita plant came to light, the government decided that it deserved protection, too.

One of the more interesting questions in astronomy surrounds how solar system objects actually form. Astronomers are particularly concerned about the boundary between a planet and a star. When examining the objects in our own solar neighborhood, the question seems trivial - the Sun dominates the mass of our system, while even the largest planet, Jupiter, is dwarfed by comparison.

In other parts of the galaxy, stars exist that are only a tiny fraction of the size of our Sun, yet scientists have discovered planets that are many times larger than Jupiter. At around a dozen Jupiter-masses, the line between star and planet begins to blur, and astronomers refer to these objects as brown dwarfs.

They are massive enough that simple proton-proton fusion exists in their cores, yet the energy produced by this mechanism is not sufficient enough to sustain it as a star. For this reason brown dwarfs are sometimes also known as failed stars. However, new data is complicating their classification even further.

Located about 440 light-years from Earth is a strange object that has the properties of a brown dwarf. However, a careful study of its mass indicates that it is not massive enough to be categorized as such.

Religion and astronomy may not overlap often, but a new NASA X-ray image captures a celestial object that resembles the "Hand of God."

The cosmic "hand of God" photo was produced when a star exploded and ejected an enormous cloud of material, which NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, glimpsed in high-energy X-rays, shown in blue in the photo. NASA's Chandra X-ray Observatory had imaged the green and red parts previously, using lower-energy X-rays.

"NuSTAR's unique viewpoint, in seeing the highest-energy X-rays, is showing us well-studied objects and regions in a whole new light," NuSTAR telescope principal investigator Fiona Harrison, of the California Institute of Technology in Pasadena, said in a statement.

The new image depicts a pulsar wind nebula, produced by the dense remnant of a star that exploded in a supernova. What's left behind is a pulsar, called PSR B1509-58 (B1509 for short), which spins around 7 times per second blowing a wind of particles into material ejected during the star's death throes.

A new study has found that radioactive particles from nuclear tests that took place decades ago persist in the upper atmosphere.

Previously, scientists believed that nuclear debris found high above the Earth would now be negligible.

However, this research shows that plutonium and caesium isotopes are still present at surprisingly high concentrations, the BBC reported.

Lead author Dr Jose Corcho Alvarado, from the Institute of Radiation Physics at Lausanne University Hospital in Switzerland, said that most of the radioactive particles are removed in the first few years after the explosion, but a fraction remains in the stratosphere for a few decades or even hundreds or thousands of years.

However, he said that the levels were not high enough to pose a risk to human health.

At the height of the Cold War, when the nuclear arms race was in full swing, weapons were being developed and tested around the world.

But more than 50 years on, their radioactive legacy remains.

Astronomers have a front-row seat to observe a mysterious gas cloud spiraling toward our galaxy's supermassive black hole.

University of Michigan astronomers could be the first to witness a rare collision expected to happen at the center of our galaxy by spring.

With NASA's orbiting Swift telescope, the University of Michigan team is taking daily images of a mysterious gas cloud about three times the mass of Earth that's spiraling toward the supermassive black hole at the Milky Way's core. From our vantage point, the core lies more than 25,000 light-years away in the southern summer sky near the constellations Sagittarius and Scorpius.

In 2011, German astronomers discovered a gas cloud called G2. They expected it to hit the black hole called Sagittarius A* (pronounced "Sagittarius A-star") late last year. That didn't happen, but the cloud continues to drift closer. Astronomers now predict that the impact will occur in the next few months.

Astronomers have never seen anything like this, much less with a front-row seat.

"Everyone wants to see the event happening because it's so rare," said Nathalie Degenaar from the Department of Astronomy at the College of Literature, Science and the Arts.

Students in a University of Maryland undergraduate astronomy class have made a startling discovery. A previously unstudied asteroid isn't just one object, but is instead made up of a pair of asteroids that orbit and regularly eclipse each other. The rare discovery may help researchers investigate these sorts of asteroids in the future.

So far, fewer than 100 eclipsing binary asteroids have been identified in the main asteroid belt between Mars and Jupiter. This latest discovery, known as 3905 Doppler, is therefore unusual. It was first detected in 1984, but over the next few decades, it attracted scant attention. Then in September 2013, the students chose to study it due to its position in the autumn sky.

Aciculate peaks and curvilinear ridges outline giant circular depressions in the French Alps.

As previously written, stone monoliths can be found all over the world. There are colossal formations that make up the French Alps, for instance. In particular, Mont Aiguille (Needle Mountain) is similar to the structures from the Amazonian region of South America that were discussed in another Picture of the Day.

Flat-topped mesas are common throughout Europe, the southwestern United States, the Amazon, and elsewhere. Arizona's Monument Valley includes elevations that almost exactly mirror those found in the Alps, although they are composed of different rock matrices. Those in Arizona are sandstone tors with sharply delineated sidewalls and those in the French Alps, such as Mont Aiguille, are composed of limestone.