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- A Complete Guide to the March 20th Total Solar Eclipse
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Posted: 12 Mar 2015 08:05 PM PDT
Posted: 12 Mar 2015 08:05 PM PDT
Excerpt from universetoday.com
The first of two eclipse seasons for the year is upon us this month, and kicks off with the only total solar eclipse for 2015 on Friday, March 20th.
And what a bizarre eclipse it is. Not only does this eclipse begin just 15 hours prior to the March equinox marking the beginning of astronomical spring in the northern hemisphere, but the shadow of totality also beats path through the high Arctic and ends over the North Pole.
Already, umbraphiles — those who chase eclipses — are converging on the two small tracts of terra firma where the umbra of the Moon makes landfall: the Faroe and Svalbard islands. All of Europe, the northern swath of the African continent, north-central Asia and the Middle East will see a partial solar eclipse, and the eclipse will be deeper percentage-wise the farther north you are .
2015 features four eclipses in all: two total lunars and two solars, with one total solar and one partial solar eclipse. Four is the minimum number of eclipses thatcan occur in a calendar year, and although North America misses out on the solar eclipse action this time ’round, most of the continent gets a front row seat to the two final total lunar eclipses of the ongoing tetrad on April 4th and September 28th.
How rare is a total solar eclipse on the vernal equinox? Well, the last total solar eclipse on the March equinox occurred back in 1662 on March 20th. There was also a hybrid eclipse — an eclipse which was annular along a portion of the track, and total along another — on March 20th, 1681. But you won’t have to wait that long for the next, as another eclipse falls on the northward equinox on March 20th, 2034.
The path of the March 20th eclipse across Europe, including start times for the partial phases, and the path of totality, click to enlarge. For more maps showing the percentage of occlusion, elevation, and more, click here. Credit: Michael Zeiler/GreatAmercianEclipse.
The March 20th eclipse also occurs only a day after lunar perigee, which falls on March 19th at 19:39 UT. This is also one of the closer lunar perigees for 2015 at 357,583 kilometres distant, though the maximum duration of totality for this eclipse is only 2 minutes and 47 seconds just northeast of the Faroe Islands.
This eclipse is number 61 of 71 in solar saros series 120, which runs from 933 to 2754 AD. It’s also the second to last total in the series, with the final total solar eclipse for the saros cycle occurring one saros later on March 30th, 2033.
What would it look like to sit at the North Pole and watch a total solar eclipse on the first day of Spring? It would be a remarkable sight, as the disk of the Sun skims just above the horizon for the first time since the September 2014 equinox. Does this eclipse occur at sunrise or sunset as seen from the pole? It would be a rare spectacle indeed!
Safety is paramount when observing the Sun and a solar eclipse. Eye protection is mandatory during all partial phases across Europe, northern Asia, North Africa and the Middle East. A proper solar filter mask constructed of Baader safety film is easy to construct, and should fit snugly over the front aperture of a telescope. No. 14 welder’s goggles are also dense enough to look at the Sun, as are safety glasses specifically designed for eclipse viewing. Observing the Sun via projection or by using a pinhole projector is safe and easy to do.
Weather is always the big variable in the days leading up to any eclipse. Unfortunately, March in the North Atlantic typically hosts stormy skies, and the low elevation of the eclipse in the sky may hamper observations as well. From the Faroe Islands, the Sun sits 18 degrees above the horizon during totality, while from the Svalbard Islands it’s even lower at 12 degrees in elevation. Much of Svalbard is also mountainous, making for sunless pockets of terrain that will be masked in shadow on eclipse day. Mean cloud amounts for both locales run in the 70% range, and the Eclipser website hosts a great in-depth climatology discussion for this and every eclipse.
But don’t despair: you only need a clear view of the Sun to witness an eclipse!
Solar activity is also another big variable. Witnesses to the October 23rd, 2014 partial solar eclipse over the U.S. southwest will recall that we had a massive and very photogenic sunspot turned Earthward at the time. The Sun has been remarkably calm as of late, though active sunspot region 2297 is developing nicely. It will have rotated to the solar limb come eclipse day, and we should have a good grasp on what solar activity during the eclipse will look like come early next week.
And speaking of which: could an auroral display be in the cards for those brief few minutes of totality? It’s not out of the question, assuming the Sun cooperates. Of course, the pearly white corona of the Sun still gives off a considerable amount of light during totality, equal to about half the brightness of a Full Moon. Still, witnessing two of nature’s grandest spectacles — a total solar eclipse and the aurora borealis — simultaneously would be an unforgettable sight, and to our knowledge, has never been documented!
We also put together some simulations of the eclipse as seen from Earth and space:
Note that an area of southern Spain may witness a transit of the International Space Station during the partial phase of the eclipse. This projection is tentative, as the orbit of the ISS evolves over time. Be sure to check CALSky for accurate predictions in the days leading up to the eclipse.
The ISS transits the Sun during the eclipse around 9:05 UT as seen from southern Spain. Credit: Starry Night.
Posted: 12 Mar 2015 07:45 PM PDT
Determining exactly when humans began wearing clothes is a challenge, largely because early clothes would have been things like animal hides, which degrade rapidly. Therefore, there’s very little archaeological evidence that can be used to determine the date that clothing started being worn.
There have been several different theories based on what archaeologists have been able to find. For instance, based on genetic skin-coloration research, humans lost body hair around one million years ago—an ideal time to start wearing clothes for warmth. The first tools used to scrape hides date back to 780,000 years ago, but animal hides served other uses, such as providing shelter, and it’s thought that those tools were used to prepare hides for that, rather than clothing. Eyed needles started appearing around 40,000 years ago, but those tools point to more complex clothing, meaning clothes had probably already been around for a while.
All that being said, scientists have started gathering alternative data that might help solve the mystery of when we humans started covering our bits.
A recent University of Florida study concluded that humans started wearing clothes some 170,000 years ago, lining up with the end of the second-to-last ice age. How did they figure that date out? By studying the evolution of lice.
Scientists observed that clothing lice are, well, extremely well-adapted to clothing. They hypothesized that body lice must have evolved to live in clothing, which meant that they weren’t around before humans started wearing clothes. The study used DNA sequencing of lice to calculate when clothing lice started to genetically split from head lice.
The findings of the study are significant because they show that clothes appeared some 70,000 years before humans started to migrate north from Africa into cooler climates. The invention of clothing was probably one factor that made migration possible.
This timing also makes sense due to known climate factors in that era. As Ian Gilligan, a lecturer at the Australian National University, said that the study gave “an unexpectedly early date for clothing, much earlier than the earliest solid archaeological evidence, but it makes sense. It means modern humans probably started wearing clothes on a regular basis to keep warm when they were first exposed to Ice Age conditions.”
As to when humans moved on from animal hides and into textiles, the first fabric is thought to have been an early ancestor of felt. From there, early humans took up weaving some 27,000 years ago, based on impressions of baskets and textiles on clay. Around 25,000 years ago, the first Venus figurines—little statues of women—appeared wearing a variety of different clothes that pointed to weaving technology being in place by this time.
From there, more recent ancient civilizations discovered many materials they could fashion into clothing. For instance, Ancient Egyptians produced linen around 5500 BC, while the Chinese likely started producing silk around 4000 B.C.
As for clothing for fashion, instead of just keeping warm, it is thought that this occurred relatively early on. The first example of dyed flax fibers were found in a cave in the Republic of Georgia and date back to 36,000 years ago. That being said, while they may have added colour, early clothes seem to have been much simpler than the clothing we wear today—mostly cloth draped over the shoulder and pinned at the waist.
Around the mid-1300s in certain regions of the world, with some technological advances in previous century, clothing fashion began to change drastically from what it was before. For instance, clothing started to be made to form fit the human body, with curved seams, laces, and buttons. Contrasting colours and fabrics also became popular in England. From this time, fashion in the West began to change at an alarming rate, largely based on aesthetics, whereas in other cultures fashion typically changed only with great political upheaval, meaning changes came more slowly in most other cultures.
The Industrial Revolution, of course, had a huge impact on the clothing industry. Clothes could now be made en mass in factories rather than just in the home and could be transported from factory to market in record time. As a result, clothes became drastically cheaper, leading to people having significantly larger wardrobes and contributing to the constant change in fashion that we still see today.
Posted: 12 Mar 2015 07:07 PM PDT
Excerpt from latimes.com
Astronomers have found the most conclusive evidence yet that a large watery ocean lies beneath the surface of Jupiter's moon Ganymede.
Scientists have suspected for decades that a subterranean ocean might slosh between the rocky mantle and icy crust of the largest moon in our solar system, but they had not been able to prove it definitively until now.
"The solar system is now looking like a pretty soggy place," said Jim Green, director of planetary science at NASA. "The more we look at individual moons, the more we see that water is really in enormous abundance."
Ganymede is the only moon in the solar system that has its own magnetic field. However, it is also affected by the magnetic field of Jupiter - the giant planet next door.
The effect of Jupiter's magnetic field on Ganymede changes every 10 hours, which is the length of time it takes the planet to make a full rotation on its axis. For five hours its magnetic field points toward Ganymede, then for another five hours it points away.
"It's like a lighthouse," said Joachim Saur of the University of Cologne in Germany, who led the research.
Saur figured that these regular shifts in Jupiter's magnetic field would affect the position of the aurorae in Ganymede's atmosphere differently depending on whether or not the moon has a subsurface ocean.
A natural color view of Ganymede from the Galileo spacecraft, during its first encounter with the satellite, is shown.
The reason for the difference is that a saltwater ocean is electrically conductive and creates a secondary magnetic field that would suppress the effects of Jupiter's magnetic field.
Saur looked at measurements taken by the Hubble Telescope in 2010 and 2011 of auroras over both the north and south poles of Ganymede and saw that the auroras only moved two degrees over a seven-hour period.
"We ran more than 100 models on supercomputers with different parameters, but every time we got the same result - with no ocean present the aurorae rock by six degrees, if you add an ocean it reduces the rock to two degrees," Saur said at a news conference Thursday announcing the findings.
The new technique of looking to aurorae for signs of a liquid ocean could lead to discoveries of water on bodies far beyond our solar system, researchers say.
A telescope larger than Hubble may be required to observe distant aurorae, but "now we have a tool that we didn't have before," she said.
Posted: 12 Mar 2015 06:53 PM PDT
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