BLUE MOON - What Is a Blue Moon?

What Is a Blue Moon?:

Night sky watcher Tomsajinsa sent in this photo of the blue moon taken in NYC, August 31, 2012.

Credit: Tomsajinsa


A Blue Moon is a fairly infrequent phenomenon involving the appearance of an additional full moon within a given time period. But which time period — there are two definitions of the term, and one was borne out of a misunderstanding of the other.

The older meaning defines a Blue Moon as the third full moon in a season that has four full moons. This kind of Blue Moon occurs about every 2.7 years. Why the third moon? Seasons normally have three full moons, and some of them, for traditional and religious reasons, must occur at specific times of the year. So, the "Moon Before Yule" is always the one before Christmas.

The other meaning is that a Blue Moon is the second full moon within a single calendar month. This definition has gained popularity in recent years because of a misinterpretation of an almanac's original definition.

Which one is correct? Well, since language and the meaning of words constantly evolve — take your pick. Both are commonly used today.

By the newer definition, there is a Blue Moon on Saturday, May 21, 2016. The online Slooh Community Observatory will offer a free live webcast of the May full moon beginning at 8 p.m. EDT (0000 GMT). You can follow the Slooh webcast at Slooh.com. You can also watch the Blue Moon webcast on Space.com here, courtesy of Slooh.

By the way, Blue Moons are not typically blue in color — that happens only, well, once in a blue moon, but there is the possibility for a hint of blue in any full moon (more on this below).

Origin of the term

The phrase "once in a blue moon" has been around for more than 400 years, according to Philip Hiscock, a folklorist at the Memorial University of Newfoundland. In a 2012 article in Sky & Telescope magazine, he explained that the earliest use of term was much like saying the moon is made of green cheese — it indicated something absurd. "He would argue that the moon is blue" was similar to saying, "He would argue that black is white."

The meaning evolved to something akin to "never," according to Hiscock. "I'll marry you when the moon turns blue" became the equivalent of "I'll marry you when pigs fly."

But, never say never. It turns out that the moon can appear bluish, as it did in 1883 after the volcano Krakatoa erupted. Dust in the air acted as a filter, causing sunsets and the moon to turn green and blue all over the world. Other events such as forest fires and dust storms can cause the moon to turn blue.

So, the meaning of "once in a blue moon" changed from "never" to "rarely," according to Hiscock.

When does a Blue Moon occur?

Now we get to the contradictory definitions of "Blue Moon."

The calendrical meaning for the term "Blue Moon" has been traced back to the now-defunct Maine Farmer's Almanac as far back as the mid-1800s. On the page for August 1937, the almanac explained that the moon "usually comes full 12 times in a year, three times for each season. Occasionally, however, there will come a year when there are 13 full moons during a year, not the usual 12. And that extra full moon also meant that one of the four seasons would contain four full moons instead of the usual three."

The almanac followed certain rules for what to call each moon. For example, the last full moon of winter had to fall during Lent; it was called the Lenten Moon. The first full moon of spring was called the Egg Moon — or Easter Moon, or Paschal Moon — and had to fall within the week before Easter. There was also the Moon Before Yule and the Moon After Yule.

So when a particular season had four moons, the third was dubbed a "Blue Moon," so that the other full moons could occur at the proper times relative to the solstices and equinoxes.

Second definition

But what about the definition that many people have heard — that a Blue Moon is the second full month in a single month? That came from a misinterpretation of the original definition.

In the Sky & Telescope article, Hiscock helped figure out where this meaning came from. He explained that in a question-and-answer column from the July 1943 issue of Sky & Telescope, writer Lawrence J. Lafleur referenced the Maine Farmer's Almanac definition. LaFleur correctly quoted the almanac's account, but he made one important omission: He never specified any dates for the Blue Moon.

In 1946, James Hugh Pruett, an amateur astronomer, was writing in Sky & Telescope magazine and repeated some of LaFleur's comments. Pruett made an incorrect assumption about how the term had been used in the almanac, according to Hiscock. Pruett wrote, "Seven times in 19 years there were — and still are — 13 full moons in a year. This gives 11 months with one full moon each and one with two. This second in a month, so I interpret it, was called Blue Moon." Hiscock explained that Pruett must not have had the 1937 almanac handy, or he would have noticed that the Blue Moon fell on August 21st (obviously not the second full moon that month) and that 1937 had only 12 full moons.

Sky & Telescope adopted Pruett's new definition, and the column was used as a source for a nationally syndicated radio program in 1980, which, according to Hiscock, is when this definition gained widespread use.

Today, either definition of "Blue Moon" is considered valid. As Texas astronomer Donald W. Olson wrote in a 2006 column for the magazine, "With two decades of popular usage behind it, the second-full-moon-in-a-month (mis)interpretation is like a genie that can't be forced back into its bottle. But that's not necessarily a bad thing."

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ASTRONOMY - Discover the Treasures of Hercules with Mobile Astronomy Apps

Discover the Treasures of Hercules with Mobile Astronomy Apps:

The spring and summer constellation of Hercules is easily located between the bright stars Vega and Arcturus, immediately south of the northerly constellation of Draco the Dragon. The area of sky above the plane of the Milky Way contains a number of globular clusters.

Credit: SkySafari for Android and iOS


At the end of May, the summer constellations are moving into view for evening stargazers. In this edition of mobile astronomy, we'll showcase one of my favorites — mighty Hercules!

This easily recognizable constellation features interesting folklore, some lovely double stars within reach of backyard telescopes and one of the deep sky's best showpieces for amateur astronomers. Your favorite astronomy app can help you find the treasures within Hercules and tell you all about them.

Getting oriented

Hercules doesn't contain any very bright stars, but you can use your sky-charting app to find it very easily. As the sky darkens in late May, look low in the eastern sky for a very bright blue-white star. That's Vega, the brightest star in the small constellation of Lyra. Higher, and to the south, is another prominent star: orange Arcturus. Between these two stellar signposts is the realm of mighty Hercules. [Stunning Photos of Our Milky Way Galaxy (Gallery)]

The spring and summer constellation of Hercules is easily located between the bright stars Vega and Arcturus, immediately south of the northerly constellation of Draco the Dragon. The area of sky above the plane of the Milky Way contains a number of globular clusters.

Credit: SkySafari for Android and iOS


Hercules' body is defined by a very distinctive keystone-shaped quartet of modestly bright stars. The keystone is about 6 degrees across (a palm's width), with the wide end to the north and the narrow end to the south. The hero of mythology is upside down for Northern Hemisphere observers. His sharply bent legs extend northward, and his two arms are outstretched to the southeast and southwest. The star marking his left hand (to the lower left) combines with four others to form a loose chain of five stars running left to right, each separated by a couple of finger widths. In classical drawings, Hercules is grasping the three-headed dog Cerberus, which he was tasked with capturing as one of his 12 labors.

Hercules is the fifth-largest constellation as measured by area, and was one of the original 48 constellations tabulated in the "Almagest," an early astronomy treatise produced in ancient Greece by Ptolemy. The early Greeks depicted Hercules with his legs bent — "The Kneeler" praying to his father, Zeus, to aid him in an upcoming battle. Below his feet, to the north, are the stars of Draco the Dragon, ready to be crushed underfoot. To the southwest is the little circle of stars that form the constellation of Corona Borealis, the Northern Crown.

Hercules and its treasures will be in the night sky from now until early autumn. Let's take a look at some of the best objects within the constellation.

For Northern Hemisphere observers, Hercules is inverted. In this reoriented original plate from Johann Bayer's 1603 "Uranometria Sky Atlas," Hercules is shown with bent legs, a raised club and flowers. In Johannes Hevelius' "Firmamentum Sobiescianum" star atlas of 1690, he's holding the three heads of Cerberus.

Credit: SkySafari for Android and iOS

Seeing stars in Hercules

Hercules contains quite a few double and binary stars within reach ofthat can be viewed with a backyard telescope. One of the nicest is modest Rasalgethi, or Ras Algethi ("Head of the Kneeler"), which sits about 16 degrees to the southwest (lower right) of the bottommost corner of the keystone. In a small telescope, this star easily splits into a lovely pair of orange and greenish stars. The slightly brighter one is a red-giant-class star that varies in brightness randomly over months to years. The partner is a yellow, sun-like star that is itself a binary star too tightly spaced to resolve. The stars are about 360 light-years away and are orbiting one another witha period of 3,600 years. This double star, like many others, was given a single name centuries before telescopes revealed that there was more than one star there.

The brightest star in Hercules, Kornephoros ("the club bearer"), sits just below Corona Borealis. Only 3 degrees (about two finger widths) to its right is the double star Gamma (γ) Herculis. This is another pair that easily splits into two yellow stars in a modest telescope. But this double is an optical illusion; the fainter star is actually much closer to us! [Jupiter, Virgo Cluster and More: May 2016 Skywatching Video]

Marsic ("the Elbow"), or Kappa (κ) Herculis, is another "line of sight" double star that's easy to spot in a small telescope. It's not far from Gamma Herculis. I'll leave it to you to track it down using your sky-charting app.

Only a few stars of Hercules were prominent enough for proper names. The others bear the Greek letter designations of Bayer's system. Deep-sky objects are represented by symbols. On your app, tap a symbol to call up details about that object.

Credit: SkySafari for Android and iOS

Globular Cluster Messier 13

Hercules contains one of my favorite objects, a globular cluster known as the Great Hercules Cluster or Messier 13 (M13). This object is a tightly packed ball of about 300,000 old stars. At magnitude 5.9, it is visible with unaided eyes under dark skies as a faint smudge, but reveals much more under magnification. M13 is located along the western (right) edge of the keystone, about one-third of the way from the wide end. Midway between Hercules' knees, there is another, smaller globular cluster called Messier 92. This one is also readily visible in binoculars. A third, fainter globular cluster, designated NGC 6229, is 6.5 degrees, or a palm's width, above M92.

Globular clusters are one of the most interesting classes of objects for amateur astronomers. These spherical concentrations of old, densely packed stars orbit in the region just outside our Milky Way galaxy, and we've observed many of them around other galaxies, including the Andromeda Galaxy. In a telescope under dark skies, they will appear similar to a pile of salt poured onto black velvet, with a dense, white center surrounded by a sprinkling of outlying stars. Each one looks different, varying in the scattering of stars. Photographs reveal that these objects contain a mixture of reddish, blue and yellow stars in different proportions.

The Great Hercules Globular Cluster was first observed by British astronomer Edmond Halley in 1714 and was later included as No. 13 in Charles Messier's famous list of noncometary objects. The cluster is relatively close, at 21,500 light-years away, making it a bright magnitude 5.8, and it actually covers an area of sky 20 arc-minutes across. That's about two-thirds of the moon's diameter! [The Moon: 10 Surprising Lunar Facts]

More than 150 of these clusters have been mapped around our galaxy. They are so densely packed that the stars in their interiors are extremely close together, stirring the imagination of those contemplating extraterrestrial intelligent life. Advanced civilizations around stars deep in a globular cluster would be able to exchange radio messages on timescales of weeks or months — and travel between adjacent solar systems would not require the decades or centuries we would need to visit our nearest neighbors. In fact, M13 was also one of the first targets for potential contact with other civilizations, when a radio message was beamed there from the Arecibo Observatory in Puerto Rico in 1974.

Your astronomy app lists these objects under the Deep Sky category. In the SkySafariand Stellariumapps, they are displayed using a crosshatched circle. In Star Walk 2,they are rendered as fuzzy patches. (All three apps are available for iOS and Android.) Ensure that your app has the deep-sky object display enabled as you tour around the night sky all summer, especially from more remote locations.

Depending on your app, you may need to enlarge the constellation for the symbols to appear. SkySafari has an option to show objects even in wide fields. As the Milky Way climbs overhead in the summer months, many globular clusters are distributed on both sides of it. How many can you spot?

The great Globular Cluster of Hercules, also known as Messier 13 (or M13), is a large and bright spherical cluster of old stars that is readily seen with unaided eyes away from city lights. A telescope reveals the salt-spilled-on-velvet appearance.

Credit: Wikipedia

Going beyond

The figures that constellations depict are unique to our vantage point on Earth. Each star lies at a different distance from the sun, and if we could travel to another star, the shape of the constellations would change.

You can try this for yourself. In the SkySafari app, search for Proxima Centauri, the nearest star to the sun. Tap the Orbit icon, and the app will fly you there. Once there, you can use the search option to find Hercules and center it. The shape will become quite a bit different! A tap on the Globe icon flies you home again, but while you're out there, try looking at some other familiar constellations. Some will be completely unrecognizable. The Star Walk 2 app allows you to select a constellation and rotate it in 3D. You may have to purchase the additional content pack to use it.

The stars of Hercules host at least 15 known exoplanets, including TrES-4, whose mass is 1.7 times that of Jupiter and is one of the biggest alien worlds ever discovered. However, its calculated density is extremely low — about that of cork! This is one of the "hot Jupiter" class of exoplanets, with a surface temperature in excess of 2,750 degrees Fahrenheit (2,000 degrees Celsius). There a number of exoplanet apps for iOS and Android, including the free Exo Planets Explorer 3Dfor Android and Exoplanet for iOS.

In future editions of mobile astronomy, we'll look at photographing objects with your smartphone, some cool astronomy virtual-reality apps and hardware, how to use astronomy apps in the classroom, and more. Until then, keep looking up!

Editor's note: Chris Vaughan is an astronomy public outreach and education specialist, and operator of the historic 1.88-meter David Dunlap Observatory telescope. You can contact him by email, and follow him on Twitter @astrogeoguy, as well as Facebook and Tumblr.

This article was provided by Simulation Curriculum, the leader in space science curriculum solutions and the makers of the SkySafari app for Android and iOS. Follow SkySafari on Twitter @SkySafariAstro. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.

ALIENS - Alien Megastructure? Kickstarter Campaign Launched to Study 'Tabby's Star'

Alien Megastructure? Kickstarter Campaign Launched to Study 'Tabby's Star':

Artist's illustration showing fragments of a shattered comet passing in front of a star, perhaps the best explanation for the mysterious dimming of "Tabby's Star."

Credit: NASA/JPL-Caltech


The mystery of whether a darkening star is home to an alien megastructure might be solved with the aid of crowdfunding, researchers said.

Last fall, a star named KIC 8462852 made news when volunteers from the Planet Hunters citizen-science program uncovered something odd about the object's light. This discovery was made using data from NASA's Kepler space telescope (so far, Kepler has helped scientists find more than 2,200 alien planets.)

KIC 8462852 is an otherwise-ordinary F-type star, slightly larger and hotter than Earth's sun. It sits about 1,480 light-years away from Earth, in the constellation Cygnus. However, astronomer Tabetha "Tabby" Boyajian of Yale University in Connecticut and her colleagues found dozens of strange instances of the star dimming by up to 22 percent. [13 Ways to Hunt Intelligent Alien Life]

Since these events are far too substantial to be caused by planets crossing the star's face, researchers dubbed KIC 8462852 "the most mysterious star in our galaxy."

These analyses of the star — now nicknamed "Tabby's Star," or the WTF star for "Where's the Flux?" — raised the possibility that scientists had detected signs of intelligent alien life. Specifically, researchers have suggested that KIC 8462852 is home to a Dyson sphere, a hypothetical megastructure built around a star to capture as much of the sun's energy as possible. This energy would then be used to power an advanced civilization, it is proposed. (Science fiction often depicts Dyson spheres — which are named after mathematician and physicist Freeman Dyson — as solid shells around stars, but the structures could also be globular swarms of giant solar panels.)

There is still no widely accepted answer as to why Tabby's Star behaves so strangely. "Comets are currently the best natural explanation," Boyajian told Space.com. "That said, 'best' does not necessarily mean 'good.'"

Unfortunately, Kepler has moved on to a different mission and can no longer observe KIC 8462852 in an attempt to unlock the star's confounding secrets.

"It's exciting when you realize that you are working on something new and unusual, but also, at the same time, extremely frustrating," Boyajian said.

To keep working on the mystery of Tabby's Star, and hopefully ease some of that frustration, Boyajian and her colleagues are now turning to crowdfunding. They said they hope a Kickstarter campaign will help raise at least $100,000 by June 17 to secure observing time on a global network of ground-based telescopes. That way, researchers can see when the star's brightness dips again, the investigators said.

The scientists are currently observing Tabby's Star using the Las Cumbres Observatory Global Telescope Network (LCOGT), a privately run network specifically designed to continuously monitor objects in space. Although this network does not have Kepler's precision, it will be sensitive enough to detect fluctuations in the star's brightness, researchers said.

So far, the network has gifted the researchers with 200 hours to begin the project, which will take them to the end of the summer. The new Kickstarter campaign may help cover the expenses of monitoring this star for a year, including a total of 2 hours per night dedicated to observing the star.

The scientists said they are turning to private observatories because government-run sites do not have the capabilities for the long-term, continuous monitoring this project needs. The traditional way to pay for private observatories is through a government grant, but the researchers said that more than five-sixths of grant applications for time on such facilities are turned down. And the proposals that do get accepted are usually relatively "safe" ones that promise certain and immediate returns, the researchers said; that's why the team is now turning to crowdfunding.

The researchers warned that patience will likely be needed, even if this project gets funded. When Kepler was observing KIC 8462852, after all, the star fluctuated in brightness only 5 percent of the time, and at unpredictable times.

Still, "this project is the ultimate opportunity to help discover something new," Boyajian said.

You can learn more about the Kickstarter campaign here:
https://www.kickstarter.com/projects/608159144/the-most-mysterious-star-in-the-galaxy

Follow Charles Q. Choi on Twitter @cqchoi. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.

SATURN PLANET - Saturn Dances with the Moon Sunday Night: How to See It

Saturn Dances with the Moon Sunday Night: How to See It:

Astrophotographer Andrew Kwon captured this photo of Saturn at opposition in May 2014 from Mississauga, Ontario, Canada.

Credit: Andrew Kwon


While the celestial object of the moment is no doubt Mars, thanks to its closest approach to Earth in more than 10 years, on May 30, another planet will be attracting its own share of admirers in the coming weeks.

As summer kicks into gear, the top target of star parties and balmy outdoor astronomy gatherings will almost certainly be Saturn, the "Lord of the Rings."

Even seasoned veterans with many years of skywatching under their belts still experience a surge of excitement when they gaze at Saturn and its incredible system of rings; it's the most spectacular planet in the solar system. I always love showing Saturn to people, especially kids, who have never before seen it through a telescope. [Photos: The Rings and Moons of Saturn]

Talk about a "wow!" moment.

Saturn's famous rings are believed to be composed primarily of countless billions of icy particles that range from as large as boulders all the way down to tiny crystals.

Saturn will be visible near the moon in the southeastern sky late at night on Sunday, May 21, 2016. This Starry Night sky map shows how the moon and Saturn (as well as Mars) will look at 11 p.m. local time.

Credit: Starry Night Software

Summer favors Saturn

From now through 2023, Saturn will be at its best during the summertime.

And the planet's famous ring system has been "opening up" each year since the rings were turned edge-on to Earth in 2009; they'll continue to tip more and more toward Earth until they reach their maximum inclination late next year. But if you point your telescope toward Saturn even now, you will be rewarded with a truly gorgeous sight.

Saturn currently forms an eye-catching triangle with Mars and the ruddy, first-magnitude star Antares.  Interestingly, in a telescope, Saturn appears to be virtually the same size as Mars. But the surface of Saturn is much dimmer, because the ringed world is seven times farther away than the Red Planet.

Saturn is becoming more prominent as the date of its opposition to the sun, June 3, looms closer. (A planet is at opposition when it and the sun are on exact opposite sides of Earth from each other.) Saturn now appears to the unaided eye as a very bright (magnitude 0.1) yellowish-white "star" shining with a steady, sedate glow. It rises above the east-southeast horizon just before 9 p.m. local daylight time and stands due south by around 1:45 a.m. the following morning.

In fact, Saturn would rank as the eighth-brightest star, between Rigel in the constellation Orion and Procyon in Canis Minor.

See Saturn Sunday

Here's a great way to make a positive identification of Saturn: Late on Sunday evening (May 22), you will find the ringed planet positioned 4 degrees to the right of the nearly full moon. (Your clenched fist held at arm's length measures approximately 10 degrees).

A telescope magnifying 30-power or more will readily reveal the famous ring system, whose northern face is now tilted 26 degrees to our line of sight. For really superb views, try a 4-inch (10 centimeters) telescope at 100-power or an 8-inch (20 cm) telescope at 200-power. Or, for a really jaw-dropping view, use a 12-inch (30 cm) telescope at 300-power.

Remember that the apparent proximity of Saturn to the moon is just an illusion of perspective. On Sunday, the moon will be about 249,000 miles (400,000 kilometers) from Earth, while Saturn is more than 3,370 times farther away, at a distance of 840 million miles (1.35 billion km).

A final note: Should unsettled weather hide Sunday's Saturn-moon pairing, the two bodies will have another get-together less than a month from now, on June 18.

Editor's note: If you snap an amazing photo of Saturn or any other night-sky sight and would like to share it with Space.com and our news partners for a possible story or image gallery, send images and comments to Managing Editor Tariq Malik at spacephotos@space.com.

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmer's Almanac and other publications, and he is also an on-camera meteorologist for News 12 Westchester, N.Y. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.

MARS PLANET - Hubble's Decades-Long Look at Mars Reveals Much About the Red Planet (Video)

Hubble's Decades-Long Look at Mars Reveals Much About the Red Planet (Video):

Mars is at opposition with the Earth this Sunday (May 22), meaning the Red Planet and the Blue Marble are at their closest proximity to each other as they orbit the sun.

In celebration of this event, the Hubble Space Telescope snapped a new picture of Mars. The image shows a hazy blue rim around the dusty orange sphere. Space.com spoke with Jennifer Wiseman, a NASA Hubble senior scientist, about the benefits of observing Mars with different instruments, and the insights that Hubble has given scientists about our own solar system.

"With telescopes like Hubble we actually get a global view of the planet," Wiseman said. For Mars, those global observations can then be combined with observations by instruments orbiting the planet, as well as those on its surface. "And we need all of this information together to give us an idea of what's going on on Mars now, and what Mars was like in the past, as well." [Mars at Opposition: See the Red Planet with Your Own Eyes This Weekend]

The new Hubble image shows a wide variety of features on the Martian surface. The large orange region in the center is known as Arabia Terra, and is thought to be extremely old. Check out this video from Space.com to see the names of more of the physical features that appear in the new Hubble image.

This global view of Mars was captured by the Hubble Space Telescope on May 12, 2016 ahead of the planet's arrival at opposition on May 22. The wide view lets scientists observe how climate impacts the entire planet.

Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), J. Bell (ASU), and M. Wolff (Space Science Institute)


"You can see clouds around the whole planet and that's what you're seeing in that kind of wispy bluish white color," Wiseman said. "Off to the right-hand side you can see the clouds surrounding an extinct volcano. And you can also see the polar regions clearly. So this image actually gives us a huge variety of features that we can see."

The Hubble telescope has produced incredible images of very distant cosmic objects, including thousands of galaxies, as well as gorgeous nebulas, and other jaw-dropping universal features.

But Hubble has also unearthed incredible new information about Earth's solar system.

"Hubble has been operating for over 26 years now and that means we have a long time-baseline of looking at planets in the solar system, including Mars." Wiseman said. "Because of this wealth of information, we can see how the planet as a whole changes over time. For planets like Jupiter, we've seen its atmosphere change, that red spot shrinking. For Saturn, we've seen things like the aurora on the poles come and go. We've even used Hubble to discover new moons around Pluto that we didn't know about before."

On Mars, scientists have seen dust storms completely blanket the planet's surface.

"It shows us that Mars is a very dynamic planet and we need that long time-baseline that Hubble has given us to really understand those dynamics," Wiseman added.

Follow Calla Cofield @callacofield.Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.

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MARS PLANET - Massive 400 Ft. Tsunamis On Ancient Mars

Massive 400 Ft. Tsunamis On Ancient Mars:

About 3.4 billion years ago, (according to a new study) when the Late Heavy Bombardment had ended, and the first cells resembling prokaryotes were appearing on Earth, two enormous meteoroids slammed into the ancient, frigid ocean on Mars. These impacts generated massive 400 ft. high tsunamis that reshaped the shoreline of the Martian ocean, leaving behind fields of sediments and boulders.



It was long thought that ancient Mars had oceans. Sedimentary deposits discovered in the Martian north by radar in 2012 helped make the case for Martian oceans. 3.4 billion years ago, this ocean covered most of the Northern Martian lowlands. It's thought that the ocean itself was fed by catastrophic flooding, perhaps fuelled by geothermal activity on Mars at the time.



These catastrophic tsunamis would have dwarfed most Earthly disasters. Waves 120 meters high would have swamped landmarks like the Statue of Liberty (93 m. high), and caused enormous destruction along the Martian coastline. If the research behind this new study stands up to scrutiny, then it will help prove the existence of the ancient Martian ocean.







The Martian surface shows the remains of an ancient ocean. In some areas, radar data shows a layer of water-borne sediment on top of a layer of volcanic rock. There's also evidence of a shoreline, described by some scientists as being like a bathtub ring. The problems is, the shoreline can't be seen everywhere it should be.



The tsunami hypothesis helps explain this missing shoreline.



According to the new study, led by Alexis Rodriguez, a Mars researcher at the Planetary Science Institute in Tucson Arizona, the tsunamis would have wiped away portions of the coastline, and left behind fields of sediment and boulders, and large backwash channels cut into the Martian surface.



The study is focussed on a specific region on Mars where a highland feature called Arabia Terra abuts the Chryse Planitia lowlands. This area was part of the shoreline of the Martian ocean. In that area, the team behind the study identified two separate geological formations that they say were created by two separate tsunami events.







The first formation, and older of the two, looks every bit like a disturbed shoreline. An enormous wave washed over the beach, and in its wake deposited boulders over 10 meters across. Then, as the water drained back down into the ocean, it cut large backwash channels through its debris and boulder field.







Then, some time passed. Millions of years, probably, until the second meteor hit, triggering another enormous tsunami. But this one behaved a little differently.



Conditions on Mars had changed by then, with temperatures dropping, and glaciers marching across the landscape, gouging out deep valleys on the surface of Mars. When the second tsunami hit the shore, its effect was different.



This time, the tsunami was more like an icy slurry, according to the team. Because of the cold temperatures, the icy water froze in place in some areas, before it could wash back into the ocean. The result? Deposits of frozen debris formed in dense lobes on the surface.







But according to Rodriguez, this is just a snapshot of a process that likely occurred multiple times in the history of Mars. Successive meteors could have caused successive mega-tsunamis that would have repeatedly wiped away evidence of a shoreline. This could have happened as often as every 3 million years.



This study isn't the knockout blow that proves the existence of a Martian ocean in ancient times. But it is certainly intriguing, and is a reasonable hypothesis that explains missing shorelines.



Rodriguez intends to keep looking for other evidence of tsunamis on the Martian surface. If he finds more, it will help make the case for the meteor-tsunami explanation.



Rodriguez will also be visiting places on Earth that are analogues for the Martian surface of ancient times. This summer he plans on visiting high-altitude, cold, alpine lakes in Tibet, where he hopes to learn something about the processes and geological formations involved.



Even better would be a mission to Mars, to sample the area where the tsunamis came ashore. A group of small craters near the shore that were drenched by the tsunamis is of particular interest to Rodriguez and his team. Martian ocean water could have been trapped there for millions of years. This site could provide evidence about the briny nature of the ancient ocean on Mars, and possibly tell us something about the evolution of life there.

The post Massive 400 Ft. Tsunamis On Ancient Mars appeared first on Universe Today.

NEPTUNE PLANET - What is the Surface Temperature of Neptune?

What is the Surface Temperature of Neptune?:

Our Solar System is a fascinating place. Between its eight planets and many dwarf planets, there are some serious differences in terms of orbit, composition, and temperature. Whereas conditions within the inner Solar System, where planets are terrestrial in nature, can get pretty hot, planets that orbit beyond the Frost Line - where it is cold enough that volatiles (i.e. water, ammonia, methane, CO and CO²) condense into solids - can get mighty cold!



While Neptune has no "surface" to speak of, Earth-based research and flybys have been conducted that have managed to obtain accurate measurements of the temperature in the planet's upper atmosphere. All told, the planet experiences temperatures that range from approximately 55 K (-218 °C; -360 °F) to 72 K (-200 °C; -328 °F), making it the coldest planet in the Solar System.

Orbital Characteristics:

Of all the planets in the Solar System, Neptune orbits the Sun at the greatest average distance. With a very minor eccentricity (0.0086), it orbits the Sun at an semi-major axis of approximately 30.11 AU (4,504,450,000,000 km), ranging from 29.81 AU (4.459 x 10⁹ km) at perihelion and 30.33 AU (4.537 x 10⁹ km) at aphelion.







Neptune takes 16 hours 6 minutes and 36 seconds (0.6713 days) to complete a single sidereal rotation, and 164.8 Earth years to complete a single orbit around the Sun. This means that a single day lasts 67% as long on Neptune, whereas a year is the equivalent of approximately 60,190 Earth days (or 89,666 Neptunian days).



Because Neptune's axial tilt (28.32°) is similar to that of Earth (~23°) and Mars (~25°), the planet experiences similar seasonal changes. Combined with its long orbital period, this means that the seasons last for forty Earth years. In addition, the planets axial tilt also leads to variations in the length of its day, as well as variations in temperature between the northern and southern hemispheres (see below).

"Surface" Temperature:

Due to their composition, determining a surface temperature on gas or ice giants (compared to terrestrial planets or moons) is technically impossible. As a result, astronomers have relied on measurements obtained at altitudes where the atmospheric pressure is equal to 1 bar (or 100 kilo Pascals), the equivalent of air pressure here on Earth at sea level.

It is here on Neptune, just below the upper level clouds, that pressures reach between 1 and 5 bars (100 - 500 kPa). It is also at this level that temperatures reach their recorded high of 72 K (-201.15 °C; -330 °F). At this temperature, conditions are suitable for methane to condense, and clouds of ammonia and hydrogen sulfide are thought to form (which is what gives Neptune its characteristically dark cyan coloring).



But as with all gas and ice giants, temperatures vary on Neptune due to depth and pressure. In short, the deeper one goes into Neptune, the hotter it becomes. At its core, Neptune reaches temperatures of up to 7273 K (7000 °C; 12632 °F), which is comparable to the surface of the Sun. The huge temperature differences between Neptune's center and its surface create huge wind storms, which can reach as high as 2,100 km/hour, making them the fastest in the Solar System.

Temperature Anomalies and Variations:

Whereas Neptune averages the coldest temperatures in the Solar System, a strange anomaly is the planet's south pole. Here, it is 10 degrees K warmer than the rest of planet. This "hot spot" occurs because Neptune's south pole is currently exposed to the Sun. As Neptune continues its journey around the Sun, the position of the poles will reverse. Then the northern pole will become the warmer one, and the south pole will cool down.



Neptune's more varied weather when compared to Uranus is due in part to its higher internal heating, which is particularly perplexing for scientists. Despite the fact that Neptune is located over 50% further from the Sun than Uranus, and receives only 40% its amount of sunlight, the two planets' surface temperatures are roughly equal.







Deeper inside the layers of gas, the temperature rises steadily. This is consistent with Uranus, but oddly enough, the discrepancy is larger. Uranus only radiates 1.1 times as much energy as it receives from the Sun, whereas Neptune radiates about 2.61 times as much. Neptune is the farthest planet from the Sun, yet its internal energy is sufficient to drive the fastest planetary winds seen in the Solar System. The mechanism for this remains unknown.



And while temperatures on Pluto have been recorded as reaching lower - down to 33 K (-240 °C; -400 °F) - Pluto's status as a dwarf planet mean that it is no longer in the same class as the others. As such, Neptune remains the coldest planet of the eight.



We have written many articles about Neptune here at Universe Today.  Here's The Gas (and Ice) Giant Neptune, What is the Surface of Neptune Like?, 10 Interesting Facts About Neptune, and The Rings of Neptune.



If you'd like more information on Neptune, take a look at Hubblesite's News Releases about Neptune, and here's a link to NASA's Solar System Exploration Guide to Neptune.



We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

The post What is the Surface Temperature of Neptune? appeared first on Universe Today.

NASA IMAGE - 3D Mercury Transit

3D Mercury Transit:

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2016 May 20

Explanation: On May 9, innermost planet Mercury crossed IN FRONT of the Sun. Though pictures project the event in only two dimensions, a remarkable three dimensional perspective on the transit is possible by free viewing this stereo pair. The images were made 23 minutes apart and rotated so that Mercury's position shifts horizontally between the two. As a result, Mercury's orbital motion produced an exaggerated parallax simulating binocular vision. Between the two exposures, the appropriately named planet's speedy 47.4 kilometer per second orbital velocity actually carried it over 65,000 kilometers. Taken first, the left image is intended for the right eye, so a cross-eyed view is needed to see Mercury's tiny silhouette suspended in the foreground. Try it. Merging the text below the images helps.

NASA IMAGES - Milky Way and Planets Near Opposition

Milky Way and Planets Near Opposition:

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2016 May 21

Milky Way and Planets Near Opposition

Image Credit & Copyright: Tunç Tezel (TWAN)


Explanation: In this early May night skyscape, a mountain road near Bursa, Turkey seems to lead toward bright planets Mars and Saturn and the center of our Milky Way Galaxy, a direction nearly opposite the Sun in planet Earth's sky. The brightest celestial beacon on the scene, Mars, reaches its opposition tonight and Saturn in early June. Both will remain nearly opposite the Sun, up all night and close to Earth for the coming weeks, so the time is right for good telescopic viewing. Mars and Saturn form the tight celestial triangle with red giant star Antares just right of the Milky Way's central bulge. But tonight the Moon is also at opposition. Easy to see near bright Mars and Saturn, the Full Moon's light will wash out the central Milky Way's fainter starlight though, even in dark mountain skies.

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GIANT STARS - Friendly Giants Have Cozy Habitable Zones Too

Friendly Giants Have Cozy Habitable Zones Too:

It is an well-known fact that all stars have a lifespan. This begins with their formation, then continues through their Main Sequence phase (which constitutes the majority of their life) before ending in death. In most cases, stars will swell up to several hundred times their normal size as they exit the Main Sequence phase of their life, during which time they will likely consume any planets that orbit closely to them.



However, for planets that orbit the star at greater distances (beyond the system's "Frost Line", essentially), conditions might actually become warm enough for them to support life. And according to new research which comes from the Carl Sagan Institute at Cornell University, this situation could last for some star systems into the billions of years, giving rise to entirely new forms of extra-terrestrial life!



In approximately 5.4 billion years from now, our Sun will exit its Main Sequence phase. Having exhausted the hydrogen fuel in its core, the inert helium ash that has built up there will become unstable and collapse under its own weight. This will cause the core to heat up and get denser, which in turn will cause the Sun to grow in size and enter what is known as the Red Giant-Branch (RGB) phase of its evolution.







This period will begin with our Sun becoming a subgiant, in which it will slowly double in size over the course of about half a billion years. It will then spend the next half a billion years expanding more rapidly, until it is 200 times its current size and several thousands times more luminous. It will then officially be a red giant star, eventually expanding to the point where it reaches beyond Mars' orbit.



As we explored in a previous article, planet Earth will not survive our Sun becoming a Red Giant - nor will Mercury, Venus or Mars. But beyond the "Frost Line", where it is cold enough that volatile compounds - such as water, ammonia, methane, carbon dioxide and carbon monoxide - remain in a frozen state, the remain gas giants, ice giants, and dwarf planets will survive. Not only that, but a massive thaw will set in.



In short, when the star expands, its "habitable zone" will likely do the same, encompassing the orbits of Jupiter and Saturn. When this happens, formerly uninhabitable places - like the Jovian and Cronian moons - could suddenly become inhabitable. The same holds true for many other stars in the Universe, all of which are fated to become Red Giants as they near the end of their lifespans.



However, when our Sun reaches its Red Giant Branch phase, it is only expected to have 120 million years of active life left. This is not quite enough time for new lifeforms to emerge, evolve and become truly complex (i.e. like humans and other species of mammals). But according to a recent research study that appeared in The Astrophysical Journal - titled "Habitable Zone of Post-Main Sequence Stars" - some planets may be able to remain habitable around other red giant stars in our Universe for much longer - up to 9 billion years or more in some cases!







To put that in perspective, nine billion years is close to twice the current age of Earth. So assuming that the worlds in question also have the right mix of elements, they will have ample time to give rise to new and complex forms of life. The study's co-author, Professor Lisa Kaltennegeris, is also the director of the Carl Sagan Institute. As such, she is no stranger to searching for life in other parts of the Universe. As she explained to Universe Today via email:

"We found that planets - depending on how big their Sun is (the smaller the star, the longer the planet can stay habitable) - can stay nice and warm for up to 9 Billion years. That makes an old star an interesting place to look for life. It could have started sub-surface (e.g. in a frozen ocean) and then when the ice melts, the gases that life breaths in and out can escape into the atmosphere - what allows astronomers to pick them up as signatures of life. Or for the smallest stars, the time a formerly frozen planet can be nice and warm is up to 9 billion years. Thus life could potentially even get started in that time."

Using existing models of stars and their evolution - i.e. one-dimensional radiative-convective climate and stellar evolutionary models - for their study, Kaltenegger and Ramirez were able to calculate the distances of the habitable zones (HZ) around a series of post-Main Sequence (post-MS) stars. Ramses M. Ramirez - a research associate at the Carl Sagan Institute and the lead author of the paper - explained the research process to Universe Today via email:

"We used stellar evolutionary models that tell us how stellar quantities, mainly the brightness, radius, and temperature all change with time as the star ages through the red giant phase. We also used a  climate model to then compute how much energy each star is outputting at the boundaries of the habitable zone. Knowing this and the stellar brightness mentioned above, we can compute the distances to these habitable zone boundaries."

At the same time, they considered how this kind of stellar evolution could effect the atmosphere of the star's planets. As a star expands, it loses mass and ejects it outward in the form of solar wind. For planets that orbit close to a star, or those that have low surface gravity, they may find some or all of their atmospheres blasted away. On the other hand, planets with sufficient mass (or positioned at a safe distance) could maintain most of their atmospheres.



"The stellar winds from this mass loss erodes planetary atmospheres, which we also compute as a function of time," said Ramirez. "As the star loses mass, the solar system conserves angular momentum by moving outwards. So, we also take into account how the orbits move out with time." By using models that incorporated the rate of stellar and atmospheric loss during the Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) phases of star, they were able to determine how this would play out for planets that ranged in size from super-Moons to super-Earths.



What they found was that a planet can stay in a post-HS HZ for eons or more, depending on how hot the star is, and figuring for metallicities that are similar to our Sun's. As Ramirez explained:

"The main result is that the maximum time that a planet can remain in this red giant habitable zone of hot stars is 200 million years. For our coolest star (M1), the maximum time a planet can stay within this red giant habitable zone is 9 billion years. Those results assume metallicity levels similar to those of our Sun. A star with a higher percentage of metals takes longer to fuse the non-metals (H, He..etc) and so these maximum times can increase some more, up to about a factor of two."

Within the context of our Solar System, this could mean that in a few billion years, worlds like Europa and Enceladus (which are already suspected of having life beneath their icy surfaces) might get a shot at becoming full-fledged habitable worlds. As Ramirez summarized beautifully:

"This means that the post-main-sequence is another potentially interesting phase of stellar evolution from a habitability standpoint. Long after the inner system of planets have been turned into sizzling wastelands by the expanding, growing red giant star, there could be potentially habitable abodes farther away from the chaos. If they are frozen worlds, like Europa, the ice would melt, potentially unveiling any preexisting life. Such pre-existing life may be detectable by future missions/telescopes looking for atmospheric biosignatures."

But perhaps the most exciting take-away from their research study was their conclusion that planets orbiting within their star's post-MS habitable zones would be doing so at distances that would make them detectable using direct imaging techniques. So not only are the odds of finding life around older stars better than previously thought, we should have no trouble in spotting them using current exoplanet-hunting techniques!



It is also worth noting that Kaltenegger and Dr. Ramirez have submitted a second paper for publication, in which they provide a list of 23 red giant stars within 100 light-years of Earth. Knowing that these stars, all of which are in our stellar neighborhood, could have life-sustaining worlds within their habitable zones should provide additional opportunities for planet hunters in the coming years.



And be sure to check out this video from Cornellcast, where Prof. Kaltenegger shares what inspires her scientific curiosity and how Cornell’s scientists are working to find proof of extra-terrestrial life.



https://youtu.be/GnnTVjgSuEs



Further Reading: The Astrophysical Journal

The post Friendly Giants Have Cozy Habitable Zones Too appeared first on Universe Today.

AUSTRALIA ASTEROID - 30 km Wide Asteroid Impacted Australia 3.4 Billion Years Ago

30 km Wide Asteroid Impacted Australia 3.4 Billion Years Ago:

New evidence found in northwestern Australia suggests that a massive asteroid, 20 to 30 kilometres in diameter, struck Earth about 3.5 billion years ago. This impact would have dwarfed anything experienced by humans, and dinosaurs, releasing as much energy as millions of nuclear weapons. Impacts this large can trigger earthquakes and tsunamis, and change the geological history of Earth.



The evidence was uncovered by Andrew Glikson and Arthur Hickman from the Australian National University. While drilling for the Geological Survey of Western Australia, the two obtained drilling cores from some of the oldest known sediments on Earth. Sandwiched between two layers of sediment were tiny glass beads called spherules, which were formed from vaporized material from the asteroid impact.







The enormity of this impact cannot be overstated. "The impact would have triggered earthquakes orders of magnitude greater than terrestrial earthquakes, it would have caused huge tsunamis and would have made cliffs crumble," said Dr. Glikson, from the ANU Planetary Institute.



This asteroid impact is the second oldest one that we know of. It is also one of the largest found yet, and at 20 to 30 kilometers in diameter, it is 2 the 3 times the size of the famous Chicxulub asteroid that struck the Yucatan in Mexico. That impact is thought to be responsible for ending the age of dinosaurs on Earth.







The crater itself would have been hundreds of kilometers in diameter, though all traces of it are now gone. "Exactly where this asteroid struck the earth remains a mystery," Dr. Glikson said. "Any craters from this time on Earth's surface have been obliterated by volcanic activity and tectonic movements."



"Material from the impact would have spread worldwide. These spherules were found in sea floor sediments that date from 3.46 billion years ago," said Glikson.



At 3.46 billion years ago, this puts this impact event close to a period of time 4.1 to 3.8 billion years ago known as the Late Heavy Bombardment. This was a period of time when a disproportionate number of asteroids struck the Earth and the Moon, and probably Mercury, Venus, and Mars, too. The Late Heavy Bombardment was probably caused by the gas giants in our Solar System. As these planets migrated, their gravity caused enormous disruption, pulling objects in the asteroid belt and the Kuiper Belt into trajectories that sent them towards the inner Solar System.







The surfaces of Mercury and the Moon are covered in impact craters. Samples of rock from the lunar surface, brought back to Earth by the Apollo astronauts, have been subjected to isotopic dating. Their age is constrained to a fairly narrow band of time, corresponding to the Late Heavy Bombardment. Obviously, the Earth would have been subjected to the same thing. But on geologically active Earth, most traces of impact events have been erased. It's the sediment that hints at these events.



Australia is geologically ancient, and contains some of the most ancient rocks on Earth. Glikson and Hickman found the glass spherules in cores while drilling at Marble Bar in north-western Australia. Because the sediment layer containing the spherules was preserved between two volcanic layers, its age was determined with great precision.







For over 20 years, Dr. Glikson has been searching for evidence of asteroid impacts. When these glass beads were found in the core samples, he suspected an asteroid impact. Testing confirmed that the levels of elements such as platinum, nickel and chromium, matched those in asteroids.



This is not the first evidence of impact events that Glikson has uncovered. In 2015, Glikson discovered evidence of another massive asteroid strike in the Warburton Basin in Central Australia. At that site, buried in the crust 30 kilometers deep, in rock that is 300 to 500 million years old, Glikson found evidence of a double impact crater covering an area 400 kilometers wide.



This crater was believed to be the result of an asteroid that broke into two before slamming into Earth. “The two asteroids must each have been over 10 kilometers (6.2 miles) across — it would have been curtains for many life species on the planet at the time,” said Glikson.



"There may have been many more similar impacts, for which the evidence has not been found, said Dr. Glikson. "This is just the tip of the iceberg. We've only found evidence for 17 impacts older than 2.5 billion years, but there could have been hundreds."



Finding the sites of ancient impacts is not easy. Advances in satellite imaging helped locate and pinpoint the Chicxulub crater, and others. If there have been hundreds of enormous asteroid impacts, like Dr. Glikson suggests, then they would have had an equally enormous impact on Earth's evolution. But pinpointing these sites remains elusive.



The post 30 km Wide Asteroid Impacted Australia 3.4 Billion Years Ago appeared first on Universe Today.

LIGHT OF THE UNIVERSE - How Does Light Travel?

How Does Light Travel?:

Ever since Democritus - a Greek philosopher who lived between the 5th and 4th century's BCE - argued that all of existence was made up of tiny indivisible atoms, scientists have been speculating as to the true nature of light. Whereas scientists ventured back and forth between the notion that light was a particle or a wave until the modern, the 20th century led to breakthroughs that showed that it behaves as both.



These included the discovery of the electron, the development of quantum theory, and Einstein's Theory of Relativity. However, there remains many fascinating and unanswered questions when it comes to light, many of which arise from its dual nature. For instance, how is it that light can be apparently without mass, but still behave as a particle? And how can it behave like a wave and pass through a vacuum, when all other waves require a medium to propagate?

Theory of Light to the 19th Century:

During the Scientific Revolution, scientists began moving away from Aristotelian scientific theories that had been seen as accepted canon for centuries. This included rejecting Aristotle's theory of light, which viewed it as being a disturbance in the air (one of his four "elements" that composed matter), and embracing the more mechanistic view that light was composed of indivisible atoms.



In many ways, this theory had been previewed by atomists of Classical Antiquity - such as Democritus and Lucretius - both of whom viewed light as a unit of matter given off by the sun. By the 17th century, several scientists emerged who accepted this view, stating that light was made up of discrete particles (or "corpuscles"). This included Pierre Gassendi, a contemporary of René Descartes, Thomas Hobbes, Robert Boyle, and most famously, Sir Isaac Newton.







Newton's corpuscular theory was an elaboration of his view of reality as an interaction of material points through forces. This theory would remain the accepted scientific view for more than 100 years, the principles of which were explained in his 1704 treatise "Opticks, or, a Treatise of the Reflections, Refractions, Inflections, and Colours of Light". According to Newton, the principles of light could be summed as follows:

• Every source of light emits large numbers of tiny particles known as corpuscles in a medium surrounding the source.
• These corpuscles are perfectly elastic, rigid, and weightless.

This represented a challenge to "wave theory", which had been advocated by 17th century Dutch astronomer Christiaan Huygens. . These theories were first communicated in 1678 to the Paris Academy of Sciences and were published in 1690 in his “Traité de la lumière“ (“Treatise on Light“). In it, he argued a revised version of Descartes views, in which the speed of light is infinite and propagated by means of spherical waves emitted along the wave front.

Double-Slit Experiment:

By the early 19th century, scientists began to break with corpuscular theory. This was due in part to the fact that corpuscular theory failed to adequately explain the diffraction, interference and polarization of light, but was also because of various experiments that seemed to confirm the still-competing view that light behaved as a wave.



https://youtu.be/ZGoDK18b3LE



The most famous of these was arguably the Double-Slit Experiment, which was originally conducted by English polymath Thomas Young in 1801 (though Sir Isaac Newton is believed to have conducted something similar in his own time). In Young's version of the experiment, he used a slip of paper with slits cut into it, and then pointed a light source at them to measure how light passed through it.



According to classical (i.e. Newtonian) particle theory, the results of the experiment should have corresponded to the slits, the impacts on the screen appearing in two vertical lines. Instead, the results showed that the coherent beams of light were interfering, creating a pattern of bright and dark bands on the screen. This contradicted classical particle theory, in which particles do not interfere with each other, but merely collide.



The only possible explanation for this pattern of interference was that the light beams were in fact behaving as waves. Thus, this experiment dispelled the notion that light consisted of corpuscles and played a vital part in the acceptance of the wave theory of light. However subsequent research, involving the discovery of the electron and electromagnetic radiation, would lead to scientists considering yet again that light behaved as a particle too, thus giving rise to wave-particle duality theory.

Electromagnetism and Special Relativity:

Prior to the 19th and 20th centuries, the speed of light had already been determined. The first recorded measurements were performed by Danish astronomer Ole Rømer, who demonstrated in 1676 using light measurements from Jupiter's moon Io to show that light travels at a finite speed (rather than instantaneously).







By the late 19th century, James Clerk Maxwell proposed that light was an electromagnetic wave, and devised several equations (known as Maxwell's equations) to describe how electric and magnetic fields are generated and altered by each other and by charges and currents. By conducting measurements of different types of radiation (magnetic fields, ultraviolet and infrared radiation), he was able to calculate the speed of light in a vacuum (represented as c).



In 1905, Albert Einstein published "On the Electrodynamics of Moving Bodies”, in which he advanced one of his most famous theories and overturned centuries of accepted notions and orthodoxies. In his paper, he postulated that the speed of light was the same in all inertial reference frames, regardless of the motion of the light source or the position of the observer.



Exploring the consequences of this theory is what led him to propose his theory of Special Relativity, which reconciled Maxwell’s equations for electricity and magnetism with the laws of mechanics, simplified the mathematical calculations, and accorded with the directly observed speed of light and accounted for the observed aberrations. It also demonstrated that the speed of light had relevance outside the context of light and electromagnetism.



For one, it introduced the idea that major changes occur when things move close the speed of light, including the time-space frame of a moving body appearing to slow down and contract in the direction of motion when measured in the frame of the observer. After centuries of increasingly precise measurements, the speed of light was determined to be 299,792,458 m/s in 1975.

Einstein and the Photon:

In 1905, Einstein also helped to resolve a great deal of confusion surrounding the behavior of electromagnetic radiation when he proposed that electrons are emitted from atoms when they absorb energy from light. Known as the photoelectric effect, Einstein based his idea on Planck's earlier work with "black bodies" - materials that absorb electromagnetic energy instead of reflecting it (i.e. white bodies).



https://youtu.be/q74suqg5pCk



At the time, Einstein's photoelectric effect was attempt to explain the "black body problem", in which a black body emits electromagnetic radiation due to the object's heat. This was a persistent problem in the world of physics, arising from the discovery of the electron, which had only happened eight years previous (thanks to British physicists led by J.J. Thompson and experiments using cathode ray tubes).



At the time, scientists still believed that electromagnetic energy behaved as a wave, and were therefore hoping to be able to explain it in terms of classical physics. Einstein's explanation represented a break with this, asserting that electromagnetic radiation behaved in ways that were consistent with a particle - a quantized form of light which he named "photons". For this discovery, Einstein was awarded the Nobel Prize in 1921.

Wave-Particle Duality:

Subsequent theories on the behavior of light would further refine this idea, which included French physicist Louis-Victor de Broglie calculating the wavelength at which light functioned. This was followed by Heisenberg's "uncertainty principle" (which stated that measuring the position of a photon accurately would disturb measurements of it momentum and vice versa), and Schrödinger's paradox that claimed that all particles have a "wave function".



In accordance with quantum mechanical explanation, Schrodinger proposed that all the information about a particle (in this case, a photon) is encoded in its wave function, a complex-valued function roughly analogous to the amplitude of a wave at each point in space. At some location, the measurement of the wave function will randomly "collapse", or rather "decohere", to a sharply peaked function. This was illustrated in Schrödinger famous paradox involving a closed box, a cat, and a vial of poison (known as the "Schrödinger Cat" paradox).







According to his theory, wave function also evolves according to a differential equation (aka. the Schrödinger equation). For particles with mass, this equation has solutions; but for particles with no mass, no solution existed. Further experiments involving the Double-Slit Experiment confirmed the dual nature of photons. where measuring devices were incorporated to observe the photons as they passed through the slits.



When this was done, the photons appeared in the form of particles and their impacts on the screen corresponded to the slits - tiny particle-sized spots distributed in straight vertical lines. By placing an observation device in place, the wave function of the photons collapsed and the light behaved as classical particles once more. As predicted by Schrödinger, this could only be resolved by claiming that light has a wave function, and that observing it causes the range of behavioral possibilities to collapse to the point where its behavior becomes predictable.



The development of Quantum Field Theory (QFT) was devised in the following decades to resolve much of the ambiguity around wave-particle duality. And in time, this theory was shown to apply to other particles and fundamental forces of interaction (such as weak and strong nuclear forces). Today, photons are part of the Standard Model of particle physics, where they are classified as boson - a class of subatomic particles that are force carriers and have no mass.



So how does light travel? Basically, traveling at incredible speeds (299 792 458 m/s) and at different wavelengths, depending on its energy. It also behaves as both a wave and a particle, able to propagate through mediums (like air and water) as well as space. It has no mass, but can still be absorbed, reflected, or refracted if it comes in contact with a medium. And in the end, the only thing that can truly slow down or arrest the speed of light is gravity (i.e. a black hole).



https://youtu.be/jFvT2YPJQeM



What we have learned about light and electromagnetism has been intrinsic to the revolution which took place in physics in the early 20th century, a revolution that we have been grappling with ever since. Thanks to the efforts of scientists like Maxwell, Planck, Einstein, Heisenberg and Schrodinger, we have learned much, but still have much to learn.



For instance, its interaction with gravity (along with weak and strong nuclear forces) remains a mystery. Unlocking this, and thus discovering a Theory of Everything (ToE) is something astronomers and physicists look forward to. Someday, we just might have it all figured out!



We have written many articles about light here at Universe Today. For example, here's How Fast is the Speed of Light?, How Far is a Light Year?, What is Einstein's Theory of Relativity?



If you'd like more info on light, check out these articles from The Physics Hypertextbook and NASA's Mission Science page.



We've also recorded an entire episode of Astronomy Cast all about Interstellar Travel. Listen here, Episode 145: Interstellar Travel.

The post How Does Light Travel? appeared first on Universe Today.

New Horizons Sends Back First Science On Distant Kuiper Belt Object

New Horizons Sends Back First Science On Distant Kuiper Belt Object:

Even the most curmudgeonly anti-space troll has to admit that the New Horizons mission to Pluto has been an overwhelming success.



It's not like New Horizons discovered life or anything, but it did bring an otherwise cold, distant lump to life for humanity. Vivid images and detailed scientific data revealed Pluto as a dynamic, changing world, with an active surface and an atmosphere. And we haven't even received all of the data from New Horizons' mission to Pluto yet.



Fresh off its historic visit to Pluto, New Horizons is headed for the Kuiper Belt, and just sent back its first science on one of the denizens of the distant belt of objects. The target in this case is 1994 JR1, a 145 km (90 mi.) wide Kuiper Belt Object (KBO). that orbits the Sun at a distance greater than 5 billion km. (3 billion mi.) New Horizons has now observed 1994 JR1 twice, and the team behind the mission has garnered new insights into this KBO based on these observations.



The spacecraft's Long Range Reconnaissance Imager (LORRI) captured images of 1994 JR1 on April 7th-8th from a distance of 111 million km. (69 million mi.). That's far closer than the images New Horizons captured in November 2015 from a distance of 280 million km (170 million miles).







New Horizons science team member Simon Porter, of the Southwest Research Institute (SwRI) in Boulder Colorado, commented on the importance of these images. "Combining the November 2015 and April 2016 observations allows us to pinpoint the location of JR1 to within 1,000 kilometers (about 600 miles), far better than any small KBO," Porter said.



Porter added that this accurate measurement of the KBO's orbit allows New Horizons science team members to quash the idea that JR1 is a quasi-satellite of Pluto.



The team was also able to determine, by measuring the light reflected from the surface, that JR1's rotational period is only 5.4 hours. That's fast for a KBO. John Spencer, another New Horizons science team member from SwRI, said "This is all part of the excitement of exploring new places and seeing things never seen before."







KBOs are ancient remnants of the early days of the Solar System. Whereas the inner regions of the Solar System were largely swept clean as the planets formed, the Kuiper Belt remained mostly as it is, untouched by the gravity of the planets.



There are trillions of objects in this cold, distant part of the Solar System. The Kuiper Belt itself spans a distance that is 30 to 50 times greater than the distance from the Earth to the Sun. It's similar to the asteroid belt between Mars and Jupiter, but Kuiper Belt objects are icy, whereas asteroid belt objects are rocky, for the most part.



The New Horizons team has requested a mission extension, and if that extension is approved, the target is already chosen. In August 2015, NASA selected the KBO 2014 MU69, which resides in an orbit almost a billion miles beyond Pluto. There were two potential destinations for the spacecraft after it departed Pluto, and 2014 MU69 was recommended by the New Horizons team, and chosen by NASA.







Choosing New Horizons' next target early was important for fuel use. Fuel conservation allows the spacecraft to perform the maneuvers necessary to reach 2014 MU69. If all goes well, New Horizons should reach its next target by January 2019.



According to Alan Stern, New Horizons Principal Investigator, there are good reasons to visit 2014 MU69. “2014 MU69 is a great choice because it is just the kind of ancient KBO, formed where it orbits now, that the Decadal Survey desired us to fly by,” he said. “Moreover, this KBO costs less fuel to reach [than other candidate targets], leaving more fuel for the flyby, for ancillary science, and greater fuel reserves to protect against the unforeseen.”



The Decadal Survey in 2003 strongly recommended that flybys of Pluto and small KBOs should be conducted. The KBO is an unexplored region, and these flybys will allow us to sample the diversity of objects in the belt.



If New Horizons makes it to its next target, 2014 MU69, and delivers the types of results it has so far in its journey, it will be an unprecedented success. The kind of success that will make it harder and harder to be a curmudgeonly anti-space troll.



Wait. Who am I kidding.



Haters gonna hate.



The post New Horizons Sends Back First Science On Distant Kuiper Belt Object appeared first on Universe Today.