Beware Falling Rocks: Asteroid Day

Reconstruction of the path of an asteroid that exploded over Chelyabinsk, Russia, on Feb. 15, 2015. This year, on Feb. 9, researchers held a press conference to discuss the study of asteroids and the dangers of impacts.

Credit: Sandia Labs CC BY-NC-ND 2.0



An international band of asteroid experts gathered Tuesday to discuss the future of asteroid research and avoidance in preparation for the second annual Asteroid Day.

On June 30, 1908, a large meteorite or comet exploded above the remote Russian countryside, flattening 770 square miles (1,990 square kilometers) of forest. Now, June 30 is Asteroid Day, part of a campaign to raise awareness of the dangers of an asteroid strike on Earth.

At a press conference Feb. 9, the organizations behind Asteroid Day announced their plans for the latest effort, inviting a panel of experts to speak about the need for more study of asteroids as well as a commitment to preventing a large body from striking the Earth. The event was held at the European Space Research and Technology Centre (ESTEC). [Near-Earth Asteroids: Famous Space Rock Flybys and Close Calls]


Strikes from asteroids and comets big enough to threaten people are rare in any given year, but over time they are just about inevitable, the researchers said. For instance, on Feb. 13, 2015, a meteor fell near Chelyabinsk, Russia, and exploded some 18 miles (29 km) above the Earth's surface, the shock wave breaking windows and causing injuries to 1,500 people.

"An event like Chelyabinsk happens about once every 50 years, and we don't have a system designed to discover and track these things," Mark Boslough, a physicist at Sandia National Laboratories who is one of the founders of Asteroid Day, said at the conference.

(Even more recently, reports came in of a meteorite that may have killed a person in India, but it is unclear whether the object was actually a meteorite.)

At a press conference Feb. 9, researchers gathered in Noordwijk, Netherlands, to announce Asteroid Day 2016. The European Space Agency's director of technical and quality management, Franco Ongaro, is pictured on the screen.

Credit: ESA

The organizers of Asteroid Day, among them Brian May, an astrophysicist and former guitarist for the rock band Queen, noted that concerted efforts are needed to find asteroids that might collide with the Earth, and to send spacecraft to study them.

"This is not about fearmongering," said Grig Richters, filmmaker and co-founder of Asteroid Day. "It's about being aware there is a potential threat, and understanding better where we are from."

"Bringing space technology to bear to deflect asteroids will require widespread public support," said Tom Jones, a former space shuttle astronaut who also chairs the Association of Space Explorers' Committee on Near-Earth Objects. "We only need modest resources compared to the cost of absorbing impact. Asteroid Day is to educate the public so we can work together to avoid an impact."

To that end, the scientists who came to ESTEC highlighted some of the work being done to study asteroids — to learn more about them, understand what they are made of and come up with better strategies for preventing a disaster by avoiding getting hit.

One such mission is the proposed Asteroid Impact & Deflection Assessment (AIDA). Planned for a 2020 launch, the spacecraft in this mission would approach the asteroid 65803 Didymos, a binary asteroid that consists of two bodies, one about 800 meters (2,600 feet) across and the other about 150 m (490 feet) across. The craft would orbit the larger of the two bodies, launching a 660-lb. (300 kilograms) impactor at the smaller asteroid as it makes a close approach to the Earth. (While Didymos can get within a few million miles of the planet, there's no danger the object will hit Earth.)

Researchers would measure how much the impact moves the smaller asteroid, and how the asteroid's structure and surface hold up after the strike. [100-Foot Asteroid to Buzz Earth Next Month]

Aside from sending probes to investigate what asteroids are made of, the first big task is to catalogue where the possible threats are, said Detlef Koschny, the Space Situational Awareness Near-Earth Object co-manager at the European Space Agency. ESA established a near-Earth object segment in 2008 to help Europe detect such asteroids by observing wide swathes of the sky. One part of the program, at the University of Pisa in Italy, will track where the asteroids are going; ESA is also discussing further work with other countries.

In Europe, a prototype telescope that can scan the whole sky should be in place next year, said Patrick Michel, a planetary scientist and senior researcher at the French National Centre for Scientific Research. (He noted that the United States has its own efforts in place as well.) And citizens can help, too, he said: "You need to make sure you observe an object again, to make sure we don't lose it again. Amateur astronomers play an important role."

Detection is so important because the further out you find an asteroid, the easier it is to move it, the researchers said. The nuclear bomb approach, made famous by the movie "Armageddon" (and the 1979 film "Meteor") would only be worth doing if there is very little warning, Boslough said, "and we wouldn't be able to test it in space."

The technology, he said, isn't ready yet in any case.

Famed science communicator Bill Nye was also a panelist, and said since humans have the capacity to alter asteroid paths if necessary, it behooves humanity to do it. "We've no evidence the dinosaurs had a space program," he said, "and it cost them."

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The Moon Visits the Hyades Monday Night

Monday, Feb. 15, evening. The First Quarter Moon will occult the bright red star Aldebaran against the backdrop of the Hyades star cluster, as seen from Hawaii, Japan, southern China, and southeast Asia.

The moon will interact with the beautiful, V-shaped Hyades cluster on Presidents Day evening.

If the skies are clear in your area on Feb. 15, be sure to look up toward the moon, just past first quarter phase and high in the southern part of the sky as darkness falls. And with a pair of binoculars or a small telescope, you'll quickly see that our nearest neighbor in space will be passing through one of the most beautiful open star clusters.The moon will interact with the beautiful, V-shaped Hyades cluster on Presidents Day evening.

If the skies are clear in your area on Feb. 15, be sure to look up toward the moon, just past first quarter phase and high in the southern part of the sky as darkness falls. And with a pair of binoculars or a small telescope, you'll quickly see that our nearest neighbor in space will be passing through one of the most beautiful open star clusters.

V marks the spot

The constellation of Taurus, the bull, is currently at its high point in our midwinter early-evening sky. The famous Pleiades cluster is in the bull's shoulder, while the bull's face is plainly marked by the fine V-shaped cluster of the Hyades. Notice the bright-red star at the end of the lower arm of the V, which represents the bull's fiery eye. That's orange-red Aldebaran, "the follower"; it rises about 80 minutes after the Pleiades and pursues them across the sky. Although it looks like it's among the crowd, Aldebaran is actually a foreground star that does not belong to the Hyades; it's just an innocent bystander. [5 Dawn Planets And A Dusk Comet In Feb. 2016 Skywatching (Video)]

The Hyades are among the nearest of the star clusters, which explains why so many of the separate stars can be seen. At a distance of 130 light-years, the Hyades members travel through space like a flock of geese in the general direction of the star Betelgeuse, in Orion, while receding from us at 100,000 mph (160,000 km/h). Aldebaran is moving toward the south, almost at right angles to the cluster's motion, and twice as fast. Taurus' V-shaped head is, therefore, going to pieces. For 25,000 years or more, it will pass for a V, but after 50,000 years, it will be quite out of shape.

Slowly shifting moon


This image shows the region around the well-studied Hyades star cluster, the nearest open cluster to Earth.Credit: NASA, ESA, STScI, and Z. Levay (STScI)

As darkness falls over North America on Monday evening, the view of the Hyades will be augmented by the presence of the moon, 58 percent illuminated, just one night past first quarter phase and floating several degrees to the right of Aldebaran.

The moon has always been a prime target for telescope observers everywhere and shows amazing detail in even the smallest telescope. Even binoculars will show the mare ("seas"), mountain ranges and ringed plains, as well as the great craters — and with a telescope of only 3-inch aperture, you can see practically everything as clear as in the very best Earth-based photos. Most observers agree that the very best time to view the moon is in the two- or three-day interval following first quarter. That's when the moon is in a good position for evening study, with most of its major features visible, while not overly bright (as is the case at full phase) to cause a loss of detail through glare. The best views are along the sharp sunrise line separating darkness from light, called the terminator. Through a telescope, features near the terminator stand out in bold relief; shadows are strong, and details are more easily seen. Sometimes, you can even notice bright specks of light where high mountains catch the light of the rising sun before it has reached the plains below. [Earth's Moon Phases, Monthly Lunar Cycles (Infographic)]

If you're using binoculars, take note how, as the night progresses, the moon shifts — at its own apparent diameter each hour — past the fourth-magnitude star Gamma Tauri, located at the bottom of the V.

But for some, this will be more than just the moon's close brush with a star.
Tales of the occult

The moon's passage through a cluster of stars like the Hyades can mean that one or more stars are hidden by the moon (astronomers call this an occultation). Gamma Tauri is one of those prospective candidates. Indeed, the moon will occult it for parts of the northeastern U.S., northeastern Canada and Greenland.

Then, there's a close pair of stars, Theta 1 and Theta 2 Tauri, which will undergo occultations for a swath of the northern U.S. and Canada, as well as Alaska.

And finally, in what certainly will prove to be the best stellar eclipse of all, Aldebaran will put on a disappearing act for those in Hawaii.

In all of these cases, the stars will disappear behind the moon's dark limb and reappear on the bright limb. When they disappear, there will be no gradual fading; rather, the star will suddenly and rather abruptly "pop off" as if a switch were flipped. Similarly, the star will "pop back on" when it reappears.

"The spectacle, reported on paper, does not sound as arresting as it is in nature," noted the late H.A. Rey in his classic book, "The Stars — A New Way to See Them" (Houghton Mifflin, 1952), adding, "It is well worth watching.”

Thanks to the International Occultation Timing Association (IOTA), we provide links for the local viewing circumstances of the four stars listed above. Each page provides a map showing the zone of visibility of the occultation, as well as listings of the times for the disappearance and reappearance of the selected star for hundreds of locations, including Canada (denoted by "CA") and the United States (denoted by "US"). All times are in Universal Time (UT). Subtract 5 hours to convert to Eastern time, 6 hours for Central time, 7 hours for Mountain time and 8 hours for Pacific time.

Occultation of Gamma Tauri:

http://www.lunar-occultations.com/iota/bstar/0216zc635.htm

Occultation of Theta 1 Tauri

http://www.lunar-occultations.com/iota/bstar/0216zc669.htm

Occultation of Theta 2 Tauri

http://www.lunar-occultations.com/iota/bstar/0216zc671.htm

Aldebaran:

http://www.lunar-occultations.com/iota/bstar/0216zc692.htm

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, New York.

Gravitational waves formed by Black holes and detected for the first time

TWO black holes circle one another. Both are about 100km across. One contains 36 times as much mass as the sun; the other, 29. They are locked in an orbital dance, a kilometre or so apart, that is accelerating rapidly to within a whisker of the speed of light. Their event horizons—the spheres defining their points-of-no-return—touch. There is a violent wobble as, for an instant, quintillions upon quintillions of kilograms redistribute themselves. Then there is calm. In under a second, a larger black hole has been born.

It is, however, a hole that is less than the sum of its parts. Three suns’ worth of mass has been turned into energy, in the form of gravitational waves: travelling ripples that stretch and compress space, and thereby all in their path. During the merger’s final fifth of a second, envisaged in an artist’s impression above, the coalescing holes pumped 50 times more energy into space this way than the whole of the rest of the universe emitted in light, radio waves, X-rays and gamma rays combined.


And then, 1.3 billion years later, in September 2015, on a small planet orbiting an unregarded yellow sun, at facilities known to the planet’s inhabitants as the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO), the faintest slice of those waves was caught. That slice, called GW150914 by LIGO’s masters and announced to the world on February 11th, is the first gravitational wave to be detected directly by human scientists. It is a triumph that has been a century in the making, opening a new window onto the universe and giving researchers a means to peer at hitherto inaccessible happenings, perhaps as far back in time as the Big Bang.


Finger on the pulsar


The idea of gravitational waves emerged from the general theory of relativity, Albert Einstein’s fundamental exposition of gravity, unveiled almost exactly 100 years before GW150914’s discovery. Mass, Einstein realised, deforms the space and time around itself. Gravity is the effect of this, the behaviour of objects dutifully moving along the curves of mass-warped spacetime. It is a simple idea, but the equations that give it mathematical heft are damnably hard to solve. Only by making certain approximations can solutions be found. And one such approximation led Einstein to an odd prediction: any accelerating mass should make ripples in spacetime.


Einstein was not happy with this idea. He would, himself, oscillate like a wave on the topic—rescinding and remaking his case, arguing for such waves and then, after redoing the sums, against them. But, while he and others stretched and squeezed the maths, experimentalists set about trying to catch the putative waves in the act of stretching and squeezing matter.


Their problem was that the expected effect was a transient change in dimensions equivalent to perhaps a thousandth of the width of a proton in an apparatus several kilometres across. Indirect proof of gravitational waves’ existence has been found over the years, most notably by measuring radio emissions from pairs of dead stars called pulsars that are orbiting one another, and deducing from this how the distance between them is shrinking as they broadcast gravitational waves into the cosmos. But the waves themselves proved elusive until the construction of LIGO.


As its name states, LIGO is an interferometer. It works by splitting a laser beam in two, sending the halves to and fro along paths identical in length but set at right angles to one another, and then looking for interference patterns when the halves are recombined (see diagram). If the half-beams’ paths are undisturbed, the waves will arrive at the detector in lock-step. But a passing gravitational wave will alternately stretch and compress the half-beams’ paths. Those half-beams, now out of step, will then interfere with each other at the detector in a way that tells of their experience. The shape of the resulting interference pattern contains all manner of information about the wave’s source, including what masses were involved and how far away it was.





To make absolutely certain that what is seen really is a gravitational wave requires taking great care. First, LIGO is actually two facilities, one in Louisiana and the other in Washington state. Only something which is observed almost, but not quite, simultaneously by both could possibly be a gravitational wave. Secondly, nearly everything in the interferometers’ arms is delicately suspended to isolate it as far as possible from distant seismic rumblings and the vibrations of passing traffic.


Moreover, in order to achieve the required sensitivity, each arm of each interferometer is 4km long and the half-beam in it is bounced 100 times between the mirrors at either end of the arm, to amplify any discrepancy when the half-beams are recombined. Even so, between 2002 when LIGO opened and 2010, when it was closed for upgrades, nary a wave was seen.


Holey moly

Those improvements, including doubling the bulk of the devices’ mirrors, suspending them yet more delicately, and increasing the laser power by a factor of 75, have made Advanced LIGO, as the revamped apparatus is known, four times as sensitive as the previous incarnation. That extra sensitivity paid off almost immediately. Indeed, the system’s operators were still kicking its metaphorical tyres and had yet to begin its official first run when GW150914 turned up, first at the Louisiana site, and about a hundredth of a second later in Washington—a difference which places the outburst somewhere in the sky’s southern hemisphere. Since then, the team have been checking their sums and counting their lucky stars. As they outline in Physical Review Letters, the likelihood that the signal was a fluke is infinitesimal.


When one result comes so quickly, others seem sure to follow—particularly as the four months of data the experiment went on to gather as part of the first official run have yet to be analysed fully. A rough estimate suggests one or two other signals as striking as GW150914 may lie within them.


For gravitational astronomy, this is just the beginning. Soon, LIGO will not be alone. By the end of the year VIRGO, a gravitational-wave observatory in Italy, should join it in its search. Another is under construction in Japan and talks are under way to create a fourth, in India. Most ambitiously, a fifth, orbiting, observatory, the Evolved Laser Interferometer Space Antenna, or e-LISA, is on the cards. The first pieces of apparatus designed to test the idea of e-LISA are already in space.


Together, by jointly forming a telescope that will permit astronomers to pinpoint whence the waves come, these devices will open a new vista on the universe. As technology improves, waves of lower frequency—corresponding to events involving larger masses—will become detectable. Eventually, astronomers should be able to peer at the first 380,000 years after the Big Bang, an epoch of history that remains inaccessible to every other kind of telescope yet designed.


The real prize, though, lies in proving Einstein wrong. For all its prescience, the theory of relativity is known to be incomplete because it is inconsistent with the other great 20th-century theory of physics, quantum mechanics. Many physicists suspect that it is in places where conditions are most extreme—the very places which launch gravitational waves—that the first chinks in relativity’s armour will be found, and with them a glimpse of a more all-embracing theory.


Gravitational waves, of which Einstein remained so uncertain, have provided direct evidence for black holes, about which he was long uncomfortable, and may yet yield a peek at the Big Bang, an event he knew his theory was inadequate to describe. They may now lead to his theory’s unseating. If so, its epitaph will be that in predicting gravitational waves, it predicted the means of its own demise.

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