When ‘Oumuamua crossed Earth’s orbit on October 19th, 2017, it became the first interstellar object to ever be observed by humans. These and subsequent observations – rather than dispelling the mystery of ‘Oumuamua’s true nature – only deepened it. While the debate raged about whether it was an asteroid or a comet, with some even suggesting it could be an extra-terrestrial solar sail.
In the end, all that could be said definitively was that ‘Oumuamua was an interstellar object the likes of which astronomers had never before seen. In their most recent study on the subject, Harvard astronomers Amir Siraj and Abraham Loeb argue that such objects may have impacted on the lunar surface over the course of billions of years, which could provide an opportunity to study these objects more closely.
In 2008, scientists from Oxford and Aberdeen University made a startling discovery in the northwest of Scotland. Near the village of Ullapool, which sits on the coast opposite the Outer Hebrides, they found a debris deposit created by an ancient meteor impact dated to 1.2 billion years ago. The thickness and extent of the debris suggested that the meteor measured 1 km (0.62 mi) in diameter and took place near to the coast.
Until recently, the precise location of the impact remained a mystery to scientists. But in a paper that recently appeared in the Journal of the Geological Society , a team of British researchers concluded that the crater is located about 15 to 20 km (~9 to 12.5 mi) west of the Scottish coastline in the Minch Basin, where it is buried beneath both water and younger layers of rock.
When ‘Oumuamua was first detected on October 19th, 2017, astronomers were understandably confused about the nature of this strange object. Initially thought to be an interstellar comet, it was then designated as an interstellar asteroid. But when it picked up velocity as it departed our Solar System (a very comet-like thing to do), scientists could only scratch their heads and wonder.
After much consideration, Shmuel Bialy and Professor Abraham Loeb of the Harvard-Smithsonian Center for Astrophysics (CfA) proposed that ‘Oumuamua could in fact be an artificial object (possibly an alien probe). In a more recent study, Amir Siraj and Prof. Loeb identified another (and much smaller) potential interstellar object, which they claim could be regularly colliding with Earth.
When a meteor strike the Earth’s atmosphere, a magnificent (and potentially deadly) explosion is often the result. The term for this is “fireball” (or bolide), which is used to describe exceptionally bright meteor explosions that are bright enough to be seen over a very wide area. A well-known example of this is the Chelyabinsk meteor, a superbolide that exploded in the skies over a small Russian town in February of 2013.
On December 18th, 2018, another fireball appeared in the skies over Russia that exploded at an altitude of about 26 km (16 mi) above the Bering Sea. The resulting debris was observed by instruments aboard the NASA Terra Earth Observation System (EOS) satellite, which captured images of the remnants of the large meteor a few minutes after it exploded.
A meteor that exploded in the air near the Dead Sea 3,700 years ago may have wiped out communities, killed tens of thousands of people, and provided the kernel of truth to an old Bible story. The area is in modern-day Jordan, in a 25 km wide circular plain called Middle Ghor. Most of the evidence for this event comes from archaeological evidence excavated at the Bronze Age city of Tall el-Hammam located in that area, which some scholars say is the city of Sodom from the Bible.
I couldn’t live without the sky. The concerns of Earth absorb so much of our lives that the sky provides an essential relief valve. It’s a cosmos-sized wilderness that invites both deep exploration and reflection. Galileo would kill to come back for one more clear night if he could.
To me, the stars are irresistible, but my sense is that many people don’t look up as much as they’d like. We forget. Get busy. Bad weather intervenes. So I thought hard about the essential “must-sees” for any watcher of the skies. Some are obvious, like a total solar eclipse or Saturn through a telescope, but others are just as interesting — if sometimes off the beaten path.
For instance, we always hear about asteroids in the news. What does a real one look like from your own backyard? I give directions and a map for seeing the brightest of them, Vesta. And if you’ve ever looked up at the Big Dipper and wondered how to find the rest of the Great Bear, I’ll get you there. I love red stars, so you’re going to find out where the reddest one resides and how to see it yourself. There’s also a lunar Top 10 for small telescope users and chapters on the awesome Cygnus Star Cloud and how to see a supernova.
The 57 different sights are a mix of naked-eye objects plus ones you’ll need an ordinary pair of binoculars or small telescope to see. At the end of each chapter, I provide directions on how and when to find each wonder. Because we live in an online world with so many wonderful tools available for skywatchers, I make extensive use of mobile phone apps that allow anyone to stay in touch with nearly every aspect of the night sky.
For the things that need a telescope, the resources section has suggestions and websites where you can purchase a nice but inexpensive instrument. Of course, you may not want to buy a telescope. That’s OK. I’m certain you’ll still enjoy reading about each of these amazing sights to learn more about what’s been up there all your life.
While most of the nighttime sights are visible from your home or a suitable dark sky site, you’ll have to travel to see others. Who doesn’t like to get out of the house once in a while? If you travel north or south, new places mean new stars and constellations. I included chapters on choice southern treats like Alpha Centauri, the Southern Cross and the Magellanic Clouds, the closest and brightest galaxies to our own Milky Way.
One of my favorite parts of the book is the epilogue, where I share a lesson my dog taught me about the present moment and cosmic time. I like to joke that if nothing else, the ending’s worth the price of the book.
The staff at Page Street Publishing did a wonderful job with the layout and design, so “Wonders” is beautiful to look at. Everyone who’s flipped through it likes the feel, and several people have even commented on how good it smells! And for those who understandably complained that the typeface in my first book, Night Sky with the Naked Eye, made it difficult to read, I’ve got good news for you. The new book’s type is bigger and easy on the eyes.
“Wonders” is 224 pages long, printed in full color and the same size as my previous book. Unlike the few but longer chapters of the first book, the new one has many shorter chapters, and you can dip in anywhere. I think you’ll love it.
The publication date is April 24, but you can pre-order it right now at Amazon, BN and Indiebound. I want to thank Fraser Cain here at Universe Today for letting me tell you a little about my book, and I look forward to the opportunity to share my night-sky favorites with all of you.
Earth is no stranger to meteors. In fact, meteor showers are a regular occurrence, where small objects (meteoroids) enter the Earth’s atmosphere and radiate in the night sky. Since most of these objects are smaller than a grain of sand, they never reach the surface and simply burn up in the atmosphere. But every so often, a meteor of sufficient size will make it through and explode above the surface, where it can cause considerable damage.
A good example of this is the Chelyabinsk meteoroid, which exploded in the skies over Russia in February of 2013. This incident demonstrated just how much damage an air burst meteorite can do and highlighted the need for preparedness. Fortunately, a new study from Purdue University indicates that Earth’s atmosphere is actually a better shield against meteors than we gave it credit for.
Their study, which was conducted with the support of NASA’s Office of Planetary Defense, recently appeared in the scientific journal Meteoritics and Planetary Science – titled “Air Penetration Enhances Fragmentation of Entering Meteoroids“. The study team consisted of Marshall Tabetah and Jay Melosh, a postdoc research associate and a professor with the department of Earth, Atmospheric and Planetary Sciences (EAPS) at Purdue University, respectively.
In the past, researchers have understood that meteoroids often explode before reaching the surface, but they were at a loss when it came to explaining why. For the sake of their study, Tabetah and Melosh used the Chelyabinsk meteoroid as a case study to determine exactly how meteoroids break up when they hit our atmosphere. At the time, the explosion came as quite the a surprise, which was what allowed for such extensive damage.
When it entered the Earth’s atmosphere, the meteoroid created a bright fireball and exploded minutes later, generating the same amount of energy as a small nuclear weapon. The resulting shockwave blasted out windows, injuring almost 1500 people and causing millions of dollars in damages. It also sent fragments hurling towards the surface that were recovered, and some were even used to fashion medals for the 2014 Sochi Winter Games.
But what was also surprising was how much of the meteroid’s debris was recovered after the explosion. While the meteoroid itself weighed over 9000 metric tonnes (10,000 US tons), only about 1800 metric tonnes (2,000 US tons) of debris was ever recovered. This meant that something happened in the upper atmosphere that caused it to lose the majority of its mass.
Looking to solve this, Tabetah and Melosh began considering how high-air pressure in front of a meteor would seep into its pores and cracks, pushing the body of the meteor apart and causing it to explode. As Melosh explained in a Purdue University News press release:
“There’s a big gradient between high-pressure air in front of the meteor and the vacuum of air behind it. If the air can move through the passages in the meteorite, it can easily get inside and blow off pieces.”
To solve the mystery of where the meteoroid’s mass went, Tabetah and Melosh constructed models that characterized the entry process of the Chelyabinsk meteoroid that also took into account its original mass and how it broke up upon entry. They then developed a unique computer code that allowed both solid material from the meteoroid’s body and air to exist in any part of the calculation. As Melosh indicated:
“I’ve been looking for something like this for a while. Most of the computer codes we use for simulating impacts can tolerate multiple materials in a cell, but they average everything together. Different materials in the cell use their individual identity, which is not appropriate for this kind of calculation.”
This new code allowed them to fully simulate the exchange of energy and momentum between the entering meteoroid and the interacting atmospheric air. During the simulations, air that was pushed into the meteoroid was allowed to percolate inside, which lowered the strength of the meteoroid significantly. In essence, air was able to reach the insides of the meteoroid and caused it to explode from the inside out.
This not only solved the mystery of where the Chelyabinsk meteoroid’s missing mass went, it was also consistent with the air burst effect that was observed in 2013. The study also indicates that when it comes to smaller meteroids, Earth’s best defense is its atmosphere. Combined with early warning procedures, which were lacking during the Chelyabinsk meteroid event, injuries can be avoided in the future.
This is certainly good news for people concerned about planetary protection, at least where small meteroids are concerned. Larger ones, however, are not likely to be affected by Earth’s atmosphere. Luckily, NASA and other space agencies make it a point to monitor these regularly so that the public can be alerted well in advance if any stray too close to Earth. They are also busy developing counter-measures in the event of a possible collision.
Halley’s Comet may be at the far end of its orbit 3.2 billion miles (5.1 billion km) from Earth, but this week fragments of it will burn up as meteors in the pre-dawn sky as the Eta Aquarid meteor shower. The comet last passed our way in 1986, pivoted about the Sun and began the long return journey to the chilly depths of deep space.
Today, Halley’s a magnitude +25 speck in the constellation Hydra. Although utterly invisible in most telescopes, you can imagine it below tonight’s half-moon near the outermost point in its orbit four Earth-sun distances beyond Neptune. Literally cooling its jets, the comet mulls its next Earth flyby slated for summer 2061.
Some meteor showers have sharp peaks, others like the Eta Aquarids, a broad, plateau-like maximum. The shower’s been active since mid-April and will continue right up till the end of this month with the peak predicted Saturday morning May 6. Observers in tropical latitudes, where the constellation Aquarius rises higher than it does from my home in northern Minnesota, will spy 25-30 meteors an hour from a dark sky in the hour or two before dawn.
Skywatchers further north will see fewer meteors because the radiant will be lower in the sky; meteors that flash well below the radiant get cut off by the horizon, reducing the rate by about half ( about 10-15 meteors an hour). That’s still a decent show. I got up with the first robins a couple years back to see the shower and was pleasantly surprised with a handful of flaming Halley particles in under a half hour.
While a low radiant means fewer meteors, there’s an up side. You have a fair chance of seeing an earthgrazer, a meteor that skims tangent to the upper atmosphere, flaring for many seconds before either burning up or skipping back off into space.
The Eta Aquarids will be active all week. With the peak occurring Saturday morning, you should be able to see at least a few prior to dawn each morning. The quarter-to-waxing gibbous moon will set in plenty of time through Friday morning, leaving dark skies, but cuts it close Saturday when it sets about the same time the radiant rises in the east.
For best viewing, find as dark a place as possible with an open view to the east and south. I like to tote out a reclining lawn chair, face east and get comfy under a warm sleeping bag or wool blanket. Since twilight starts about an hour and three-quarters before your local sunrise, plan to be out watching an hour before that or around 3:30 a.m. I know, I know. That sounds harsh, but I’ve discovered that once you make the commitment, the act of watching a meteor shower becomes a relaxed pleasure punctuated by the occasional thrill of seeing a bright meteor.
You’ll be in magnificent company, too. The Milky Way rides high across the southeastern sky at that hour, and Saturn gleams due south in Sagittarius at the start of dawn. If you’d like to contribute observations of the shower to help meteor scientists better understand its behavior and evolution, check out the International Meteor Organization’s Eta Aquariids 2017 campaign for more information.
If one of your New Year’s resolutions is to spend more time under the stars in 2017, you’ll have motivation to do so as soon as Tuesday. That morning, the Quadrantid (kwah-DRAN-tid) meteor shower will peak between 4 to about 6 a.m. local time just before the start of dawn. This annual shower can be a rich one with up to 120 meteors flying by an hour — under perfect conditions.
Those include no moon, a light-pollution free sky and most importantly, for the time of maximum meteor activity to coincide with the time the radiant is highest in the pre-dawn sky. Timing is everything with the “Quads” because the shower is so brief. Meteor showers occur when Earth passes through either a stream of dusty debris left by a comet or asteroid. With the Quads, asteroid 2003 EH1 provides the raw material — bits of crumbled rock flaked off the 2-mile-wide (~3-4 km) object during its 5.5 year orbit around the sun.
Only thing is, the debris path is narrow and Earth tears through it perpendicularly, so we’re in and out in a hurry. Just a few hours, tops. This year’s peak happens around 14 hours UT or 8 a.m. Central time (9 a.m. Eastern, 7 a.m. Mountain and 6 a.m. Pacific), not bad for the U.S. and Canada. The timing is rather good for West Coast skywatchers and ideal if you live in Alaska. Alaska gets an additional boost because the radiant, located in the northeastern sky, is considerably higher up and better placed than it is from the southern U.S. states.
The Quads will appear to radiate from a point in the sky below the Big Dipper’s handle, which stands high in the northeastern sky at the time. This area was once home to the now defunct constellation Quadrans Muralis (mural quadrant), the origin of the shower’s name. As with all meteor showers, you’ll see meteors all over the sky, but all will appear to point back to the radiant. Meteors that point back to other directions don’t belong to the Quads are called sporadic or random meteors.
Off-peak observers can expect at least a decent shower with up to 25 meteors an hour visible from a reasonably dark sky. Peak observers could see at least 60 per hour. Tropical latitude skywatchers will miss most of the the show because the radiant is located at or below the horizon, but they should be on the lookout for Earthgrazers, meteors that climb up from below the horizon and make long trails as they skirt through the upper atmosphere.
Set your clock for 4 or 5 a.m. Tuesday, put on a few layers of clothing, tuck hand warmers in your boots and gloves, face east and have at it! The Quads are known for their fireballs, brilliant meteors famous for taking one’s breath away. Each time you see one chalk its way across the sky, you’re witnessing the fiery end of an asteroid shard. As the crumble burns out, you might be fulfilling another resolution: burning away those calories while huddling outside to see the show.
Children ice skating in Khakassia, Russia react to the fall of a bright fireball two nights ago on Dec.6
In 1908 it was Tunguska event, a meteorite exploded in mid-air, flattening 770 square miles of forest. 39 years later in 1947, 70 tons of iron meteorites pummeled the Sikhote-Alin Mountains, leaving more than 30 craters. Then a day before Valentine’s Day in 2013, hundreds of dashcams recorded the fiery and explosive entry of the Chelyabinsk meteoroid, which created a shock wave strong enough to blow out thousands of glass windows and litter the snowy fields and lakes with countless fusion-crusted space rocks.
Documentary footage from 1947 of the Sikhote-Alin fall and how a team of scientists trekked into the wilderness to find the craters and meteorite fragments
Now on Dec. 6, another fireball blazed across Siberian skies, briefly illuminated the land like a sunny day before breaking apart with a boom over the town of Sayanogorsk. Given its brilliance and the explosions heard, there’s a fair chance that meteorites may have landed on the ground. Hopefully, a team will attempt a search soon. As long as it doesn’t snow too soon after a fall, black stones and the holes they make in snow are relatively easy to spot.
OK, maybe Siberia doesn’t get ALL the cool fireballs and meteorites, but it’s done well in the past century or so. Given the dimensions of the region — it covers 10% of the Earth’s surface and 57% of Russia — I suppose it’s inevitable that over so vast an area, regular fireball sightings and occasional monster meteorite falls would be the norm. For comparison, the United States covers only 1.9% of the Earth. So there’s at least a partial answer. Siberia’s just big.
Every day about 100 tons of meteoroids, which are fragments of dust and gravel from comets and asteroids, enter the Earth’s atmosphere. Much of it gets singed into fine dust, but the tougher stuff — mostly rocky, asteroid material — occasionally makes it to the ground as meteorites. Every day then our planet gains about a blue whale’s weight in cosmic debris. We’re practically swimming in the stuff!
Most of this mass is in the form of dust but a study done in 1996 and published in the Monthly Notices of the Royal Astronomical Society further broke down that number. In the 10 gram (weight of a paperclip or stick of gum) to 1 kilogram (2.2 lbs) size range, 6,400 to 16,000 lbs. (2900-7300 kilograms) of meteorites strike the Earth each year. Yet because the Earth is so vast and largely uninhabited, appearances to the contrary, only about 10 are witnessed falls later recovered by enterprising hunters.
A couple more videos of the Dec. 6, 2016 fireball over Khakassia and Sayanogorsk, Russia
Meteorites fall in a pattern from smallest first to biggest last to form what astronomers call a strewnfield, an elongated stretch of ground several miles long shaped something like an almond. If you can identify the meteor’s ground track, the land over which it streaked, that’s where to start your search for potential meteorites.
Meteorites indeed fall everywhere and have for as long as Earth’s been rolling around the sun. So why couldn’t just one fall in my neighborhood or on the way to work? Maybe if I moved to Siberia …