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See a shooting star shower this weekend

AUSSIE SKY-WATCHERS WILL HAVE THEIR GAZE fixed firmly on the sky this weekend, as one of the best meteor showers of the year puts on a display.

The Eta Aquariids shower will be best seen in the early morning hours, between about 3:30am and sunrise.

“The Eta Aquariids is one of the year’s best meteor showers for the Southern Hemisphere, partly because it is such a consistent shower, regularly producing bright meteors in the early morning for about a week, and also because it is well placed in our sky,” says Dr Tanya Hill, astronomer at the Melbourne Planetarium.

A meteor shower occurs when Earth passes through a clump of dust, or meteoroid stream, that’s orbiting the Sun. For the Eta Aquariids, the dust has been left behind by Comet Halley.

The Eta Aquariids meteor shower is can be seen in the early morning hours from late April to late May, but the best nights are May 5-8.

The Eta Aquariids meteor shower is can be seen in the early morning hours from late April to late May, but the best nights are May 5-8.

It takes about six weeks for Earth to cross completely through the stream, from mid-April through to late May. But we pass through the thickest part around May 5 to 8.

“The special thing about meteor showers is that all the meteors appear to come from the same part of the sky,” says Dr Hill, referring to what astronomers call the meteor shower’s ‘radiant’.

For the Eta Aquariids, the radiant is near the faint star Eta Aquarii, which at this time of the year rises in the east around 2:00am and is high in our northern sky by sunrise. (For our Northern Hemisphere readers, the radiant rises just a couple of hours before sunrise and remains much lower in the sky.)

“The higher the radiant in the sky, the more meteors can be seen,” says Dr Hill.

From a dark spot in a city location, you can expect to see perhaps one meteor every 5 or 6 minutes. From a dark country spot, perhaps one every 3 minutes.

You don’t need to have a telescope or binoculars. Just your own eyes is all you require.

Here are Dr Hill’s top tips for getting the most out of the meteor shower:

  1. Get comfortable. You’ll need to spend a considerable amount of time under the stars to catch the meteors. For example, it takes at least 15 minutes for your eyes to start to become dark adapted and allow you to notice the fainter meteors. That also means you should dress warmly.
  2. Find somewhere dark. Choose an observing spot away from street lights and with a good view of the entire sky. And don’t just look in the one spot. “While the meteors appear to radiate from near Eta Aquarii, they can travel quite a way across the sky,” says Dr Hill. “You want to be looking about 30 to 45 degrees to the left or right of the radiant — choose the direction with the least light pollution.”
  3. Watch with a friend. “Meteor observing is much more fun with family and friends around,” says Dr Hill. “That way there’ll be lots of oohs and aahs to share.”

Earth has been hit 566 times over 20 years

This map uses data gathered from 1994-2013 and shows where small asteroids hit Earth's atmosphere and produced very bright meteors, technically called 'bolides' and commonly referred to as 'fireballs'. The objects ranged in size from about 1 metre (3 feet) to almost 20 metres (60 feet).

This map uses data gathered from 1994-2013 and shows where small asteroids hit Earth’s atmosphere and produced very bright meteors, technically called ‘bolides’ and commonly referred to as ‘fireballs’. The objects ranged in size from about 1 metre (3 feet) to almost 20 metres (60 feet).

A map released by NASA’s Near Earth Object (NEO) Program reveals that small asteroids frequently enter and disintegrate in Earth’s atmosphere with random spread around the globe.

Released to the scientific community, the map visualises data gathered by U.S. government sensors from 1994 to 2013. (‘Sensors’ probably means, or at least includes, spy satellites. Ed.)

The data indicate that Earth’s atmosphere was hit by small asteroids, resulting in a bolide (or fireball), on 556 separate occasions in a 20-year period.

Almost all asteroids of this size disintegrate in the atmosphere and are usually harmless. The notable exception was the Chelyabinsk event, which was the largest asteroid to hit Earth in this period.

Trail left by the Chelyabinsk meteor.

Trail left by the Chelyabinsk meteor.

The new data could help scientists better refine estimates of the distribution of the sizes of NEOs including larger ones that could pose a danger to Earth.

Finding and characterising hazardous asteroids to protect our home planet is a high priority for NASA, and is one of the reasons the agency has increased by a factor of 10 investments in asteroid detection, characterisation and mitigation activities over the last five years.

In addition, NASA has aggressively developed strategies and plans with its partners in the U.S. and abroad to detect, track and characterise NEOs.

These activities also will help identify NEOs that might pose a risk of Earth impact, and further help inform developing options for planetary defence.

The public can help participate in the hunt for potentially hazardous Near Earth Objects through the Asteroid Grand Challenge, which aims to create a plan to find all asteroid threats to human populations and know what to do about them.

NASA is also pursuing an Asteroid Redirect Mission (ARM) which will identify, redirect and send astronauts to explore an asteroid.

Among its many exploration goals, the mission could demonstrate basic planetary defence techniques for asteroid deflection.

Adapted from information issued by NASA’s Jet Propulsion Laboratory. Chelyabinsk meteor image courtesy Alex Alishevskikh under CC. Map courtesy Planetary Science.

Shooting star, seen from above

ISS image of a meteor

The bright streak of a Perseid meteor as it flashes into Earth's upper atmosphere. The image was snapped by an astronaut aboard the International Space Station.

THIS ASTRONAUT PHOTOGRAPH, taken from the International Space Station (ISS) while over China (approximately 400 kilometres to the northwest of Beijing), provides the unusual perspective of looking down on a meteor as it passed through the atmosphere.

Many people have spent time outdoors under a dark sky, watching for “shooting stars” to streak across the firmament. In some cultures, this event is an occasion to make a wish; in others it is viewed as a herald of important events, such as the birth of a future ruler.

While not actual stars, “shooting stars” do come from outer space, in the form of meteoroids entering the Earth’s atmosphere.

Meteor or meteorite?

Meteoroids are small objects moving through the Solar System that are attracted to the Earth by its gravitational pull.

These small objects—typically fragments of asteroids or comets, though they can also originate from the Moon or Mars—begin to heat and burn up as they collide with air molecules in Earth’s atmosphere, creating a bright vapour trail or streak.

At this point, the object is known as a meteor. If any remnant of the object survives to impact the Earth’s surface, it becomes known as a meteorite.

While most meteorites are natural in origin, on occasion manmade space debris can re-enter the atmosphere and also become a meteor or even a meteorite!

Comes from a comet

The image was taken on August 13, 2011, during the Perseid Meteor Shower that occurs every August. The Perseid meteors are particles that originate from Comet Swift-Tuttle; the comet’s orbit is close enough for these particles to be swept up by the Earth’s gravitational field every year—leading to one of the most dependable meteor shower displays.

Green and yellow airglow appears in thin layers above the limb of the Earth, extending from image left to the upper right. Atoms and molecules above 50 kilometres in the atmosphere are excited by sunlight during the day, and then release this energy at night, producing primarily green light that is observable from orbit.

Part of a ISS solar panel is visible at upper right; behind the panel.

Astronaut photograph provided by the ISS Crew Earth Observations experiment and Image Science & Analysis Laboratory, Johnson Space Centre. Text adapted from information issued by William L. Stefanov, Jacobs/ESCG at NASA-JSC.

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Dinosaur discovery boosts meteor theory

Illustration of a large meteor impact with Earth

Evidence is strong that a huge meteor impact 65 million years ago led to the demise of the dinosaurs.

SCIENTISTS HAVE DISCOVERED the fossilised remains of a dinosaur that was alive not long before the catastrophic meteor impact 65 million years ago. The finding indicates that dinosaurs did not go extinct prior to the impact and provides further evidence as to whether the impact was in fact the cause of their extinction.

Researchers from Yale University discovered the fossilised horn of a ceratopsian—likely a Triceratops, which are common to the area—in the Hell Creek formation in Montana last year.

Yale graduate student Stephen Chester

Yale graduate student Stephen Chester discovered the last known dinosaur before the catastrophic meteor impact 65 million years ago.

They found the fossil buried just five inches below the K-T boundary, the geological layer that marks the transition from the Cretaceous period to the Tertiary period at the time of the mass extinction that took place 65 million years ago.

Since the impact hypothesis for the demise of the dinosaurs was first proposed more than 30 years ago, many scientists have come to believe the meteor caused the mass extinction and wiped out the dinosaurs.

But a sticking point has been an apparent lack of fossils buried within the three metres of rock below the K-T boundary. The seeming anomaly has come to be known as the “three-metre gap.”

Dinosaurs were doing fine

Until now, this gap has caused some palaeontologists to question whether the non-flying dinosaurs of the era—which included Tyrannosaurus rex, Triceratops, Torosaurus and the duckbilled dinosaurs—gradually went extinct sometime before the meteor struck. (Flying, or avian, dinosaurs survived the impact, and eventually gave rise to modern-day birds.)

“This discovery suggests the three-metre gap doesn’t exist,” said Yale graduate student Tyler Lyson, director of the Marmarth Research Foundation and lead author of the study, published online July 12 in the journal Biology Letters.

Illustration of primitive mammals and a Triceratops skeleton

Three small primitive mammals walk over a Triceratops skeleton, one of the last dinosaurs to exist before the mass extinction that gave way to the age of mammals.

“The fact that this specimen was so close to the boundary indicates that at least some dinosaurs were doing fine right up until the impact.”

While the team can’t determine the exact age of the dinosaur, Lyson said it likely lived tens of thousands to just a few thousand years before the impact.

“This discovery provides some evidence that dinosaurs didn’t slowly die out before the meteor struck,” he said.

The team is now examining other fossil specimens that appear to be buried close to the K-T boundary and expect to find more, Lyson said. He suspects that other fossils discovered in the past may have been closer to the boundary than originally thought and that the so-called three-metre gap never existed.

Adapted from information issued by Yale University. Images courtesy NASA / Mark Hallett / Tim Webster.

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Fire in the sky

  • Perseid meteor shower to put on a show
  • Best times to see it, August 12-13

The Perseids meteor shower is due to put on a sky show for Northern Hemisphere stargazers over the next couple of nights.

The best time to see the Perseids will be from the hours of 10pm to dawn, on the nights of August 12 and 13.

Adding to the spectacle will be the sight of the planets Venus, Mars and Saturn, along with a crescent Moon, in the western sky. These four will have dipped below the horizon by the time the meteor shower begins.

A meteor is the flash of light seen in the sky when a meteoroid—which in size can be anything from smaller than a grain of sand, all the way up to metres across—enters the Earth’s atmosphere.

The tremendous speed of entry means that the thin air gets compressed around the meteoroid, and briefly glows. The meteoroid itself usually disintegrates during the process.

If a meteoroid is large enough and solid enough, it might—or pieces of it might—survive and fall to the ground. When this happens, those pieces are known as meteorites.

Most meteoroids, particularly those involved in showers like the Perseids, are tiny in size.

Sky diagram showing the Perseid meteor shower

To see the Perseids, look to the western sky between 10pm and dawn, August 12 and 13, 2010.

Meter showers occur when the Earth’s orbit intersects the dusty trail left behind by a comet.

To avoid disappointment, it’s important to know, however, that meteor showers do not look like continuous fireworks displays. Most showers, including the Perseids, have a maximum of tens of meteors per hour—so working that out, you might see one every couple of minutes.

The Perseids will appear to “radiate” from one region of the sky, namely, the constellation Perseus. Perseus is a far northern constellation, which means that the best views of the shower are to be had by those who live in the Northern Hemisphere.

Southern Hemisphere stargazers are not favoured by the Perseids. Perhaps a handful of particular strong meteors might be seen zipping over the northern horizon, but generally they will not be visible.

Story by Jonathan Nally, editor SpaceInfo.com.au. Video courtesy NASA. Images by Pete Lawrence of Selsey, UK, and NASA.

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