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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.”

Biggest and best full-frame image of Pluto

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NASA has released this image of Pluto, the final and best full-frame image taken by New Horizons as it speeded towards its encounter with the dwarf planet. Visible is the light-coloured area informally dubbed ‘the heart’. Credit: NASA.

Live coverage of the Pluto encounter

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NASA’s New Horizons spacecraft is due to make its closest approach to Pluto at 9:49:57pm Australian Eastern Standard Time tonight (Tuesday, 14 July 2015).

At that time, the craft will be busy taking numerous images and other data of the icy world and its retinue of moons, so it won’t be simultaneously beaming back signals. Those signals will have to wait until after the encounter, when the data will slowly be returned to Earth.

Nevertheless, there will be great excitement at mission control, and you’ll be able to follow it all through NASA’s live coverage online.

NASA TV will be broadcasting special coverage beginning at 9:30pm AEST.

You can also follow New Horizons’ Twitter feed.

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.

Philae has landed

The European Space Agency’s (ESA) Rosetta mission has soft-landed its Philae probe on a comet, the first time in history that such an extraordinary feat has been achieved.

After a tense wait during the seven-hour descent to the surface of Comet 67P/Churyumov-Gerasimenko, the signal confirming the successful touchdown arrived on Earth at 16:03 GMT on November 12.

The confirmation was relayed via the Rosetta orbiter to Earth and picked up simultaneously by ESA’s ground station in Malargüe, Argentina and NASA’s station in Madrid, Spain. The signal was immediately confirmed at ESA’s Space Operations Centre, ESOC, in Darmstadt, and DLR’s Lander Control Centre in Cologne, both in Germany.

The first data from the lander’s instruments were transmitted to the Philae Science, Operations and Navigation Centre at France’s CNES space agency in Toulouse.

“Our ambitious Rosetta mission has secured a place in the history books: not only is it the first to rendezvous with and orbit a comet, but it is now also the first to deliver a lander to a comet’s surface,” noted Jean-Jacques Dordain, ESA’s Director General.

“With Rosetta we are opening a door to the origin of planet Earth and fostering a better understanding of our future. ESA and its Rosetta mission partners have achieved something extraordinary today.”

Philae, as seen from the Rosetta parent craft, descending to the comet.

Philae, as seen from the Rosetta parent craft, descending to the comet.

A game-changer

“After more than 10 years travelling through space, we’re now making the best ever scientific analysis of one of the oldest remnants of our Solar System,” said Alvaro Giménez, ESA’s Director of Science and Robotic Exploration.

“Decades of preparation have paved the way for today’s success, ensuring that Rosetta continues to be a game-changer in cometary science and space exploration.”

“We are extremely relieved to be safely on the surface of the comet, especially given the extra challenges that we faced with the health of the lander,” said Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Centre.

“In the next hours we’ll learn exactly where and how we’ve landed, and we’ll start getting as much science as we can from the surface of this fascinating world.”

Rosetta was launched on 2 March 2004 and travelled 6.4 billion kilometres through the Solar System before arriving at the comet on 6 August 2014.

“Rosetta’s journey has been a continuous operational challenge, requiring an innovative approach, precision and long experience,” said Thomas Reiter, ESA Director of Human Spaceflight and Operations.

“This success is testimony to the outstanding teamwork and the unique know-how in operating spacecraft acquired at the European Space Agency over the decades.”

510 million kilometres from Earth

The landing site, named Agilkia and located on the head of the bizarre double-lobed object, was chosen just six weeks after arrival based on images and data collected at distances of 30–100 km from the comet.

Those first images soon revealed the comet as a world littered with boulders, towering cliffs and daunting precipices and pits, with jets of gas and dust streaming from the surface.

Following a period spent at 10 km to allow further close-up study of the chosen landing site, Rosetta moved onto a more distant trajectory to prepare for Philae’s deployment.

Philae's first view from the surface of Comet 67P/Churyumov-Gerasimenko. One of the lander’s three feet can be seen in the foreground. The image is a two-image mosaic.

Philae’s first view from the surface of Comet 67P/Churyumov-Gerasimenko. One of the lander’s three feet can be seen in the foreground. The image is a two-image mosaic.

Five critical go/no-go decisions were made last night and early this morning, confirming different stages of readiness ahead of separation, along with a final pre-separation manoeuvre by the orbiter.

Deployment was confirmed at 09:03 GMT (10:03 CET) at a distance of 22.5km from the centre of the comet. During the seven-hour descent, which was made without propulsion or guidance, Philae took images and recorded information about the comet’s environment.

“One of the greatest uncertainties associated with the delivery of the lander was the position of Rosetta at the time of deployment, which was influenced by the activity of the comet at that specific moment, and which in turn could also have affected the lander’s descent trajectory,” said Sylvain Lodiot, ESA Rosetta Spacecraft Operations Manager.

“Furthermore, we’re performing these operations in an environment that we’ve only just started learning about, 510 million kilometres from Earth.”

Not all went according to plan

Touchdown was planned to take place at a speed of around 1 m/s, with the three-legged landing gear absorbing the impact to prevent rebound, and an ice screw in each foot driving into the surface.

But during the final health checks of the lander before separation, a problem was detected with the small thruster on top that was designed to counteract the recoil of the harpoons to push the lander down onto the surface.

The conditions of landing – including whether or not the thruster performed – along with the exact location of Philae on the comet are being analysed.

An extended science phase using the rechargeable secondary battery may be possible, assuming Sun illumination conditions allow and dust settling on the solar panels does not prevent it.

This extended phase could last until March 2015, after which conditions inside the lander are expected to be too hot for it to continue operating.

Philae's first multi-image panorama from the surface of the comet.

Philae’s first multi-image panorama from the surface of the comet.

Answering the big questions

Science highlights from the primary phase will include a full panoramic view of the landing site, including a section in 3D, high-resolution images of the surface immediately underneath the lander, on-the-spot analysis of the composition of the comet’s surface materials, and a drill that will take samples from a depth of 23 cm and feed them to an onboard laboratory for analysis.

The lander will also measure the electrical and mechanical characteristics of the surface. In addition, low-frequency radio signals will be beamed between Philae and the orbiter through the nucleus to probe the internal structure.

The detailed surface measurements that Philae makes at its landing site will complement and calibrate the extensive remote observations made by the orbiter covering the whole comet.

“Rosetta is trying to answer the very big questions about the history of our Solar System. What were the conditions like at its infancy and how did it evolve? What role did comets play in this evolution? How do comets work?” said Matt Taylor, ESA Rosetta project scientist.

“Today’s successful landing is undoubtedly the cherry on the icing of a 4 km-wide cake, but we’re also looking further ahead and onto the next stage of this ground-breaking mission, as we continue to follow the comet around the Sun for 13 months, watching as its activity changes and its surface evolves.”

A long and hard journey

While Philae begins its close-up study of the comet, Rosetta must manoeuvre from its post-separation path back into an orbit around the comet, eventually returning to a 20 km orbit on 6 December.

Next year, as the comet grows more active, Rosetta will need to step further back and fly unbound ‘orbits’, but dipping in briefly with daring flybys, some of which will bring it within just 8 km of the comet centre.

The comet will reach its closest distance to the Sun on 13 August 2015 at about 185 million km, roughly between the orbits of Earth and Mars. Rosetta will follow it throughout the remainder of 2015, as they head away from the Sun and activity begins to subside.

“It’s been an extremely long and hard journey to reach today’s once-in-a-lifetime event, but it was absolutely worthwhile. We look forward to the continued success of the great scientific endeavour that is the Rosetta mission as it promises to revolutionise our understanding of comets,” said Fred Jansen, ESA Rosetta mission manager.

You can keep up to date with the latest Rosetta news at ESA’s Rosetta blog.

Adapted from information issued by ESA. Images courtesy ESA / Rosetta / Philae / CIVA.

Mysterious dance of dwarfs may force a cosmic rethink

THE DISCOVERY THAT many small galaxies throughout the universe do not ‘swarm’ around larger ones as bees do but ‘dance’ in orderly orbits is a challenge to our understanding of how the universe formed and evolved.

The finding, by an international team of astronomers, including Professor Geraint Lewis of the University of Sydney, was published in the prestigious science journal Nature today.

“Early in 2013 we announced our startling discovery that half of the dwarf galaxies surrounding the Andromeda Galaxy are orbiting it in an immense plane” said Professor Lewis. “This plane is more than a million light years in diameter, but is very thin, with a width of only 300,000 light years.”

The universe contains billions of galaxies. Some, such as the Milky Way, are immense, containing hundreds of billions of stars. Most galaxies, however, are dwarfs, much smaller and with only a few billion stars.

Many of the larger galaxies have dwarf galaxies circling around them. Astronomers call them satellite galaxies.

Result contradicts standard understandings

For decades astronomers have used computer models to predict how these dwarf galaxies should orbit the large galaxies, and they’d always found that the dwarfs should be scattered randomly.

“Our Andromeda discovery did not agree with expectations, and we felt compelled to explore if it was true of other galaxies throughout the universe,” said Professor Lewis.

Using the Sloan Digital Sky Survey, a remarkable resource of colour images and 3-D maps covering more than a third of the sky, the researchers dissected the properties of thousands of nearby galaxies.

An artist's impression of the orbit of dwarf galaxies about a large galaxy

An artist’s impression of the orbit of dwarf galaxies about a large galaxy. Credit Geraint Lewis. The Hubble Image Archive was used as a source of the galaxies used in this illustration.

They were surprised to find that a large proportion of pairs of satellite galaxies are travelling in opposite directions if they are on opposite sides of larger galaxy hosts, said lead author Neil Ibata of the Lycée International in Strasbourg, France. And each of the dwarfs seemed to orbiting in the same plane, or angle, around the parent galaxy.

“Everywhere we looked we saw this strangely coherent co-ordinated motion of dwarf galaxies,” said Professor Lewis. From this the astronomers have extrapolated that this phenomenon is widespread in the universe, and seen in about 50 percent of galaxies.

“This is a big problem that contradicts our standard cosmological models. It challenges our understanding of how the universe works including the nature of dark matter,” said Professor Lewis.

Keeping an open mind

The researchers think the explanation might lie in some currently unknown physical process that governs how gas flows in the universe, although, as yet, there is no obvious mechanism that can guide dwarf galaxies into narrow planes.

Some experts, however, have made more radical suggestions, including bending and twisting the laws of gravity and motion.

“Throwing out seemingly established laws of physics is unpalatable,” said Professor Lewis, “but if our observations of nature are pointing us in this direction, we have to keep an open mind. That’s what science is all about.”

Adapted from information issued by the University of Sydney.

Watch NASA’s celebrations of the Apollo 11 landing

NASA’s APOLLO 11 CREW landed on the Moon July 20, 1969 (July 21 in Australia). The world watched 45 years ago as astronauts Neil Armstrong and Buzz Aldrin set their lunar module Eagle down in the Sea of Tranquility, while crewmate Michael Collins orbited above in the command module Columbia.

The agency is commemorating Armstrong’s “one giant leap for mankind” through a number of events, as well as on the agency’s website and NASA Television.

Buzz Aldrin stands next the lunar module Eagle on the surface of the Moon, July 1969.

Buzz Aldrin stands next the lunar module Eagle on the surface of the Moon, July 1969.

On July 21 at 12:39pm Monday, Eastern Australian time, (Sunday at 10:39pm, US EDT), which was the time 45 years ago when Armstrong opened the spacecraft hatch to begin the first spacewalk on the Moon, NASA TV will replay the restored footage of Armstrong and Aldrin’s historic steps on the lunar surface.

LIVE COVERAGE OF EVENTS: Watch NASA Television

On Tuesday at 12:15am, Eastern Australian time (Monday, July 21 at 10:15am, US EDT), from the agency’s Kennedy Space Centre in Florida, NASA TV will air live coverage of the renaming of the centre’s Operations and Checkout Building in honour of Armstrong, who passed away in 2012.

The renaming ceremony will include NASA Administrator Charles Bolden, Kennedy Centre Director and former space shuttle pilot Robert Cabana, as well as Apollo 11’s remaining crewmembers, Collins and Aldrin, and astronaut Jim Lovell, who was the mission’s back-up commander.

International Space Station NASA astronauts Steve Swanson, who is the current Station commander, and Reid Wiseman, also will take part in the ceremony from their orbiting laboratory 415 kilometres above Earth.

Launch of Apollo 11.

Launch of Apollo 11.

The Apollo 11 crew: Neil Armstrong, Michael Collins and Edwin 'Buzz' Aldrin.

The Apollo 11 crew: Neil Armstrong, Michael Collins and Edwin ‘Buzz’ Aldrin.

Armstrong and Aldrin on the Moon.

Armstrong and Aldrin on the Moon.

Kennedy’s Operations and Checkout Building has played a vital role in NASA’s spaceflight history. It was used during the Apollo program to process and test the command, service and lunar modules. Today, the facility is being used to process and assemble NASA’s Orion spacecraft, which the agency will use to send astronauts to an asteroid in the 2020s and Mars in the 2030s.

On Friday at 8:00am, Eastern Australian time (Thursday, July 24 at 6:00pm US EDT), which is the 45th anniversary of Apollo 11’s return to Earth, the agency will host a panel discussion – called NASA’s Next Giant Leap – from the Comic-Con International in San Diego, California.

Moderated by actor Seth Green, the panel will include Aldrin, NASA Planetary Science Division Director Jim Green, JPL systems engineer Bobak Ferdowsi (the man seen with the unique haircut in mission control during the landing of the Curiosity rover on Mars), and NASA astronaut Mike Fincke, who will talk about Orion and the Space Launch System rocket, which will carry humans on America’s next great adventure in space.

Adapted from information issued by NASA.

Hubble to search for worlds beyond Pluto

NASA’S NEW HORIZONS spacecraft, launched in January 2006, is closing in on its primary target, the dwarf planet Pluto. Arrival at the icy outer world is on track for 14 July 2015.

But when it reaches Pluto, New Horizons won’t be able to stop and admire the scenery. By necessity (ie. orbital mechanics and the fact that it doesn’t have a rocket motor to slow itself down) it will go sailing straight past, after having given us our first-ever close up glimpse of what used to be called the ninth planet. (I still do call it the ninth planet. Ed.)

This was always the plan. And the plan also calls for a second stage for the mission – a visit to one or more other icy worlds that orbit the Sun far beyond Pluto.

Artist's impression of the New Horizons spacecraft at Pluto

Artist’s impression of the New Horizons spacecraft at Pluto.

They’re called Kuiper Belt objects (KBOs), as they belong to a family of small, ice bodies that live in that part of the Solar System, called the Kuiper Belt.

The aim is to redirect New Horizons – once it has passed Pluto – onto a course that will take it near one or more of these KBOs.

But even though astronomers have been hunting for candidate KBOs for some years, they’ve yet to find one that is in the right place for New Horizons to visit. Yet there are probably some there that they just can’t see at the moment. So they’ve put out a call for help from the telescope best suited to spot any hidden KBOs – the Hubble Space Telescope.

This week, the Hubble Space Telescope Time Allocation Committee – the body that decides who gets to use the telescope – has recommended it be pressed into service.

The telescope will examine a small region of space to see if it can spot any KBOs. The first step will be doing a pilot study to see if Hubble can indeed spot KBOs in that region and at that distance – 8 billion kilometres from the Sun.

If it finds any, that will give the astronomers enough confidence to push ahead with a deeper, longer search to find the candidate KBOs for New Horizons to visit.

Image courtesy NASA.

Spotting the stars that eat Earths

SOME SUN-LIKE STARS are ‘earth-eaters.’ During their development they ingest large amounts of the kind of rocky material from which ‘terrestrial’ planets like Earth and Mars and are made.

Trey Mack, a graduate student in astronomy at Vanderbilt University, has developed a model that estimates the effect that such a diet has on a star’s chemical composition and has used it to analyse a pair of twin stars that both have their own planets.

“Trey has shown that we can actually model the chemical signature of a star in detail, element by element, and determine how that signature is changed by the ingestion of Earth-like planets,” said Vanderbilt Professor of Astronomy Keivan Stassun, who supervised the study.

A star’s chemical make-up is determined by analysing is light after it has been split into a high-resolution spectrum.

This ability will add substantially to astronomers’ understanding of the process of planet formation as well as assisting in the ongoing search for Earth-like exoplanets, according to the astronomers.

Heavy metal stars

First, some background: Stars consist of more than 98 percent hydrogen and helium. All the other elements make up less than 2 percent of their mass.

Astronomers have arbitrarily defined all the elements heavier than hydrogen and helium as ‘metals’ and have coined the term ‘metallicity’ to refer to the ratio of the relative abundance of iron to hydrogen in a star’s chemical makeup.

Since the mid-1990s, when astronomers developed the capability to detect extrasolar planets in large numbers, there have been several studies that attempt to link stars’ metallicity factor with the likelihood of planets forming in orbit around them.

In one such study, researchers at Los Alamos National Laboratory argued that stars with high metallicity are more likely to develop planetary systems than those with low metallicity.

Another study concluded that hot, Jupiter-sized planets are found predominantly circling stars with high metallicity while smaller planets are found circling stars with a wide range of metal content.

Twin star study

Building on the work of colleague Simon Schuler of the University of Tampa, , who expanded the examination of stars’ chemical composition beyond their iron content, Mack looked at the abundance of 15 specific elements relative to that of the Sun

He was particularly interested in elements like aluminium, silicon, calcium and iron that have melting points higher than 600 degrees Celsius because these are the materials that serve as building blocks for Earth-like planets.

Mack, Schuler and Stassun decided to apply this technique to the planet-hosting binary pair of stars designated HD 20781 and HD 20782. Both stars should have condensed out of the same cloud of dust and gas and so both should have started with the same chemical compositions.

This particular binary pair is the first one discovered where both stars have planets of their own.

Both of the stars in the binary pair are G-class dwarf stars similar to the Sun. One star is orbited closely by two Neptune-size planets. The other possesses a single Jupiter-size planet that follows a highly eccentric orbit.

The difference in their planetary systems make the two stars ideal for studying the connection between exoplanets and the chemical composition of their stellar hosts.

Artist’s impression of a Jupiter-like planet orbiting a star. Courtesy ESO/L. Calçada.

Artist’s impression of a Jupiter-like planet orbiting a star. Courtesy ESO/L. Calçada.

Voracious planet eaters

When they analysed the spectrum of the two stars the astronomers found that the relative abundance of the refractory elements was significantly higher than that of the Sun.

They also found that the higher the melting temperature of a particular element, the higher was its abundance, a trend that serves as a compelling signature of the ingestion of Earth-like rocky material.

They calculated that each of the twins would have had to consume an additional 10-20 Earth-masses of rocky material to produce the chemical signatures.

Specifically, the star with the Jupiter-sized planet appears to have swallowed an extra ten Earth masses while the star with the two Neptune-sized planets wolfed down an additional 20.

The results support the proposition that a star’s chemical composition and the nature of its planetary system are linked.

“Imagine that the star originally formed rocky planets like Earth. Furthermore, imagine that it also formed gas giant planets like Jupiter,” said Mack.

“The rocky planets form in the region close to the star where it is hot and the gas giants form in the outer part of the planetary system where it is cold. However, once the gas giants are fully formed, they begin to migrate inward and, as they do, their gravity begins to pull and tug on the inner rocky planets.”

“With the right amount of pulling and tugging, a gas giant can easily force a rocky planet to plunge into the star. If enough rocky planets fall into the star, they will stamp it with a particular chemical signature that we can detect.”

Systems like our own?

Following this logic, it is unlikely that either of the binary twins possesses terrestrial planets.

For one star, the two Neptune-sized planets are orbiting the star quite closely, at one-third the distance between the Earth and the Sun. For the other star the trajectory of the Jupiter-sized planet grazes the star, taking it closer than orbit of Mercury at the point of closest approach.

The astronomers speculate that the reason the star with the two Neptune-size planets ingested more terrestrial material than its twin was because the two planets were more efficient at pushing material into their star than the single Jupiter-sized planet was at pushing material into its star.

If the chemical signature of G-class stars that swallow rocky planets proves to be universal, “when we find stars with similar chemical signatures, we will be able to conclude that their planetary systems must be very different from our own and that they most likely lack inner rocky planets,” said Mack.

“And when we find stars that lack these signatures, then they are good candidates for hosting planetary systems similar to our own.”

Adapted from information issued by Vanderbilt University.

Partial eclipse of the Sun on Tuesday

A PARTIAL ECLIPSE WILL BE VISIBLE across Australia on Tuesday afternoon, April 29. It will be highest in the sky in Western Australia, including Perth and Albany, and it will be visible low in the sky near sunset in Melbourne and Sydney.

A small bit of Antarctica, an inaccessible part, will experience an annular eclipse, which occurs when the Moon is a little farther than average from the Earth so that it doesn’t entirely cover the Sun, instead leaving a thin ring of sunlight visible.

Partial solar eclipse

A partial solar eclipse will be experienced across Australia on the afternoon of April 29. Image courtesy Jay Pasachoff.

At an annular or a partial solar eclipse, the sky never gets dark, and to view it directly you must use a special, safe solar filter or project the image onto a wall or screen and then look away from the eclipse at the screen. Don’t be tempted to use ‘backyard’ filters such as looking through exposed film or X-rays – they are dangerous and you can end up blinded.

At Perth and Albany in Western Australia, where the Sun’s diameter will be 60%-65% covered by the Moon, the eclipse will start at 1:15pm local time and end at 3:59pm, with maximum coverage at 2:41pm. This means that the whole event will be visible.

In Melbourne, the eclipse will occur from 3:58pm to and will be about halfway through by the time the Sun sets.

In Sydney, it will start at 4:13pm, and again, the Sun will set while it is still halfway through.

In Adelaide, it will begin at 3:26pm local time, with mid-eclipse at 4:37pm and sunset at 5:34pm.

In Hobart, it will begin at 3:51pm, with mid-eclipse at 5:01pm and sunset at 5:16pm.

In Darwin, it will start at 4:22pm local time, with mid-eclipse at 4:56pm and the end of the eclipse at 5:28pm.

In Brisbane, it will begin at 4:31pm, with mid-eclipse and sunset happening at the same time, 5:17pm.

In Cairns, it will begin at 4:57pm with mid-eclipse at 5:32pm and sunset at 5:58pm.

French amateur astronomer Xavier Jubier has put a Google map online that can be zoomed into, and you can click to find out what you would see from any particular location.

Safe solar viewing

you should never look directly at the Sun, either normally or when there is an eclipse. The Sun’s visible and invisible rays can blind you very quickly. It is particularly important to not use any kind of optical aid to view the Sun — instant blindness will result. Do not use dark glasses, pieces of exposed film and so on — none of these things work.

There are three safe ways to witness a solar eclipse.

First, if you have some special ‘eclipse glasses’ from a previous eclipse, you can use those – as long as they are in good condition and don’t have any holes or scratches.

The second way is to make a ‘pinhole camera’ from two sheets of white cardboard. Using a pin or a needle, punch a hole in the middle of one of the sheets. Then, standing with your back to the Sun, so that the sunlight is coming over your shoulder, with one hand hold the sheet of cardboard with the pinhole in it up to one side of your head. Then with the other hand, hold the other sheet out at about arm’s length in front of you. Arrange it so that the sunlight goes through the pinhole and falls onto the second sheet of cardboard. You’ll see a small image of the Sun on the second sheet. When the eclipse is happening, you’ll see a chunk taken out of the round Sun. Experiment to get the right distance between the sheets of cardboard.

The third way is to view it online, as there will telescopes videocasting it on the internet – see below for details.

Here are some links to information on how to safely view solar eclipses, total or partial, including how to make a pinhole camera:

Solar viewing safety advice from the Queensland government

How to build a pinhole camera

How to build a different kind of pinhole camera

View the eclipse online

Slooh will broadcast the partial phases of the eclipse live from Australia. Viewers can watch free on Slooh.com or by downloading the Slooh iPad app. Coverage will begin on Monday, April 28th, starting at 11pm US PDT on April  28, which is 2am US EDT on the 29th, 6am GMT on the 29th and 4pm Australia Eastern Standard Time.

The live image stream will be accompanied by commentary from scientists. Viewers can ask questions during the show by using the hashtag #Slooh.

The deepest part of the eclipse, where the Moon might be viewed as being completely enveloped by the larger-seeming and more distant Sun, can only be observed from deep within Antarctica, in a remote uninhabited region. This is why this eclipse has been nicknamed the ‘penguin’ eclipse.

A sequence of images showing an annular solar eclipse

A sequence of images showing an annular solar eclipse. Unfortunately, this time, no one will get to see the annular or ‘ring of fire’ parts of the eclipse, but Australians will be treated to the partial phases. Image courtesy of Jay Pasachoff.

Says Slooh astronomer Bob Berman, “Researchers at the Amundsen-Scott South Pole Station will not view any kind of solar eclipse. After all, their long six-month night began over a month ago, and the Sun is below the horizon for them. If they could somehow rise off the icy surface and stretch their necks into space, they’d see a central annular eclipse, as it sweeps into space, narrowly missing our planet.”

“But hundreds of miles farther north, where the very low Sun still sits on the horizon, barely up, well, anyone there would see the Moon covering the slightly larger-seeming Sun behind it. The result is a lopsided, off-centre ring of fire surrounding the inky Moon.”

“However, no human will be in that small region of Antarctica. Thus, this is one of the few annular eclipses that will most likely only be seen by penguins.”

More information:

eclipses.info

totalsolareclipse.org

Melbourne Planetarium

Adapted from information issued by Williams College and Slooh. Images courtesy Jay Pasachoff and Slooh.