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What’s up? Night sky for April 2012

Star trails over an observatory

The southern sky is full of wonderful treats for the stargazer. (This star trail photo by Iztok Boncina was made by keeping the camera shutter open.)

Except where indicated, all of the phenomena described here can be seen with the unaided eye. And unless otherwise specified, dates and times are for the Australian Eastern Standard Time zone, and sky directions are from the point of view of an observer in the Southern Hemisphere. (If you’re in the Northern Hemisphere, please see the video at the bottom of the page for What’s Up in your night sky.)

April 3

The Moon, now just over three-quarters full, will be about 11 Moon widths above and to the left of the bright blue star, Regulus, the brightest star of the constellation Leo. A little further below is what looks like a red star, but is actually the planet Mars. The colours of Regulus and Mars make a nice contrast. About 77.5 light years from Earth, Regulus is not one star but four, grouped into two pairs. Multiple star systems are very common throughout the Milky Way galaxy.

April 4

The Moon is still in the vicinity of Mars tonight, being above and to the right of the planet. Incidentally, when I use a term such as “vicinity”, it is not to be taken as suggesting the two bodies are physically near each other out there in space. Rather, they are simply within similar lines-of-sight from our vantage point on Earth.

April 4 sky view

April 4, 8:00pm. The Moon, Mars and the star Regulus will make an attractive triangle in the northern part of the sky. Note the colour difference between blue Regulus and ruddy Mars.

April 7

Full Moon occurs today at 5:19am Sydney time (19:19 Universal Time on April 6). In a similar fashion to its “encounters” with Regulus and Mars a few days earlier, tonight the Moon will be about six Moon widths to the right of another bright star, Spica, and about 10 Moon widths above the planet Saturn. Spica is the brightest star of the constellation Virgo; it is a blue giant star about 260 light years from Earth. This is a great time to see Saturn (see April 16), so it’s a good idea to use the nearby Moon to identify it.

April 8

Today the Moon will be at the closest point in its orbit, called perigee. The distance between the two bodies today will be 358,311 kilometres.

April 10

This evening, take a look about 12 Moon widths below the Moon and you’ll see a reddish looking star that looks a bit like Mars. It’s the star Antares, and its name actually “rival of Mars”. Antares is the brightest star of the constellation Scorpius, and is a red supergiant star about 883 times bigger than our Sun!

Saturn

Saturn, as it appears through a backyard telescope. Image by Steve Massey.

April 13

It is Last Quarter Moon tonight at 8:50pm Sydney time (10:10 Universal Time).

April 16

Today the planet Saturn reaches what astronomers call “opposition”. This means that, from an Earthly perspective, it is the opposite direction to the Sun—so if you could look down on the Solar System from above you’d see the Sun, Earth and Saturn (in that order) in a straight line … although Saturn, of course, is much further from us than the Sun. The period around opposition is a considered a great time to view a planet, as it rises in the east around the same time as the Sun sets in the west, and is therefore nice and high in the sky by late evening.

April 19

If you’re an early riser, out to east this morning before sunrise you’ll see the very thin crescent Moon. Above and to its right is a bright looking star. Well that’s not a star; it’s the planet Mercury, the closest planet to the Sun.

April 19 sky view

April 19, 6:30am. The thin crescent Moon and the planet Mercury will be visible together in the eastern sky before sunrise.

April 21

New Moon occurs today at 5:18pm Sydney time (07:18 Universal Time).

April 23

Today the Moon will again reach the farthest point in its orbit, apogee, at a distance from Earth of 406,421 kilometres.

April 24

Today the Moon makes another apparent close approach to a star, this time Aldebaran, the brightest star of the constellation Taurus. The pair will be low in the western sky after sunset. Like Antares, Aldebaran too is a red star, but not a supergiant—it is only about 44 times the size of our Sun. It’s about 65 light years from Earth.

April 25

There’ll be a lovely astronomical pairing in this evening’s sky, with the Moon very close to Venus. The Moon is the second-brightest object in our night sky, and Venus is the third-brightest.

April 25 sky view

April 25, about 7:15pm. The thin crescent Moon and Venus will be close together in the western sky.

April 29

It is First Quarter Moon today at 7:58pm Sydney time (09:58 Universal Time). First Quarter is a good time to look at the Moon through a telescope, as the sunlight angle means the craters and mountains are throwing nice shadows, making it easier to get that 3D effect.

There’s more great night sky viewing information at Melbourne Planetarium’s Skynotes site.

If you’re in the Northern Hemisphere, here’s a Jet Propulsion Laboratory video that details what you can see this month:

If you have any questions or comments on the night sky, we’d be happy to answer them. Please use the Feedback Form below. Happy stargazing!

Images courtesy IAU and Iztok Boncina / ESO.

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Earth’s other moons

EARTH USUALLY HAS MORE THAN ONE MOON, according to a team of astronomers from the University of Helsinki, the Paris Observatory and the University of Hawaii at Manoa.

Our 3,400-kilometre-diameter Moon, so beloved by poets, artists and romantics, has been orbiting Earth for over 4 billion years. Its much smaller cousins, dubbed “minimoons,” are thought to be only metres across and to usually orbit our planet for less than a year before resuming their previous lives as asteroids orbiting the Sun.

Mikael Granvik (formerly at UH Manoa and now at Helsinki), Jeremie Vaubaillon (Paris Observatory) and Robert Jedicke (UH Manoa) calculated the probability that at any given time Earth has more than one moon. They used a supercomputer to simulate the passage of 10 million asteroids past Earth. They then tracked the trajectories of the 18,000 objects that were captured by Earth’s gravity.

They concluded that at any given time there should be at least one asteroid with a diameter of at least one metre orbiting Earth. Of course, there may also be many smaller objects orbiting Earth, too.

Captured by Earth’s gravity

According to the simulation, most asteroids that are captured by Earth’s gravity would not orbit Earth in neat circles. Instead, they would follow complicated, twisting paths. This is because a minimoon would not be tightly held by Earth’s gravity, so it would be tugged into a crazy pathby the combined gravity of Earth, the Moon and the Sun.

Path of a simulated minimoon

The path of a simulated minimoon that is temporarily captured by Earth. The object approaches Earth from the right and finally escapes capture along the red path to the upper right. The size of Earth and the Moon are not to scale but the size of the minimoon’s path is to scale in the Earth-Moon system. Inset: Radar image of near-Earth asteroid 1999. This 3.5-km-wide asteroid is more than 1,000 times larger than the biggest minimoons, but it shows the irregular shape and expected of minimoons.

A minimoon would remain captured by Earth until one of those tugs breaks the pull of Earth’s gravity, and the Sun once again takes control of the object’s trajectory. While the typical minimoon would orbit Earth for about nine months, some of them could orbit our planet for decades.

“This was one of the largest and longest computations I’ve ever done,” said Vaubaillon. “If you were to try to do this on your home computer, it would take about six years.”

In 2006, the University of Arizona’s Catalina Sky Survey discovered a minimoon about the size of a car. Known by the unimaginative designation 2006 RH120, it orbited Earth for less than a year after its discovery, then resumed orbiting the Sun.

“Minimoons are scientifically extremely interesting,” said Jedicke. “A minimoon could someday be brought back to Earth, giving us a low-cost way to examine a sample of material that has not changed much since the beginning of our Solar System over 4.6 billion years ago.”

The team used the Jade supercomputer at the National Computer Centre for Higher Education (Centre Informatique National de l’Enseignement Supérieur, or CINES) at Montpelier, France.

The team’s paper, “The population of natural Earth satellites,” appears in the March issue of the journal Icarus.

Adapted from information issued by the University of Hawaii at Manoa. 1999 JM8 image made with NASA’s Goldstone Solar System Radar in California and the Arecibo Observatory in Puerto Rico by a team of astronomers led by Dr. Lance Benner of NASA’s Jet Propulsion Laboratory in Pasadena, California

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Earth from Space: Sideways view of Antarctica

Oblique ISS view of Livingston Island and Deception Island

An astronaut aboard the International Space Station took this photo at a highly oblique angle. It shows a small part of the Antarctic coastline.

THE INCLINED EQUATORIAL ORBIT of the International Space Station (ISS) limits astronauts to nadir views of Earth—looking straight down from the spacecraft—between approximately 52 degrees North latitude and 52 degrees South.

However, when viewing conditions are ideal, the crew can obtain detailed oblique images—looking outwards at an angle—of features at higher latitudes, such as Greenland or, in this image, Antarctica.

While the bulk of the continent of Antarctica sits over the South Pole, the narrow Antarctic Peninsula extends like a finger towards the tip of South America. The northernmost part of the Peninsula is known as Graham Land, a small portion of which (located at approximately 64 degrees South latitude) is visible at the top left in this astronaut photograph.

Off the coast of Graham Land to the north-northwest, two of the South Shetland Islands—Livingston Island and Deception Island—are visible. Both have volcanic origins, and active volcanism at Deception Island has been recorded since 1800. (The last verified eruptive activity occurred in 1970.)

Closer to the coastline of Graham Land, Brabant Island (not part of the South Shetlands) also includes numerous outcrops of volcanic rock, attesting to the complex tectonic history of the region.

The ISS was located over the South Atlantic Ocean, approximately 1,800 kilometres to the northeast when this image was taken. This long viewing distance, combined with the highly oblique angle, accentuates the shadowing of the ground and provides a sense of the topography similar to the view you get from an airplane.

It also causes foreshortening of features in the image, making them appear closer to each other than they actually are. For example, the distance between Livingston and Deception Islands is approximately 20 kilometres.

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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Earth from Space – Eruption in the Red Sea

Satellite image of a volcanic eruption in the Zubair Group

NASA Earth Observing-1 (EO-1) satellite image of a volcanic eruption in the Zubair Group of islands in the Red Sea.

AN ERUPTION OCCURRED in the Red Sea in December 2011. According to news reports, fishermen witnessed lava fountains reaching up to 30 metres tall on December 19.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites observed plumes on December 20 and December 22. Meanwhile, the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite detected elevated levels of sulphur dioxide, further indicating an eruption.

The activity in the Red Sea included more than an eruption. By December 23, 2011, what looked like a new island had appeared.

The Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite captured these high-resolution, natural-colour images on December 23, 2011 (above), and October 24, 2007 (below).

Satellite image of Zubair Group islands

A satellite image of the same region, taken in 2007, shows no sign of the new volcanic island.

The image from December 2011 shows an apparent island where there had previously been an unbroken water surface. A thick plume rises from the island, dark near the bottom and light near the top, perhaps a mixture of volcanic ash and water vapour.

The volcanic activity occurred along the Zubair Group, a collection of small islands off the west coast of Yemen. Running in a roughly northwest-southeast line, the islands poke above the sea surface, rising from a shield volcano.

This region is part of the Red Sea Rift where the African and Arabian tectonic plates pull apart and new ocean crust regularly forms.

Wider satellite image of a volcanic eruption in the Zubair Group

This wider view shows more of the islands in the Zubair Group.

Close up satellite image of a volcanic eruption in the Zubair Group

And this close up gives a better view of the new island and the huge plume of smoke and steam.

NASA Earth Observatory image created by Jesse Allen, using EO-1 ALI data provided courtesy of the NASA EO-1 team. Text adapted from information issued by Michon Scott.

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Earth from Space – Cocos (Keeling) Islands

NASA satellite image of the South Keeling Islands

NASA satellite image of the South Keeling Islands, part of the Cocos (Keeling) Islands archipelago in the Indian Ocean between Australia and Sri Lanka.

THE COCOS (KEELING) ISLANDS lie in the eastern Indian Ocean, about 2,900 kilometres northwest of Perth, Western Australia. It is about halfway between Australia and Sri Lanka.

Comprised of coral atolls and islands, the archipelago includes North Keeling Island and the South Keeling Islands. Total human population is about 600.

The Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite captured this natural-colour image of South Keeling Islands on July 31, 2009.

Coral atolls—which are largely composed of huge colonies of tiny animals such as cnidaria—form around islands. After the islands sink, the coral remains, generally forming complete or partial rings. Only some parts of South Keeling Islands still stand above the water surface. In the north, the ocean overtops the coral.

Along the southern rim of this coral atoll, the shallow water appears aquamarine. Water darkens to navy blue as it deepens toward the central lagoon. Above the water line, coconut palms and other plants form a thick carpet of vegetation.

In 2005, the Australian government issued a report on the Cocos (Keeling) Islands, summarising field research conducted between 1997 and 2005. It found that hard corals, which play a primary role in reef building, were not the only corals at South Keeling Islands. Soft corals were also thriving at study sites throughout the reef. Although coral and rock predominated, the researchers also found varying amounts of silt, sand, rubble, sponges, and seaweed

Some of the coral had recently died, and coral predators appeared in high densities at some sites. But overall, the report noted, “the coral reef community at Cocos (Keeling) Islands is very healthy and in a stable period, with little impact from anthropogenic activities.”

The Cocos Islands are served by regular Virgin Australia flights, which land on and depart from the single 2,438-metre-long runway shown in the enlargement below:

Cocos (Keeling) Islands runway

Close up satellite image of the runway on the Cocos (Keeling) Islands.

For a full-size version of the main image, click here (3MB)

NASA Earth Observatory image created by Jesse Allen and Robert Simmon, using EO-1 ALI data provided courtesy of the NASA EO-1 team. Text adapted from information issued by Michon Scott.

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What’s up? Night sky for January 2012

Stargazers with telescopes at night

Summer nights are perfect for stargazing.

Except where indicated, all of the phenomena described here can be seen with the unaided eye. And unless otherwise specified, dates and times are for the Australian Eastern Daylight Time (AEDT) zone, and sky directions are from the point of view of an observer in the Southern Hemisphere.

January 1

It is First Quarter Moon today at 5:15pm AEDT. First Quarter is a good time to look at the Moon through a telescope, as the sunlight angle means the craters and mountains  throw nice shadows, making it easier to get that 3D effect.

January 3

Today the Moon will reach the farthest point in its orbit from the Earth, which is called apogee. It’s distance from our planet will be 404,578 kilometres.

While you’re out looking at the Moon, you’ll notice a bright looking star above and to the left. Well, that’s not a star; it’s actually the planet Jupiter. If you have access to a telescope, or even a pair of 7×50 (or better) binoculars, train them on Jupiter and you should see up to four tiny pinpoints of light on either or both sides of the planet—these are the moons Galileo discovered, Io, Europa, Ganymede and Callisto. If you take a look again tomorrow night, you’ll see that their positions will have changed as they whiz around the planet.

And in fact, we’re only a few days away from the anniversary of their discovery. On the 7th of this month, it will be 402 years since Galileo spotted them!

January 5

Today the Earth reaches perihelion in its orbit around the Sun. Perihelion is the point in a solar orbit when the body in question (eg. Earth) is at its closest to the Sun. Perihelion occurs today at midday AEDT, at a distance between Earth and Sun of about 147,098,000 kilometres. (The opposite of perihelion is aphelion, which for Earth will occur on July 5, 2012 at a distance of about 152,098,000 kilometres.)

If you have a pair of binoculars, you’ll see a pretty sight tonight, with the soon-to-be-full Moon appearing to sit above a beautiful star cluster called the Pleiades, or Seven Sisters. When the Moon is not around and the sky is dark, most people can make out 6 to 7 of the Pleiades stars, although eagle-eyed stargazers can see a few more. There are actually hundreds of stars in this beautiful open star cluster, and it is also filled with beautiful whispy gas clouds, although the stars and the gas are not actually related to each other—we just happen to be seeing them at a time when the stars are drifting through the gas.

Diagram of Moon near Pleiades in January 5's night sky

This is the view in the evening of January 5, with the Moon sitting above the beautiful star cluster known as the Pleiades. A pair of binoculars will show the scene well. Tomorrow night the Moon will have shifted east, and will be near to Albebaran, the brightest star in the constellation Taurus.

January 6

Tonight you might notice a fairly bright, reddish-looking star just above the Moon. This is Aldebaran, the brightest star in the constellation Taurus.

January 9

Full Moon occurs today at 6:30pm AEDT.

January 12

Tonight, the Moon will appear above and to the right of a bright blue star. This is Regulus, the brightest star in the constellation Leo.

January 14

In this morning’s pre-dawn sky out to the east, the Moon will appear above and to the left of the planet Mars, which looks like a ruddy-coloured star. As you gaze at it, spare a thought for the Mars Science Laboratory, which was launched a little under two months ago and which is due to reach the Red Planet on August the 6th this year.

January 16

It is Last Quarter Moon today at 8:08pm AEDT.

January 17

In this morning’s sky, the Moon will be just above and to the right of the planet Saturn, which looks like a bright star. Nearby is Spica, the brightest star in the constellation Virgo.

Diagram showing the Moon near Spica and Saturn in January 17's night sky

The Moon will be near to both the star Spica and the planet Saturn (the bright yellowish "star" below the Moon) on January 17. If you have access to a small telescope, take a look at both the craters and mountains on the Moon and Saturn and its glorious rings.

January 18

Today the Moon will be at the closest point in its orbit, called perigee. The distance between the two bodies today will be 369,887 kilometres.

January 20

In the early dawn sky, take a look for the Moon and you should see a reddish-looking star just above it. This is Antares, the brightest star in the constellation Scorpius. Compare Antares with Mars—do you think they look similar? The ancients thought so, and in fact the name Antares means “rival of Mars”.

January 23

New Moon occurs today at 8:39pm AEDT.

January 27

Tonight, there’ll be a lovely sight in the evening sky out to the west, with the crescent Moon paired with the bright planet Venus (about 20 Moon widths to its left).

January 30

This evening, the Moon meets up with Jupiter again, appearing below the planet in the northwestern part of the sky.

Also today, the Moon will again reach apogee again, at a distance from Earth of 404,323 kilometres.

Diagram showing the Moon near Jupiter in January 30's night sky

The Moon will sit just below the planet Jupiter in the evening sky of January 30.

January 31

And finally for January, we have a second First Quarter Moon, which occurs today at 3:10pm AEDT.

There’s more great night sky viewing information at Melbourne Planetarium’s Skynotes site.

If you have any questions or comments on the night sky, we’d be happy to answer them. Please use the Feedback Form below. Happy stargazing!

Main image courtesy IAU.

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Earth from Space – Videos of our World, Pt 2

HERE ARE SOME MORE AMAZING short videos put together from images taken by astronauts aboard the International Space Station.

This first one was made from images taken on December 4, 2011, and shows a pass from just northwest of Morocco to central Kazakhstan. The first thing that can be seen is Spain and Portugal, with Lisbon lit up brightly in the foreground near the Atlantic Ocean and Madrid in the middle of Spain.

The pass continues into France, with the English Channel in the far left and the Italian Peninsula in the far right. Further down the pass and on the left video, the Baltic Sea appears as a dark patch surrounded by light as the ISS continues to the east-northeast towards Moscow, Russia. The pass continues toward central Russia before the sunrise in the east comes up.

This next one was taken November 24, 2011 and shows a pass over the South Pacific Ocean northeast to the North Atlantic Ocean, just east of Newfoundland. The video begins over the dark Pacific Ocean as the ISS travels northeast towards the western coast of Mexico. The bright lights of Mexico City can be seen left of track, along with the lights of Honduras and Guatemala just right of track.

The pass continues over the Yucatan Peninsula, where Cozumel and Merida are visible as brighter spots on the peninsula. As the ISS tracks northeast over the Caribbean Sea, southeastern United States becomes visible, with the Florida Peninsula standing out well. The city lights of the larger cities such as Miami, Tampa, and Orlando light up the peninsula. The pass ends by tracking up the eastern coast of the United States, where Washington D.C., Baltimore, and New York City stand out.

The third video was taken November 18 to 19, 2011, and shows a pass from South Africa, west of Johannesburg, to southern Pakistan. The Russian vehicle Soyuz is shown off-centre throughout the video, just days before astronauts Mike Fossum, Satoshi Furukawa, and Sergey Volkov boarded this vehicle to come back to Earth.

Near the beginning of the video, the bright lights of Johannesburg as displayed as the ISS tracks northeast up the eastern Africa coastline. A few lightning storms can also be seen near Johannesburg. As the pass continues, the Arabian Peninsula is only briefly seen in the far right of the video before the pass ends over the Arabian Sea, just south of Pakistan.

This one was taken on November 16, 2011, on a pass over the Pacific Ocean, from just west of California to just west of Costa Rica and Panama in Central America. The camera in the cupola is facing west-southwest towards North and Central America. The pass begins looking just north of the Baja Peninsula, where Los Angeles and San Diego can carefully be seen near the coast. Continuing down the Baja Peninsula and the Gulf of California, the pass continues looking into Mexico. Finally, as the cloud cover thickens, the pass closes over Central America, looking far west at Costa Rica and Honduras.

Taken on October 15, 2011, this sequence of shots shows a pass from just west of San Francisco, California over the Pacific Ocean to the southern tip of the Hudson Bay. The video begins as the ISS is just west of San Francisco flying northeast. The coastal lights distinguish the land and water here.

The pass continues northeast toward Wyoming and North Dakota, before crossing over into Canada. From here, the Aurora Borealis is seen, with an interesting looking angle from underneath the lights. A blanket of clouds covers Manitoba and Ontario as the ISS tracks closer to the Northern Lights.

This video was taken on December 4, 2011,, on a pass from just northwest of Morocco to central Kazakhstan. The first thing that can be seen is Spain and Portugal, with Lisbon lit up brightly in the foreground near the Atlantic Ocean and Madrid in the middle of Spain.

The pass continues into France, with the English Channel in the far left and the Italian Peninsula in the far right. Further down the pass and on the left video, the Baltic Sea appears as a dark patch surrounded by light as the ISS continues to the east-northeast towards Moscow, Russia. The pass continues toward central Russia before the sunrise in the east comes up.

The next video was taken on October 20, 2011, on a descending pass from eastern China to western New Guinea, and rounds out to an ascending pass just as the video ends north of Australia. As the pass begins southeastward towards the South China Sea, the first noticeably-lit area is that of Hong Kong and Macau. The island of Taiwan can also be easily seen left of track.

The ISS passes over the South China Sea towards the Philippines, which have some cloud cover and storms. Finally, the pass ends just north of Australia, where the Yorke Peninsula can be seen as a dark, rusty colour protruding into the water.

And this final video was taken on October 22, 2011, on a pass from the North Atlantic Ocean, just west of Portugal and Spain, to northwest of Mozambique in southeastern Africa. This video begins just northwest of the United Kingdom and shows the ISS travelling southeast towards Africa. The camera points at the sky, capturing clusters of stars as they seem to fly by.

Videos courtesy NASA and the Image Science and Analysis Laboratory, NASA-Johnson Space Centre.

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Australia from Space: Part 5

IT’S DIFFICULT TO GET A TRUE PICTURE of the scale of Australia’s Red Centre from the ground, but satellite images help us to comprehend the breadth and beauty of the region. These remarkable images were taken by the Proba, Envisat and Landsat satellites, and show two of Australia’s most famous landmarks—Uluru and Lake Eyre.

Uluru

The rock formation Uluru, also known as Ayers Rock, as seen by the European Proba satellite. Uluru is the world's largest monolith, and a sacred site to Australia's indigenous peoples. It is 3.6 km long and two km wide. The walk around it covers 9.4 km.

Uluru 2

This black and white Proba image gives us a closer view of Uluru, and shows the layers of rock titled towards the vertical.

Lake Eyre Basin

This Envisat image highlights the Lake Eyre Basin, one of the world’s largest internally draining systems, in the heart of Australia. White cloud streaks stand in contrast to the Red Centre’s vast amounts of crimson soil and sparse greenery. The basin covers about 1.2 million sq km (about the size of France, Germany and Italy combined), including large portions of South Australia (bottom), the Northern Territory (upper left) and Queensland (upper right) and a part of western New South Wales (bottom right). This image was acquired by the European Envisat satellite’s Medium Resolution Imaging Spectrometer on 3 July 2010 at a resolution of 300 metre.

Lake Eyre

This Landsat satellite image shows a portion of Lake Eyre (lower-left corner) and the north-south sand dunes of the Simpson and Tirari deserts in the remote outback of South Australia. The Thematic Mapper on Landsat 5 acquired this image on 31 May 2011.

Earlier Australia from Space pictorials:

Australia from Space: Part 1

Australia from Space: Part 2

Australia from Space: Part 3

Australia from Space: Part 4

Adapted from information issued by ESA.

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Australia from Space: Part 4

MORE WONDERFUL IMAGES of Australia’s coastline, courtesy of the European Envisat Earth-monitoring satellite. Envisat was launched in March 2002 and at 8.5-tonnes is one of the largest satellites ever put into orbit. It circles the Earth every 101 minutes from north to south.

Satellite image of the Great Barrier Reef

An Envisat MERIS image of the Great Barrier Reef centred on Cape York Peninsula. Taken on 19 August 2004, this MERIS Full Resolution mode images has a spatial resolution of 300 metres.

Satellite image of the Southern Great Barrier Reef

This Envisat image features the southern part of the Great Barrier Reef off Australia’s Queensland coast. It is the world’s most protected marine area, one of its natural wonders and a World Heritage site. Spanning more than 2,000 km and covering an area of some 350,000 sq km, it is the largest living structure on Earth and the only one visible from space. This image was acquired by Envisat’s Medium Resolution Imaging Spectrometer (MERIS) on 8 November 2010 at a resolution of 300 metres

Satellite image of the Northern Great Barrier Reef

Another view of the Great Barrier Reef. Australian researchers have discovered that Envisat's Medium Resolution Imaging Spectrometer (MERIS) sensor can detect coral bleaching down to 10 metres depth. This means Envisat could potentially map coral bleaching on a global scale. MERIS acquired this image on 18 May 2008, working in Full Resolution mode to yield a spatial resolution of 300 metres.

Close up of the sea off northwestern WA

Sea and coral atolls off the West Australian coast, as seen by Envisat's MERIS ocean colour sensor.

Earlier Australia from Space pictorials:

Australia from Space: Part 1

Australia from Space: Part 2

Australia from Space: Part 3

Adapted from information issued by ESA.

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What’s up? The night sky for December 2011

Telescope dome at night

Stargazing is great fun, now that the warmer summer weather is here.

Except where indicated, all of the phenomena described here can be seen with the unaided eye. And unless otherwise specified, dates and times are for the Australian Eastern Standard Time zone, and sky directions are from the point of view of an observer in the Southern Hemisphere.

December 2

It is First Quarter Moon today at 8:52pm Australian Eastern Daylight Time (AEDT). First Quarter is a good time to look at the Moon through a telescope, as the sunlight angle means the craters and mountains  throw nice shadows, making it easier to get that 3D effect.

December 6

Today the Moon will reach the farthest point in its orbit, apogee, at a distance from Earth of 405,412 kilometres. And if you take a look at the Moon this evening, you’ll see a bright ‘star’ above and to its right. That’s not a star—it’s actually the planet Jupiter!

December 9

Take a look at the Moon in this evening’s sky, and you’ll see a brightish star a little way out to its right. And yes, this one really is a star. It’s called Aldebaran, and it’s the brightest star in the constellation Taurus. Aldebaran is a red giant star roughly 44 times as big as the Sun, and is about 65 light-years from Earth.

December 10

Full Moon occurs today at 1:36am AEDT, and tonight everyone in Australia and New Zealand will experience a total lunar eclipse. See our separate lunar eclipse story for full details on how, when and where to see it.

Eclipses aside…although it looks very pretty high up there in the sky, astronomers, both amateur and professional, generally hate the full Moon. This is because its light tends to drown out many of the fainter objects they’re interested in seeing. (It does this by actually making the sky glow.) It’s also not a good time to look at the Moon itself through a telescope, as the overhead sunlight (as seen from the perspective of the Moon) doesn’t throw any shadows across the lunar surface—and shadows are what give the craters and mountains their 3D look.

Man looking through a telescope

The Moon looks great through a telescope, but you won't need one to see the total lunar eclipse on December 10, 2011.

December 17

If you’re up early today, look for the Moon and you’ll see that it seems to have two companions. A little way below and to its left is the star Regulus, and below and to its right is the planet Mars. Regulus is actually a quadruple star system, comprised of four stars in two groups of two, gravitationally bound to one another. But the main star is a young, blue star a little over three times the mass of the Sun, and about three to four times as big as the Sun too.

December 18

It is Last Quarter Moon today at 11:48am AEDT. The Moon is still near Mars in the sky, being above and to the right of the planet in the hours before dawn.

December 21

The Moon, a star and a planet make a nice triangle in this morning’s sky. The star is Spica, the brightest star in the constellation Virgo, and the planet is Saturn. Saturn will be to the left of the Moon, and Spica will be above Saturn. Spica, a blue giant star, is the 15th brightest star in the night sky and is about 260 light-years from Earth.

December 22

There are two items of note for today. First, the Moon will be at the closest point in its orbit, called perigee, which is the opposite of apogee. The distance between the two bodies today will be 364,800 kilometres. And secondly, today marks the summer solstice in the Southern Hemisphere. This is the day of the year when the Sun is highest in the sky.

December 25

New Moon occurs today at 5:06am AEDT.

December 27-28

The Moon is back in the western evening sky. Over these two nights, it’ll be paired up with the planet Venus—the duo will make a very attractive sight in the evening dusk.

There’s more great night sky viewing information at Melbourne Planetarium’s Skynotes site.

If you have any questions or comments on the night sky, we’d be happy to answer them. Please use the Feedback Form below. Happy stargazing!

Story by Jonathan Nally. Images courtesy IAU.

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