Archive for February, 2013

GALLERY: Light and dark in the Milky Way

SET AGAINST A BACKGROUND of millions of glowing stars from the brightest part of the Milky Way, a region so dense with stars that barely any dark sky can be seen, lies the bright star cluster NGC 6520 and its neighbour, the dark nebula Barnard 86.

This part of the constellation Sagittarius is one of the richest star fields in the whole sky – the Large Sagittarius Star Cloud. The huge number of stars dramatically emphasise the blackness of dark clouds like Barnard 86.

Known as a Bok globule, Barnard 86 was described as “a drop of ink on the luminous sky” by its discoverer Edward Emerson Barnard, an American astronomer who discovered and photographed numerous comets, dark nebulae, one of Jupiter’s moons, and made many other contributions. An exceptional visual observer and keen astrophotographer, Barnard was the first to use long-exposure photography to explore dark nebulae.

Through a small telescope Barnard 86 looks like a hole in the star fields, or a window onto a patch of distant, clearer sky. However, it is actually in the foreground of the star field – a cold, dark, dense cloud made up of small dust grains that block starlight and make the region appear black. It is thought to have formed from the remnants of an interstellar cloud that formed the star cluster NGC 6520, seen just to the left of Barnard 86.

NGC 6520 is an open star cluster that contains many hot stars that glow bright blue-white, a telltale sign of their youth. Open clusters usually contain a few thousand stars that all formed at the same time, giving them all the same age. Such clusters usually only live comparatively short lives, on the order of several hundred million years, before drifting apart.

Both NGC 6520 and Barnard 86 are thought to lie at a distance of around 6,000 light-years from our Sun. The stars that appear to be within Barnard 86 are actually in front of it, between us and the nebula.

The image was taken with the Wide Field Imager, an instrument mounted on the MPG/ESO 2.2-metre telescope at the ESO La Silla Observatory.

Adapted from information issued by ESO. Images courtesy ESO / Digitised Sky Survey 2. Acknowledgement: Davide De Martin

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Name Pluto’s moons

THE DISCOVERER OF PLUTO’S two tiniest moons are inviting the public to help select names for the new moons. By tradition, the moons of Pluto have names associated with Hades and the underworld.

“The Greeks were great storytellers, and they have given us a colourful cast of characters to work with,” said Mark Showalter, Senior Research Scientist at the Carl Sagan Centre of the SETI Institute in Mountain View, California.

Pluto has five moons – Charon (discovered 1978), Nix and Hydra (discovered 2005), and two known simply as P4 and P5, discovered in 2011 and 2012 respectively. Astronomers are now looking for names for P4 and P5.

Moons of the underworld

All the bodies in the Pluto system are named after mythological figures of the underworld – Pluto, the god of the underworld; Charon, the ferryman of the dead; Nix, Greek goddess of darkness and night; and Hydra, the nine-headed serpent that battled Hercules.

Showalter and the teams of astronomers who made the discoveries will select two names based on the outcome of the voting. Like Pluto’s three other moons, Charon, Nix and Hydra, they need to be assigned names derived from Greek or Roman mythology.

Beginning today, people can vote by visiting http://plutorocks.seti.org/, and select from a list of suggest ‘underworld’ names.

Visitors to the website will also be able to submit their own suggestions. These will be reviewed by the team and could be added to the ballot. Voting will end February 25, 2013. The final names will be announced after their formal approval by the International Astronomical Union.

First mission to Pluto

P4 was discovered in 2011 in images taken by the Hubble Space Telescope. P5 was discovered a year later during a more intensive search for previously unseen objects orbiting the distant, dwarf planet. The moons are only 20 to 30 kilometres across.

Currently, Pluto is receiving special scrutiny by astronomers, because NASA’s New Horizons spacecraft is slated to arrive there in July 2015.

Launched in 2006, the craft is carrying some of the ashes of the man who discovered Pluto in 1930, Clyde Tombaugh.

A Google+ Hangout is scheduled on February 11 at 11:00am US PST (19:00 GMT) with two of the scientists involved in the discovery. Mark Showalter is from the SETI Institute, and Hal Weaver is a researcher at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

Questions from viewers will be taken during the event using Twitter hashtag #PlutoRocks, the SETI Institute Facebook page and the Google hangout.

Adapted from information issued by the SETI Institute. Pluto moons image courtesy NASA; ESA; M. Showalter, SETI Institute. New Horizons graphic courtesy NASA.

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NASA to keep watch on asteroid

THE RECORD-SETTING CLOSE APPROACH of an asteroid on February 15 (early morning February 16, Australian time) is an exciting opportunity for scientists, and a research team will use US National Radio Astronomy Observatory (NRAO) and NASA telescopes to gain a key clue that will help them predict the future path of this nearby cosmic neighbour.

A 45-metre-wide asteroid called 2012 DA14, discovered just a year ago, will pass only 28,000 kilometres above the Earth’s surface. That’s closer than the geosynchronous communication and weather satellites. While the object definitely will not strike the Earth, this is a record close approach for an object of this size. Astronomers around the world are preparing to take advantage of the event to study the asteroid.

A team including NRAO astronomer Michael Busch will use a novel observing technique to determine which way the space rock is spinning as it speeds on its orbit through the solar system. The direction of its spin is an important factor in predicting how the object’s orbit will change over time.

“Knowing the direction of spin is essential to accurately predicting its future path, and thus determining just how close it will get to Earth in the coming years,” Busch said.

Radar observations

Busch’s team will use the Karl G. Jansky Very Large Array (VLA) and the Very Long Baseline Array (VLBA) antennae at Pie Town and Los Alamos, New Mexico, along with a radar on NASA’s 70-metre-diameter antenna at Goldstone, California.

The Goldstone antenna will transmit a powerful beam of radio waves toward the asteroid, and NRAO’s New Mexico antennae will receive the waves reflected from the asteroid’s surface.

Because of the asteroid’s uneven surface and the different reflectivity of portions of the surface, the reflected radar signal will have a characteristic signature, or ‘speckles,’ as seen from Earth. By measuring which antenna in a widely-separated pair receives the speckle pattern first, the astronomers can learn which way the asteroid is spinning.

This way of using the telescopes is significantly different to their normal astronomical observing, and the research team has developed special techniques for processing the data.

Asteroid’s ‘afternoon’ heat

How does this tell anything about the asteroid’s orbital changes? Just as the afternoon is the warmest part of the day on Earth, the space rock develops a warm region that radiates infrared light in its maximum amount during ‘afternoon’ on the asteroid. That outgoing infrared radiation provides a gentle but firm jet-like push to the asteroid.

The direction of the asteroid’s spin determines whether ‘afternoon’ is either forward or rearward of its direction of motion.

If the hot spot is forward of the direction of motion, the infrared push will slow the asteroid’s orbital speed, and if the hot spot is rearward of the direction of motion, it will speed up the orbital motion. This effect, over time, can make a significant change in the orbit. This is called the Yarkovsky Effect, after the engineer who first identified it.

“When the asteroid passes close to the Earth or another large body, its orbit can be changed quickly by the gravitational effect of the larger body, but the Yarkovsky Effect, though smaller, is at work all the time,” Busch said.

Adapted from information issued by the National Radio Astronomy Observatory. Yarkovsky Effect graphic by Alexandra Bolling, NRAO / AUI / NSF. Orbit graphic by P. Chodas, NASA / JPL.

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GALLERY: Orion’s fiery sword

THE TANGLE OF CLOUDS and stars that lie in Orion’s sword is showcased in a new, expansive view from NASA’s Wide-field Infrared Survey Explorer, or WISE, spacecraft.

The constellation Orion, named for a mythical hunter, is visible in evening skies throughout the world from about December through April. The constellation appears tranquil and still to the naked eye, but in the hunter’s ‘sword’, what at first appears to be a slightly fuzzy star is actually a turbulent cauldron of stellar birth – the Orion Nebula.

WISE captured this vast view of the nebula in infrared light, picking up the glow from interstellar dust heated by newborn stars. The colours green and red in this false-colour view, highlight the warmed dust, while the white regions are even hotter. The energy from massive stars has ‘burned’ through the dust, carving out cavities, the largest of which is seen at the centre of the picture.

Astronomers think that our Sun was probably born in a similar cloud some five billion years ago. Over time, the cloud would have dispersed and the stars would have drifted apart, leaving us more isolated in space. The crowded newborn stars in the Orion nebula are less than 10 million years old – billions of years from now, they will likely spread out.

Adapted from information issued by NASA/JPL-Caltech/UCLA.

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Next-gen spacecraft on display in Florida

TWO OF THE NEXT GENERATION of space vehicles are going through their paces on the ground in Florida.

The Orion Ground Test Vehicle is seen in the photo below in the high bay of the Operations and Checkout Building at the Kennedy Space Centre, during a tour for media representatives.

Orion is the spacecraft designed to carry crews to space beyond low-Earth orbit. It will provide emergency abort capability, sustain the crew during the space travel and provide safe re-entry from deep space return velocities.

In many respects, Orion is similar to the old Apollo command module, but with the ability of carry at least four astronauts (Apollo could carry only three).

It was announced only weeks ago, that the Orion service module will be provided by the European Space Agency, based upon its successful Automated Transfer Vehicle uncrewed cargo craft.

The first unpiloted test flight of the Orion is scheduled in 2014 atop a Delta IV rocket, and in 2017, on a Space Launch System rocket.

Meanwhile, the Space Exploration Technologies, or SpaceX, Dragon spacecraft with solar array fairings attached, is seen inside a processing hangar at Cape Canaveral Air Force Station.

The spacecraft will launch on the upcoming SpaceX CRS-2 mission, perhaps in March. The flight will be the second commercial resupply mission to the International Space Station by SpaceX.

NASA has contracted for a total of 12 commercial resupply flights from SpaceX and eight from the Orbital Sciences Corp.

Adapted from information issued by NASA. Photos by Frankie Martin and Kim Shiflett.

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What’s up? Night sky for February 2013

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.

Feb 3

If you’re a night owl, look out to the east after midnight and you’ll see the Moon near the horizon. Below and to its right is what seems to be a bright star. It’s actually the planet Saturn. If you have access to even a small telescope, take a look. Its rings never fail to entrance. The gas giant planet has 62 confirmed natural satellites (ie. moons), and one artificial satellite – the NASA/ESA Cassini spacecraft, which has been exploring the Saturnian system since 2004. Saturn is presently about 1,455 million kilometres from Earth.

Feb 4

It is Last Quarter Moon today at 12:56am Australian Eastern Daylight Time (Feb 3, 13:56 Universal Time).

Feb 5

This evening, the Moon will appear close to the star Antares, the brightest star in the constellation Scorpius. Antares is a red supergiant star, about 880 times bigger and 10,000 times brighter than our Sun! It is about 550 light-years from Earth.

Feb 7

Today the Moon will be at the closest point in its orbit around Earth, called perigee. The distance between the two bodies will be 365,318 kilometres.

Feb 10

New Moon occurs today at 6:20pm Australian Eastern Daylight Time (07:20 Universal Time).

Feb 12

Just after sunset this evening, you might be able to see a very thin crescent Moon low on the horizon due west. To its left will be a brightish-looking ‘star’; it’s actually the planet Mercury. And just to Mercury’s left will be the ruddy-coloured planet Mars. Today Mercury is about 161 million kilometres from Earth, while Mars is about 348 million kilometres away.

Feb 18

There will be a major sky event this evening for those in the southern half of Australia! – the Moon will appear to move in front of the planet Jupiter. This is called an occultation (where ‘to occult’ means to ‘make go dark’). You’ll see the Moon slowly approaching Jupiter (which, to the naked eye, just looks like a bright star). Then, all of a sudden, as the Moon’s edge ‘reaches’ the planet, Jupiter will wink out. A short while later, after the Moon has moved on a bit (you’re actually watching it trundle along in its orbit), Jupiter will reappear on the other side.

Timings for the beginning of the event, in Standard (that is, non-Daylight Saving time – please adjust for your location if necessary) for capital cities are:

Adelaide: 10:00pm

Hobart: 10:22pm

Melbourne 10:33pm

Perth: 7:39pm

Unfortunately, the other capital cities will miss out.

Incidentally, it is First Quarter Moon this morning at 7:31am Australian Eastern Daylight Time (Feb 27, 20:31 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.

Feb 19

In tonight’s evening sky, to the northwest you’ll see the Moon, and to it’s left will be a bright star. And it really is a star this time, not a planet. It’s Aldebaran, the brightest star in the constellation Taurus. Just to Aldebaran’s left, you might be able to see a wide grouping of stars (binoculars will help). This is called the Hyades star cluster.

And today the Moon is at the farthest point in its orbit around the Earth, called apogee, at a distance of 404,472 kilometres.

Feb 25

Just near the Moon in this evening’s sky, will be the star Regulus, the brightest star in the constellation Leo.

Feb 26

Full Moon occurs today at 7:26am Australian Eastern Daylight Time (Feb 25, 20:26 Universal Time).

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!

Images courtesy IAU.

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