Posted on by Jenny Winder

It’s Time to Welcome Night Shining Clouds

Noctilucent clouds taken from the ISS Image Credit: NASA
Noctilucent clouds taken from the ISS Image Credit: NASA

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Astronomers usually curse and shake their fist at clouds for obscuring the sky and spoiling their observations. This month however, we enter the season when, after dark, thin veils of clouds appear to glow with an eerie blue light and are eagerly awaited and sought after.

Polar mesospheric, noctilucent or night shining clouds (NLC) form at the edge of space, between 76 and 85 kilometers up in the arid atmosphere, where there is one hundred millionth the amount of moisture found in the air at the Sahara Desert! Here temperatures can fall below -100 degrees Celsius, so what little water vapour is present freezes directly or forms on dust particles from micrometeors or volcanic eruptions.

During the Summer months, as the Sun stays close to the horizon, its rays illuminate these layers of ice crystals, producing a fine network of tenuous, incandescent filaments. They appear, in the Northern hemisphere, from mid May to mid August (mid November to mid February in the South) in latitudes between 50º and 70º, when the Sun is 6 to 16 degrees below the horizon. Look for them low in the Northwestern sky from an hour after sunset, or low in the Northeast before dawn.

They were first noted in 1885, two years after the eruption of Krakatoa when people were accustomed to looking at the spectacular sunsets and the glowing clouds were thought to be produced by the ash from the volcano in our atmosphere. Eventually the ash disappeared, but the clouds remained. In fact throughout the twentieth century noctilucent clouds have been occurring more frequently and across a wider area, as well as becoming brighter, perhaps due to climate change as increased greenhouse gases cool the mesosphere.  The clouds also vary with the solar cycle, as ultraviolet radiation from the Sun splits the water molecules and so the clouds decrease in brightness during solar maximum. Changes in brightness seem to follow fluctuations in solar radiation but about a year later, though nobody knows the reason for this time delay.

The clouds have been found to be highly reflective to radar, possibly due to sodium and iron atoms, stripped from micrometeors, forming a thin metal coating on the ice grains. In 2006 Mars Express discovered similar clouds, forming from carbon dioxide 100 kilometers up in the Martian atmosphere, that were also only observed when the Sun was below the horizon. In 2009 the Charged Aerosol Release Experiment (CARE) created artificial noctilucent clouds using rocket exhaust that were observed for several weeks. In July 2008 the crew aboard the ISS were treated to a noctilucent cloud display over Mongolia and were able to capture the image above.

So over the Summer months, keep an eye on the northern horizon after dark for a chance to catch these beautiful and unusually welcome clouds.

Find out more at NLC

Posted on by Jason Major

Enceladus On Display In Newest Images From Cassini

Enceladus' southern ice geysers are brilliant in backlit sunlight (NASA/JPL/SSI/J. Major)

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The latest images are in from Saturn’s very own personal paparazzi, NASA’s Cassini spacecraft, fresh from its early morning flyby of the ice-spewing moon Enceladus. And, being its last closeup for the next three years, the little moon didn’t disappoint!

The image above is a composite I made from two raw images (this one and this one) assembled to show Enceladus in its crescent-lit entirety with jets in full force. The images were rotated to orient the moon’s southern pole — where the jets originate — toward the bottom.

Cassini was between 72,090 miles (116,000 km) and 90,000 miles (140,000 km) from Enceladus when these images were acquired.

This morning’s E-19 flyby completed a trio of recent close passes by Cassini of the 318-mile (511-km) -wide moon, bringing the spacecraft as low as 46 miles (74 km) above its frozen surface. The goal of the maneuver was to gather data about Enceladus’ internal mass — particularly in the region around its southern pole, where a reservoir of liquid water is thought to reside — and also to look for “hot spots” on its surface that would give more information about its overall energy distribution.

Cassini had previously discovered that Enceladus radiates a surprising amount of heat from its surface, mostly along the “tiger stripe” features — long, deep furrows (sulcae) that gouge its southern hemisphere, they are the source of the water-ice geysers.

Cassini also used the flyby opportunity to study Enceladus’ gravitational field.

By imaging the moon with backlit lighting from the Sun the highly-reflective ice particles in the jets become visible. More direct lighting reduces the jets’ visibility in images, which must be exposed for the natural light of the scene or risk “blowing out” due to Enceladus’ natural high reflectivity.

The images below are raw spacecraft downloads right from the Cassini’s imaging headquarters in Boulder, CO.

Enceladus' geysers in action on May 2, 2012. (NASA/JPL/SSI)
Enceladus sprays ice into the hazy E ring, which orbits Saturn (NASA/JPL/SSI)

Cassini also swung closely by Dione during this morning’s flyby but the images from that encounter aren’t available yet. Stay tuned to Universe Today for more postcards from Saturn!

As always, you can follow along with the ongoing Cassini mission on JPL’s dedicated site here, as well as on the Cassini Imaging Central Laboratory for Operations (CICLOPS) site.

Posted on by Nancy Atkinson

Supermoon This Weekend

A 'side by side' comparison of 4 different shots taken over the period of 30 hours before the March 19, 2011 'SuperMoon'. It shows the progression of Moon in it's orbit until the closest point. Credit: Ramiz Qureshi, from Karachi, Pakistan.

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This weekend will provide the full Moon’s closest approach of the year to Earth. On Saturday, May 5, 2012 the Moon could appear as much as 14% bigger and 30% brighter than other full Moons of 2012, according to some calculations. Will you notice it? Not if you haven’t really been paying attention, or have a reference point to compare it to other full Moons. And it certainly won’t have any adverse effects on Earth, as this closest approach happens every year — just a fact of orbital mechanics. But perhaps a great way to celebrate Cinco de Mayo is to spend the evening gazing at the Moon!


Every month, as the Moon circles the Earth in its elongated orbit, its distance from the Earth varies. This weekend, the Moon is reaching what’s known as its perigee, the closest point to Earth in its orbit. It will be about 356,953 kilometers (221,802 miles) from Earth on Saturday. Apogee — when the Moon is farthest away — varies, but is around 405,000 km (252,000 miles) away.

What is most interesting is that the timing of the perigee and full Moon is really, really close: The full moon occurs at 03:34 UTC on May 6 (11:34 p.m. EDT on May 5 )eastern and perigee follows at 03:35 UTC (11:35 p.m. EDT)

David Morrison, from NASA says “supermoon” is not an astronomical term and he confirms a supermoon has no effect on Earth, and that the change in size is hardly noticeable to the average person. If you miss it, the Moon will be very nearly as close at the next full Moon, and very nearly as close as it was at the last full Moon.

But even better is that two weeks after the “supermoon” on May 5th, the Moon will be at apogee as it lines up in front of the Sun for an amazing annular eclipse on May 20th. An annular eclipse occurs when the Sun and Moon are exactly in line, but the apparent size of the Moon is smaller than that of the Sun. Hence the Sun appears as a very bright ring, or annulus, surrounding the outline of the Moon.

If you’re a photographer, take a picture of the Moon and send it to us. If we get a some good images, we’ll share them. Join our Flickr group, or send us your images by email (this means you’re giving us permission to post them). Please explain a little about it such as when you took it, the equipment you used, etc.

Here’s a video NASA put out about the Supermoon:

Posted on by Nancy Atkinson

Black Holes are More Like Venus Fly Traps than Vacuum Cleaners

These images, taken with NASA's Galaxy Evolution Explorer (GALEX) and the Pan-STARRS1 telescope in Hawaii, show a galaxy that brightened suddenly, caused by a flare from its nucleus. Credit: NASA, S. Gezari (JHU), A. Rest (STScI), and R. Chornock (Harvard-Smithsonian CfA)

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I’m going to try and say this before the Bad Astronomer does: Holy Haleakala! A team of astronomers using the Pan-STARRS1 telescope on Mount Haleakala in Hawaii have found evidence of a black hole ripping a star to shreds. While this isn’t the first time this type of activity has been detected, these new observations are the best views so far of what happens to objects that are consumed by a black hole. Plus, astronomers, for the first time, know what kind of star was destroyed and watched as it happened. This all helps in providing more insight into how black holes behave: They aren’t enormous vacuum cleaners that suck up and destroy everything around them, or sharks that seek out and consume their victims. Instead, like Venus Fly Traps, they wait for objects to come to them.

“Black holes, like sharks, suffer from a popular misconception that they are perpetual killing machines,” said Ryan Chornock of the Harvard-Smithsonian Center for Astrophysics (CfA). “Actually, they’re quiet for most of their lives. Occasionally a star wanders too close, and that’s when a feeding frenzy begins.”

If a star passes too close to a black hole, tidal forces can rip it apart. The remaining gases then swirl in toward the black hole. But just a small fraction of the material near a black hole falls in, while most of it just circles for a while – sometimes forever. The material close the black hole gets superheated, causing it to glow. By searching for newly glowing supermassive black holes, astronomers can spot them in the midst of a feast.

So, kind of like with Junior, the giant Venus Fly Trap in the movie “Little Shop of Horrors,” the feast is evident from what doesn’t get eaten.

This computer simulation shows a star being shredded by the gravity of a massive black hole. Some of the stellar debris falls into the black hole and some of it is ejected into space at high speeds. The areas in white are regions of highest density, with progressively redder colors corresponding to lower-density regions. The blue dot pinpoints the black hole’s location. The elapsed time corresponds to the amount of time it takes for a Sun-like star to be ripped apart by a black hole a million times more massive than the Sun.

The team discovered this type of glow on May 31, 2010, with Pan-STARRS1 and also with NASA’s Galaxy Evolution Explorer (GALEX). The flare brightened to a peak on July 12th before fading away over the course of a year. The event took place in a galaxy 2.7 billion light-years away, and the black hole contains as much mass as 3 million Suns, making it about the same size as the Milky Way’s central black hole.

“We observed the demise of a star and its digestion by the black hole in real time,” said Harvard co-author Edo Berger.

“We’re also witnessing the spectral signature of the ejected gas, said Suvi Gezari of The Johns Hopkins University who lead the research, “which we find to be mostly helium. It is like we are gathering evidence from a crime scene. Because there is very little hydrogen and mostly helium in the gas we detect from the carnage, we know that the slaughtered star had to have been the helium-rich core of a stripped star.”

Follow-up observations with the MMT Observatory in Arizona showed that the black hole was consuming large amounts of helium. Therefore, the shredded star likely was the core of a red giant star. The lack of hydrogen showed this is likely not the first time the star had encountered the same black hole, and that it lost its outer atmosphere on a previous pass.

The star may have been near the end of its life, the astronomers say. After consuming most of its hydrogen fuel, it had probably ballooned in size, becoming a red giant. The astronomers think the bloated star was looping around the black hole in a highly elliptical orbit, similar to a comet’s elongated orbit around the Sun.

This computer-simulated image shows gas from a tidally shredded star falling into a black hole. Some of the gas also is being ejected at high speeds into space. Astronomers observed a flare in ultraviolet and optical light from the gas falling into the black hole and glowing helium from the stars's helium-rich gas expelled from the system. Credit: NASA, S. Gezari (The Johns Hopkins University), and J. Guillochon (University of California, Santa Cruz)

“This is the first time where we have so many pieces of evidence, and now we can put them all together to weigh the perpetrator (the black hole) and determine the identity of the unlucky star that fell victim to it,” Gezari said. “These observations also give us clues to what evidence to look for in the future to find this type of event.”

The team’s results were published today in the online edition of the journal Nature.

Nature Science Paper by S. Gezari et al. (PDF document)

Sources: Harvard Smithsonian CfA, NASA

Posted on by Jason Major

ESA Turns On The JUICE For New Jupiter Mission

Galileo image of Ganymede, Jupiter's - and the Solar System's - largest moon. (Ted Stryk)

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The European Space Agency has given the go-ahead for an exciting mission to explore the icy moons of Jupiter, as well as the giant planet itself.

JUICE — JUpiter ICy moons Explorer — will consist of a solar-powered spacecraft that will spend 3.5 years within the Jovian system, investigating Ganymede, Europa and the upper atmosphere of Jupiter. Anticipated to launch in June 2022, JUICE would arrive at Jupiter in early 2030.

As its name implies, JUICE’s main targets are Jupiter’s largest icy moons — Ganymede and Europa — which are thought to have liquid oceans concealed beneath their frozen surfaces.

The largest moon in the Solar System, Ganymede is also thought to have a molten iron core generating a magnetic field much like Earth’s. The internal heat from this core may help keep Ganymede’s underground ocean liquid, but the dynamics of how it all works are not quite understood.

JUICE will also study the ice-coated Europa, whose cueball-smooth surface lined with cracks and jumbled mounds of frozen material seem to be sure indicators of a subsurface ocean, although how deep and how extensive is might be are still unknown — not to mention its composition and whether or not it could be hospitable to life.

The rust-colored cracks lining Europa's otherwise smooth surface hint at a subsurface ocean. (Ted Stryk)

“JUICE will give us better insight into how gas giants and their orbiting worlds form, and their potential for hosting life,” said Professor Alvaro Giménez Cañete, ESA’s Director of Science and Robotic Exploration.

The JUICE spacecraft was originally supposed to join a NASA mission dedicated to the investigation of Europa, but NASA deemed their proposed mission too costly and it was cancelled. According to Robert Pappalardo, study scientist for the Europa mission based at JPL, NASA may still supply some instruments for the spacecraft “assuming that the funding situation in the United States can bear it.”

Artist's rendering of JUICE at Jupiter. (ESA/AOES)

JUICE will also capture images of Jupiter’s moon Callisto and search for aurorae in the gas giant’s upper atmosphere, as well as measure the planet’s powerful magnetic field. Once arriving in 2030, it will spend at least three years exploring the Jovian worlds.

Read more in today’s news release from Nature, and stay tuned to ESA’s JUICE mission page here.

Recalibrated Galileo images © Ted Stryk. See more of Ted’s excellent work on his site Planetary Images From Then And Now.

Posted on by Nancy Atkinson

Beautiful, Glowing Dust in Orion

This image of the region surrounding the reflection nebula Messier 78, just to the north of Orion’s belt, shows clouds of cosmic dust threaded through the nebula like a string of pearls. Credit: ESO/APEX (MPIfR/ESO/OSO)/T. Stanke et al./Igor Chekalin/Digitized Sky Survey 2

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On Earth, dust can be pretty mundane. But in space, dust can be beautiful, especially when the dust reflects starlight – and even more so when we have the chance to see the reflections in different wavelengths. Here in NGC 2068, also called Messier 78, this dazzling submillimetre-wavelength view from the Atacama Pathfinder Experiment (APEX) telescope Dust shows the glow of interstellar dust grains, pointing the way to where new stars are being formed.
This reflection nebula lies just to the north of Orion’s Belt. When seen in visible light glimmers in a pale blue glow of starlight, but much of the light is blocked by the dust. In this image, the APEX observations are overlaid on the visible-light image in orange. APEX’s view reveals the gentle glow of dense cold clumps of dust, some of which are even colder than -250 C.

A visible light image from ESO of the reflection nebula Messier 78. Credit: ESO and Igor Chekalin

Compare the new image with this earlier, visible light image of M78.

One filament seen by APEX appears in visible light as a dark lane of dust cutting across Messier 78. This tells us that the dense dust lies in front of the reflection nebula, blocking its bluish light. Another prominent region of glowing dust seen by APEX overlaps with the visible light from Messier 78 at its lower edge. The lack of a corresponding dark dust lane in the visible light image tells us that this dense region of dust must lie behind the reflection nebula.

Observations of the gas in these clouds reveal gas flowing at high velocity out of some of the dense clumps. These outflows are ejected from young stars while the star is still forming from the surrounding cloud. Their presence is therefore evidence that these clumps are actively forming stars.

At the top of the image is another reflection nebula, NGC 2071. While the lower regions in this image contain only low-mass young stars, NGC 2071 contains a more massive young star with an estimated mass five times that of the Sun, located in the brightest peak seen in the APEX observations.

This chart shows the location of Messier 78 in the famous constellation of Orion (The Hunter). This map shows most of the stars visible to the unaided eye under good conditions, and Messier 78 itself is highlighted with a red circle on the image. This reflection nebula is quite bright and can be seen well in moderate-sized amateur telescopes. Credit: ESO, IAU and Sky & Telescope

Source: ESO

Posted on by Jason Major

Where All The Hottest Stars Gather

The star cluster NGC 6604 (ESO)

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An ESO telescope captures a group of hot young stars that would outshine any Hollywood party!

At the upper left of this image is the star cluster NGC 6604, a grouping of hot young stars within a larger collection located in the sky near the much more famous Eagle Nebula (of “Pillars of Creation” fame.) The young stars, which burn bright and blue, are helping make a new generation of stars with their strong stellar winds, which condense nearby gas and dust into even more star-forming regions.

Eventually the new stars will replace the ones seen here, which, although big and bright, will quickly burn through their stellar fuel and fade. Such is the life cycle of massive stars — live fast and die young.

This image was acquired by the MPG/ESO 2.2-meter telescope at the European Southern Observatory’s La Silla Observatory in Chile. NGC 6604 is about 5,500 light-years from Earth, located in the constellation Serpens. Read more on the ESO news release here.

Posted on by Fraser Cain

Astronomy Cast Episode 259: Exploration of Venus

Mars gets all the attention, but you might be surprised to know how much Venus has been explored. From initial telescope observations and the early flyby missions, to the landers… yes landers and orbiters. We know quite a lot about Venus, but the planet sure didn’t give up its secrets easily.

You can watch us record Astronomy Cast live every Monday at 12:00 pm PDT (3:00 pm EDT, 2000 GMT). Make sure you circle Fraser on Google+ to see it show up in the feed. You can also see it live over on our YouTube channel.

If you’d like to be notified of all our live events, sign up for our notification email at Cosmoquest. You can check out our calendar here.

Posted on by Nancy Atkinson

Cassini’s Last Flyby of Enceladus Until 2015

Below a darkened Enceladus, a plume of water ice is backlit in this view. Credit: NASA/JPL-Caltech/Space Science Institute

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On May 2, the Cassini spacecraft will be swooping past the moon we all love to love — Enceladus — and coming within 74 kilometers (46 miles) of its fractured, jet-spewing surface. The images should be spectacular, and the science should be just as enticing. With Cassini’s radio science experiment, scientists hope to learn more about how mass is distributed under Enceladus’ south polar region, the very interesting place which features jets of water ice, water vapor and organic compounds spraying out of long fractures.

This is the last close flyby of Enceladus until 2015, so we have to take advantage of the views!

Cassini scientists will be looking specifically for a concentration of mass in that region could indicate subsurface liquid water or an intrusion of warmer-than-average ice that might explain the unusual plume activity. They’ll also be observing the plumes and looking for hot spots to try and understand the global energy balance of Enceladus.

They also hope to learn more about the moon’s internal structure by measuring variations in the gravitational pull of Enceladus against the steady radio link to NASA’s Deep Space Network on Earth.

Additionally, Cassini’s composite infrared spectrometer instrument will be observing the side of Enceladus that always faces away from Saturn to monitor for hot spots. The imaging camera team also plans to take images of the plume to look for variability in the jets.

Cassini will also be flying by Dione at a distance of about 8,000 kilometers (5,000 miles), enabling the imaging cameras to create several mosaic images of the icy moon, and the composite infrared spectrometer to monitor heat emission.

We’ll try to post images and info as they become available!

Posted on by Nancy Atkinson

Hundreds of Rogue Stars Found Just Outside the Milky Way

astronomers have identified nearly 700 rogue stars that appear to have been ejected from the Milky Way galaxy. When these stars received the powerful kick that knocked them out of the galaxy, they were small, yellow stars like the sun. But in the multi-million-year journey they evolved into red giant stars. Credit: Michael Smelzer, Vanderbilt University

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It’s not quite like being kicked off a reality TV show, but some stars can get kicked out from their home galaxy. These stars – called various names like rogue, runaway or hypervelocity stars – were predicted to exist for quite some time, and finally just in the past couple of years a few of them have actually been discovered. But now a group of nearly 700 rogue stars have been found on the outskirts of the Milky Way. The astronomers who found them argue they are hypervelocity stars that have been ejected from the center of the galaxy.

“These stars really stand out. They are red giant stars with high metallicity which gives them an unusual color,” said Kelly Holley-Bockelmann from Vanderbilt University, who conducted the study with graduate student Lauren Palladino.

They found these stars analyzing the millions of stars cataloged in the Sloan Digital Sky Survey.

“We figured that these rogue stars must be there, outside the galaxy, but no one had ever looked for them. So we decided to give it a try,” said Holley-Bockelmann, who is studying the behavior of the black hole at the center of the Milky Way galaxy.

Runaway stars are kicked into motion either through a supernova explosion of a companion star, through gravitational interactions with other stars in a cluster, or through encounters with a black hole. One scenario could involve a binary pair of stars that get caught in the black hole’s grip, and as one of the stars spirals in towards the black hole, its companion is flung outward at a tremendous velocity.

This is the scenario the researchers focused on, and so they looked for red giant stars just outside the Milky Way.

Red giant stars are the end stage in the evolution of small, yellow stars like the Sun. So, the stars in this new red giant rogues category should have been small stars like the Sun when they got ejected. As they traveled outward, they continued to age until they reached the red giant stage. Even traveling at hypervelocities, it would take a star about 10 million years to travel from the central hub to the spiral’s edge, 50,000 light years away.

“Studying these rogue stars can provide us with new insights into the history and evolution of our home galaxy,” said Holley-Bockelmann

There are a few methods for discovering runaway rogue stars. The first is to examine stars individually and analyze their motion in the plane of the sky (proper motion) along with their motion towards or away from us (radial velocity) to determine if a given star has sufficient velocity to escape. The second is to look at the effects some stars have on the local environment. Since young clusters contain large amounts of gas and dust, stars plowing through it will create bow shocks, similar to those a boat makes in the ocean.

A fast-moving star, Alpha Camelopardalis, creates a stunning bow shock in this image from WISE. Credit: NASA/JPL-Caltech/WISE Team

The team from Vanderbilt selected these stars based on their location in intergalactic space between the Milky Way and the nearby Andromeda galaxy and by their peculiar red coloration.

The researchers’ next step is to determine if any of their candidates are unusually red brown dwarfs instead of red giants. Because brown dwarfs produce a lot less light than red giants, they would have to be much closer to appear equally bright.

Read the team’s paper.

Source: Vanderbilt University