Crater-pocked Ceres looks back at Earth

These two views of Ceres were acquired by NASA's Dawn spacecraft on Feb. 12, 2015, from a distance of about 52,000 miles (83,000 kilometers) as the dwarf planet rotated. The images have been magnified from their original size. Credit: NASA

These two views of Ceres were acquired by NASA’s Dawn spacecraft on Feb. 12, 2015, from a distance of about 52,000 miles (83,000 km) as the dwarf planet rotated. The images have been magnified from their original size. The terminator or sunset line is along the right, where the craters are most obvious. Credit: NASA

Thought you’d like to see the latest photo of the asteroid Ceres taken by NASA’s Dawn spacecraft from a distance of 52,000 miles (83,000 km). That’s only a fifth the distance to the moon.

Perhaps similar to Ceres the bright spots we see when the moon is near full are actually relatively fresh craters that have blasted away pieces of the moon's crust exposing lighter material beneath. Credit: Bob King

Possibly similar to Ceres’ white spots, the bright patches we see when the moon’s at or near full are relatively fresh craters created by impacts that blasted away pieces of the moon’s crust exposing lighter material beneath. Three of the more prominent craters are labeled. At left, near the sunrise terminator, craters are shadowed exactly as they are along Ceres’ terminator. Credit: Bob King

We’re really getting clear views now of just how cratered this place is. Bright spots pop out from about the center of the disk to the left side. These areas are far from the shadowy terminator which defines the sunset line on Ceres’ globe.  From here, the Sun is higher in the Ceresian sky and nearly fully illuminates the orb’s surface features. I suspect that some of those shiny highlights are impact sites where fresh material glows brightly, similar to the moon.

Large arc-shaped feature on Ceres that may be impact related. Credit: NASA

Large arc-shaped feature on Ceres that may be impact related. Credit: NASA

Over time, cosmic rays and the solar wind darken rocks and soil tossed out during impacts until they blend into a uniform gray. The Dawn spacecraft is due to arrive at Ceres on March 6, 2015.

The white spot shines brightly in nearly overhead sunlight and shows little detail. Another white spot above center looks very much like a crater possible from a fresher impact that those that created the surrounding craters. Rays form around craters when material is blasted into space from an impact and rains down to create hundreds of secondary impacts moments later. Credit: NASA

The white spot at upper left, one of many on the asteroid, shines brightly in direct sunlight and shows little detail. Another white spot (center) looks like a fresher impact crater compared to its neighbors. Rays form around craters when material blasted into space from an impact rains down to excavate hundreds of secondary craters moments later. The largest white spot, seen in earlier photos, does not show in these most recent images. Credit: NASA

Sweet Valentine’s Day closeups of Rosetta’s Comet

Four image mosaic of Comet 67P/Churyumov-Gerasimenko comprising images taken on 14 February at 14:15 GMT from a distance of 8.9 km from the surface. The image scale is 0.76 m/pixel and the mosaic measures 1.35×1.37 km across. The image focuses on the stunning features of the Imhotep region, on the comet’s large lobe. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Four image mosaic of Comet 67P/Churyumov-Gerasimenko taken on Feb. 14 at 8:15 a.m. (CST) from a distance of 5.5 miles from the surface. The view measures 0.8 miles across. The image focuses on the stunning features of the Imhotep region, on the comet’s large lobe. Click for a large version. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

If you’ve ever wondered what it would be like to fly over a comet in a jet airplane, soak in these photos. This past Saturday, the Rosetta spacecraft swung within 3.7 miles (6 km) of the surface of Comet 67P/C-G. Pictures for the mosaic image (above) were taken from an altitude of just 29,000 feet, nearly 10,000 feet lower than a typical transatlantic flight.

It really is like looking out the plane window especially when you consider you’re viewing a chunk of landscape barely a mile across. You and I could walk across that mosaic in less than 20 minutes! Assuming no obstacles of course.

Cropped, close-in view of several raised circular structures near the center of the mosaic. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Cropped, close-in view of several raised circular structures near the center of the mosaic. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Closest approach occurred over the Imhotep region on the comet’s large lobe. What caught my eye was the long, layered mesa-like feature in the lower left of the frame. In the cropped version, you can make out the outlines of several raised, near-circular structures with smooth floors. Boulders, ranging in size from 12 feet (a few meters) to a 35 feet (10 meters) lie scattered across the whole surface of the comet. The big boulder near the top of the mosaic and seen up close below is named Cheops. It’s 148 feet or about 45 meters across.

Close-up view of the large, mesa-like formation photographed by Rosetta on Saturday from 29,000 feet. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Close-up, rotated view of the layered formation photographed by Rosetta on Saturday from 29,000 feet. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

The big boulder Cheops casts a shadow at upper right. It's not far from what looks like a section of the comet's crust that's collapsed. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

The big boulder Cheops (upper right) sits in its shadow. It’s not far from what looks like a collapsed area of the comet’s crust (left). Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

What appears to be a collapsed section of a cliff or wall. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

What appears to be a collapsed section of a cliff or wall. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Download the mosaic to your desktop and take a few minutes to explore it. You’ll find flows, depressions, more of of those circular features and a delightful assortment of boulders of all shapes and sizes. What are those things – dust-covered ice chunks?

Rosetta is now moving out for a far view of the comet and will reach a distance of about 158 miles (255 km) from the comet’s center tomorrow. Stop by in a day or two for new pictures of 67P’s atmosphere or coma. In the meantime you can download a zip file of the 16 individual frames comprising the mosaic here.

Tracking down February’s mystery supermoon – where is it?

This week’s new moon will be unusually close to Earth. Think of it as a ghostly supermoon. As is true for any new moon, it will be too close to the Sun in the daytime sky to see. This illustration shows the moon’s appearance and location if our eyes could somehow make it out through all the daylight. Source: Stellarium

Here comes the supermoon! But wait, doesn’t that only happen around full moon? Well, not always. Every month the moon swings around Earth in its elliptical (oval) orbit. On one side of the ellipse, it’s closest to Earth and on the opposite side, farthest. When it’s at its closest point, called perigee, at the time of full moon, we call it a supermoon.

During the closest supermoons, our satellite can appear up to 30% brighter and 14% larger. Whether anyone can actually see the difference is open to debate simply because there’s no normal-distance moon nearby with which to make a comparison.

No one pays attention to first quarter or crescent supermoons even though the moon can be closest to us at those phases, too. Thanks to incessant media coverage, only full supermoons get coverage. We like full moons for all sorts of reasons. When an extra close one’s in the offing, as happens on Sept. 27 this year, that’s just one more reason to like them.

The moon’s orbit around Earth is an ellipse with the Earth off-center at one the ellipse’s foci. During its 27-day-long orbit, the moon passes through perigee (closest) and apogee (farthest) points. This week’s new moon will be the second closest perigee of the year after the Sept. 27 full moon. Illustration not to scale. Credit: Bob King

Lest crescents and quarters get short shrift I’m here to hawk this month’s supermoon. Full disclosure. Since it occurs during new moon phase on Feb. 18 you won’t see it. No one sees a new moon except when it happens to be eclipsing the Sun. But northern hemisphere skywatchers can spot the moon two days before new and just one day after new this month, and it’ll be nearly as super as on the18th.

Tomorrow morning Feb. 16 the planet Mercury will lie about 9.5° (about one fist held at arm’s length) to the lower left of the thin crescent two days before new moon phase. This map shows the sky facing southeast about 40 minutes before sunrise. Source: Stellarium

What’s more, if you have a good view of the southeast horizon, tomorrow morning’s skinny crescent will lie near the planet Mercury low in the southeastern sky 40 minutes before sunrise. Be sure to carry along a pair of binoculars as Mercury is near “last quarter” phase and not nearly as bright as it can be.

The moon’s average distance is 240,000 miles, but tomorrow morning at 6 a.m. (CST) it will lie just 226,549 miles from Earth. At 1 a.m. Feb. 18 – the time of the invisible supermoon –  it will be 4,723 miles closer. The following day the moon slides out a bit to 222,092 miles en route to a striking double conjunction with Mars and Venus on Friday the 20th.

Even though we won’t see February’s supermoon, our planet will sense the difference. The additional gravitational force exerted by the close moon will make for unusually high tides. High tides occur when the Sun, moon and Earth are all in a line as they during both new moon phase and at full moon.

The moon, still very close to perigee, pops up in the western sky at dusk on Thurs. Feb. 19 well below Venus and Mars, now in close embrace. This map shows the sky about 35-45 minutes after sunset facing west. Source: Stellarium

So tomorrow morning you can catch the moon near Mercury at dawn, and on Thursday the 19th you’ll have the chance to enjoy the delicate grin of a one-day-old crescent in the west at dusk. Finally, on Friday, don’t miss the close conjunction of the moon with Mars and Venus.

Our satellite has a busy schedule this week!

 

Watch Charon make Pluto wobble

This close up look at Pluto and Charon, taken as part of the mission’s latest optical navigation (“OpNav”) campaign from Jan. 25-31, 2015, comes from the Long Range Reconnaissance Imager (LORRI) on the New Horizons spacecraft. Credit: NASA

NASA’s New Horizons spacecraft continues to take pictures of Pluto to better refine the locations of dwarf planet and its largest moon Charon in preparation for the spacecraft’s close encounter with the small planet on July 14.

You’ve probably heard Pluto’s a small object but until you see it next to the say the moon, it’s hard to appreciate just how small.

If we could move Pluto to the same distance as the moon from Earth (240,000 miles) it would look something like this in our night sky. Our moon is about 1 1/2 times larger than the dwarf planet but reflects far less light. Source: Stellarium

Its diameter is 1,471 miles (2,368 km) or 68% percent as large as the moon. Unlike the moon, which is as dark as asphalt, Pluto reflects far more light because its surface appears to be covered in methane ice. The dwarf planet’s albedo – the percentage of light it reflects back from the Sun – ranges between 49-66% – making it nearly twice that of Earth. Of course we have to remember that despite its shininess, the little world is more than 4 billion miles from the Sun. Sunlight falling there resembles a dark overcast day here on Earth.

In the animation we see an entire rotation of both Pluto and Charon; a “day” for each lasts 6.4 Earth days. Charon neither rises nor sets, but hovers over the same spot on Pluto’s surface, and the same side of Charon always faces Pluto. Astronomers call this arrangement tidal locking. If you went around the side of Pluto not facing Charon, you’d never see the moon.

The center of gravity, very similar to the center of mass, is the exact center of all the material (mass) that makes up an object. For a ruler, it’s in the middle. For a sledge hammer, the center is very close to the head. This is where you’d have to put your finger to balance the object. Credit: NASA

You’ll also notice that Charon is not exactly rotating around Pluto. Instead the two bodies are circling about the center of mass in the Pluto-Charon system. Called the barycenter, this is the point between two celestial objects where their gravities balance each other.

Let’s look at the Earth-moon system. The moon doesn’t orbit the exact center of the Earth, but a point on a line between the center of the Earth and the moon, approximately 1,062 miles (1,710
km) below the surface of the Earth, where their masses balance.

Diagram showing how two celestial objects orbit about their barycenter. Credit: NASA

Charon is 728 miles across – nearly half Pluto’s diameter. Compared to the dwarf planet it’s massive enough that the two bodies orbit about a barycenter well outside of Pluto. Look at the animation again and you’ll see how they orbit a mutual point in space where their gravities cancel out.

The Earth and Sun also revolve about their center of mass, but because the Sun is incredibly more massive than our planet that point is very close to the center of the Sun. Not so with Jupiter which is 318 times as massive as Earth. The Sun and Jupiter orbit about a point just outside our star’s blazing surface.

As seen from the side, a large planet and star orbit their shared center of mass, or barycenter, with the star seeming to shift back and forth as well as toward us and away. Credit: NASA

In the animation, you’ll notice that Pluto appears to wobble in a cyclical way every 6.4 days during its mutual revolution with Charon. Not only does the dwarf planet describe a small circle about the barycenter, it’s also moves toward and away from us during the cycle. When moving toward us, Pluto’s speed ticks up slightly; when away it’s slightly less.

Astronomers can detect these tiny wobbles or changes in speed in stars as well. We may not be able to see what’s tugging on the star, but by measuring the changing velocity of the star as it orbits about the planet-star barycenter, we can determine the mass(es) of any orbiting planets. It’s called the radial velocity method. With this tool, we’ve discovered hundreds of extrasolar planets.

 

 

 

A triple-scoop conjunction with a cherry on top!

Venus and Mars (at right) are drawing closer every night. This photo was taken at dusk Thursday Feb. 12 an hour and 15 minutes after sunset. On Feb. 20-21 they’ll be just half a degree apart or 8 times closer. The moon joins the pair on the 20th. Details: 35mm lens, f/3.5, ISO 800, 12 second exposure. Credit: Bob King

Get ready. One week from tonight fate has arranged a celestial spectacle. That night (Feb. 20) a two-day-old crescent moon will “triple up” with the planets Venus and Mars after sundown.

The entire bunch will fit within a circle 1.5° wide or just three times the diameter of the full moon. Like a glittering pendant around your sweetheart’s neck the trio will dangle above the western horizon in the afterglow of sunset. This is a not-to-miss event and one that should be fairly easy to photograph.

Moon, Mars and Venus around 6:45 p.m. (CST) on Feb. 20 in the western sky. Be sure to look for the darkly-lit part of the moon illuminated by sunlight reflecting off Earth called earthshine. It’s a beautiful sight in binoculars. Source: Stellarium

Look toward the west in the direction of the setting Sun; the best viewing time will be 45 to 90 minutes after sunset. With plenty of light to work with, taking a picture of the scene shouldn’t be too difficult. Attach your camera to a tripod and use the information in the photo caption as a place to start. Try to keep your exposure times to 20 seconds or less. Any longer and the planets will stretch into short trails instead of compact dots due to Earth’s rotation.

When you look at the LCD screen on the back of your camera, don’t be surprised if the crescent moon is completely filled out. Time exposures in semi-darkness necessarily overexpose the bright sunlit crescent. The rest of the moon is illuminated by dimmer earthshine, sunlight reflected from the Earth to the moon and back.

From the East Coast, the moon will lie a little farther to the right of Venus and Mars than depicted in the map; from the West Coast, it sits above the pair. Conjunction with Venus occurs around 5 p.m. (CST) and with Mars an hour later.

Venus and Mars will be close conjunction the following night (Feb. 21) only 0.5° or one moon diameter apart. If the weather doesn’t cooperate on the 21st, don’t sweat it – the two planets will be close from the 19th through the 22nd. You’ll easily tell the two apart. Venus is SO much brighter than Mars (about a hundred times) and the lunar crescent brighter yet. This promises to be one of the best moon-planet gatherings of the year.

Uranus in early twilight (left) just before its dramatic disappearance behind the earth-lit edge of the moon on Feb. 21 as seen from Portland, Maine. 36 minutes later Uranus emerges at the bright crescent’s edge. Both disappearance and reappearance occur in a dark enough sky to see in a small telescope. Source: Stellarium

Here’s a wider view of Uranus and the moon on Feb. 21 as seen from the Midwest about an hour and a quarter after sunset. Source: Stellarium

Ah, but the moon won’t be quite finished with its magic. There’s still the cherry on top. The very same night – Feb. 21 – the crescent covers up or occults the planet Uranus for skywatchers in northeastern U.S. and southeastern Canada during twilight. For the Central Time Zone Uranus will lie 0.5° west of the moon, 1° from the Mountain States and 1.5° for the West Coast. Amazing stuff – yet another opportunity to easily spot planet #7 in binoculars.

Map showing where the occultation of Uranus by the moon will be visible. Between the white lines, it’ll be visible in a dark sky. Blue is twilight and the red dotted line is daytime. Uranus is too faint to see in the daytime sky. Click the map to get a list of disappearance and reappearance times for a variety of cities. Credit: IOTA/Occult

Most of the time the moon occults stars along its path since there are a lot more of those than planets. Because they’re so remote, stars are little more than points of light; as the moon moves over them they disappear with surprisingly suddenness. Since Uranus displays a real, measurable disk it takes a second or two to disappear behind the moon’s edge. This should be a very fun occultation for those lucky skywatchers living out East. Maybe it will help take their minds off the unrelenting snow.

Glowing comets and deep fried ice cream

Comet 67P/C-G taken on February 6 from a distance of 77 miles (124 km) to the comet center. We see the comet’s small lobe on the left and larger lobe to the right. The image has been processed to bring out the details of the comet’s jetting activity. Exposure time was 6 seconds. Credits: ESA/Rosetta/NAVCAM

Everything’s glowing! This new photo from the Rosetta spacecraft was taken on Feb. 6 and processed to show jets active all over comet 67P. They’re brightest and most effervescent in the Hapi region, the name given to the neck of the comet, but take a look around the nucleus. You can see that the entire comet is swathed in a soft, nebulous halo of vaporizing ices and dust motes.

Some of the grainy white spots around the comet’s nucleus are background noise brought to the fore as a consequence of processing the images to see the jets more clearly, but some is actual comet stuff jetted into 67P’s coma like dried leaves from a leafblower.

Rosetta’s moved out from the comet temporarily as part of an orbit change that will see it fly just 3.7 miles (6 km) of its surface this Saturday. Photos from the flyby will be downlinked to Earth Sunday and Monday.

In other comet news, a team of astronomers have simulated what happens to a comet’s ices when it nears the Sun. It’s not what you’d expect.

Familiar ice like that on ponds, lakes and clinking as ice cubes in a glass are made of neatly ordered arrangements of water molecules. Amorphous ice is also made of water but its structure is disordered. Credit: Wikipedia

“A comet is like deep fried ice cream,” said Murthy Gudipati of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., corresponding author of a recent study appearing in The Journal of Physical Chemistry. “The crust is made of crystalline ice, while the interior is colder and more porous. The organics are like a final layer of chocolate on top.”

Comets, which formed in the bitter cold of the outer solar system, are probably composed of amorphous ice, a form of water ice where the H20 molecules are randomly arranged instead of packed into neat lattices like those that make up the more familiar crystalline ice we use to chill our sodas.

Researchers at NASA’s Jet Propulsion Laboratory use a cryostat instrument, nicknamed “Himalaya,” to study the icy conditions under which comets form. Image credit: NASA/JPL-Caltech

First, the team flash-froze water vapor infused with carbon compounds called polycyclic aromatic hydrocarbons (PAHs) at -405° F to preserve the disorderly states of the water molecules and create amorphous ice. Then, using a cryostat instrument nicknamed “Himalaya”, they gradually raised the temperature of the mixture from -405° F to -190° F (-243° C to -123° C).

The PAHS stuck together and were expelled by the ice as it crystallized. With the carbon compounds now gone, the water molecules moved into the empty spaces linking up to form more compact crystalline ice.

That rings true when it comes to the Rosetta mission’s Philae lander which hit 67P/C-G with a big bounce proving it had a hard surface. Some of the dust seen around 67P might well have been “squeezed” out when amorphous ice transformed into the crystalline variety.

Similar to the fried ice cream pictured here, comets have cold, icy interiors surrounded by a crust of organics expelled when amorphous ice warms to become crystalline ice. Credit: Wikipedia

“What we saw in the lab — a crystalline comet crust with organics on top — matches what has been suggested from observations in space,” said Gudipati. Deep fried ice cream is really the perfect analogy, because the interior of the comets should still be very cold and contain the more porous, amorphous ice.”

Darkside of the moon? What dark side?


Take a walk on the lunar farside

We may never see it from Earth but sure as pants, the moon’s farside basks in sunshine just like the “man in the moon” side. In this new NASA video, compiled using images taken by the Lunar Reconnaissance Orbiter (LRO), we can watch it happen right before our eyes as the moon’s farside waxes from crescent to full and back to crescent phase.

The far side of the moon lacks the many dark patches called lunar seas, which are gigantic, lava-flooded impact-carved basins. The largest lunar basin, named South Pole-Aitken and lacking the lava coverage of the others, might be seen with the naked eye as slightly grayer than the rest of the farside. Click for a map of farside features. Credit: NASA

We also get to see clearly how different the farside looks compared to the near. The near complete lack of “dark spots” or lunar seas would make it impossible to see a face up there. At best we might discern two small dark patches – the Sea of Moscow (Mare Moscoviense) and the floor of the crater Tsiolkovski which is flooded in dark, now frozen lava. The rest of the Full Farside Moon would appear a glaring white to the naked eye.

Since the moon completes a rotation in the same time it takes to revolve about Earth, an observer on Earth always see the same face. All parts of the moon receive sunlight during a lunar orbit. Illustration: Bob King

So how did we get stuck with just one side of the moon? Because the moon orbits around the Earth in the same time it takes to spin on its axis, it always keeps the same hemisphere pointing at us. This is called synchronous rotation and is caused by the gravity of the Earth acting upon the moon to slow its rotation to a rate equal to its orbital period of 27 days. That’s why we’re stuck with seeing the same face for as long as humanity has gazed at the moon. Much farther back in time, the moon rotated faster. If we’d been around to gaze up, we would have been able to see all 360° of the lunar sphere.

Nowadays you’ve got to get out there and orbit the moon in a spaceship to catch a view of the backside. The Apollo astronauts are the only humans who’ve seen it.

Another view from NASA’s Lunar Reconnaissance Orbiter of the moon’s farside with Earth in the background. Credit: NASA

When you look at the moon, the white stuff is ancient, crater-saturated crust that cooled more than 4 billion years ago. The dark “seas” formed later, mostly between 3 and 3.5 billion years ago. The farside is mostly ancient crust and thicker than the nearside crust – 50 miles vs. 37 miles.The extra thickness is likely reason for its dearth of seas; molten rock from below couldn’t reach the surface to fill basins carved by impacts.

This series of photos taken by the LRO show the moon through nearly a full rotation so you can see how the near side transitions to the far. Credit: NASA/Goddard/Univ. of Arizona

How the moon’s crustal thickness came to vary is still open to debate. Tides raised in the still-molten moon by Earth’s gravity may have played a role. Crust ejected and piled on top of the original lunar crust by the impact that excavated the enormous 1,600-mile-wide (2,500 km) South Pole-Aitken Basin may also have been responsible.

Now that you’ve seen both sides, the next time you see a thin crescent moon think about the farside. If you could just get around the back of the crescent for a look, you’d see a nearly full moon on the other side.

And as for the “dark side” of the moon? That’s what you see during a partial or total eclipse of the Sun. A rare sight if there ever was!

 

 

 

Doomed stellar relationship to end in supernova catastrophe

This artist impression shows the central part of the planetary nebula Henize 2-428. The core of this unique object consists of two white dwarf stars, each with a mass a little less than that of the Sun. They are expected to slowly draw closer to each other and merge in around 700 million years and explode as a dazzling supernova. Credit: ESO/L. Calcada

I’ve had a few relationships explode but none like what’s going to happen to this couple in 700 million years.

A team of astronomers, led by Miguel Santander-Garciá (Observatorio Astronómico Nacional, Alcalá de Henares, Spain), has discovered a close pair of white dwarf stars in the core of the planetary nebula Henize 2-428 in constellation Aquila the Eagle. White dwarfs are super-dense stellar remnants left over when stars like the Sun run out of nuclear fuel.

The planetary nebula Henize 2-428 photographed with the ESO’s Very Large Telescope at the Paranal Observatory in Chile. In its heart are two closely-orbiting white dwarf stars. Credit: ESO

Self-gravity causes a dwarf to collapse into an Earth-sized object so dense that a teaspoonful of matter scooped up from its surface would weigh outweigh even a large elephant. Lacking sufficient heat and pressure to fuse additional elements, white dwarfs sit and cool their heels for billions of years until becoming black dwarfs, mere cinders of their former selves.

Before settling into white-dwarfdom, many of the stars eject their atmospheres into space like the wizard Gandalf puffing clouds of smoke from his pipe. Ultraviolet light from the white dwarf causes the material to fluoresce in pinks and greens and assume intricate and amazing shapes. We call them planetary nebulas because many are round or oval-shaped and reminded early astronomers of planets.

Planetary nebulae are some of nature’s most artistic creations. Here’s a selection taken with the Hubble Space Telescope. Each is set glow by a white dwarf star (s) in its center. From left: the Butterfly Nebula, Cat’s Eye Nebula, Ring Nebula and Hourglass Nebula. Credit: NASA/ESA

Under the right circumstances a white dwarf can become a ticking time bomb. Santander-Garciá and crew weren’t looking for a bomb when they keyed in on the central star in Henize 2-428. They wanted to find out how some stars produce strangely shaped and asymmetric nebulae late in their lives. What they discovered led them to a fascinating prediction.

“When we looked at this object’s central star with ESO’s Very Large Telescope, we found not just one but a pair of stars at the heart of this strangely lopsided glowing cloud,” said co-author Henri Boffin from ESO.

This supported the current theory that a lot of planetary nebula shapes are woven from gases spun up and around by a pair of stars rather than a single white dwarf. Further observations allowed the group to determine the stars’ masses and separation. Each is slightly less massive then the Sun and they orbit one other every four hours, close enough to eventually merge into a single star within the next 700 million years.

Sequence showing two white dwarfs spiraling into one another, merging and then exploding as a supernova. As they spiral around each other, they emit gravitational waves causing them to grow ever closer. Credit: GSFC/Dana Berry.

According to Einstein’s general theory of relativity, two massive objects in very close orbit emit gravitational waves causing them to lose orbital energy and slowly spiral in toward one another. Henize 2-428’s whirling white dwarfs are destined to merge one day, and when they do, there’ll be fireworks of the first order.

Left in peace, a white dwarf won’t bother anybody, but take a big step back if one decides to put on extra weight. If a dwarf increases its mass, say by siphoning matter from a nearby companion star, it will collapse under its own weight, heat up and burn explosively as a supernova. Many supernovae we observe in galaxies across the universe occur in close binary systems where one star is a white dwarf and the other an ordinary star like our Sun. Another way of getting a supernova – at least theoretically – is by squishing two white dwarfs together.

Back in 1930, the Indian-American astrophysicist Subrahmanyan Chandrasekhar determined that the greatest mass a white dwarf star can have and still support itself against gravitational collapse was about 1.4 times the mass of the Sun. So you can guess what’ll happen when Henize 2-428’s two white dwarfs merge. Ka-boom!

“Until now, the formation of supernovae Type Ia by the merging of two white dwarfs was purely theoretical,” explained David Jones, coauthor of the article and ESO Fellow at the time the data were obtained. “The pair of stars in Henize 2-428 is the real thing!”

Gosh, I only wish we could be around to watch.

Hitch your wagon to Comet Lovejoy till the flowers bloom

Comet Lovejoy has a scenic encounter with the edge-on spiral galaxy NGC 891 on Feb. 2. Click for a lusciously large view. Credit: Rolando Ligustri

In the occasional bits of clear sky that pass this way I’ve been able to check in on what remains the year’s brightest comet – Q2 Lovejoy. A few nights ago it dallied near the bright and beautiful double star Gamma Andromedae and could still be seen with the naked eye. The comet was a faint, fuzzy spot of magnitude 4.7 poised atop the hard sparkle of the star.

Comet Lovejoy remains a naked eye object and still shows a tail in binoculars. Photographs, like this one taken on Feb. 6 through a 3-inch telescope, show beautiful rays of fluorescing gas in the comet’s ion tail. Credit: Chris Schur

10×50 binoculars showed a faint eastward-pointing tail more than 2° or four full moon diameters long. The view in the telescope still shows a blue coma and smoky tail stretching from one end of the field of view to the other. Though Lovejoy passed Earth back in January and made its closest approach to the Sun more than a week ago, it remains a fine object. With the moon gone and the comet high in western sky at nightfall I encourage you to keep it in view.

Comet Lovejoy’s path across Andromeda, Perseus and Cassiopeia tonight through April 9. Map time is 8 p.m. CST and stars are shown to magnitude +6.5. Click to enlarge. Created with Chris Marriott’s SkyMap software

Having passed Gamma, Lovejoy continues trekking north across a bit of Perseus and into the familiar, W-shaped Cassiopeia. From Feb. 15-19 you’ll find it near the 4th magnitude stars 51 And and Psi Persei. At the end of the month the comet enters Cassiopeia and two weeks later makes a close pass by Ruchbah on March 15. All the while Lovejoy will be fading from its current magnitude ~4.8 to 8th by the time it encounters Ruchbah. That means the comet should remain visible in binoculars for at least another month.

Given that few comets are predicted to become brighter in 2015 for northern hemisphere skywatchers, Lovejoy’s the best we’ve got. To learn more about bright comet prospects for the coming year, click HERE.

Jupiter doesn’t get any better than NOW

Jupiter shows off its north and south equatorial belts – the two thick stripes – and Great Red Spot in this picture taken on Feb. 6. Credit: Christopher Go

Brash Jupiter finally has its day. Big and bright, the planet’s been easing up in the east earlier and earlier each night this winter. I’ve been watching it through my car window while driving home from work at dusk.

Jupiter reached opposition yesterday, when it beamed directly opposite the Sun in the sky. Like the full moon, the planet rose at sunset and remained visible all night, setting at sunrise. Opposition occurs when Earth and Jupiter line up on the same side of the Sun putting them closer together than at any other time of the year.

Jupiter and Earth are lined up on the same side of the Sun at opposition and closest for the year. Now is the best time to observer the solar system’s largest planet in a telescope or pair of binoculars. Credit: Bob King

Skywatchers seize the time of opposition to regularly observe a planet; closeness equals greater brightness and also larger apparent size. And size is what we need to see the fascinating details that make these quivering disks come alive as real places.

This weekend, Jupiter’s chubby face will be 1.5 times larger than when viewed around solar conjunction on August 26th when the planet drops into the Sun’s glare in the western sky.

Jupiter straddles the border of Leo and Cancer not far from Leo’s brightest star Regulus. The inset shows how the planet and its four brightest moons will look in a small telescope this evening around 9 p.m. CST. North is at upper left in inset. Created with Stellarium

So what’s there to see? Lots! Jupiter is a meteorologist’s paradise, but you don’t have to be one to appreciate the planet’s changeable weather and balletic moons. Even binoculars will show a tiny disk, and if you look very closely, you’ll see up to four star-like points flanking either side of the planet. These are the four brightest moons – Io, Europa, Ganymede and Callisto in order of increasing distance from Jupiter.

Jupiter’s about 11 times larger than the Earth and has no solid surface. Its globe is covered in clouds of ammonia ice.

As they revolve about the planet, they create new arrangements every night. I’ve seen lots of eye-catching groupings with some of the most surprising symmetries over the years. And while I enjoy The Tonight Show, Jupiter’s moons are usually more entertaining. To find out where they are and what they’re up to any given night, check out Sky and Telescope’s Jupiter Moons Observing Tool.

Sometimes a moon will “disappear” when it passes in front of or behind the great planet. Other times, Jupiter’s shadow will eclipse a moon. This season, because Earth’s equator is aligned with Jupiter’s, we can even see the moons eclipse and occult one another in what astronomers call “mutual events”. For your observing pleasure, I’ve included a list of the best mutual events at the end of this article.

One of the most amazing discoveries I made some year back was that I could see Jupiter’s moons as actual disks, not just points. When the air is especially steady, power up to 150x or higher and look closely at each of the moons in a 6-inch or larger scope. In good seeing, each will show a minute disk with Ganymede clearly the largest of the four. One of them, Io, is colored orange from sulfur-laden lavas erupted from its interior that now coat the surface. Can you see the color?

With a small telescope and low magnification (40- 50x) two gray “tire tracks” rut the planet’s disk. These are the north and south equatorial belts, so called because they flank Jupiter’s equator. Higher power, steady air and a bit of stick-to-itiveness and you’ll also pick out the thinner stripes like the north and south temperate belts and the polar regions which look like gray beanie caps.

I’ve labeled the most prominent belts in this photo taken by Anthony Wesley on Feb. 6, 2015. Strong winds whip Jupiter’s clouds into alternating dark belts and bright zones. Sulfur and possibly phosphorus compounds may be responsible for the dark tone of the belts as well as the Great Red Spot. Credit: Anthony Wesley

Dark belts are separated by lighter zones and the whole works is streamed into stripes by narrow, high-speed winds called jets that border the zones and belts. Winds rip along at up to 400 mph (640 km/hr). Because Jupiter makes a complete spin on its axis at the amazing rate of just 9.9 hours, you can watch new features rotate into view by revisiting the planet in your telescope several times during the night.

Jupiter’s weather is as changeable as Earth’s. Belts narrow, widen, split in two or even disappear altogether for a couple years before reforming. The familiar Great Red Spot (GRS), a hurricane-like storm more than twice Earth’s diameter that’s raged for centuries, changes color from pale tan to brick red. This year it’s pink-colored and nestled in a pale “hollow”. You’ll need good seeing, a 4.5-inch or larger telescope and magnification of around 100x to spot it.

To know when to look for the GRS, click HERE and you’ll get dates and times when it’s front up and center on Jupiter. The times shown are Universal or Greenwich Time. Subtract 5 hours for Eastern, 6 for Central, 7 for Mountain and 8 for Pacific.

I can’t say enough about this planet. Mars shows lots of detail too, but it’s typically so small you have to work hard and consistently to appreciate its vague markings. Saturn of course is fantastic but features in its atmosphere are subtle and change slowly. Venus and Mercury show phases but precious little else. Only Jupiter happily gives away its secrets even to the beginning observer with a small telescope.

Now here’s something cool – a double mutual event. Europa eclipses then occults Io on January 28 captured by Theo Ramakers of Oxford, Georgia.

Below are times when the planet’s moons pass either fully or partially in front of one another (called an occultation) and eclipse each other.

During an occultation, you can watch the moons get closer and closer until they merge into a single object. Minutes later they separate and go their own way. To watch one, be sure to start observing at least 10 minutes before the times shown. Moons will fade in brightness when occulted but I’ve found this difficult in practice to see because they’re sitting atop one another and appear as one.

In an eclipse, the shadow of a moon will cause the other to fade for a few minutes and then re-brighten. If the fade is 50% or more, you can see the change in brightness through the scope. Really fun to watch. Bolded events are the best eclipses of the bunch.

Mutual events for Jupiter’s satellites in February – Times are CST:

Feb. 8 11:26-29 p.m. Io occults Europa (pair very close to Jupiter)
Feb. 8 11:32-34 p.m. Io eclipses Europa 2% shadowed (pair very close to Jupiter)
Feb. 14  6:20-28 p.m. Europa eclipses Io 85% (comfortable separation from planet; should be very easy to see fading)
Feb. 16 1:23-26 a.m. Io occults Europa
Feb. 16 1:44-47 a.m. Io eclipses Europa
Feb. 17 11:48-57 p.m Europa eclipses Callisto 44%
Feb. 19 6:34-43 p.m. Io eclipses Ganymede 84% (deep eclipse, very nice!)
Feb. 21 8:04-11 p.m. Europa occults Io
Feb. 23 7:42-47 p.m. Ganymede occults Io
Feb. 23 8:38-45 p.m. Ganymede eclipses Io 57% (pair very close to Jupiter)
Feb. 26 8:17-24 p.m. Io occults Ganymede 36%
Feb. 26 9:31-40 p.m. Io eclipses Ganymede 97% (Deepest and best eclipse event of the month)
Feb. 26 10:27-39 p.m. Callisto eclipses Ganymede 58%
Feb. 27 11:33-36 p.m. Europa eclipses Ganymede .2%
Feb. 28 10:09-16 p.m. Europa occults Io 59%
Feb. 28 11:01-11:08 p.m. Europa eclipses Io 90% (another excellent eclipse)