Jupiter and the half moon invite you to look up tonight

Look for the half moon to the lower right of Jupiter tonight. Source: Stellarium

Look for the half moon to the lower right of Jupiter tonight. This map shows the sky around 9 p.m. local time looking high in the southwest. Besides the moon and Jupiter, other bright stars in the scene are Regulus in Leo the Lion, Pollux and Castor in Gemini the Twins and Procyon in Canis Minor (Small Dog). Source: Stellarium

As if to advertise that astronomy is as easy as looking up, the first quarter moon will be near Jupiter high in the southern sky at nightfall this evening. Take a look outside at dusk and let the exquisitely-cut lunar half-pie point you to Jupiter.

Jupiter and the four Galilean moons (named after Galileo, who first discovered them) around 9:30 p.m. tonight April 25. Source: Meridian

Jupiter and the four Galilean moons (named after Galileo, who first discovered them) around 9:30 p.m. CDT tonight April 25. South is up and east to the right as seen in many small scopes. Source: Meridian

Have telescope? Even a small glass will show all four of Jupiter’s brightest moons lined up in a neat row to the east of the planet around 9-10 p.m. 10x binoculars should easily show the two moons farthest from Jupiter tonight, Ganymede and Europa, as long as you can hold them steady.

The moon this evening. Dark seas or maria were once enormous craters  blasted in the lunar crust by asteroid impacts. Later, they filled with lava bubbling up from below. Spectacular craters blanket the white, ancient crust of the moon called the lunar highlands. Source: Virtual Lunar Atlas

The moon this evening. Dark seas or maria were once enormous craters blasted in the lunar crust by asteroid impacts. Later, they filled with lava bubbling up from below to become flat plains. Spectacular craters blanket the white, ancient crust of the moon called the lunar highlands. Source: Virtual Lunar Atlas

Want more? Take that scope or binoculars and point them at the moon. First quarter phase brings hundreds of impact-sculpted craters into view especially in the southern half of the lunar disk. I’ve labeled the dark “seas” or “maria” (the Latin term) and three prominent craters. Use a magnification of 40x or higher for the best views.

Hope you had a great Astronomy Day. If you weren’t able to attend an event, consider the moon and Jupiter your own private show.

Volcano? Geyser? Ice? Vote on Ceres white spot

Ceres contest

As of 3:15 p.m. CDT, ice is the clear vote-getter for the composition of Ceres’ white spots. Credit: NASA

Since so many of us are wondering what the heck those white spots are on the dwarf planet Ceres, NASA’s decided to hold a contest. Click the image and you’ll be taken to a page where you can vote on one of six choices – volcano, geyser, rock, ice, salt deposit or other.

Until Dawn moves in for a closer look in the months ahead, it’s anyone’s guess what the spots might be. Ice is currently leading with 37% of the vote. After you’re finished, you’ll see the latest numbers. Your vote won’t change the final outcome of course, but you might just win an “I-told-you-so” for your effort.

Get high on the sky – it’s Astronomy Day!

Jim Schaff (left) helps visitors to last year's Astronomy Day understand the features they see on the Sun. Credit: Bob King

Jim Schaff (left) describes features on the Sun to visitors at last year’s Astronomy Day event. Credit: Bob King

Take off those tin foil hats and step out into the sunshine. Tomorrow, amateur astronomers around the planet will celebrate International Astronomy Day, an annual public feast of astronomy. Schools, clubs and planetariums will feature workshops, sky programs and public viewing sessions to increase awareness and appreciation for this improbable and awesome universe into which we were born.

Angie Gregory describes how neutrinos escape from a star during one of the the 2014 Astronomy Day presentations. Credit: Bob King

Angie Gregory of the Arrowhead Astronomical Society describes the rotation of the Sun at her 2014 Astronomy Day presentation. Credit: Bob King

To find out if a group near you is sponsoring an event, check the List of Events on the Astronomical League’s Astronomy Day page. You can also look under the Astronomy Clubs menu to browse the websites of clubs in any of 50 states.

Here in Duluth, Minn. we’re getting an early start on festivities with a 7 p.m. talk by UMD physics professor Marc Seigar on the 25th anniversary of the Hubble Space Telescope. The show will be held at the Marshall Alworth planetarium on the UMD campus and costs $3 for adults and $2 for kids six and up. Children under five get in free.

Astronomy Day features lots of hand-on exhibits and people who are happy to answer your questions about the sky or telescope equipment. Credit: Bob King

Astronomy Day features lots of hand-on exhibits and people happy to answer your questions about the sky or telescope equipment. Credit: Bob King

Tomorrow’s the big day with non-stop planetarium shows, workshops, safe solar observing, special lectures and lots of hands-off stuff for the kids — all free of charge. You can even look at real moon rocks collected by the Apollo astronauts and study pond life under a microscope. With Europa, Ganymede, Mars and Enceladus potential havens for microscopic life, why not get better acquainted with Earth’s tiniest inhabitants?

The whole shebang runs from 10 a.m. to 4 p.m. at the planetarium. Click HERE for directions.

“Astronomy is big, it’s exciting and it changes the way you look at the world,” said Shane Loeffler, who’s helping to organize the event.

One of our favorite exhibits - Touch the Planets. You might be surprised how different planet surfaces feel. Credit: Bob King

One of our favorite exhibits – Touch the Planets – will be back again this year. The textures might surprise you. Credit: Bob King

The school will also premiere a new full-dome planetarium show called “Sunstruck” with showings at 2:00 p.m. and again at 3:00 p.m. The 20 minute show takes viewers on a journey to discover the wonders of our sun and its potential effects on our technology and future.

Shane Loeffler, planetarium assistant, holds a disk containing samples of Apollo moon rocks. Credit: Bob King

Shane Loeffler, planetarium assistant, holds a disk containing samples of Apollo moon rocks. Credit: Bob King

Sure sounds like a lot of fun. Hope to see you there if you’re in the area.

Hubba-Hubble! 25 extraordinary years in space

This image shows the sparkling centerpiece of Hubble's 25th anniversary tribute. Westerlund 2 is a giant cluster of about 3,000 stars located 20,000 light-years away in the constellation Carina. Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team

This image shows the sparkling centerpiece of Hubble’s 25th anniversary tribute this week. Westerlund 2 is a giant cluster of about 3,000 stars located 20,000 light-years away near the Gum 29 nebula in the constellation Carina. Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team

I think it’s fair to say that the Hubble Space Telescope has produced more beautiful images of the cosmos than any other telescope … ever. Part of the reason is its longevity. Another is Hubble’s unique ability to take incredibly long time exposures far above the blurring influence of Earth’s atmosphere. As an orbiting telescope, its images show pinpoint stars and spectacular detail that have only recently being replicated by ground-based telescopes using special optical techniques.

Hubble deployed by the Space Shuttle Discovery in 1990. Credit: NASA

Hubble deployed by the Space Shuttle Discovery in 1990. Credit: NASA

It wasn’t always that way. Hubble was launched into low-Earth orbit in the spring of 1990, but within weeks the first images returned revealed a serious flaw — the 94-inch primary mirror had been ground precisely but to the wrong shape. This serious error meant that images returned suffered from a defect known as spherical aberration.

Basically, Hubble couldn’t focus star images sharply across its entire field of view. The defect was traced back to an instrument used to measure how precise the mirror had been ground. A lens within the device was ever so slightly out of position, resulting in the mirror being ground with the wrong figure.

The spiral galaxy M100 before and after the corrective optics package was installed. Credit: NASA

The spiral galaxy M100 before and after the corrective optics package was installed. Credit: NASA

A corrective optics package was developed to reverse the aberration and installed by a team of space shuttle astronauts in December 1993. Since January 1994, Hubble’s been snapping one crisp image after another.

The telescope bears the name of Edwin Hubble, the 20th century astronomer who discovered the true enormity of the universe and the fact that it’s not static but in continual expansion. This week the Hubble Space Telescope (HST) celebrates its 25th anniversary. But in a selfless role reversal, instead of sending an anniversary card to Hubble, Hubble sent us a sumptuous image of the star cluster Westerlund 2.

This image shows an example of the pillars that surround the star cluster Westerlund 2. These pillars are composed of dense gas and dust are a few light-years tall and point to the central cluster. They are thought to be incubators for new stars. Besides sculpting the gaseous terrain, intense radiation from the most brilliant of the cluster stars is creating a successive generation of baby stars.

These pillars are composed of dense gas and dust near Westerlund 2 are a few light-years tall and point to the central cluster. They are thought to be incubators for new stars. Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team

This amazing cluster is only 2 million years old and contains some of the brightest, most massive stars known. Powerful ultraviolet light and stellar winds streaming from the cluster’s giants tear into the clouds, sculpting them into fantastic shapes. When the stellar winds hit dense walls of gas, they create shocks, which generate a new wave of star birth along the wall of the cavity. The red dots scattered throughout the landscape are a rich population of forming stars that are still wrapped in their gas and dust cocoons.

The red dots scattered throughout the cosmic landscape captured in this NASA/ESA Hubble Space Telescope image are a rich population of forming stars that are still wrapped in their gas and dust cocoons. Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team

The red dots scattered throughout the cosmic landscape captured in this Hubble image are a rich population of forming stars that are still wrapped in their gas and dust cocoons. Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team

Your eyes and mine can’t see these stars, but Hubble has the ability to peer into the thermal infrared and spot them by the heat they give off. They’re still just proto-stars, but they’ll continue to collapse and compress until one day they’re hot enough to ignite hydrogen in their cores and become true stars like the Sun.

While its legacy of photographs is what most of us associate with the Hubble, it’s also a superb research instrument that’s enlarged our understanding of the universe in so many ways. Here are five of its most ground-breaking discoveries:

Hubble Ultra-Deep field photos shows thousands of galaxies. Credit: NASA/ESA

Hubble Ultra-Deep field photos shows thousands of galaxies. Credit: NASA/ESA

Galaxies evolve

The Hubble Deep Field and Ultra-Deep Field photos each show several thousand galaxies in two tiny specks of sky. Some of them are up to 10 billion years old and much smaller and irregularly shaped than the galaxies we see in the current era. Astronomers suspect that through mergers, these rough-hewn “building blocks” helped create the more familiar spiral and elliptical galaxies of the present.

800-light-year-wide spiral-shaped disk of dust fueling a massive black hole in the center of galaxy NGC 4261. Measuring the speed of the gas whirling around the black hole, we know it's 1.2 billion times more massive than the Sun. Credit: NASA/ESA

800-light-year-wide spiral-shaped disk of dust fueling a massive black hole in the center of galaxy NGC 4261. Measuring the speed of the gas whirling around the black hole, we know it’s 1.2 billion times more massive than the Sun. Credit: NASA/ESA

Supermassive black holes are everywhere!

Hubble sharp optics and ability to see in the infrared (thermal energy beyond the red end of the spectrum) led to the discovery in 1994 of the first supermassive black hole in the center of the galaxy M87 in Virgo. Based on the motion of the material whirling about the center, the object is estimated to be about 3 billion times more massive than the Sun and concentrated into a space smaller than our solar system. By 1997 we knew that the Milky Way and 27 nearby galaxies held supermassive black holes in their cores. Now we know they’re common, showing up in nearly every large galaxy observed.

Timeline of the history of the universe from the Big Bang to the current day.  Credit: Rhys Taylor, Cardiff University

Timeline of the history of the universe from the Big Bang to the current day. Credit: Rhys Taylor, Cardiff University

Measuring the age of the cosmos

Edwin Hubble discovered the expansion of the universe in the 1920s. Since that time, astronomers have been trying to determine exactly how fast it’s expanding, a value called the Hubble Constant. In 1999, astronomers using the superior sharpness of the Hubble telescope, determined its value by measuring the distance to 18 galaxies as far away as 65 million light years. Once the expansion rate was nailed down, astronomers could “roll the tape backwards” and estimate the age of the universe. Drum roll please. It turns out this big place has been around for between 12-14 billion years. That’s now been refined to 13.7 billion years, the amount of time that’s elapsed since the birth of the universe at the Big Bang.

Dark energy graphic NASA WMAP science teamThe universe slows down then speeds up

Through study of a the remote supernova 1997ff, astronomers discovered that gravity (from matter) slowed down the expansion of the universe after the Big Bang. Later, in 1998, two other supernova studies using data from Hubble, revealed that after slowing down for a long time, the expansion rate of the universe is now on the increase. What would cause it balloon up even faster? That’s the million dollar question. It’s called ‘dark energy’ and we’re still trying to figure out what THAT is.

 

Proto-planetary disk of dust and gas surrounding newborn stars in the Orion Nebula photographed by Hubble. Credit: NASA/ESA

Proto-planetary disk of dust and gas surrounding newborn stars in the Orion Nebula photographed by Hubble. Credit: NASA/ESA

Baby planets like pancakes

Through studies of nebulae like the famous and familiar Orion Nebula, Hubble discovered that pancake-shaped dust disks around young stars are common. And that implies planets are probably common. Scientists believe that our solar system formed from just such a disk 4.5 billion years ago with the Sun at center and the planets coalescing from the material remaining around it. In 2001, astronomers using the Hubble made the first direct detection of the atmosphere of a planet orbiting a star other than the Sun. The star, HD 209458, is located 150 light years from Earth in Pegasus.

So you see, the Hubble has a little something for everybody.

Hey Earth, you’re the greatest

Norway pines catch the last rays of sunlight on a ridge north of Duluth, Minn. Credit: Bob King

Norway pines catch the last rays of sunlight on a ridge north of Duluth, Minn. Credit: Bob King

Happy Earth Day skywatchers! Just because we’re always gazing up doesn’t mean we don’t appreciate a horizontal look around every once in a while. Everything about this planet sustains our fascination with the sky.

Sutures in a deer skull found near a hiking trail. Credit: Bob King

Sutures in a deer skull found near a hiking trail. Credit: Bob King

Sunlight, water and the atmosphere keep us alive, while the ground itself provides a handy platform for us to stare out into space with eye and telescope. Surfaces aren’t to be taken lightly. Not all planets have ground or even clear skies. Venus is under a permanent overcast while only Mars and Mercury have surfaces from which to look up. Having something to stand on is handy, but having air to breathe really makes life golden on the blue marble.

Flakes of frost condensed on the icy surface of a creek in Duluth. Credit: Bob King

Flakes of frost condensed on the icy surface of a creek in Duluth. Credit: Bob King

In honor of Earth Day I thought I’d share a few photos I’ve taken while looking down instead of up. The images are pretty random, grabbed from a folder that’s been sitting around on my hard drive, but they’re examples of what I like to do in my free time.

Drops of sap oozing down a white spruce tree develop a crazed surface as they dry. Credit: Bob King

Drops of sap oozing down a white spruce tree develop a crazed and crinkled surface as they dry. Credit: Bob King

I love this planet as much as you do and wish at times I could spend the rest of my life just wandering around the globe exploring every nook and cranny with my camera. Earth’s coated with life. Every rock breeds some form of tiny microbe. It’s hard to imagine a place where not a single living cell resides. Yet every night we look up, we see these places. The barren moon, airless asteroids, frozen planets, hellishly hot planets.

A chestnut-sided warbler sings from a branch on a spring morning. Credit: Bob King

A chestnut-sided warbler sings from a branch on a spring morning. Credit: Bob King

I realize that’s an assumption but not a single definitive sign of life has yet to turn up in the thousands of meteorites in our collections. Nor have any of the planets or moons in our solar system been forthcoming.

I’ve great hope we’ll find some form of microscopic life on Europa, Enceladus, Ganymede or Mars in the next couple decades. For now, I’m content to slop around the bogs and sniff my way through the fragrant forests of planet Earth.

Auroras, Lyrid meteor shower make for an exciting week ahead

The Sun photographed in extreme ultraviolet light by NASA's Solar Dynamics Observatory this morning still shows the coronal hole that will influence Earth's space weather tonight. Credit: NASA

The Sun photographed in extreme ultraviolet light by NASA’s Solar Dynamics Observatory this morning still shows the coronal hole that will influence Earth’s space weather tonight. Credit: NASA

We’re in for some sky excitement the next couple nights. Tonight there’s a fair chance for northern lights as blustery solar winds
arrive from another coronal hole at the Sun.

Forecasters are calling for a G1 or minor geomagnetic storm that’s expected to kick in this
afternoon and last into the early morning hours Wednesday. With the moon only a crescent, we’ll have dark skies for aurora watching. Look for that telltale twilight-like glow in the northern sky at nightfall as a tip-off that a display is in progress.

NASA used an all-sky camera to photograph multiple Lyrids during the 2014 shower. Credit: NASA

NASA used an all-sky camera to photograph multiple Lyrids during the 2014 shower. Credit: NASA

Then, starting Wednesday and continuing through Thursday morning the annual Lyrid meteor will salt and pepper the sky with meteors. We’ve waited more than three months since the January Quadrantids for a meteor shower to return, so I’m looking forward to this one.

The Lyrids fly from the general direction of the bright star Vega which comes up in the northeastern sky around 11 p.m. local time this week. The Big Dipper can help you find it. Source: Stellarium

The Lyrids fly from the general direction of the bright star Vega which comes up in the northeastern sky around 11 p.m. local time this week. The Big Dipper can help you find it. Source: Stellarium

Like the first flowers, the Lyrids return every April with a peak rate of 10-25 meteors per hour. They originate or radiate from a point in the sky about an outstretched fist southwest of bright Vega in the constellation Lyra the Harp.

Even though the radiant actually lies in neighboring Hercules, the shower’s always been associated with Lyra (Lyrids) both because of Vega’s dominance and the original, loosey goosey borders of the constellations. Before 1930, the borders of the 88 constellations were vague and the Lyrids were close enough to Lyra to assume its name. Had the shower turned up after the International Astronomical Union precisely defined borders, we’d be calling them the Herculids!

Lyra and Hercules border one another with the actual radiant located in Hercules. Source: Stellarium

Lyra and Hercules border one another with the actual radiant located in Hercules. Source: Stellarium

Although not a big-time shower like the August Perseids, this should be a good year for the Lyrids. You can start watching around 11 o’clock local time Wednesday night (April 22) when Vega climbs above the treeline in the northeastern sky. Rates will increase through the night and peak around 4 a.m.-5 a.m. when the radiant is highest in the sky just before dawn.

The sky facing east-southeast around 3 a.m. local time Thursday April 23. A perfect time to catch the Lyrids!

The sky facing east-southeast around 3 a.m. local time Thursday April 23. A perfect time to catch the Lyrids! Created with Stellarium

Dress warmly, pack a hot beverage and get comfy in a reclining chair. Or a hot tub. In which case, don’t dress warmly. Those are my mantras for any meteor shower. Even though Lyrids will radiate from a particular direction, they can show up anywhere in the sky. Early in the evening, you’re best to face east. Prefer the early morning? Face southeast.

We see a meteor shower when Earth passes through a comet debris stream. Every April, we pass through material shed by Comet Thatcher. Illustration: Bob King

We see a meteor shower when Earth passes through a comet debris stream. Every April, we pass through material shed by Comet Thatcher. Illustration: Bob King

Like many meteor showers, the Lyrids are the flotsam and jetsam of comets. You’ve been reading about all the dust released by Rosetta’s comet as it’s warmed by the Sun. Comets that cross Earth’s path put that dust to good use. As we speed into the debris sputtered from their nuclei, the particles strike our atmosphere and incinerate in a blaze of light to make a meteor.

C/1861 G1 (Thatcher), which takes roughly 415 years to make one orbit around the Sun, is responsible for the Lyrids. Every so often we pass through a thick filament of dust deposited by Thatcher and get treated to an outburst of Lyrids with numbers reaching more than 100 per hour. That’s expected to happen in 2040 and 2041, so stick around.

Ceres ‘Spot 5′ returns but continues to mystify

Dawn took this new photo of Ceres Dawn took these images on April 14 and 15 from a vantage point 14,000 miles (22,000 kilometers) above Ceres' north pole.

Dawn took this new photo of Ceres on April 14 from a vantage point 14,000 miles (22,000 km) above Ceres’ north pole. I rotated the image to place the crater and spots at top. Click to see the animation. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

NASA’s Dawn spacecraft just got a little closer to “Spot 5″, the name given to the pair of brilliant white spots located inside a 57-mile-wide crater on the dwarf planet Ceres.

This animated sequence of images from NASA's Dawn spacecraft shows northern terrain on the sunlit side of dwarf planet Ceres. The bright spots rotate up from the right side.  Credit: NASA/JPL-Caltech

This animated sequence of images from NASA’s Dawn spacecraft shows northern terrain on the sunlit side of dwarf planet Ceres. The bright spots – named Spot 5 by Dawn’s science team – rotate up from the right side. Credit: NASA/JPL-Caltech

Today we have pictures that are a little sharper and clearer than the last set from March, but still not close enough to do more than tantalize. They show a single spot in the crater’s center and two smaller, slightly fainter spots.

There’s also another extended bright area that pops into view at the start of the sequence (top middle) that soon fades as it rotates toward the terminator or day-night line on Ceres. The new images also show even more craters than earlier ones.

So you can see how the light changes on the pair (or three) white spots as Ceres revolves, these are individual cuts made from the video. Credit: NASA/JPL with selections made by Tom Ruen

So you can see how the light changes on the white spots as Ceres revolves, these are individual cuts made from the video starting at top left – when they were in deep shade – to lower right. Credit: NASA/JPL with montage by Tom Ruen

Starting April 23, Dawn will begin its first “science orbit”, taking observations from 8,400 miles (13,500 km) above the surface or nearly twice as close. Throughout the remainder of the spring, summer and fall, NASA mission controllers will continue to lower the probe’s orbit until it’s just 233 miles (275 km) by late November. Stay tuned!

Surprise dust jet flares on Rosetta’s comet

Looking at Comet 67P/Churyumov–Gerasimenko at exactly the right moment, Rosetta’s OSIRIS wide-angle camera captures the moment a jet bursts into action. The first image was captured at 06:13 GMT on 12 March, the second two minutes later. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Looking at Comet 67P/Churyumov–Gerasimenko at exactly the right moment, Rosetta captured the moment a jet bursts into action. The first image was captured at 1:13 CDT on March 12, the second two minutes later. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

In a rare catch, the Rosetta spacecraft photographed a new jet coming to life on Comet 67P/C-G. Giving the comet the appearance of a rocket at takeoff, the jet appeared unexpectedly from a shadowed underside off the comet’s nucleus known as Imhotep.

Scientists have seen plenty of activity at the comet for the past few months as ices like water and carbon dioxide that compose the nucleus vaporize in the Sun’s heat and leave as jets or mini-geysers. All that material feeds the glowing head of the comet called the coma. Once in the coma, the physical pressure of the Sun’s rays pushes the dust away to form a tail which glows by reflected sunlight. At the same time, the released gas responds to solar UV light and glows blue, forming a second tail.

“This was a chance discovery,” says OSIRIS principal investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany. “No one has ever witnessed the wake-up of a dust jet before. It is impossible to plan such an image.”

Not only that, but it’s interesting that the jet shot out from a shadowed area. Usually jets happen on the sunny, day-side of the nucleus, where solar energy is strongest.

“In these images we see Imhotep on the brink of dawn,” OSIRIS scientist Jean-Baptiste Vincent from the MPS explains. “It is possible that the first rays of sunlight hit some cliffs or outcrops that remained hidden to Rosetta due to the orbital position at the time.”

It’s possible that heat from adjacent warmer regions traveled beneath the surface and set off a wave of vaporization, cracking the surface and explosively releasing pent-up gas. In other words, a form of cometary flatulence.

By tracking brightness variations along the length of the new feature, scientists have measured the speed of the ejected mix at 17 miles an hour (8 meters/sec) or about the speed of a fast ride on a bicycle.

Comet 67P/C-G was just recovered from the ground this past week after being too close to the Sun to observe. This photo was taken on April 19, 2015. Credit: Jean François Soulier, Jean Gabriel Bosch, CAO, San Pedro de Atacama

Comet 67P/C-G was just recovered from the ground this past week after being too close to the Sun to observe. This photo was taken on April 19, 2015, and you can clearly see a small, bright coma and faint tail. Credit: Jean François Soulier, Jean Gabriel Bosch, CAO, San Pedro de Atacama

Most of Comet 67P/C-G’s dust outbursts last for a full rotation of 6 hours, with some still active up on the return spin. Other jets are bigger, more explosive but shorter-lived events that can spew enough material to make a comet suddenly brighten by several magnitudes. One such big pop happened on 67P on April 30, 2014, when its coma brightened and expanded over 1,100 miles (1,800 km). Once the material dissipated, 67P faded back to its original brightness.

Although I joked earlier about the rocket-like appearance of the new jet, material being shot away from the comet acts as a gentle form of thrust that over time can accelerate or decelerate its motion. This in turn can lead to changes in the time the comet reaches perihelion as well as uncertainties in exactly when it’s expected to return next.

Weird auroras / Mercury meets a dainty moon / See 5 evening planets!

An oval patch of glowing green aurora appeared in the northern sky in Cassiopeia last night (April 17). Credit: Bob King

An oval patch of glowing green aurora pulses in Cassiopeia last night (April 17). Credit: Bob King

It’s been a fantastic 4 nights of northern lights. For now, Earth’s magnetic environment has returned to quiet conditions. Similar to the run of auroras that began on St. Patrick’s Day, this one finished with the same peculiar, sausage-shaped patches.

Last night I noticed a single elongated glow about two fists across in the northern sky in late twilight that slowly pulsed in brightness, often disappearing for 10-15 seconds and then reappearing in the same spot. Like breath on a mirror.

Another view of the diffuse aurora seen last night across the northern sky. Credit: Bob King

Another view of the diffuse aurora seen last night across the northern sky. Credit: Bob King

During the night, the patch slinked slowly westward into Cassiopeia and then disappeared altogether around 11 o’clock. At midnight it reappeared in the northeastern sky below the Northern Cross.  The strange apparition added quiet intrigue to the evening’s boisterous calls from the frogs.

Use bright Venus to help point you in the right direction. This map shows the sky facing west-northwest around 40 minutes after sunset. Created with Stellarium

Use bright Venus to help point you in the right direction. This map shows the sky facing west-northwest around 40 minutes after sunset. Mercury is 7° to the lower right of the moon. Created with Stellarium

Tomorrow night (April 19), look to the northwest about 40 minutes after sunset for a rare alignment of a day-old moon and two planets. One of them, Mars, has been around since last spring. Back then it was much closer to Earth and brilliant. Since then the two planets have separated with Mars now far away and rather faint. You wouldn’t ordinary seek it out so low in a bright sky, but the youthful crescent moon will certainly lure you there.

Mercury's approximate path and altitude during its dusk appearance this spring. Notice how its phase changes from the current gibbous to half to crescent. Source: Stellarium, Bob King

Mercury’s approximate path and altitude during its dusk appearance this spring. Notice how its phase changes from the current gibbous to half to crescent. Source: Stellarium, Bob King

The moon will be just a bit more than one day old and appear as a razor-thin sliver about 5-7° high (three to four fingers held at arm’s length). It should be easily visible from anywhere with a wide open view to the west-northwest. Because of its relative faintness, Mars will probably require binoculars to see. Focus on the moon first and then slide to the right to find the star-like planet.

As an inner planet, Mercury goes through phases just like Venus and the Moon. We see it morph from crescent to “full moon” as its angle to the Sun changes during its revolution of the Sun. Credit: ESO

As an inner planet, Mercury goes through phases just like Venus and the Moon. We see it vary from crescent to “full moon” as its angle to the Sun changes during its revolution of the Sun. Credit: ESO

Mercury shines at magnitude -0.5, even brighter than Vega or Arcturus, but it’s only a few degrees high, so you might need binoculars to see it, too. Once again, the moon comes to the rescue. Look either with your eyes or binos 7° (four fingers) to its lower right.

Mercury quickly moves up from the horizon in the next two weeks for its best evening appearance of the year for northern hemisphere skywatchers. As it comes into better view, the planet will slowly fade and change phase just like the moon. You can see the phases through a small telescope magnifying about 75x. Be sure to look for Mercury early when it’s highest or the blurring effect of the atmosphere will turn it into a ball of quivering mush.

Saturn pops up in the head of the Scorpion in late April around 11-11:30 p.m. This photo was taken early this morning just after midnight. Credit: Bob King

Saturn pops up in the head of the Scorpion in late April around 11-11:30 p.m. This photo was taken early this morning just after midnight. Credit: Bob King

With Mercury joining the scene, we now have five — count ‘em — five planets visible in the evening sky. Throw in the Earth and that makes six out of a total of eight! Mercury and Mars hang low in the west; Venus can’t be missed, shining like a lighthouse high in the west at dusk; Jupiter dominates the southern sky in Cancer and if you stay up till 11:30, you’ll see Saturn rise in Scorpius low in the southeastern sky.

Such riches for planetary enthusiasts. Go out and meet your solar system at the next opportunity.

Rosetta bumps into some flaky characters

Meet more COSIMA dust grains! Credits: ESA/Rosetta/MPS for COSIMA Team MPS/CSNSM/UNIBW/TUORLA/IWF/IAS/ESA/BUW/MPE/LPC2E/LCM/FMI/UTU/LISA/UOFC/vH&S

Meet some of the more personable COSIMA dust grains. To get an idea of their size, the plate is 100 millimeters (~1/2 inch) across. Credits: ESA/Rosetta/MPS for COSIMA Team MPS/CSNSM/UNIBW/TUORLA/IWF/IAS/ESA/BUW/MPE/LPC2E/LCM/FMI/UTU/LISA/UOFC/vH&S

Here’s a family portrait only a scientist could love. 12,000 grains of Comet 67P/C-G were collected between last August and mid-March of this year on nine target plates measuring a little less than 1/2-inch square (1 cm). This photo shows one of these targets with grains collected up to December 12.

Imagine my thrill seeing that one of the motes was named “Bob”. Rosetta employed its COSIMA instrument to capture the grains wafting from the comet onto the sticky target surfaces. After taking close-up photos of the particles, COSIMA then analyzed the composition of selected grains using a secondary ion mass spectrometer, a device that shoots a beam of ions (atoms that have lost or gained an electron) at a grain and collects the ions that are bounced back for analysis. By identifying the sputtered ions, scientists can determine the individual elements that compose the grain.

Montage of photos of Comet 67P/Churyumov-Gerasimenko taken by Rosetta. Obvious in all the images are the active plumes of gas and dust grains leaving the comet, some of which have been captured by COSIMA. Credit: ESA/Rosetta/Navcam

Montage of photos of Comet 67P/Churyumov-Gerasimenko taken by Rosetta. Obvious in all the images are the active plumes of gas and dust grains leaving the comet, some of which have been captured by COSIMA. Credit: ESA/Rosetta/Navcam

Last October, COSIMA found magnesium and sodium this way in a dust grain named Boris. 95% of known minerals observed in comets resemble olivine and pyroxenes, common in meteorites and in the upper mantle of the Earth. Sodium has also been seen in comet comas and tails, and originates in dust grains, but its mineral source remains uncertain.

A false color/color enhanced view showing the smooth Hapi region connecting the head and body of Comet 67P/C-G. Color filters have been used in a way to enhance slight color differences in the comet's nucleus. The bluish coloring in the smooth area might indicate the presence of ice at or just below the dusty surface. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

A false color/color enhanced view showing the smooth Hapi region connecting the head and body of Comet 67P/C-G. Photos taken through separate color filters have been combined to enhance slight color differences in the comet’s nucleus. The bluish tint in the smooth area might indicate the presence of ice at or just below the dusty surface. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Many of the particle names are given for COSIMA team members, along with other Rosetta mission team colleagues. But by the time they had reached 2,000 particles, names were getting in short supply, so Sihane Merouane, who’s responsible for cataloguing the grains, decided they’d only name dust particles larger than 40 microns (about 1/3 the width of a human hair) with some exceptions made for special, smaller particles.

There’s nothing like a name to make even the most obscure objects approachable. Touché team!