Monthly Archives: July 2012

Is Pluto a planet? You decide

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Pluto and its five moons photographed on July 7, 2012 by the Hubble Space Telescope Credit: NASA/ESA

From the time of its discovery in 1930 until 1992, Pluto was a happy, full-fledged planet. A little odd maybe with its tipped, eccentric orbit and tiny size, but the ninth planet just the same. That all began to unravel when asteroid 1992QB1 was discovered by astronomers David Jewitt and Jane Luu on August 30 that year.

QB1 was the first object found in the Kuiper (KYE-per) belt, an orbiting reservoir of asteroids similar to but much larger than the asteroid belt between Mars and Jupiter but much larger. While the inner belt is populated by rocky asteroids, the Kuiper Belt objects, located farther from the sun in solar system’s deep freeze zone, are composed of mixtures of water, methane and ammonia ices and rock.

Before 1992 the only object we knew of in the Kuiper Belt was Pluto. We now realize it contains a blizzard of icy asteroids.

QB1 is about 100 miles across and orbits a little farther from the sun than Pluto. Here was an asteroid out near Pluto orbiting in a similar way. Were there others? QB1 would turn out to be the proverbial tip of the iceberg. As searches expanded and bigger telescopes were put to the task, dozens then hundreds of new icy asteroids were found in the Kuiper Belt. As of today, over 1,000 are known with an estimated 70,000 larger than 100 km (62 miles) remaining to be found. Suddenly Pluto had lots of company. In 2005 of Mike Brown and his team at Palomar Observatory found Eris, an asteroid more massive than Pluto and nearly equal in size.

That’s when astronomers began to wonder whether Pluto should still be considered a planet or just one of the many asteroids in the Kuiper Belt. The discovery of so many small worlds at the edge of the solar system made us realize we lived in a much less tidy but vastly more interesting place than we’d thought.

Planetary scientist Dr. Hal Levison explains his view of asteroids vs. planets to workshop participants in Boulder, Colo. earlier this month. Photo: Bob King

Dr. Hal Levison at the Department of Space Studies at Southwest Research Institute in Boulder and Alan Stern, the principal investigator for the New Horizons mission to Pluto, went head to head on the topic at a workshop I attended in Boulder, Colorado earlier this month at the Laboratory for Atmospheric and Space Physics.

While Levison plants his flag firmly in the Pluto-as-asteroid-camp, Stern would not only keep Pluto a planet but expand the definition to include many of the solar system’s larger moons. They share common ground in their mutual dislike of the definition of a planet introduced and voted on in August 2006 by members of the International Astronomical Union. One may wonder whether science is best served by 420 astronomers taking a vote on a proposal.

This is what shook out. For a body to qualify as a planet it must:
1. Orbit the sun
2. Have sufficient mass (gravity) to crush itself into a nearly spherical shape
3. Be gravitationally dominant in its orbital zone. In other words, it has to clear its orbit of all other smaller bodies

By this definition, Pluto, unable to clear its orbital neighborhood, loses planetary status. Almost as a kindness, it and several other large, round asteroids, were given the special designation of dwarf planet.

The current four dwarf planets in comparison to the moon and Earth: Pluto, Eris, Makemake and Ceres. Credit: NASA, ESA, JPL, and A. Feild (STScI)

While Levison takes exception on the roundness issue, citing Earth’s moon and Jupiter’s four largest moons as being round enough to at least in part qualify as planets, he agrees that Pluto and the thousands of other asteroids in the Kuiper Belt are related by location, size (small bodies compared to the 8 planets), inability to clear their orbits and dynamics. The last refers to how the whole lot of them were cast into the outer solar system by the planet Neptune as it migrated to its present orbit in its youth.

“There are 8 important bodies and lots of smaller ones,” said Levison. He added that if we went back to the old way of doing business and kept Pluto a planet we’d have a 1000 planets today, since there are nearly 1000 roughly spherical asteroids 250 miles across and larger. “It’s a lot easier to go from 9 to 8 instead of 9 to more than a 1000,” remarked Levison.

Dr. Alan Stern explains that a star’s a star no matter its size. Planets should be similarly defined by their qualities, not their orbits. Photo: Bob King

Alan Stern respectfully disagreed. “Just give it the Star Trek test,” he said. “Orbit it, look at it and make the most obvious call.” If the current definition of a planet were carried forward into a fictional distant century, the conversation between Spock and Captain Kirk might go something like this: “I can’t say whether it’s a planet yet Jim. We’ll first have to determine its shape and study its orbital mechanics before we can classify it. To say it’s a planet based on current information would be not be logical Captain.” Kirk is fuming at this point.

Stern offers his own “geophysical” definition of a planet that relies on an objects essential qualities rather than on how well it cleans up its orbital neighborhood. Drum roll please:

A planet is anything big enough to crush itself into a sphere but small enough that it’s unable to fire up nuclear fusion in its core and burn like a star.

He used stars to further illuminate his point. Big or small, hot or cool, double or solitary, stars are still stars. Looking at Hal with a a wry smile, Stern further added (and I paraphrase): “You’re a large man and I’m a short one, but we’re both men.” By Stern’s definition, Earth and moon become a double planet, Jupiter’s four largest moons are planets as are some well-known asteroids like Ceres and Eris. Objects found orbiting other stars as well as rogue bodies wandering around with no star to call home – all planets.

Ah, the good old days when things were relatively simple. A mechanical planetarium made by Benjamin Martin in London in 1766 on display at the Putnam Gallery in the Harvard Science Center. Credit: Sage Ross

While I’ve been one to see Pluto as just a big asteroid, Alan’s sweeping definition felt like a fresh breeze of common sense. He pointed out that the “clearing the neighborhood” requirement is heavily biased against objects in the outer solar system whose orbits cover much vaster regions of space that those of planets in the inner solar system. In fact, if you put the Earth where Pluto is, the gravitational might of our planet wouldn’t be enough to clear its orbit. Does that mean Earth’s not really a planet unless it’s close to the sun? Crazy talk.

So what are we to take home about the point-counterpoint about Pluto and planets? At least two things. First, it’s going to take time and lots more discussion before astronomers arrive at a definition they can agree upon. Second, science rarely deals in black and white. That’s both its frustration (for some) and beauty. Both Levison and Stern see the discovery of the Kuiper Belt asteroids and the hundreds of new planets around stars beyond the sun as one of the great revolutions of astronomy on par with Copernicus’ theory of the sun-centered solar system. The fact that definitions are in upheaval means a profound change in our understanding is underway.

Nature whispers in our ears through sophisticated instruments and computer models. Our charge is to listen carefully, take time to draw conclusions and not be wedded to a particular idea too soon. Listening to two scientists with opposing views treat the Pluto -planet issue with humor and respect gave me a new respect for how science works.

Give us this day our crepuscular rays

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Ragged moonbeams and shadows are cast by a cloud covering the gibbous moon last night. Photo: Bob King

Last night a raft of clouds drifted across the gibbous moon and rays of darkness shot across the sky. What I saw were crepuscular rays, more familiar during the daytime when sunlight shines between towering clouds to create a spreading fan of sunbeams and shadows. Dust and moisture in the atmosphere make the beams of light stand out even better.

What was unusual about the moon’s crepuscular rays was how the bright ones blended into the sky, but the “shadow beams” – created by clouds blocking the moonlight – stood out as dark shadows against the moonlit sky. The effect was striking.

Individual cloud turrets create the shadow rays while gaps allow sunlight to pass, creating a splendid show  of crepuscular rays shortly before sunset earlier this month. Photo: Bob King

Crepuscular comes from the Latin word “crepusculum” meaning twilight. They can occur anytime but are more apt to be noticed when the sun is low in the sky or shortly after sunset or before sunrise. What really catches the eye is how they radiate in beautiful fans like crowns of glory or angelic halos.

I wouldn’t doubt that apparitions of the Virgin Mary and the like have something to do with crepuscular rays. The stunning sight is based on a well-known optical illusion. The rays are actually parallel to one another and only appear to converge into a crown the way the rails of a train track narrow to a point in the distance. If we could look down on the clouds from high above, the rays would appear perfectly parallel to one another.

Anticrepuscular rays seen at sunset from the airplane window. I’m looking to the southeast. The bright rays are beams of sunlight passing through gaps in clouds on the opposite side of the plane. The dark rays are where the sunlight was blocked by the clouds. Photo: Bob King

Sometimes around sunset or sunrise when atmospheric conditions are right, you can see crepuscular rays beamed by clouds massed along or just below the horizon reach all the way to the opposite end of the sky called the antisolar point.

A display of anticrepuscular rays seen at sunset from the ground. The beams of light and shadow appear to draw together or converge in the eastern sky. Photo: Bob King

There they converge (illusion again) to form a curious bundle of dark beams that look like a gigantic sunless sunburst. Crepuscular rays seen opposite the sun (or moon) are called anticrepuscular rays. They’re much rarer than the crepuscular variety and well worth your time to seek. Next time you see beams of light and dark spreading up from the western horizon at sunset, try to follow them all the way back to the antisolar point in the east. You might find a lovely set of anticrepusculars waiting for you there.

I was fortunate to see them from my airplane seat window while flying back to Duluth from Colorado earlier this month. They looked peculiar – appearing below my local horizon – no doubt because of my altitude at the time.

Hasta la Vesta! Dawn begins its departure

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Huge parallel troughs, probably related to the stress of the huge impact that created the south polar crater Rheasilvia, stripe the 326-mile-diameter asteroid’s equator. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

On July 25 at 11:45 a.m. (CDT) the Dawn spacecraft, which has been orbiting the asteroid Vesta since July 16, 2011, powered up its xenon ion engine and began raising its altitude in preparation for departure. Dawn’s exit is a drawn-out affair – not until August  26 will the probe slip free of Vesta’s gravity and once again orbit the sun. Its next and final target is the asteroid Ceres, which along with Pluto and a couple other asteroids, is now classified as a dwarf planet.

Artist’s view of Dawn in orbit around Vesta. Credit: NASA/JPL-CalTech

The mission’s not over yet. Thrusting will be stopped four times during the month-long ascent to allow Dawn to photograph regions of the asteroid’s northern hemisphere that have been in seasonal shadow for most of the mission.

I can’t wait for Wednesday August 22. On that day mission controllers will halt the craft to look back and photograph Vesta as a thin crescent “moon”, a perspective never before seen. The purpose of the photos will be to measure the reflective properties of Vestan dust, but we’ll all appreciate the aesthetic bonus.

The south polar mountain inside the gigantic impact crater Rheasilvia rises 13 miles above the surrounding terrain. That’s almost three times higher than Mt. Everest. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

The scientific bonus from the mission has been immense – over 4,700 photos, 9 million spectra of the surface to help scientists unravel the composition of the asteroid’s minerals, measurements of Vesta’s gravity field to determine how matter is distributed in the planetoid’s interior and identifying many individual atomic elements in the uppermost yard of soil with a gamma ray and neutron detector.

Circling the asteroid at an altitude of only 420 miles (about twice the height the space station flies over Earth) every 4 hours, 21 minutes, Dawn snapped photos of Vesta’s sunlight hemisphere and then beamed the images back to Earth during its night side flight. Over a year’s time, the probe completely mapped the surface six times. Four of the maps were made with the camera pointed at an angle instead of straight down; scientists combined the two views to create a boatload of 3-D images.

The crust of Vesta is pocked with all variety of craters that have excavated both light and dark materials from beneath the surface. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

The biggest thrill has been seeing what was a pinpoint of light in most telescopes evolve into a misshapen sphere with craters, tall mountains, and a strange series of parallel troughs ringing the equator. Scientists believe the grooves were created by an impact that left a 314-mile diameter crater in the asteroid’s southern hemisphere called Rheasilvia.

This Howardite meteorite called NWA 3149 was found in the Sahara Desert. It almost certainly came from Vesta. Notice all the fragments. These were broken during earlier impacts on the asteroid and welded together under heat and pressure. Photo: Bob King

Material blown into space from the blast has even managed to make its way to Earth as HED meteorites. Known as Howardites, eucrites and diogenites, they’re made of the same materials Dawn found on the surface and within the crust of Vesta.

On September 1 Dawn will cast one last glance at Vesta from a vantage point 24,000 miles away before setting its sights on Ceres. We learned patience on the journey to Vesta, and we’ll need it again as we wait for the hardy craft to arrive at Ceres in February 2015.

The title of this blog refers not only to Dawn’s departure from Vesta but also to a live Twitter and Facebook event on September 8 to celebrate the mission. Click HERE for more information on how you can participate.

Aurora alert tonight July 28-29

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The extent of the aurora at 8:30 p.m. (CDT) this evening July 28. The Kp index at the time was 4, just below minor storm level. Click map to see the current index. Credit: NOAA

Be on the lookout for the northern lights tonight (July 28-29). You can even pair up your aurora-gazing with some late-night Delta Aquarid meteor watching . The shower is expected to reach maximum tomorrow morning after moonset when 10-15 meteors per hour could flash from a dark sky.

A high speed solar wind blowing from an open coronal hole in the sun’s atmosphere is presently stoking Earth’s upper atmosphere with an abundance of solar electrons and protons. Looking at the auroral oval map, the northern lights should be visible over Scandinavia tonight if twilight’s not too bright.

While there are no guarantees the activity will continue into the North American night, be on the watch. Any auroras we might get will be more obvious after moonset around 2 a.m. I’ll update later this evening if the lights show up over Duluth, Minn.

** UPDATE 11:30 p.m. (CDT): Pretty cloudy now here, so it’s difficult to tell if aurora is out. I’ve received one report of some faint ones. Auroral oval has shrunk since 10 p.m. and activity’s dropped off a little … for the moment.

Can you see the American flag on the moon? Yes!

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Bright Venus (bottom) and Jupiter are joined by the Hyades (right of Jupiter) and Seven Sisters star cluster (top) in the eastern sky at the start of morning twilight today. Photo: Bob King

I got up at 2:30 and casually surveyed the sky while poking around with the telescope till 4. Total meteor count: 0 Delta Aquarids and 2 unrelated meteors. Maybe tomorrow will be better.

Sharing the 50-degree temperatures with the crickets and katydids that inhabit the dewy grass was pleasant enough. Venus and Jupiter along with the Hyades and Seven Sisters star clusters totally jazzed up the eastern sky, and at 4:06 a.m. the space station breezed by. I hunted for the Progress cargo ship along, ahead of and behind the station but never saw it. Did you have better luck?

Apollo 16 astronaut John Young hops while saluting the flag in April 1972. Credit: NASA

The Lunar Reconnaissance Orbiter (LRO) keeps on giving. Flying only 31 miles high above the moon’s surface it snapped a set of newly-released photos of the Apollo landing sites that plainly show the U.S. flags planted by the astronauts.

The flag that John Young saluted is still visible in this picture taken by the LRO. The gray-colored blob is the flag; its contrastier shadow to the left is easier to make out. Also seen are the lunar descent module, astronaut tracks, the Lunar Rover and its tracks. Credit: NASA

One of the most common questions asked by the public when we’re looking at the moon through a telescope is why we can’t we see the American flags or any other sign of Apollo with the Hubble Space Telescope. It IS the most powerful telescope, right? Here’s the rub. The smallest possible thing Hubble can see on the moon is about 328 feet across or the length of a football field. While impressive feat of resolution, no Apollo spacecraft comes anywhere near that size. Every piece of man-made hardware is below the space telescope’s resolution limit.

Because of the lighting angle, the Apollo 17 stands out even better than Apollo 16′s. Credit: NASA

The trick to seeing flags and other details is not necessarily a bigger telescope; it’s getting a camera in orbit close to the moon. That’s what the LRO’s been doing for past few years. Its cameras can record objects 1.6 feet across. Lots of things, including lunar descent modules, experiments placed there by astronauts and even their footpaths come into focus in LRO’s eye. And now, the flags.

Astronaut Harrison Schmitt stands on the surface of the moon next to the U. S. flag at the Taurus- Littrow landing site during the Apollo 17 mission. A “half-moon” Earth is visible at top. Credit: NASA

I swear I can see the contrast difference between the stripes and the dark, starry patch and even a hint of the flagpole in the Apollo 16 photo. Pretty incredible!

The only flag we probably won’t ever see is the first one, planted there by Neil Armstrong and Buzz Aldrin on July 20, 1969. Aldrin reported it was blown over by rocket exhaust as the astronauts left the moon to return to the orbiting command module.

Since the flags are made of nylon they won’t last terribly long under the extreme conditions on the lunar surface. Strong ultraviolet light from the sun has probably already caused the colors to fade. Over a longer time, the flags will turn brittle until one day crumbling into little heaps of dust during a moonquake.

Click HERE for full resolution views of the Apollo landing sites taken by LRO.

 

Delta Aquarid meteor shower fires up for the weekend

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Meteors from southern Delta Aquarid meteor shower radiate from near the star Delta Aquarii (hence the name) not far from the bright star Fomalhaut in the Southern Fish low in the south before dawn. Created with Stellarium

It’s not a big shower, especially for the northern half of the planet, but if you’re up late this weekend and attentive, you’ll see more meteors than usual flashing across the sky. The annual Delta Aquarid meteor shower crests to a maximum tomorrow and Sunday mornings with 10-15 meteors per hour visible from a dark sky site.

Sky watchers in the southern hemisphere will see double that because the radiant, the point from which the meteors originate, is much higher in the sky. Meteors barreling down the sky south of the radiant don’t get cut off by the horizon.

When Earth’s orbit intersects rocky and icy debris left in the wake of comet tail, we experience a meteor shower. Illustration: Bob King

There are actually two meteor showers in Aquarius active this time of year – the northern and southern Delta Aquarids. The northern version sports fewer meteors and peaks in mid-August.

Both are very broad streams. Tomorrow’s southern “Deltas” started in mid-July and will peter out a month later. This weekend marks the peak.

Nearly all meteor showers originate from clouds of sand to seed-sized bits of debris fizzed off by comets as they swing near the sun. As a candy lover, I  like the image of Tootsie-Rolls tossed out at a parade.

Earth plows into these debris streams at specific times each year, creating a shower of meteors from the sky. Those bits of comet dust strike the air overhead at many thousands of miles an hour, burning up in a flash we call a meteor. Energy imparted to the air molecules by the speeding particles is converted into the light we see streaking across the sky.

A meteor from the April Lyrid shower burns up in the atmosphere some 70 miles high as seen from the International Space Station. Credit: NASA

The best time to watch the Delta Aquarids is in the early morning hours before dawn when the radiant is up in the southeastern sky. Happily, the gibbous moon will set around 1 a.m., leaving dark skies during the ideal viewing time. Find a spot with a good view to the south and set up a lawn chair. You don’t need any other equipment than your eyes … and maybe a cup or two of coffee. The Aquarids will whet your appetite for the bigger, better Perseid meteor show coming to Earth on Saturday night August 11-12.

Since most showers have a “parent” comet, you might be interested to know that the likely one for the Delta Aquarids is none other than 96P/Machholz. Yes, the very same comet that’s currently visible in medium-sized scopes low in the western sky during evening twilight. How nice to meet the artist and admire his work at the same time.

Space station gets some company this weekend

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5-minute exposure of stars reflected on the calm waters of Spring Lake north of Duluth, Minn. earlier this week. Photo: Bob King

If you haven’t seen the International Space Station (ISS) at dawn I understand your reluctance. Perhaps two additional enticements will coax you out before sunrise. Problems with a new rendezvous system on the Russian Progress M15-M supply ship prevented a successful docking with the ISS Tuesday. Bad news, right? Well yes and no. Mission controllers put Progress in a safe spot 1.8 miles below the station until the next docking attempt Sunday. That means a few more mornings of seeing the two travel together across the sky.

Wait, there’s more. The Japanese Kounotori 3 or “white stork” cargo-carrying vehicle is on its way to the station to deliver food, equipment and a module to deploy five nanosatellites (very small satellites) into orbit. Before it docks tomorrow morning July 27, you might also be able to see it.

Check out the bright gathering of Venus, Jupiter and Aldebaran in the eastern sky at dawn tomorrow. Created with Stellarium

Though considerably fainter than the ISS, Progress and Kounotori 3 should be visible following a short distance behind.

Use binoculars to help you spot them. To improve your chances, point the binoculars a little ahead of where the station is moving, let it pass through the field of view and keep watching the spot you’re aimed at for 15-30 seconds after. If your sky’s dark enough you should be able to see them with the naked eye.

Next, we check in on the planets. 90 minutes to an hour before sunrise face east to get an eyeful of planets and star clusters. The Pleiades, Hyades, Jupiter and Venus are gathered together on the sky stage like musicians at a chamber concert.

But wait, there’s even more! This weekend before dawn we get a visit from the annual Delta Aquarid meteor shower. I’ll have details on how to watch it and what to expect in tomorrow’s blog.

Space Station Viewing:
Times below are for the Duluth, Minn. region. To find passes for your town, log in to Heavens Above or type your zip code into Spaceweather’s Satellite Flybys page.

* Friday morning July 27 starting at 3:24 a.m. (CDT) almost straight overhead. Brilliant pass!
* Saturday July 28 at 4:06 a.m. Nice pass halfway up in the northern sky
* Sunday July 29 at 3:15 a.m. high in the north. Second pass at 4:50 a.m. also in the north.
* Monday July 30 at 3:56 a.m. ”     ”
* Tuesday July 31 at 3:05 and again at 4:40 a.m. ”     ”
* Wednesday August 1 at 3:48 a.m.

Tale of La Sagra: how a common asteroid became an oddball comet

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Comet P/2012 NJ (La Sagra) photographed on July 23 from France. Check out that pointy tail. Click image to see more photos. Thanks and credit to Jean-Francois Soulier

Ever wish you were somebody you’re not? No? Good, but for anyone who’s fantasized about being a rock star or rocket scientist, you’re sure to find company in the little comet called La Sagra. It’s full name is P/2012 NJ (La Sagra) and it began life as an asteroid when first discovered by the La Sagra Sky Survey.  Asteroids appear star-like in nearly all telescopes because they’re almost all tiny and relatively far away. La Sagra was no exception.

Comet NJ La Sagra has a steeply inclined orbit. It’s currently moving up and away from Earth and the sun. Credit: NASA

The survey, based in the mountains of southern Spain, and dedicated to finding small solar system bodies, employed a 17.7-inch (.45 meter) telescope to scoop up the asteroid on July 13. For a brief time it went by the name 2012 NJ, but followup observations by German astronomer Gerhard Hahn showed that the new-found rock sported a very faint needle-thin tail pointing to the southwest. Tails don’t grow from rocky asteroids. You need something like ice that vaporizes in sunlight to form a tail, and that’s exactly what a comet does.

Another tip-off was La Sagra’s  cigar-shaped orbit tilted nearly perpendicular to the solar system. Highly inclined, elongated orbits are more typical of comets than asteroids. Three days after discovery, thanks to additional observations, astronomers discovered their first conclusion had been too hasty, and La Sagra was re-branded a comet.

Comet La Sagra on July 19 taken by Stefano Mottola with a 1.23-meter telescope at Calar Alto Observatory in southern Spain.

La Sagra passed closest to the sun back in June at the rather large distance of 120 million miles and returns to Earth’s vicinity every 24.3 years.

I took at look at it three nights ago, and the comet was indistinguishable from a 14th magnitude star – no fuzziness, no tail. Just a pinpoint of light zipping along at a good clip in the constellation Pegasus the Flying Horse. In less than 10 minutes I could see it move against the background of stars.

Faraway comets often look no different from faint stars, but a pinpoint one in Earth’s neighborhood this close to the sun is out of the ordinary. Nearly all comets have a coma or atmosphere of dust and gas boiled off by sunlight when near the sun. That’s what gives them their characteristic fuzzy appearance. Either La Sagra is coma-less or its coma is very tenuous.

Currently closest to Earth at some 56 million miles, the comet is expected to fade as it heads back to the far end of its orbit in the months and years ahead. You can hunt for it now in 10-inch and larger scopes as it tracks to the northwest in Pegasus at nightfall. Click HERE to go the Horizons site where you’ll find La Sagra’s orbital elements. Input those in your sky charting software and you’re good to go.

Comet 96P/Machholz photographed July 23 by German amateur astronomer Waldemar Skorupa. Like most comets near the sun, Machholz displays a bright, fuzzy head called a coma. It also has a short tail and is visible this month in evening twilight. Click image to see more of Waldemar’s comet photos.

The origin of the comet’s unusual tail – already fading –  isn’t known. Is La Sagra a dormant comet that came back to life when a burst of fresh ice and dust erupted from a new crack in its icy surface? Or is more like asteroid 596 Scheila, which was struck in late 2010 by a tiny asteroid? The impact released a cloud of dust forming a brief-lived coma and tail.

I’m hoping astronomers continue their studies of this very interesting object while it’s still close to home.

Surprise aurora torches the western sky

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Like breath on a mirror, a solitary curtain of northern lights reflects in Spring Lake last night at 11:45 p.m. (CDT). Photo: Bob King

The chances of aurora showing up in northern Minnesota last night were slender, and yet somehow, there it was. There was a small possibility thanks to a stronger than average solar wind streaming from a coronal hole in the sun’s atmosphere or corona. All the usual indicators – Kp index, the satellite photos of the auroral oval – showed low activity.

Before fading away around midnight, the western aurora grew a “tail” that stretched some 30 degrees long. Photo: Bob King

Again by chance, I happened to be observing the sky from the boat landing of a small lake north of Duluth, Minn. Around 11 o’clock I could see a little glow coming from behind tall trees lining the lake’s northern shore. Nothing impressive. But shortly before midnight a most remarkable “torch” of pale green light gradually swelled to brilliance all alone in the western sky.

Before it faded away, the aurora grew a long tail like some giant comet about to strike Earth. 20 minutes later it was gone. Isolated blobs like this one are unusual.

Very faint, diffuse bands of aurora striped the northern sky late into the night. You might still see minor activity tonight from the same coronal hole stream. Take a look at the northern sky before you turn in this evening.

Yesterday I wrote about seeing Comet 96P/Machholz in evening twilight. That’s how I ended up along the lake last night – I needed a good horizon to the northwest to find the comet. If you’ve never set up a telescope on a 25 degree incline 6 feet from dark water you haven’t lived.

A detailed chart of 96P/Comet Machholz’s path tonight through Aug. 2. Click chart for a larger version you can print out. The numbers are the stars’ names, not their magnitudes. Created using Emil Bonnano’s MegaStar program

Mosquitos didn’t make it any easier, but I finally nailed Machholz at 10:30 p.m. It was a small, bright, fuzzy glow through my 15-inch reflector. Like the Soup Nazi on Seinfeld, I suffer for my comets. To lessen your suffering, I’ve made a more detailed chart you can use along with the one from yesterday’s blog. Click it for a larger version.

Saturn and Spica (left) along with Mars, reflect in Spring Lake last night July 24 at the end of dusk. The moon will hover below Mars tonight. Photo: Bob King

I hope you enjoyed watching the moon last night. For the northern U.S., its shallow-angled path meant it was low in the sky and set early. Tonight the moon will be a thicker crescent and make an eye-catching foursome with Mars, Saturn and Spica.

Notice that the colors of Saturn, Spica and Mars are much more obvious reflected in the water than seen “raw” in the sky. I think the water not only expands and softens the images, enriching the colors, but the underexposed reflections are more saturated than the normally exposed stars.

Lightning under the stars, a moon show and Comet Machholz at dusk

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Lightning illuminates a thundercloud in northern Minnesota last night. The stars near the storm belong to the constellation Perseus the Hero. Photo: Bob King

Came back from Colorado last night to a line of thunderheads along the northern horizon. I would have gone out earlier to shoot more lightning photos, but my dog Sammy decided to punish me for my weekend absence by running away during her walk. After a fruitless search and knowing she’d find her way back home, I sped off to a wide open horizon to watch the distant storm.

The sky facing southwest ah hour or so after sunset tonight July 23. The moon will be near Mars tomorrow night and Saturn and Spica the next. Created with Stellarium

I’d hoped to see some sprites, those energetic bursts of pink light that shoot upward from thunderstorm cloud tops into the ionosphere. No luck on that, but the jagged strokes against starlight were pleasure enough.

Tonight the crescent moon returns for easy viewing in the southwestern sky during twilight. If you wait at least an hour after sunset, you can see a nice lineup of moon, planets and Spica in a darker sky.

Comet 96P/Machholz zips through Leo and Leo Minor in the coming days. The map depicts the sky facing west about 90 minutes after sunset or around 10:15 p.m. (CDT). Tick marks show where the comet is each evening now through August 1. Stars are plotted to 8th magnitude. Created with Chris Marriott’s SkyMap software

For amateur astronomers with 6-inch scopes and larger who like a challenge, returning comet 96P/Machholz is now making an appearance in evening twilight in the western sky. It’s currently a small, condensed blob of light shining at 7.8 magnitude.

If it were in a dark sky well above the horizon, you’d see the fuzzy fellow with ease even in a 3-inch telescope. Instead, Machholz is only about 5 – 10 degrees high (one fist held at arm’s length equals about 10 degrees) during mid to late twilight. A sky with little haze and a wide open view to the west is essential if you want to grab a view.

And yes, Sammy came back. She was waiting for me at the front door.