Live in the Midwest? Enjoy a rare sunset solar eclipse

If you live in the gray band or are planning a trip there, you'll see the full annular eclipse. The red line shows where the moon will pass squarely over the sun's face. Click map to see an interactive version where you can click on your city to get local times and coverage for the eclipse. See below for more local times. Credit: NASA

Most of us won’t be in the path of the annular eclipse that cuts across the western U.S. this Sunday afternoon. That means we’ll see varying degrees of a partial eclipse. The farther west and south you are, the more of the sun will go missing. Across the Midwest, about 2/3 of the sun will be covered at maximum eclipse.  Viewed through a safe solar filter or indirectly, by projecting the sun’s image onto a sheet of white paper with binoculars, the eclipsed sun will be a lovely sight.

If you still would like to observe the sun directly but can’t find a mail-order solar filter, contact your local welding supply store and purchase a #14 welder’s glass.

Much of the U.S and Canada, will see a rare partial eclipse at sunset Sunday. This photo is from the June 10, 2002 eclipse. Credit: Christopher Go

For a wide swath of the central U.S. and Canada, the sun sets while still in eclipse, giving us a rare and scenic opportunity to observe a most unique sunset. I may be stuck in Duluth, but you better believe I’ll be somewhere where I can see right down to the northwestern horizon Sunday night.

Consider hunting up a similar spot where you live. Take the family and friends and arrive a little before eclipse start. My guess is that you’ve photographed sunsets before; this time your sun will take on a whole new appearance. If you stick around into twilight, you’ll even be able to see Venus a little more than “two fists” above and left of the sunset point. Binoculars will show it as a tiny crescent moon.

View of Sunday's partial solar eclipse from Duluth, Minn. At maximum eclipse at 8:17 p.m., the sun will be only 3 degrees or "two fingers" above the horizon. The sun sets while still in eclipse. Created with Chris Marriott's SkyMap

The whole event happens in the early evening with the sun low in the western sky.  For Duluth, Minn. the moon takes it first nibble of the solar cookie at 7:17 p.m. when the sun is only 12 degrees high or about a balled fist held at arm’s length against the sky. Maximum eclipse – when the most sun is covered – occurs an hour later at 8:17 p.m., when 66% of the sun’s disk is blocked.

Even though our weather forecast is grim, Sunday night is expected to clear out. Because clear skies often start in the west and move east, the sun sometimes pops out at sunset from beneath the blanket of clouds. Don’t miss it.

Here’s a sampling of eclipse times for major cities not in the annular path but that will still experience a nice partial eclipse. The listed times are local, meaning the time you see on your watch or cellphone if you live there.  Eclipse start and maximum coverage times are shown:

* Minneapolis, Minn. — 7:19 p.m. start / 8:19 p.m.  max / 67% covered / Sun sets in eclipse
* Fargo, ND — 7:16 p.m. / 8:18 p.m. / 66% / Sun sets in eclipse
* Winnipeg, Manitoba — 7:13 p.m. / 8:14 / 61% / ”     ”
* Madison, Wis. —  7:21 p.m. / 8:20 p.m. /  68% / ”     ”
* Chicago, Ill. — 7:22 p.m. / 8:21 p.m. / 69% / ”     ”
* Detroit, Mich. — 8:21 p.m. Sun only 4 degrees high at start and sets before maximum
* Indianapolis, Ind. — 8:24 p.m. with sun 5 degrees high. Sets before max.
* Memphis, Tenn. — 7:29 p.m. with sun 5 degrees high. ”     ”
* Montgomery, Ala. — 8:30 p.m. with sun only 1 degree high. ”     ”
* Omaha, Neb. — 7:23 p.m / 8:25 / 76%
* Kansas City, Kan. — 7:25 p.m. / 8:27 p.m. /  79% Max. eclipse happens at sunset
* Denver, Colo. — 6:23 p.m. / 7:30 p.m. / 86%
Dallas, Tex. – 7:32 p.m. / max eclipse of 94% occurs ~12 mins. after sunset
* Salt Lake City, Utah — 6:19 p.m. / 7:30 / 89% / Eclipse ends just before sunset
* Las Vegas, Nev. — 5:24 p.m. / 6:36 p.m. / 92% / Eclipse ends at sunset
* Billings, Mont. — 6:14 p.m. / 7:22 p.m. / 77% Eclipse ends before sunset
* Seattle, Wash. — 5:02 p.m. / 6:18 p.m. / 83% Eclipse ends before sunset
* Portland, Ore. — 5:04 p.m. / 6:21 p.m. / 88% ”      ”

Heads up: NASA says 4,700 potentially hazardous asteroids are out there

The little asteroid 2012 KA passes near Earth today before heading back out into space. Credit: JPL

This afternoon around 3 o’clock Central time, asteroid 2012 KA will fly silently past Earth at a distance of about 139,433 miles. That’s a little more than halfway to the moon and well out of harm’s way. 2012 KA was discovered only yesterday by the Mt. Lemmon Observatory as part of the larger Catalina Sky Survey. The survey’s goal is to find and determine orbits of larger, potentially hazardous near-Earth asteroids (PHAs) from 100 meters (330 feet) on up. PHAs are a subset of a larger group of near-Earth asteroids or NEAs.

This fly speck of an asteroid is only 25 feet across. Even if it were to hit the Earth – which it isn’t – most of it would burn up on entry. Any fragments left over would be insignificant in terms of causing damage on the ground.

Tiny asteroids like this one are discovered routinely, sometimes only days before closest approach. There are a couple reasons for that. Being small, they’re very faint. To spot one, the asteroid has to get close enough to be detectable. That doesn’t allow much lead time between discovery and flyby. They also may approach Earth from the direction of the sun and be lost in the glare of daytime. Only when an asteroid appears at night are astronomers able to find, photograph and determine an orbit. At that point, only days or hours may remain before the rock buzzes the planet.

This diagram shows an edge-on view of our solar system. The dots represent the NEAs and PHAs that scientists think are likely to exist based on the survey. Positions of a simulated population of PHAs are shown in bright orange, and the simulated NEAs are blue. Earth's orbit is green. Notice how the PHAs tend to be more closely aligned with the plane of Earth's orbit, or less tilted above and below the plane, than the NEAs. Credit: NASA/JPL-Caltech

The results of a new study based on data gathered by NASA’s Wide-field Infrared Survey Explorer (WISE) have led to a better assessment of potentially hazardous asteroids (PHAs). These are the ones measuring 330 feet across or larger that pass within 5 million miles of Earth and have the potential to cause significant destruction in the event of a collision.

Asteroids are warmed by the sun and radiate heat. WISE studied the sky in the light of infrared or heat waves and was able to see both light and dark asteroids (ones that might be missed by regular telescopes), resulting in a more representative look at the entire population.  Based on studies of 107 PHAs with WISE, astronomers estimate there are roughly 4,700 PHAs, plus or minus 1,500, with diameters larger than 330 feet. To date, an estimated 20 to 30 percent of these objects have been found. Obviously, many remain to be discovered and orbits determined. Considering that we’ve only recently begun faint asteroid surveys with large telescopes, we’ve come a long way.

This diagram shows the difference between the orbits of typical NEAs and PHAs. PHAs orbit closer to Earth and in nearly the same plane as our planet, making them potentially hazardous. The asteroid orbits are simulations of what a typical object's path around the sun might look like. Credit: NASA/JPL-Caltech

“The new analysis also suggests that about twice as many PHAs as previously thought are likely to reside in “lower-inclination” orbits, which are more aligned with the plane of Earth’s orbit. These lower-inclination objects appear to be somewhat brighter and smaller than the other near-Earth asteroids that spend more time far away from Earth,” according to the study.

Because of their similar size and brightness, it’s suggested that a collision between two asteroids with low-inclination orbits in the main asteroid belt liberated fragments that drifted into Earth’s vicinity to become PHAs.

The diagrams, which are simulations based on real data, look very crowded. That’s only because they squeeze an enormous volume of space into a box six inches wide. It’s important to keep in mind there’s a great deal of space between those dots!

Comet Garradd has its last hurrah in the constellation Cancer in the western sky at the end of twilight. For the next week it will be near Iota Cancri, one of the prettiest double stars of spring. Stars show to 8.5 magnitude. Inset photo: Rolando Ligustri. Map created with Chris Marriott's SkyMap

While we’re on the topic of small solar system bodies, Comet Garradd, the comet that’s been visible in small telescopes and binoculars for more than a year, will soon disappear in twilight and fade away as it travels into the deep southern sky. It’s still 9th magnitude and viewable in 4-inch and larger scopes. Larger instruments will show its faint dust tail pointing east. Garradd will slowly trek through the constellation Cancer the Crab through June. Get a last look while you can. It’s still the brightest comet in the sky.

Morning crescent moon anticipates weekend solar eclipse

The sky facing east tomorrow morning about an hour before sunrise. The moon will appear as a beautiful crescent. Created with Stellarium

As the solar eclipse approaches, we watch with anticipation as the moon slims to a thin crescent in the morning sky. Each day it slips a fist eastward toward the sun as if drawn by a tractor beam toward Sunday evening’s eclipse.

Tomorrow the moon will be appear in the rosy glow of dawn in the east below the familiar Great Square of Pegasus, a baseball-diamond shaped constellation prominent during fall evenings.  Watch for it if you’re up with the birds.

The May 5 full moon occurred when the moon was closest to the Earth or perigee; new moon happens 2 weeks later at apogee, when the moon is farthest away. Illustration: Bob King

A reader asked about why the moon is now so far from Earth (at apogee) when we just had a perigee or unusually close full moon.

If you recall that the moon’s orbit is an ellipse with Earth a little off to one side of center, perigee and apogee are directly opposite one another.  Since the moon orbits the planet in about four weeks, when perigee (closest approach) occurs at full moon, it’s a given that apogee will be half an orbit or about two weeks later.

Total solar eclipse August 11, 1999 occurred when the moon was near perigee. Credit: Luc Viatour

Guess what phase the moon’s in two weeks after full? New moon! And it’s only at new moon, when the moon slides between the Earth and the sun, that a solar eclipse is possible. This month’s new moon happens when it’s most distant from Earth. Its smaller apparent diameter can’t fully hide the sun, giving us an annular eclipse.

When a new moon happens around perigee, it’s more than big enough to cover the sun. That’s why the November 13 eclipse over northern Australia will be a total one. New moon occurs just a day before perigee.

Complete viewing guide to Sunday’s annular solar eclipse

The gray band is the annular eclipse visibility zone. Anyone within it will see the moon completely cross over the sun. If you're on the red line, the moon will pass exactly over the center of the sun leaving a symmetrical ring of sunlight. Other locations in North America will see a partial eclipse except the East Coast. Click map for interactive version. Credit: NASA map / overlays: Bob King

It’s almost here. Time to get ready for Sunday’s annular eclipse of the sun, the first one visible from the U.S. since 1994. Anyone living in the approximately 150-mile-wide band from southern Oregon to northern Texas will see the moon’s black disk silhouetted squarely against the sun’s.

Folks like me, who live outside that band, will witness a partial eclipse. For Duluth, Minn., the moon will cover a maximum of 63% of the sun. Chicago gets a bit more – 69% – and Dallas 94%.

Clicking on Duluth, Minn. on the NASA website map reveals eclipse details. A magnitude of .633 means 63.3% or nearly 2/3 of the sun is covered during maximum eclipse. Click map to read weather prospects for cities located along he eclipse center line. Credit: NASA

To find out circumstances of the eclipse for any town in the U.S., Canada and other regions, click on the map at top. It will take you to NASA’s eclipse website, where you can zoom in to find your town. When you click again on the town name, an info box pops up with times and “eclipse magnitude”. This is the amount of sun covered for your A magnitude of 0.59 means 59% of the sun will be blocked by the moon at maximum eclipse. The times shown in the bubble are Universal Time (UT or Greenwich time). For Eastern Daylight subtract 4 hours, Central 5 hours, Mountain 6 and Pacific 7 hours. In the example, the eclipse starts at 00:17 UT May 21. Subtracting 5 hours we get 7:17 CDT May 20.

94% of the sun will be covered by the moon during this Sunday's eclipse. Illustration: Bob King

Annular eclipses happen when the moon passes directly in front of  the sun just as it does during a total solar eclipse – with one difference. Normally the moon is big enough to completely cover the solar disk, but during this eclipse, it happens to be farthest from Earth and hence a bit smaller than usual. Small enough that it leaves an annulus or ring of sunlight remaining at maximum eclipse.

During a total eclipse (left), the moon is close enough to Earth to cover the sun and casts a shadow called the umbra on Earth. An annular eclipse happens when the moon is farther from Earth than normal. The antumbra defines the path of annularity.

Since some portion of the sun remains visible during the entire eclipse, it’s important to use a safe solar filter to protect your eyes if you plan on watching the event. You can find out where to purchase a filter in this recent blog I wrote on the topic.

I’ve seen two annular eclipses in my time and enjoyed them both immensely. Sure, it’s not the same as a total, where you can stare at the sun directly and watch pink flames lick its circumference beneath a quivering corona. But make no mistake, there’s still plenty to see and enjoy during this eclipse.

Here’s what to watch for with naked eye, binoculars and small telescopes. Again, I can’t emphasize enough how important it is to do your looking through a safe solar filter:

* Daylight perception – When about 75% or more of the sun is covered, you’ll notice a change in the quality of daylight. The sky will be darker and a steelier shade of blue than before the eclipse.

* Weird shadows – Again, in places where about 3/4 of the sun will be covered, the quality of your shadow will change from soft and fuzzy-edged to sharp as the disk of the sun narrows to a thin arc.

Simulated view of moon's edge approaching a sunspot group. Background image: NASA

* The serrated edge – For those with small telescopes, take a look at the silhouetted edge of the moon against the sun. If you look closely, you’ll notice it’s irregular in places like a serrated knife. Those are the tops of mountains and crater rims seen in profile. While an interesting sight in itself, it gets even better (see farther down).

* Sunspot hide and seek – If the sun has any sunspots – very likely – it’s fun to watch the moon’s edge approach, slice into and then cover the spots. See if you can tell which is darker – the silhouetted moon or the dark sunspot cores called umbrae.

Mountains "biting" into the edge of the sun (lower left) during annularity. Credit: W. Van Kerkhoff

* Sticky mountains – For anyone within the annular zone or very close to it, the mountains along the moon’s edge will appear to “stretch” and briefly “stick” to the inner circumference of the sun, breaking it into short segments.

This wonderful sight happens for several seconds at second and third contacts and is caused by atmospheric effects on the moon’s bumpy profile.

Second contact occurs the moment the entire moon is visible against the sun. Third contact occurs the moment the leading edge of the moon touches the inner edge of the sun as it exits the disk. During a total solar eclipse, the same mountains create the sparking “diamond ring” effect.

The Ring of Fire seen during maximum eclipse. Credit: Sancho_Panza

* Ring of fire effect -For many this will be the climax of the eclipse when observers in the path of annularity will be able to see the moon surrounded by a fiery ring of sunlight for about 4 minutes. Be sure to look take your eye away from the scope for a minute to appreciate the sight with the (filtered) naked eye. It’s eery to see nothing but a ring up there, almost like you’re living on a planet orbiting a distant sun.

Venus should be easy to see during the eclipse as long as the sky's transparent all along the eclipse path. Albuquerque is shown here. Created with SkyMap

* Planetary bonus – For those in the annular zone or near it, the sky should get dark enough to see Venus high above the moon in the western sky. Those watching from California and especially from Japan and China, where the sun will be much higher, can also look for Jupiter and Mercury below the it.

* Live Webcast – If you’re not able to see the annular eclipse, check out AstronomyLive’s live webcast.

One of the best things about an annular eclipse is seeing how quickly the moon glides from one side of the sun to the other through a telescope. Unless you witness a total eclipse, you’ll probably never feel it move faster. Now let’s just hope it’s clear. Good luck to all of you!

Bye, bye Venus, see you on the other side

A colorful 22-degree halo, the most common variety, rings the sun yesterday afternoon. Like a prism, the ice crystals spread white light out into a rainbow spectrum giving the inner edge a red-orange tint and outer edge a pale blue. Photo: Bob King

A reminder to keep an eye out for halos around the moon and sun. We’re outside more often during the warmer months with more opportunities to notice things in the sky. Yesterday I caught the bottom edge of a colorful solar halo while making that first buzz with the lawnmower through a jungle of dandelions. Halos are created when light is bent or refracted by billions of microscopic, pencil-shaped ice crystals in cirrostratus clouds. Most have a radius of 22 degrees, making them 44 degrees or “four fists” in diameter. If you see thin, wispy clouds that stretch like a veil across the sky, halos may be in the offing.

Bye, bye Venus! Watch as Venus departs the evening sky in the next two weeks. These maps show the view facing northwest about 45 minutes after sunset. Created with Stellarium

Being outside in warmer weather also makes it easy to follow Venus’ quickening exit from the evening sky. Remember when it set at midnight? No more. 45 minutes after sunset tonight, the shining planet will be only 15 degrees high (a fist and a half held at arm’s length) in the northwest. A week from now that shrinks to 10 degrees and by late May, it’ll be lost in twilight’s glow.

Venus is a thin crescent through binoculars and small telescopes.

Venus is rapidly closing in on Earth, growing larger all the time. You should now be able to see the planet as a tiny crescent moon in 10 power binoculars. Make sure to focus sharply and observe in early twilight, when the planet’s glare is reduced. Venus undergoes phases just like the moon.

When it’s on the opposite side of the sun from Earth, it looks “full”, but as the planet catches up with ours, Venus’ phase shrinks to half and finally a crescent before gliding between the Earth and sun.  If you observe Venus regularly through the end of the month, you’ll see the crescent enlarge and grow thinner as the distance between the two planets shrinks.

Venus as a "reverse" crescent on June 15

After crossing the solar disk on June 5 during a rare transit, Venus will swing west of the sun and pop out days later in the morning sky at dawn. It will still be a crescent, but because it will then be on the other side of the sun as seen from Earth, the “left” or side of the planet will be illuminated as a thin crescent. The flip-flopping crescents are fun to see in binoculars and telescope; there’s no better demonstration of how Venus keeps on truckin’ along its orbit. As for the June 5 transit, I’ll have more on how to view it soon. It will be the last time in our lives we’ll be able to see one.

As Venus orbits, its changing angle with Earth and sun lets us see it in different phases like the moon. In the evening sky, the planet is to the left or east of the sun; when visible at dawn, it's to the right or west of the sun. Illustration: Bob King.

A journey from Cassiopeia to the Southern Cross

The W of Cassiopeia the Queen is due north and low in the sky at mid-northern latitudes in May. Created with Stellarium

Walking with my older daughter the other night, we noticed how low Cassiopeia had dropped in the  northern sky. It’s also back to looking like a “W”  instead of a zigzag. The familiar constellation reaches its nadir or lowest point above the northern horizon around 11 p.m. in mid-May. For most sky watchers that means it’s lost in the trees or hidden by buildings.

Cassiopeia’s height also depends on one’s latitude. From Duluth, Minn. the W never sets, but from Phoenix, Arizona it nearly scrapes the horizon. Travel further south to Miami and you won’t see it at all on May and June evenings.

The North Star is as high above the horizon as your latitude. In Duluth, that’s 47 degrees or more than halfway between the horizon and the overhead point or zenith.  Since Cassiopeia is only 30 degrees from the pole star, it cycles around it as the Earth rotates and misses the horizon by 17 degrees, ie. never sets. Constellations that never set are called circumpolar. In addition to Cassiopeia, the Big Dipper, Little Dipper, Cepheus, Draco and parts of others are all circumpolar from where I call home.

Cassiopeia is below the horizon in May and June for Florida skywatchers. This map shows the view looking north from Miami around 11 o'clock. Credit: Chris Marriott's SkyMap software

Now let’s pretend we’re in Miami. Its latitude is 26 degrees (21 degrees south of Duluth, Minn.). That means the North Star is just 26 degrees above the horizon in the northern sky. Since the W is 30 degrees from the pole star, it’s below the northern horizon this time of year.

Before we pity the poor Miamians, let’s expand our view. While the northern sky is cut short by their southerly latitude, they’re well compensated by a deeper look into the southern sky.

In Duluth, our southern horizon cuts off constellations not far below the trapezoid-shaped Corvus the Crow. Floridians get to see another 20-plus degrees of sky beyond that.

From southern Florida and points south, the Southern Cross (Crux) and the brightest stars of Centaurus the Centaur are visible. Sky shown around 11 p.m. local time.

And guess what’s there? Only one of the starriest lots of real estate in the sky. From a boat on the Gulf, you’d be able to look due south and spy the Southern Cross just cresting above the horizon with bright Alpha and Beta Centauri in tow on May nights. You’ll recall that  the triple star Alpha is the closest star to Earth after the sun with a distance of 4.3 light years or 26 trillion miles.

In my opinion that more than makes up for the loss of the W. Besides, all Miamians need do to see Cassiopeia is go out at dawn, when Earth’s rotation brings the constellation back up in the northeastern sky.

The Southern Cross (center) and Alpha and Beta Centauri (left) are embedded in a rich section of the southern Milky Way. The dark patch to the left of the Cross is dark nebula called the Coalsack, composed of interstellar dust. Credit: Mike Salway

While clearly unfair to northerners, the Southern Cross and its cohorts are motivation for the astronomically-inclined to make a trip to the far south. After living most of one’s life where the North Star is always forever in one place in the sky, you’ll feel like a newborn babe under the southern stars.

Chance to own a piece of Sutter’s Mill meteorite

This Sutter's Mill meteorite struck Suzi Matin's garage and broke into two fragments weighing 10.3 grams and 1.4 grams. The 10.3 gram has been broken into fragments for sale. Credit: Greg Hupe

Two of the meteorite hunting community’s most respected hunters, Greg Hupe and Mike Farmer, are selling small fragments from the 10.3 gram Sutter’s Mill meteorite (provisional name) that hit Suzie Matin’s garage. The price isn’t cheap – $2000 per gram – but they’ve divided the stone into very small pieces, so that a fraction of a gram becomes more affordable.

I found out about the offer tonight and wanted to pass it along. I wouldn’t normally promote a particular sale, but this meteorite has been the focus of extraordinary public and scientific interest due to its spectacular fall and rare nature. Sutter’s Mill appears now to be something other than the “usual” carbonaceous chondrite, though a complete analysis is still underway.

To date, the total weight of Sutter’s Mill meteorites comes to about 421 grams. The largest stone, a 44 gram individual, was found Thursday by Robert Ward, who also holds the distinction of finding one of the smallest pieces — 0.1 gram.

If you’re interested or would like more information, e-mail Greg Hupe at

Video of NASA’s hunt for Sutter’s Mill meteorites using a zeppelin. One caveat: the video seems to imply they found a specimen from the air, but the one shown was found instead by a ground search.

For the record, no one asked me to advertise this sale and I will not benefit from it in any way. There have been and will be other sales of Sutter’s Mill fragments in the future. If the number of pieces is large enough to “go around” like this one, I will post them here.

Here is the list of fragments available as of 10 p.m. CDT. All weights in grams:

0.0046 no crust $20.00
0.0062 no crust $20.00
0.0062 no crust $20.00
0.0162 25% crust $33.00
0.0240 30% crust $48.00 (on hold)
0.0278 15% crust $56.00 (on hold)
0.0302 no crust $61.00
0.0558 no crust $112.00
0.0670 no crust $134.00
0.0672 no crust $135.00
0.0710 no crust $142.00
0.0888 no crust $178.00
0.0898 no crust $180.00
0.0942 no crust $189.00
0.0988 no crust $198.00
0.1000 no crust $200.00
0.1292 no crust $259.00
0.2004 30% crust $400.00
0.0882 fragments & dust $200.00
0.1924 fragments & dust $436.00

Jupiter’s disappearing act plus exciting news from Vesta

Jupiter approaches conjunction with the sun in this photo taken by the SOHO's C2 coronagraph this morning. A coronagraph uses a disk to block direct sunlight. Credit: NASA/ESA

Back in the day before orbiting telescopes and 24/7 sky surveillance, when a planet got too near the sun, it was invisible in the solar glare. Not anymore. Thanks to the two coronagraphs aboard the Solar and Heliospheric Observatory (SOHO), we can follow planets right through conjunction with the sun.

SOHO is located at a stable point some 930,000 miles sunward of Earth. With no atmosphere to contend with, SOHO studies the sun from the spotless window of outer space.

Jupiter reaches solar conjunction tomorrow when it will be closest to the sun. You can see from the photo that today it’s already very close – less than one degree away or one “pinkie” finger held at arm’s length against the sky. Notice that Jupiter is a little below or south of the sun. Tomorrow it will be even closer but still travel south and miss the solar disk. Rarely do planets line up exactly with the sun during conjunction. That’s why next month’s transit of Venus is so special.

Keep in mind as you look at the picture that Jupiter lies in the distant background on the opposite side of the sun from Earth. It’s currently 558 million miles away or six times the Earth-sun distance. As you might guess, if Jupiter precisely lined up, it would be hidden behind the sun. As for that big sunspot group, it’s still lively but no X-class flares yet.

Virtual flyover of the asteroid Vesta based on hundreds of actual photographs. Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

After almost a year’s study by the orbiting Dawn space probe, NASA shared new insights about the asteroid Vesta this week. We now know that the 326-mile-diameter orb was on its way to becoming a planet 4.6 billion years ago. It developed an iron core measuring 136 miles across, a dense, rocky mantle and crust made of lava flows that were soon battered by meteorite impacts.

Bright and dark craters on Vesta. Like everything else in the solar system, the asteroid was bombarded heavily by meteorites at the dawn of the solar system. Credit: NASA/JPL-Caltech

Terrestrial planets also possess these three basic layers. With Vesta, the decay of a radioactive form of aluminum around in the early solar system generated the heat that melted the asteroid. As it cooled, heavier elements like iron and nickel sunk to form a core, while lighter elements floated to the top and solidified into the mantle and crust.

The layering, known as differentiation, make Vesta more like a small planet or Earth’s moon than most asteroids. Smaller bodies never had enough radioactive material to melt and layer-cake.

The Rheasilvia Basin dominates Vesta's southern hemisphere. The crater is 90 percent as wide as the entire asteroid. Fragments from the collision have reached Earth over the ages as HED meteorites. Credit: NASA/JPL-Caltech

By counting craters, scientists determined the age of Vesta’s biggest crater, the 314-mile-wide Rheasilvia Basin in the southern hemisphere. The impact, which removed a sizable portion of the asteroid’s southern polar region, happened only about a billion years ago, long after Vesta formed and when most meteorite bombardment had ceased

Scientists were also able to determine what minerals are in Vesta’s crust by examining how they reflect sunlight. Here’s where things really get exciting. They discovered that the meteorites in the HED clan – howardites, eucrites and diogenties – are the same materials seen in Vesta’s crust. We’ve suspected this for years because the two reflect light in almost the same way, but this is the first time we’ve visited a source of meteorites found on Earth.

A slice of Vesta! This eucrite meteorite named NWA 2724 was found in the Sahara Desert . It represents a small cross section of an ancient lava flow on the asteroid. Photo: Bob King

Eucrites are similar to lava flows on Earth; diogenites are coarse-grained crystalline rocks from the mantle and howardites are a mix of the two, created when meteorites bash, mix and cement together fragments of both crust and mantle.

It sends a chill up my spine to touch the meteorite in the photo above and know that it came directly from Vesta, launched by an impact perhaps a billion years ago. Too bad Vesta never grew larger than it is today. You can blame Jupiter. Its dominating gravitational influence stirred up material in the asteroid belt, where Vesta resides, and prevented any large body from forming.

Read more about the new Vesta results HERE.

Purple aurora majesties

The summer Milky Way rises along the eastern horizon last night around 11:30 p.m. The slight green glow at bottom is airglow, caused by air molecules emitting light after being excited to higher energy levels by sunlight during the day. Photo: Bob King

Last night a stranger approached me in the dark. I was out in the country in a pullout along a gravel road just setting up my telescope. You never know what to expect when someone drives up to you and steps out of their car. I make the assumption their motivation is curiosity and not harm. So far, that’s been true.

We approached each other, gave names, shook hands. Both of us relaxed. Over the next half hour Tony and I shared looks at Saturn, Venus, a globular cluster, two galaxies, a meteor and one of the brightest Iridium satellite flares I’ve ever seen in my life.  At magnitude -8 or nearly as bright as a half moon, the flare demonstrated how bright a nearby supernova might look.

Unusual purple auroral rays briefly stripe the northern sky last night about 10:30 p.m. The more common green aurora is below. Photo: Bob King

We asked questions about each others interests and professions and remarked about the lone wolf howling a mile away. Then he decided it was time to go and offered an apology for disturbing me. None was needed. There’s always joy in sharing the sky. By connecting to something larger than ourselves, we find we’re more alike than different.

Later I was happy to see the smouldery glow of aurora beyond the trees to the north. Nothing bright or spectacular, just a few patches and rays. But I soon learned this was no ordinary aurora. Most auroras are pale green to the eye and shine a vivid green in time exposure photos. These rays appeared colorless, but as soon as I pressed the button to check the exposure, my jaw dropped. Purple!

A striking purple ray from last night caused by excited nitrogen molecules high in Earth's atmosphere. Photo: Bob King

Auroral colors are generated when those frisky electrons from the sun follow Earth’s magnetic field lines straight into the polar atmosphere. There they strike the the atoms and molecules of oxygen and nitrogen and pump them up to an excited state.

In the atomic world, excitement means an electron that orbits close to the nucleus of the atom gets bumped up to a higher energy level. These higher energy states don’t last for long. An excited atom typically crashes into neighboring atoms and loses its energy, but in the near vacuum of the upper atmosphere, atoms don’t meet up very often. Instead, the excited electron returns to its “rest” state, releasing a particle of light called a photon in the process. Photons are packets of energy that make up a beam of light.

Oxygen in the lower atmosphere, from about 50 miles to 120 miles high, emits photons of green light when pounded by solar electrons. Since the element is plentiful and our eyes particularly sensitive to green light, the color dominates most auroras. Picture billions of oxygen atoms beaming bits of green light and you’ve got a typical northern lights display.

Oxygen atoms from 100 miles to as high as 375 miles, where the air is even more rarefied, create the less often seen red auroras. Picture energy levels in an atom as floors in a hotel. When hit by a solar particle, an electron in an oxygen atom “takes the elevator” to a higher floor. Green light is emitted when the electron rides the elevator down from the third to second floor; red light when electrons ride from second floor to first (ground level).

Oxygen atoms are primarily responsible for the greens and reds of the aurora; nitrogen gives us red-bottomed arcs and tall purple rays. Credit: WebExhibits

Nitrogen atoms and molecules give off several colors when stimulated by incoming material from the sun, most of which we can’t see with the naked eye. A few nitrogen atoms emit a faint green that gets lost in oxygen’s brighter colors, but in intense auroras, you’ll sometimes see an intense deep red-purple fringe along the bottom of rays and arcs. This captivating color is caused by nitrogen.

Last night’s aurora was even more unusual because it not only came from very high up but also involved sunlight. Purple light is cast off in a two-step process. First, nitrogen molecules got whacked by electrons, rise to an excited state and then dump their light as purple photons. Second, the excited nitrogen absorbes energy from sunlight shining onto the very top of the atmosphere, exciting the molecules to pump out even more purple. All this happens some 600 miles high!

Too bad our eyes aren’t very sensitive to the blue-purple end of the spectrum, otherwise nitrogen-producing auroras would be much more spectacular. As it was, I saw only a faint hint of blue in the brightest ray last night.

Let’s think about the aurora process again. Electrons stream from the sun and their energy of movement (kinetic energy) is transformed into light via the elevator process described earlier. Second, once the nitrogen molecules get into their excited state, sunlight itself was enough to do the job. That boggles the mind. Simple things like atoms and molecules are a type of machine able to transform one form of energy into another.

Speaking of rarefied, the air is nearly a vacuum at the height the aurora takes place with a pressure one-millionth what it is at sea level. Were it not for the fact that we look through hundreds of miles of light-emitted oxygens and nitrogens, these tiny emissions be far too faint to see.

Just in time, the NOAA space weather forecast predicts possible auroral activity over the next three days.

Solar blowout and a wicked star-planet alignment

Sunspot group 1476 "blemishes" the sun this morning as it rose over Lake Superior in Duluth, Minn. Photo: Bob King

It’s always worth getting up to see a sunrise. Sure, you can’t concentrate and your eyes weigh a pound a piece by afternoon, but it’s worth the lift you feel watching a star rise out of a lake. I saw the sun slowly ease out of Lake Superior in Duluth this morning, and for a few minutes it was safe enough to take pictures with a telephoto lens.

I enjoy imperfections. Matter of fact, I’m built on flaws both inherited and accumulated over the years. Once the solar disk freed itself from the horizon, I could see it also had a blemish, a piece of crud that wouldn’t wipe off. A monster sunspot!

That spot group was plainly visible in the camera once the sun was up. An hour later I easily saw it from home with the naked eye from behind a pair of eclipse glasses.

The sun photograhed this morning through a 3-inch refractor with solar filter later this morning. The big group is 1476; smaller 1477 is at bottom. Photo: Bob King

Now spanning more than 12 Earths, the group is magnificent to view in a small telescope. The main spot has a long string of followers and reminds me of mother goose and her goslings.  Exquisitely small black umbral spots contrasted with the pale, encircling penumbra around the main or lead spot in the group. The photo only hints at the beauty and complexity of the group.

Because the sun rotates on its axis about once every four weeks, we can watch the evolution of this group with each passing day.

In active sunspot groups like 1476, new spots form and evolve quickly. Some expand rapidly and last days or weeks. Others appear and disappear in just a day. Day to day changes are obvious through a small telescope and show us just how dynamic a star can be. As always, you’ll need a safe filter to look directly at the sun. Here’s a link to a recent blog listing good sources.

Must-see video of last night’s M5.7 flare from Region 1476. The best part is the audio. Crank it up!

At 11:18 p.m. Central time last night, sunspot region 1476 blasted off a significant M5-class flare. Though large, it’s not directed toward Earth. For the moment, none of the more powerful X-class flares have made an appearance.

All the activity with more to come is because 1476 is a delta group, where positive and negative magnetic fields (north and south poles) are packed so close together, there’s great potential for instability and the release of energy in the form of solar flares. While there’s only a small chance of auroras for the far north this evening from effects not related to these spots, let’s cross our fingers for possible weekend auroras related to the big group.

From top to bottom: Arcturus, Saturn and Spica form a straight line in the sky last night. Photo: Bob King

Last night when members of our local astronomy club departed the planetarium after the monthly meeting, we instinctively all looked up. Aha! The sky was clear. High up in the southeast was a most striking arrangement: Arcturus, Saturn and Spica all lay in a straight line.

Being humans, we can’t help but be drawn to patterns, and this one you couldn’t miss. Try spying it yourself the next clear night. Go out from 9:30 p.m. on and look well up in the southeastern sky. Arcturus is the bright, orange-red star; below it you’ll find the duo of Saturn and Spica. It’s just cool.

The line will remain straight for about the next several nights. After that, Saturn’s motion to the right (west) will break the pattern. When will you first notice this?