A solar flare observed in Dec. 2006 by NOAA’s GOES-13 satellite. Credit: NASA

The sun is at the bottom of the roller coaster with nowhere to go but up. NASA released a revised forecast this week on when the sun is expected to bounce back from its quiet spell. Solar activity like flares and sunspots wax and wane in an 11-year cycle. Among the more visible effects of high activity are increased sightings of the aurora borealis. We were supposed to bottom out on the cycle’s low end in March of 2008 with a new maximum in 2011 or 2012. The reality is we’re in the deepest valley of solar quietude in a century. Sunspot counts are extremely low and there’ve been no significant flares for more than two years.

Science is all about revision and modification based upon new information from the biggest source of all — Mother Nature. According to the latest solar forecast, the sun should remain generally calm over the next year and then start to rumble to life again. The new maximum of Solar Cycle 24 is predicted for May 2013 but with the fewest number of sunspots visible per day since 1928. Already there have been some uptick in activity with the appearance of a trickle of new spots and an increase the amount of energy the sun gives off in the radio end of the spectrum.

Yearly-averaged sunspot numbers from 1610 to 2008. Researchers believe upcoming Solar Cycle 24 will be similar to the cycle that peaked in 1928, marked by a red arrow. Credit: NASA/MSFC

Scientists make predictions based on current trends but don’t know for certain what route the sun might take. Will we experience a new Maunder Minimum – a 70-year-long period in the 17th century when the sun was spotless? Dean Pesnell of the Goddard Space Flight Center put it best: "Go ahead and mark your calendar for May 2013," says Pesnell. "But use a pencil."

This past week saw the 90th anniversary of the first empirical test of Einstein’s Theory of Relativity. That’s a fancy way of saying that scientists found proof in the real world of Einstein’s prediction that gravity bends light. According to the theory, objects like the sun are massive enough to literally curve local space and time – spacetime for short – around themselves, creating a kind of pocket or dimple in its fabric.

To help you visualize curved spacetime, imagine a child standing on a trampoline. The child’s weight changes the depth and curve of the dimple beneath their feet. A heavier child makes a deeper dimple. Substitute the sun for the child, and space for the trampoline surface and you begin to get the idea of how gravity affects space.

For an excellent, graphical illustration of spacetime, be sure to check out this short video:

Einstein predicted that light from a background star just touching the edge of the sun would be deflected upward and away from the edge by the sun’s enormous gravity. Credit: Jose Wudka

So how you prove the sun really warps space? Let’s say we look at a star in the same direction as the sun. Since the sun is too brilliant to see any stars near it, we’d have to wait for a total solar eclipse to do this. With the sun’s light blacked out by the moon during totality, we might get lucky enough to see a star close to the sun’s edge. Einstein said that the warping of space near the massive sun would cause the beam of starlight to appear to come from a slightly different direction compared to its real position in the sky.

Isaac Newton’s original Theory of Gravity predicted massive objects with lots of gravity would bend light too, but his prediction of how much was only half of Einstein’s. Relativity Theory predicted that a beam of starlight grazing the sun’s edge would be deflected by the incredibly tiny but measurable amount of 1.75 arc seconds. That’s the size of a dime seen from a distance of 1.3 miles. For comparison, the full moon is 1800 arc seconds across.

As soon as World War I ended, English astronomer Frank Dyson recruited Arthur Eddington, professor of astronomy at Cambridge, to sail to the island of Principe, off the coast of West Africa for the best view of the May 29, 1919 total solar eclipse. Eddington was charged to test Einstein’s theory by photographing stars near the sun to see if they were deflected by the amount predicted. Luckily, the eclipse happened against the background of a rich and bright star cluster, the Hyades in Taurus. Chances were excellent at least of few of them would be close enough to the sun’s edge to show a measurable deflection. (Einstein in 1921, left, and Arthur Eddington)

One of Eddington’s photos of the totally-eclipsed sun taken on May 29, 1919. Star used to prove Einstein’s prediction are shown between pairs of tick marks. Credit: Philosophical Transactions of the Royal Society of London

The total part of the eclipse lasted 400 seconds but only in the last 10 seconds did the sky clear. Eddington got an image and compared it to one taken of the same stars when the sun was not present. The result was a 1.61 arc second shift, in very close agreement with the prediction.

Media attention propelled Einstein to overnight celebrity. Since then, the Theory of Relativity has passed every test scientists have thrown at it. Despite its weird, counterintuitive predictions of warped space and time, Einstein’s brainchild accurately describes many aspects of the natural world.

(Credit on Einstein portrait: Oren Jack Turner; Eddington portrait: American Institute of Physics Niels Bohr Library)

A starry sky with a bright moon? Snowstorm in spring? No, just millions of poplar seeds flying by in the wind yesterday afternoon. Photo: Bob King

If you’ve ever wanted to accuse me of writing fluff, today would be the day. In northern Minnesota, we’re at the peak of pollen season. Pollen reveals itself by small colorful halos around the moon or yellow dust on the hood of your car or on the surface of ponds. Some of us don’t have to see it to know it’s there — our itchy eyes and constant sneezing are evidence enough. But there’s more than pollen flying around these sunny days. Born by the wind, the air is filled with small bits of fluff blowing by.

Yesterday you couldn’t miss them, and if you looked in the direction of the sun, taking care to shield your eyes from direct sunlight, they powdered the blue sky like stars. Hundreds of thousands, no, millions of them passed overhead. Take a look today and allow you eyes to focus into the deep distance. You’ll see what I mean.

From past experience, I knew these fluffies were seeds, many if not most from the poplar trees that are common to our region. The seeds are attached to silky hairs that allow efficient dispseral by the wind.

A close up of one tufted seed. Light reflecting off and around the delicate hairs that keep the seed aloft diffracted light into iridescent colors. Photo: Bob King

After seeing about 8 million of them from afar, I wanted to track one down and see what it looked like up close. This was harder than I imagined. The silky balls were so tiny and delicate, my fingers were much too blunt an instrument to hold them individually. I finally had to gather up a small pile that had accumulated in the garage. Through the closeup lens, the tiny hairs, much thinner than thread, sparkled with vivid colors in sunlight. Evidently, the hairs are so narrow that they diffract light, causing a display of colors similar to light passing through a spider web or water droplets in clouds. Nature always proves that the closer you look, the more surprises you’ll find.

I always look forward to the 5-day-old moon because of three magnificent craters that vividly illustrate layers of time in the moon’s history. Last night’s moon showed them splendidly. Theophilus, Cyrillus and Catharina are all about 60 miles in diameter but each has a different age that you can tell just by looking.

The trio of featured craters along the moon’s terminator last night. Theophilus is 14,000 feet deep and its rim rises 3 1/2 miles above the surrounding terrain. Details: 1400mm focal length at f/14, 1/15 second exposure at ISO 100. Higher res photo. Photo: Bob King 

Theophilus has a crisp, sharp outline and distinct central mountain peak, all indications of its youth. Youth is relative on the moon — we’re talking 1-3 billion years old. Notice that Theophilus overlaps Cyrillus, indicating that the asteroid that created Theophilus, struck after Cyrillus formed. Another indicator of Cyrillus’ greater age is the broken, worn-down appearance of its rim and a less distinct central peak. Being older, Cyrillus was subjected to millions more years of meteorite and asteroid bombardment than its neighbor.

Catharina is older yet. Its central peak was probably buried under lava that welled up from cracks in the crater’s floor and part of its rim has been obliterated by impacts, all signs of age. Small telescope users can see the trio with their own eyes tonight. Look west of the moon’s terminator, the line separating day and night.

The moon will hang between the planet Saturn and the star Regulus in Leo tonight (May 30). This map shows the sky around 10 o’clock. More advanced observers can watch for the shadow of Saturn’s moon Titan to cross the planet’s northern hemisphere starting at 11:34 p.m. Central time. Created with Stellarium.

I’ve been bitten by the Scorpion again. ‘Round about midnight last night I got up for a walk after falling asleep on the couch in front of too much late-night comedy. All the fully leafed-out trees gave the wind a full-throated, strong voice. This is such a satisfying sound especially when you recall the thin hissing of the winter wind through bare branches.

The W of Cassiopeia is easy to see low in the northern sky during late May and early June. For much of the U.S., the constellation is circumpolar, meaning that it never sets as it circles the North Star. Details: 35mm lens at f/2.8 with diffusion filter. 25 second time exposure at ISO 1600. Photo: Bob King

To the north below the North Star was Cassiopeia the Queen, looking more like a W than at any other season. Except for southern Florida, Cassiopeia never sets for virtually all of the U.S. But the further north you live, the higher up in the sky and easier it is to see. Here in Duluth, where the North Pole is always in sight, Cassiopeia is not hard to find.

Scorpius, harbinger of summer, becomes visible again in the southeast around the midnight hour in late May. The stinger is the pair of stars at far left. Beta Scorpii is a fine double star for small telescopes. Created with Stellarium.

But it was Scorpius the Scorpion that really caught my eye. I turned the corner and found it rearing up in the southeastern sky to the left of our good friend Libra the Scales. Like Orion, Scorpius has three stars in a row but lined up vertically rather than horizontally like Orion’s Belt. A few "fingers" to the left of the three is the pinkish twinkler Antares, Scorpius’ brightest star. Antares is a red supergiant star with a diameter about 700 times that of the sun. Put in the sun’s place, Antares would extend beyond the orbit of Mars. Goodbye inner planets! At its current distance of 600 light years, we’re still safe.

Late May through June is the best time to view Antares because it rises around sunset and stays up all night. The sun is near Antares every year in late November, a time when days are short and the sun rides low in the sky . You know winter’s long past when Antares leaves the sun’s glare and joins the evening stars. Next week, the gibbous moon will occult or pass in front of the star during its monthly swing through the constellation. You can check here next Wednesday for details.

The Head of Scorpius, with orange-colored Antares, pokes out between the trees last night. Details: same as above. Photo: Bob King

Every scorpion has a stinger. If you look at the map, you’ll see a pair of stars off to the left sitting right on the horizon — that’s Scorpius’ business end. It’s only half a fist high at best from Duluth and takes some effort to see. Down in Florida, the star is nearly three fists high! You get some, you lose some. We get a queen and Miamians get a stinger.

Telescope users will have fun looking at one of the prettiest double stars in the sky in Scorpius. Check out Beta, the topmost of the three stars that form the scorpion’s head. There are also some marvelous globular clusters near Antares which we’ll also explore as the constellation becomes better placed for viewing in June.

(Credit: Scorpion image by Tomas Castelazo)

The thick crescent moon photographed through a small telescope last night around 10 o’clock. The shapely, dark oval patch at the 4 o’clock position is Mare Crisium or the Sea of Crisis. Details: 1300mm focal length at f/14, 1/15" at ISO 100. All photos: Bob King

The clouds took their time wafting away last night. First to escape their cover was the 4-day-old crescent moon, then Castor and Pollux, followed by Leo the Lion and all the rest. I had some fun taking pictures of the moon through a small 4-inch refracting telescope. The mount I use is equipped with a clock drive, a device that turns the telescope to track the stars. Once you find your target, you tighten a couple knobs on the mount and just sit back and enjoy. The clock drive locks on and prevents what you’re looking at from drifting away.

We all know that the Earth rotates, and if you’ve been studying the sky for any length of time, you’re probably aware that Earth’s rotation makes the stars all move slowly westward during the night. When you look at something through a telescope at 200x, you’re also magnifying the rotation rate 200 times. Believe me, after seeing Saturn sprint across the field of view without the help of a clock drive, you have a whole new appreciation for Earth’s rotation.

The sunlit crescent is overexposed in this photo in order to capture the fainter portion lit by Earthlight. Details: same setup as above but with a 15-second time exposure.

In the photos, you see both the sunlit crescent and the larger, dimly lit remainder, illuminated by light reflected off the Earth. Does the Earthlit moon have a slight bluish tint? It does to my eye. Perhaps it’s because our planet has far more ocean than land, giving the reflected more light a more bluish cast that overwhelms the browns, greens and white of land and clouds. If you’ve ever walked under a bright red tree on a sunny fall day, you may have noticed how the leaves color the light around you. The same principle might be at work with Earthshine.

In this version, I’ve added the names of a few craters you can see in binoculars or a small telescope. The terminator is the boundary line between lunar day and night. It looks so bumpy because the sun is just rising along that arc, highlighting crater rims and mountains against deep shadow.
 

In my 10×50 binoculars I could easily make out a few of the lunar seas, those large dark areas that form the face of the "man in the moon". Craters were more difficult but I did see Tycho. Through a small telescope you can see all the features I’ve labeled and many more. If the sky is clear tonight, try it yourself and see what you can find. Detail in the dark portion is easier to see if you place the bright crescent out of your field of view.

Whenever I study the Earthlit portion of the moon, I feel like some kind of nocturnal animal pawing around in the darkness looking for tasty morsels. I’ll be there prowling again tonight.

Just look at those tiny gems sparkling along the moon’s edge. Each is either a mountain peak or the top of a crater catching the first rays of the rising sun. The dark portion of the moon is bathed in Earthlight, which is bright enough to reveal craters like Tycho. At left, the brilliant crescent is illuminated by the sun.

My favorite sights last night were the three mountain peaks — or more likely, crater walls — that caught the low, glancing rays of sunlight so only their very tops were shining. They were simply beautiful and conveyed the ruggedness of the lunar landscape in a most picturesque way. By tonight, those tiny, star-like peaks will have filled out into crater rims, and if we’re lucky, another one or two or three new ones will take their place further along the moon’s circumference.

On May 22nd, Dutch amateur astronomer Quintus Oostendorp recorded a space station flare through his backyard telescope. Here’s the movie he made using his Canon 1000D. The bright flash you’ll see is sunlight reflecting off one of the station’s solar panels.

OK, yesterday I said there was just one good pass of the space station for our region, but after seeing this video, I was inspired to let you know of one last, not-so-great-but-still-visible pass tonight (May 27). Beginning at 9:54 p.m., watch for the station to appear in the west and make a very low pass from southwest to southeast over the next few minutes. It’ll only be about one outstretched fist above the horizon at best. I hope you’ll catch a flare like the one Oostendorp spotted. Pretty amazing, isn’t it?

The moon walks with the twins Pollux and Castor in Gemini during twilight this evening (Weds. May 27). All maps created with Stellarium.

At the very same time you’re out satellite seeking, look west to the crescent moon, which will be parked near the stars Pollux (PAHL-lucks) and Castor, the two Gemini twins. The spooky, dark portion of the moon, caused by sunlight reflecting from Earth to moon and back again, will be very obvious. It’s called Earthshine but also goes by the more poetic "the old moon in the new moon’s arms".

As night finally takes hold around 10:30 p.m., face due south to spot the bright star Spica in Virgo, about four fists above the horizon. Spica can help you navigate to a small, dim constellation of the zodiac called Libra the Scales. Libra is the warm-up band for the big acts of Scorpius, Sagittarius and the Milky Way that follow.

The sky as you look toward the southeast around 10:30 -11 p.m. this week. Libra is a faint group about two fists above the horizon and two fists to the left (east) of Spica in Virgo.

The four stars represent both a real, physical balance and the concept of balance. Alpha and Beta Librae, which go by the delightful Arabic names of Zubenelgenubi (ZU-ben-el-je-NEW-bee – Alpha) and Zubeneschamali (ZU-ben-es-scha-Molly — Beta) outline the balance beam. Two fainter stars below are the pans used for weighing. Remember the wobble of the Earth’s axis called precession from the other day? Not only does that wobble cause our polestar to shift, but over the centures, it also shifts the sun’s position along the ecliptic, that imaginary path taken by all the planets, moon and sun in their wanderings across the zodiac.

Libra represents a balance in more ways than one.

Back in Rome’s heyday, Libra was part of Scorpius. The two "Zubens" are Arabic for the Scorpion’s southern and northern claws, referring to the pincers of the scorpion. Approximately 2000 years ago, when Caesar was king, the sun was in Libra during the fall equinox. You’ll recall that the equinox is a sort of balance point in the seasons when day and night are briefly of equal length. The Romans re-assigned the stars that were once in Scorpius to the constellation of balance, Libra the Scales.

Alpha Librae, also known as Zubenelgenubi, is a double star that you can easily see in any pair of binoculars. Credit: AAO/STScI/WikiSky

Libra has a treat in store for binoculars users … and perhaps for the eagle-eyed as well. Alpha is a double star 77 light years from Earth and one level fainter than the Big Dipper stars. With binoculars you’ll have no problem seeing the companion sitting right above it. The two take more than 200,000 years to orbit about the other. Those with acute vision will likely be able to split them with eyes alone. It’s tight though! Let us know how you fair the next clear night.

One final thought. Notice how close Alpha is to the ecliptic. That means it stands a better chance than most stars of being covered by the moon, sun and planets as they travel along the ecliptic path. Astronomers call those events occultations. The next occultation of Alpha by a planet will occur on November 10, 2052 when Mercury will pass directly in front of the star. Perhaps we should call the event a planetary pinching??

Evening visibility of the International Space Station is about to wrap up for May with just one good pass left. Watch tonight (May 26) in twilight for the ISS to rise in the northwest at 9:28 p.m., cross the southern sky and then enter Earth’s shadow in the southeast at 9:33. After a short spell of invisibility, the station will resume morning passes over the U.S. in June.

The galaxy M87 is located in the "Y" of Virgo not far from the planet Saturn. This map shows the sky around 10:30 p.m. looking southwest. Created with Stellarium.

Several days ago (‘May night masterpiece’ blog) we visited one of the sky’s brightest globular clusters, M13 in the constellation Hercules. Only about 150 of these big chandeliers of stars reside in the Milky Way galaxy. The situation is far different in a galaxy called M87, the 87th entry in a catalog of deep sky objects compiled by French astronomer Charles Messier. This enormous galaxy, nearly five times the size of our own, is about 50 million light years away and located at the center of a cluster of 2000 galaxies called the Virgo Cluster.

M87 is the large galaxy in the center of this photograph. Most of the little fuzzy dots surrounding it are some of its stash of 12,000 globular star clusters. Two smaller galaxies are seen below right. Credit: Anglo-Australian Observatory/David Malin images

According to 2006 data, this monster has upwards of 12,000 globulars, more than any other galaxy known. Just look at that photo. All those fuzzy spots centered on M87 are globular star clusters. Since many globulars contain 100,000 stars or more, that comes to over a trillion stars between them. For comparison, our entire galaxy contains only about 400 billion stars. How did M87 get such a huge share of clusters?

The galaxy M87 is at the center of the Virgo Cluster, an assembly of 2000 galaxies moving through space together. The cluster is found within and just above the "Y" outline of Virgo. Credit: Digital Sky Survey 2/Mt.Palomar

As you’ve gathered by now, M87 is huge, and that means it has a lot of gravitational pull in the neighborhood. Like some titanic bully, M87 has likely used its gravity to steal globular clusters from other nearby galaxies as they swarmed about the cluster’s center. The more it grabbed, the bigger it got and the better able it was to snatch more. M87 just can’t help itself.

I couldn’t resist sharing this photo of the globular cluster Omega Centauri, the brightest one visible from Earth and the largest in our galaxy. About 10 million stars orbit the center of the cluster. It’s easily visible with the naked eye but only from the southern U.S. and points south. Credit: NASA/ESA/Hubble Heritage Team

Our own Milky Way even has a connection to this globular snatcher. The Virgo Cluster has enough mass to wield its gravitational influence even out here in the hinterlands. The group of galaxies we cluster with, called the Local Group, is tugged toward Virgo, in part by the ravenous maw of M87.

One of a skywatcher’s secret joys is a clear sky when the weather forecast calls for certain clouds. This happened last night. Up until 11, the stars shone placidly over the neighborhood. Not long after, all the meteorologists smiled again as their prediction ultimately came true.

Take a look low in the northwestern sky during twilight tonight (Mon. May 25) to find the crescent moon. You can use the bright stars Procyon and Capella to help point you there. All maps reated with Stellarium.

The crescent moon returns tonight, appearing as a wire-thin arc low in the northwestern sky. You’ll need an open horizon to the northwest to see it. Start looking about 40 minutes after sunset or around 9:30-45 p.m. for the northern states. It’s fun and instructive to imagine how the sky might look from the moon or another planet in the solar system. One thing wouldn’t change — the constellations. The stars are simply too far away to show any noticeable shift in the sky no matter what planet you’re on. Even from icy Neptune you’d still see Orion’s Belt and be able to use the Big Dipper to find the North Star.

Ah, to be an astronaut on the moon tonight! You’d see the nearly full Earth rising not far from bright Antares (red star) in the constellation Scorpius.

Other things change radically. We’ll see the moon is in the constellation Taurus the Bull tonight, but put yourself on the moon and look back at Earth and you’ll find our planet in Scorpius. Likewise with Mars. We see the dusty planet in morning twilight in Pisces the Fish, while the Martians would have a tough time finding Earth just now. From their perspective, we’re in Virgo but too close to the sun to see in a dark sky. Check out the other gems in the neighborhood. As you can see from the map, Venus and Mercury are just a stone’s throw away.

From Mars, Earth joins the company of Venus and Mercury near the star Spica in Virgo. The sky is black because I "removed" the Martian atmosphere so we could see the planets, which are all so close to the sun in Mars’ sky they’re lost in the glare of daylight.

I could go on but you get the idea. It’s all about location, location, location.

There was a whole going on near the Big Dipper during twilight last night (May 23). Details: 35mm lens at f/2.8, 1-minute time exposure at ISO 200. Photo: Bob King

Did you happen to see the International Space Station (ISS) pass through the Big Dipper last night? It was around 9:45 p.m. and though the sky was still blue with twilight, you could just make out the familiar form of the Dipper. While photographing the ISS, I didn’t think I’d also record a sky high traffic jam. As the space station was passing out the frame to the right, another satellite briefly flared and left a short trail. At the same time, a flashing airplane crossed the field. All this in the space of just about a minute.

Much later the Milky Way rose up in the eastern sky. Just when I thought I was done for the night, that hazy band tempted me with more clusters and nebulas than I could shake an eyepiece at. The galaxy is the ultimate candy store for any skywatcher. Strewn along its misty arch is just about anything you’d ever want to see with the naked eye, binoculars or telescope.

I’ve marked the location of the Milky Way galaxy’s center in this photo taken last night. Notice the dark splotches among the starry chunks. These are clouds of dust blocking the light of more distant stars. If you could vacuum all the dust out of the galaxy, the Milky Way would be bright enough to cast faint shadows. Details: 16mm lens at f/2.8, 35-second time exposure at ISO 1600. Photo: Bob King

Earth, sun and all the planets huddle together smack dab within the galaxy’s flattened disk. When we look straight out and into the disk, the stars pile up over thousands of light years to form a thick band. Picture yourself standing in a field (the solar neighborhood) at the edge of forest (the greater Milky Way). As you look past the first few nearby trees, the more distant ones fill your field of vision until the impression is one of impenetrable forest. Something similar happens when we look into the Milky Way — the stars pile up over great distances until they form a fog of unresolved light. This is the band of milky light we call the Milky Way. If you look away from the band, your gaze takes you above or below the disk, where there are far fewer stars.

A 360-degree panorama of the Milky Way taken from Texas (for the northern hemisphere half) and Australia (southern half). The blue box shows the section recorded in my photo last night. Credit: Digital Sky LLC

Early in the 20th century, astronomers learned that the galaxy’s center was located in the constellation Sagittarius, better known as the Teapot. While the Milky Way is broad and bright in that direction, we can only see stars about one-fifth of the way to the center because of intervening dust. The dark rift splitting the Milky Way band in two is dust in the galaxy’s plane left by generations of evolving stars. It absorbs the light of distant stars, giving the band a broken, lumpy appearance. Until telescopes were invented that could penetrate the dust and see into the core, no one had a clue what went on there. Thanks to radio and infrared telescopes, we now know that the Milky Way harbors at least one massive black hole at its center.

If you could rocket out of the Milky Way disk and look at it from above, you’d see our galaxy’s bright core and multiple spiral arms. I have to believe some being somewhere must have this incredible perspective in their night sky. Credit: NASA/JPL-CalTech

As spring gives way to summer and Sagittarius becomes better placed for evening viewing, we’ll revisit the Milky Way and its heart of darkness. For now, go to a dark place, stay up late and enjoy the return of the galaxy.

The Great Hercules Cluster is a highlight of the spring sky and one of the brightest globular clusters. It can be found with binoculars and is a spectacular sight in amateur telescopes. See the hi-res image. Credit: Jim Misti

Like great works of art, there are some deep sky objects that skywatchers return to time after time, season after season. On each occasion you marvel at the sheer beauty of the thing or see something there you’ve never noticed before. One of my very favorite masterpieces goes by the humdrum catalog number of M13. It’s a globular star cluster in the constellation of Hercules the Strongman.
 
M13 is also known as the Great Hercules Cluster and easily ranks among the Top Ten favorite sky objects for most northern observers. Your first impression on seeing it in a telescope — and you’ll need a 6-inch or larger scope for a good look — is a glowing ball of tiny, densely-packed stars enveloped by starry whorls and tendrils. On a good night, the view is riveting. Just read Rhino’s report in yesterday’s comments.

Hercules is large and rather faint but the Keystone (circled) isn’t too hard to spot. It’s on a line between the bright stars Arcturus and Vega. Look two outstretched fists to the upper right of Vega or three fists to the lower left of Arcturus to get there. The map is drawn for around 10:30 p.m. looking northeast in a dark sky. Maps created with Stellarium. 

Globular clusters are enormous balls of stars held together by their mutual gravity. In the case of M13, the cluster packs over 100,000 stars into a sphere 150 light years across. The density of stars in its core is 100 times as great as in the sun’s neighborhood, guaranteeing a night sky algow with hundreds of stars as bright as Jupiter and Venus.

In the book of galactic genesis, the first sentence might read like this: "In the beginning, there were the globulars, and they were most awesome." Globulars contain some of the oldest stars in the universe (12.7 billion years old) and probably pre-date the formation of our galaxy’s disk. The Hercules cluster and about 150 other globulars form a grand halo around the center of the Milky Way galaxy in the direction of the constellation Sagittarius. If you want to hunt for these beauties, you typically wait for late spring and summer when Sagittarius enters the evening sky.

If you can find the Keystone, you’re almost there. In this closer view, you can see that M13 is not quite halfway between the two stars on the west (top) side of the Keystone. Look for a little fuzzy ball that’s obviously bigger than the stars around it. 

You don’t have to own a telescope to see M13. I’ve seen it with my naked eye from the country and binoculars will pick it out with ease … if you know where to look. I wish I could say there were bright stars to guide you to the cluster but you’ll need a bit of a roadmap to get there. M13 is along the west (right) side of a four-sided figure called the Keystone of Hercules. Hercules is a large, dim, gangly constellation tucked between Vega and Corona Borealis (Northern Crown).

Using the maps, get there by first finding Arcturus, below the Dipper’s Handle, and then moving to the left or north to the semi-circular Corona Borealis. The Keystone lies midway between Corona Borealis and brilliant Vega in the northeast. Look for dense little fuzzy spot framed by two small stars along the top side of the Keystone. 10x binoculars will help you to distinguish the brighter core from the fainter halo.

One of nature’s greatest works hangs on the wall of spacetime 25,000 light years away. M13 awaits your gaze.

I took this time exposure of the International Space Station (ISS) last night.
Notice that the color and brightness of the trail changes about 2/3 the
way down. The station fades and takes on sunset colors as it approaches and
then disappears into Earth’s shadow. Astronauts  aboard the ISS see a sunset
about once every 90 minutes. You can see the color change yourself with just
a pair of binoculars. Scroll down to yesterday’s blog for times to look this weekend.
Details: 35mm lens at  f/2.8, 25-second exposure at ISO 800. Photo: Bob King

Last night was calm and clear. I spent my time looking for galaxy pairs while listening to trilling toads shift back and forth between major and minor keys. I love the subtle pitch changes of their amorous song. Their music creates a sonic underpinning that keeps the night flowing along.

The Earth’s wobbling axis describes a circle in the northern sky. The numbers with a minus sign are B.C., those with a plus are A.D. Thuban in Draco was the polestar around 3000 B.C. while Vega will be in 14,000 A.D. We live in the "Polaris era". Credit: Tao’lunga

Last March in this blog we talked about precession, the slight wobble of our planet’s axis that causes the pole star to shift over time. One complete wobble takes 25,800 years. During that time our axis traces out an imaginary circle in the sky. Whatever star lies on that circle will perform "pole star duty" sometime during that long span of time. Polaris, also known as the North Star, is the pole’s current resident. It’s fairly bright and easy to find by shooting a line through the two stars at the end of the Bucket of the Big Dipper.

The North Star is the short, bright arc just below the center of the "whirlpool". The Earth’s north polar axis points at the very center of the whirlpool, a spot called the north celestial pole. As our planet spins on its axis, the stars appear to describe trails around this point, creating a tunnel effect. Photo: Bob King

Polaris is very near but not exactly at the spot of sky our north polar axis points. Close inspection reveals that the North Star is some 1.5 full moon diameters away from exact center. That’s close enough to appear motionless in the sky to our eyes. Just for fun, I pointed my 200mm telephoto at Polaris and made a 20 minute time exposure. A quick glance at the picture shows that the North Star is slightly offset from true north. If it were possible to continue the exposure for 24 hours, you’d see Polaris describe a small circle about the pole point.

As Earth’s axis continues its cyclic wobble, it will bring Polaris ever closer to the pole point. Closest approach will occur around the year 2100 when it will be just one moon diameter away. By and by, Polaris will be replaced by another polestar. The next obvious one will be the star Gamma in the constellation Cepheus the King around 4000 A.D.

You can find the house-shaped constellation Cepheus (SEE-fee-us) between the W of Cassiopeia and the North Star. The star Gamma will become the new polestar 2000 years from now. The map shows the sky around 10-10:30 p.m. as you look north. Created with Stellarium.

Polaris will return to duty around 28,000 A.D. Think how ancient today will seem to our distant descendants. 28,000 years ago the last of the Neanderthals were still living in what is now southern Spain. Perhaps they knew Polaris too.