Tag Archives: Big Dipper

Big Dipper sure, but have you seen the Great Bear?

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The Great Bear Ursa Major stands high in the northwestern sky at the end of evening twilight this month and into July. The moon is shown for tonight June 16. Created with Stellarium

The Big Dipper is the #1 most familiar star group in the northern hemisphere. Just about everyone has seen it. Orion comes in second and everything else a distant third. As many of you already know, the Dipper is only part of a constellation, what astronomers call an asterism. If you connect the rest of the dots you’ll make a bear up there by the name of Ursa Major. The Great Bear.

June and and the first half of July are good times to take a few minutes at the end of dusk and see if you can go beyond the familiar Dipper outline.

Mythological depiction of Ursa Major on the 19th century Urania’s Mirror atlas.

While none of Ursa Major’s additional stars are as bright as the Dipper, they form distinct shapes, especially the long, furry legs and two-toed claws, although in the sky the whole works appears rather bony. The head is triangular and with a little imagination bears some resemblance to a bear’s. What you’ve always pictured as a dipper bowl is repurposed as back and belly, and the handle is an unnaturally long but still very believable tail.

The seven brightest stars of Ursa Major form the familiar Big Dipper. Many civilizations past and present recognized the form and often pictured it as a bear. Each star has its own name, all derived from Arabic.  The star in the bend of the handle is a true double star. Credit: Bob King

I’ve always been impressed with the large size of the Ursa Major constellation. In that regard it’s most like a real bear with a commanding physical presence. Checking a list of constellation size by area, I see that the Great Bear takes 3rd place behind Virgo and Hydra with 1,280 square degrees of heavenly territory. Good thing it isn’t trapped in its cage. Earth’s rotation day and night ensures our ursine friend gets plenty of exercise circling round the polestar Polaris.

Behold the Groth Strip and extend your vision of the universe

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The Extended Groth Strip is the skinny box at upper right off the handle of the Big Dipper. The middle panel shows the full strip, a small portion of which is enlarged at right. Credit: NASA/ESA/ M. Davis

Another snowstorm will soon bear down on my town, the third in two weeks. While blizzards and gales are wonderful phenomena, many of us are ready for sunshine and flowers. A snowstorm of a different sort sends photons of light our way every clear spring night. From high over head in the constellation of the Great Bear 50,000 galaxies hidden in a tiny box of sky tell us about the universe’s pre-teen to early adult years.

The Extended Groth Strip is only about 1 degree long or the wide of two side-by-side full moons yet it contains over 50,000 galaxies. Click to see a full-sized version. Credit: NASA/ESA

Astronomers used the Hubble Space telescope between June 2004 and March 2005 to make over 500 separate exposures during 63 separate pointings of a narrow sliver of sky 1.1 degrees long by 0.15 degrees wide or about the width of the very tip of your little finger held at arm’s length against the sky. They chose the Big Dipper area because there’s little cosmic dust and few intervening Milky Way stars in that region to block the view of deepest space.

The box, called the Extended Groth Strip, after Princeton University physicist Edward Groth, contains far more galaxies than even the famed Hubble Ultra-Deep Field (approx. 10,000 galaxies) and Extreme Deep Field (15,000 galaxies) images. Click HERE to see a monster version of Groth and sample some of these galaxies for yourself.

A small, cropped portion of the full strip shows several stars (at left). Just about every other tiny blip you see is a galaxy. Credit: NASA/ESA

Whenever we cast our gaze at the starry sky, we look back in time. Since most naked eye stars are within a few hundred light years of Earth, the light we see left them decades to centuries ago giving us a picture of them as they were. Since stars have lifetimes measured in the hundreds of millions to billions of years, all the stars we see tonight are undoubtedly still there and look much the same if we could see them in “real time.”

A selection of normal galaxies from the Groth Strip similar to those we see in the current era  dominated by a concentration of stars in center called the “bulge” and surrounded by a flattened disk of stars. Click to enlarge and learn more. Credit: NASA/ESA

This doesn’t hold true when we use a telescope like Hubble, which can see far more deeply into space and sample the billions-year-old light of the most remote galaxies. Recording the light of a galaxy 8 billion light years away we see it as it was 8 billion light years ago. 

Many galaxies from that earlier era are small, blue and hot with new star formation. If we could see them “now”, they would appear redder. Much of the gas available during that great burst of star-making would be processed and enriched with new elements created by earlier generations of stars.

Some of the more distant (hence younger) oddball galaxies photographed in the Strip by the Hubble scope. Top row: Elliptical galaxies bending the light objects in the more distant background into blue arcs; center row: small galaxies in the process of merging; bottom row: galaxies with irregular, clumpy shapes with blue knots of new star formation. Credit: NASA/ESA

Even their shapes could have changed. It takes time for the graceful arms of a spiral galaxy like our own Milky Way to evolve. Many young galaxies have a tattered appearance due to random mergers with other small, nearby galaxies in their youth.

In the Groth strip, foreground galaxies are larger and younger; those most remote appear like stellar dots.

“The goal was to study the universe as it was when it was about half as old as it is at present, or about 8 billion years ago, a time when youthful galaxies undergoing active formation were becoming quieter mature adults,” said  Marc Davis, professor of astronomy at the University of California at Berkeley.

Hubble sees the galaxies from pre-teen chaos evolving into the more common types of spiral and elliptical galaxies seen in the current era. Funny how the galactic life cycle shares something in common with the human.

Other discoveries made from the photo include the general galactic texture – clumps of galaxies separated by more scattered regions – indicating dark matter at play, a giant red galaxy with dual black holes in its core and a whole lotta oddball galaxies to keep astronomers busy writing papers for a long time.

Ultraviolet view of the Extended Groth Strip taken with the Galaxy Evolution Explorer (Galex) and available on Google Sky. Credit: NASA

The Hubble picture was part of a much larger campaign called the All-wavelength Extended Groth Strip International Survey (AEGIS) involving four orbiting and four ground-based telescopes utilizing everything from visible light to radio waves to X-rays to map this strip of sky in every color of light possible. If you’re game to explore some of these, I invite you to explore the Interactive Groth Strip on the AEGIS site. The various sky views are also found at Google Sky as options at the bottom of the atlas page.

Think pink for spring – Arcturus is back!

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This map shows the sky around 10 p.m. local time in facing east tonight Feb. 24. Arcturus, the brightest star in the constellation Bootes the Herdsman, is well below the Big Dipper. The nearly full moon joins the scene a short distance from Leo’s brightest star Regulus. Maps created with Stellarium

I was startled two nights ago when I turned down the road and spied pink Arcturus scintillating low in the eastern sky. With snow all around and more on the way, my psyche was steeped in winter. So what was this big, bright spring star doing staring me in the face?

Find Arcturus using the old adage “Arc to Arcturus” by sliding down the arc of the Big Dipper’s handle.

After the sun, Arcturus is the 4th brightest star in the sky. It pokes up around 10 o’clock in late February. You’ll find it with ease simply by following the curve of the Big Dipper’s handle downward toward the eastern horizon. Its name comes from the ancient Greek word “arktos” for bear and means “Guardian of the Bear”. Appropriate considering it rides herd on Ursa Major the Great Bear, the brightest part of which is the Big Dipper.

The calendar notwithstanding, Arcturus is a true “spring star”. Come May, when the first mosquitos begin to whine, you’ll find it perched high in the southern sky lording over the landscape much as Orion does now during the early evening hours.

Right now the Bear Watcher is hunkered down in the east, sparking through tree branches and over neighborhood rooftops. Twinkling, most obvious in the brighter stars, is caused by shifting air currents that are more pronounced at lower altitudes.

Arcturus, an orange giant star some 21 million miles in diameter, compared to the sun, Jupiter and other familiar stars.

Funny that the atmosphere can jiggle the light of such a massive star about as if it were as flighty a thing as a dandelion seed. Arcturus is an orange giant star 25 times larger than the sun, but all that girth is reduced to a trembling point of light 36 light years (216 trillion miles) from Earth. Its true brilliance is likewise masked by distance. Put in place of the sun, Arcturus would dazzle 113 times brighter and cover an area of sky half as big as the Big Dipper. As for color, it looks pinkish to my eye. Others see it as red-orange.

Watch this flush-faced star loft higher and higher in the east in the coming weeks with the return of the spring season. There’s a special bonus if you go out tonight. The moon, on its way to becoming the Full Snow Moon tomorrow night, will shine near Leo the Lion’s brightest star Regulus.

Venus and her sisters; Tell time at night with the Big Dipper sky clock

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Venus and the Seven Sisters star cluster last night - what a sight! Details: 200mm at f/5.6, ISO 800 and 20-second guided exposure. Photo: Bob King

It was great to stand in the front yard last night under a clear sky and see Venus and the Pleiades. A casual glance showed a sprinkling of little stars around the brilliant planet. Binoculars gave the best view of the “8 sisters” with Venus the dominant by far. I tried to see how many Pleiads I could count with the naked eye. The five brightest were easy enough but the sixth – Taygeta – was tricky. Pleione was beyond me. It was also fun to recall that 8 years ago to the day I stood in the yard and watched Venus in almost the same position inside the cluster. Apparently I was on time for my next appointment.

A wider view of Venus and the Pleiades along with Jupiter (at bottom). 35mm at f/5.6, ISO 800 and 20 seconds. Photo: Bob King

Tonight Venus glides up and to the left of the star cluster, so if it was cloudy by you last night, you have another shot at seeing them together.

After a good swig of the western sky show, I checked out a new paperless way to tell time using the Big Dipper and North Star. In yesterday’s blog we looked at a simple star clock you can make with paper and scissors. Today we’ll pretend we’re out at night with neither watch nor guide.

The map below shows the North Star as the center of a clock face with the two Pointer Stars in the Bowl of the Big Dipper as the hour hand.  Our example shows the sky at 9 p.m. local time.

To start, face north and look high in the northeastern sky to find the Big Dipper. Draw a line through the two Pointer Stars until you arrive at the first easy-to-see star. That’s the North Star or Polaris. It’s about 5 “Pointer lengths” away. The line connecting the North Star and Pointer Stars now becomes the hour hand on our celestial clock.

To find the time using the Big Dipper and North Star we imagine the northern sky as the face of a clock. Key hours are marked. Illustrations created with Chris Marriott's SkyMap

1. Estimate the time the Pointer hour hand indicates to the nearest quarter hour (15 minutes). In our example, it’s 1 o’clock.

2. This next step is key. We now adjust the clock for the time of year. On March 7, the Pointer Stars stand directly above the North Star at midnight standard time. All you have to do is figure to the nearest quarter month how much time has elapsed since March 7. Since tonight’s April 4th, that rounds off to one (1) month. If it was April 15 instead, the number would be 1 1/4 or 1.25.

3. Add the two figures from above and then multiply by 2 as in: 1 (from 1 o’clock) and 1 (one month) = 2. Then 2 x 2 = 4. Now subtract that sum from 24, so 24-4 = 20. The result will be the time in 24-hour or military style. 20 hours military is the 20th hour of the day or 8 p.m. Add an hour for daylight-saving time and we arrive at 9 p.m. By gosh, that’s correct! Note: If your final number is greater than 24, subtract from 48 instead.

Facing north about 5:15 this morning, the Pointers were now off the left of the North Star in the 9 o'clock position. I figured the time as: 9+1=10. Multiply by 2 = 20. Subtract 24 - 20 = 4 and added one hour for DST to arrive at 5 or 5 a.m. Close enough.

It’s important to remember to add that hour for daylight time when it’s in use and to face north. With practice – and checking against a watch for accuracy – you’ll soon become a master of time at night. Be aware that where you are within your time zone will affect your time estimate. If you try this a few times, you’ll soon be able to factor that in and fine tune your time. I tried this simple method both last night and this morning before dawn and was frankly surprised how well it worked. If you’ve got some time on your hands, let us know how you fare.

Rockin’ ’round the Big Dipper clock

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The need to know the time is a trait that goes back to the early days of civilization. Photo: Petar Milosevic

Does anyone use a watch anymore? Unless it’s a Rolex for show, it seems time keeping has migrated to mobile phones.  Not that I miss the good old days. I enjoy how ingenious we are, constantly re-inventing and re-packaging old ideas.

Time-telling is as ancient as the stars.  Planting, harvesting and important civil and religious ceremonies were tied to calendars based on the movements of the sun, planets and particular stars and star groups. If you’re in a retro mood and willing to extricate phone from palm, how about a mind-meld with the ancients the next clear night?

Before you go out, visit this site and make yourself a star clock. This simple device, which you can assemble from two pieces of paper, lets you tell time using the Big Dipper. Here is a direct link to the Adobe Reader pdf file to print out the star clock. If your computer doesn’t have Adobe Reader, you can download a free copy here.

This simple star clock uses the Big Dipper and polestar to tell time. Turn the outer dial so the current month is at the top. Then turn the inner wheel to match the Big Dipper’s position in the sky (as you face north), and read the time off to the side. Remember to add an hour for daylight-saving time. Photo: Bob King

You can treat the two Pointer stars at the end of the Dipper’s Bowl as an hour hand on a clock with the North Star at the center. As the Earth turns, the Big Dipper describes a circle around the North Star every 24 hours, or one rotation of the Earth. From the northern U.S., that circle never gets cut off by the horizon and so the Dipper never sets.

The star clock is a fun little project that even I could put together in under 10 minutes. It’s the lowest of low-tech and would make a fun exercise for the classroom. There’s even a paperless way which I’ll share tomorrow after I check out how it works tonight. Stay tuned.

(Psst … the paperless method worked out great. Here’s the link.)

Jupiter in polka dots, a bear stands on its tail and Venus Act II

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There will be shadow transits of both Ganymede (moon III) and Europa (moon II) over Jupiter's clouds tonight. During the times shown, the Great Red Spot will rotate onto the front of the disk - a bonus! South is at top and east to the right as viewed in most telescopes. Illustration created with Claude Duplessis' Meridian software

Got a telescope? Tonight two of Jupiter’s moons will briefly cast shadows on the planet at the same time. Ganymede, also known as Jovian moon III, starts the fun when its shadow takes its first tiny bite from the planet’s eastern limb at 8:08 p.m. CST. Add an hour if you live in the Eastern time zone and subtract two hours if you live on the West Coast.

For nearly two hours, the shadow will travel across Jupiter’s southern polar region until it slides off the disk at 9:57 p.m. Ganymede itself will lie to the left of Jupiter as shown on the diagram above. Both moon and shadow move westward due to Ganymede’s orbital motion around Jupiter. When using the diagram as a guide, remember that it shows a much enlarged view of the planet. The scale will be smaller at scope-side.

Meanwhile, beginning at 9:52 p.m., Europa’s shadow makes its first appearance along the eastern limb to begin its journey across Jupiter’s south temperate region. That means from 9:52 until 9:57 p.m. both moons’ shadows will be visible at either end of the planet, an uncommon happening. At the same time, the pale pink Great Red Spot will be in full view. While you’ll only need a small to medium telescope and 60x to see the black pinhead shadows, the Red Spot is a low contrast feature that shows more clearly at 100x or higher.

The performance is over at 12:17 a.m. when Europa’s shadow exits, stage west.

This map shows the sky facing north around 10 p.m. local time. The top stars of the Dipper's bucket point to Polaris, the North Star. Cassiopeia, now looking more like the letter 'M' instead of 'W', is high in the northwestern sky. Created with Stellarium

Many of you don’t own a telescope, so let’s turn our attention instead to the Big Dipper. If you poke your head outside just before the 10 o’clock news, you’ll find it standing on end in the northeastern sky. Yes, its slumbers along the northern horizon last fall are coming to an end with a bit of grandstanding worthy of a circus act. The handle of the Big Dipper represents the tail of Ursa Major the Greater Bear. As the sky clock turns and the hours glide by, the bear climbs higher and higher in the sky as if using its tail as a spring. By dawn,  it’s nearly overhead.

The International Space Station continues making easy-to-see passes over the U.S. and Canada during the early evening hours this week. Below are times for the Duluth, Minn. region to watch for it. For times for your city, log in to Heavens Above or type your zip code into Spaceweather’s Satellite Flybys page. The station, like many satellites, travels from west to east across the sky.

* Tonight Dec. 27 starting at 5:58 p.m. across the northern sky. Very bright!
* Wednesday Dec. 28 at 5:01 p.m. “          ”
* Thursday Dec. 29 at 5:41 p.m.  “          ”
* Friday Dec. 30 at 4:44 p.m. in bright twilight across the north. Second pass at 6:20 p.m. when the station rises in the northwest and becomes nearly as bright as Venus before disappearing in Earth’s shadow near the top of the sky
* Saturday Dec. 31 at 5:24 p.m. High pass in the north – very bright!
* Sunday Jan. 1 at 6:04 p.m. high in the southern sky. Another bright one

The moon and Venus tonight (left) and a photo taken of them last night at dusk (right). Photo: Bob King

Finally, if missed last night’s pairing of the thin crescent moon and Venus, they’ll be back together tonight just as close but in a different arrangement.

Uptick in meteors as summer ripens

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Look northwest at nightfall in late July to find the Big Dipper. Following the arc of its handle will take you to the brilliant star Arcturus. From Arcturus, hop from star to star to see the kite-shaped constellation Bootes. Below the Dipper's handle is the diminuitive Canes Venatici, pair of stars that represent Bootes' hunting dogs. Created with Stellarium

Like the raspberries in the woods, summer is ripening. Stars that were once prominent in June are on their way westward. And if you’re out at dawn, be prepared for a shock -  the early winter constellations of Taurus and Auriga have returned. Last night I noticed that the Big Dipper has dropped considerably in the northwestern sky. It’s tipped at the same angle I tipped the little rubbed-coated  spoon we used to feed our daughters when they were babies.

Once the Dipper is in your sights, it’s simple to “Arc to Arcturus” and bop into Bootes. Don’t forget to make a stop at the small, two-star constellation of Canes Venatici (KAY-nees ven-AT-iss-see). I know it’s a meager group, but if you own a small telescope, the brighter of the two stars, called Cor Caroli, is one of the prettiest double stars in the sky.

A brilliant fireball meteor photographed in 2009 above the constellation Orion. Credit: Wally Pacholka

While you’re out, you may notice more meteors than usual this time of year. We’re now in a multi- meteor shower season with contributions from several different minor showers. Meteor showers occur when Earth’s orbit intersects a debris trail left by a comet (or rarely, an asteroid). Meteors or ‘shooting stars’ are the glowing trails left by bits of comet dust when they strike our atmosphere at speeds of many thousands of miles per hour and vaporize in a flash. Each meteor shower has its own ‘parent’ comet. The familiar Perseid shower of mid-August originates from dust left by Comet Swift-Tuttle.

* Alpha Capricornids: this shower appears to radiate from near the star Alpha in Capricornus about three outstretched fists to the lower left of the Summer Triangle. It’s active from mid-July to mid-September and peaks around August 1. With only about a half dozen meteors per hour, it’s definitely in the ‘minor’ category, but it has a saving grace – the shower’s known for its slow, bright meteors. Best viewing time is from 11:30 p.m. until the start of dawn. The 169P/NEAT.

The southern Delta Aquarid meteor shower peaks the night of July 29-30. The radiant, or point in the sky from which the meteors appear to radiate, lies in the dim constellation Aquarius, the brightest stars of which are outlined above. You can also use much brighter Fomalhaut to help you find it. The map shows the sky facing south around 2 a.m. local time July 30.

* Southern Delta Aquarids (SDA): Active from mid-July to mid-August. This shower is the best of the bunch with a peak on the night of July 29-30 (Friday night-Saturday morning).  From a dark sky site, especially from the southern U.S. where the radiant is higher up, an observer would expect to see 15-20 meteors per hour. Face south or southeast for the best view.

Because the radiant lies in Aquarius, the best time for viewing the shower is from about midnight until dawn, when the constellation is high enough in the south for meteors to clear the horizon. The parent comet is one of the ‘sungrazers’ that closely approach the sun, often breaking up or partially vaporizing under the influence of its gravity and heat. The SDA produces medium-speed meteors that speed into our atmosphere at 26 miles per second or over 93,000 mph!

* Northern Delta Aquarids: This weaker shower radiates from northern Aquarius and is active from mid-July into September with a maximum of 10 meteors per hour in mid-August.

Credit: NASA/MFSC

You can tell which is which by following a meteor’s path backward in the sky. If it points to below the Summer Triangle, it’s probably an Alpha Capricornid. If you can trace it back to a spot in the sky above the bright star Fomalhaut, it’s a southern Delta Aquarid.

Granted, with all these meteoric dribs and drabs, it might be hard to know exactly which meteor belongs to which shower, but it’s still fun watching them. Sharpening your meteor-watching skills will prepare you for the bigger Perseid shower due to peak in a little more than two weeks. Hey, you might even see a few early Perseids later this week. If so, they’ll originate from Perseus in the northeastern sky.

Cool meteor animation and a day to feel closer to the sun

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A bright Quadrantid meteor flashes by, leaving a smoke trail in its wake. Credit: Mike Hankey

I hope you got to see a Quadrantid meteor or two last night. I worked too late to stay up meteor gazing and so missed the shower. Activity was low for the Midwest, but Europe must have had a good show. No reports yet on how many meteors were seen at peak.

Mike Hankey of Freeland, Maryland put his camera to work full time on last night’s shower. He shot 25-second time exposures from 8 p.m. to 6 a.m. in hopes of capturing some of the elusive prey. He got exactly one meteor, but what a beauty it was! The meteor left behind a smoke trail that lasted nearly 10 minutes. Hankey put ten of the images together to create a spectacular animation of the meteor flash and its dissipating trail. To see more of Mike’s work, click on over to Mike’s Astro Photos.

The Big Dipper is part of the extensive constellation of Ursa Major, Latin for Great Bear. Maps created with Stellarium

If you went out to look last night, perhaps you were impressed like I was with how grand the Big Dipper looked standing on its handle in the northeastern sky. The handle does double duty as the tail of the Great Bear or Ursa Major. As you can see from the mythological outline above, the seven stars of the Dipper form his back and that unusually long tail.

During early evening, the Big Dipper is still hibernating along the northern horizon, but he’s up and about after 10 o’clock. Since most everyone can find his familiar form, it’s an ideal place from which to leap into the unknown. For instance, you can shoot a line through the Bowl to the right (east) and arrive at the ‘Backwards Question Mark’ that outlines the head of Leo the Lion. The ‘dot’ at the bottom of the question mark is Regulus, the constellation’s brightest star, which shines at first magnitude or one level brighter than the second magnitude Dipper stars.

Look four fists held at arm's length to the right and below the Dipper's Bowl to find the head of Leo the Lion, also known as the Sickle or Backwards Question Mark.

Leo is associated more with spring than winter, because that’s when it’s highest in the sky during the early evening. Seeing him paw about in January hints at the inevitable changes in weather to come.

Earth's elliptical orbit around the sun causes our distance to vary by about 3 million miles over the course of a year. Illustration: Bob King

Early January is also the time Earth is closest to the sun during its yearly orbit. If our orbit were perfectly circular, the distance would be constant throughout the year, but our planet, like the others, revolves in an oval or elliptical orbit with the sun offset from center.

The difference between perihelion (closest) and aphelion (farthest) is only 3.4% or about three million miles, too small to make a noticeable difference in temperature from one end of our orbit to the other. I suppose you could argue that since perihelion occurs during northern hemisphere winter, we’re a fraction of a degree warmer than if it winter happened at aphelion. Well, let me tell you – I’m looking hard at the thermometer right now and can’t seem to find a fraction that would make it feel more like spring today.

Dibs on the Big Dipper

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The Big Dipper seen from Duluth (left) and Kansas City, MO. this week around 8 o'clock. Maps created with Stellarium

Though the moon remains big and bright early this week, there are a few constellations that stand out despite the glare of moonlight. One of them is the Big Dipper, not a constellation really, but the better half of the larger outline of Ursa Major the Great Bear. From the northern states and Canada, the Big Dipper remains above the horizon year round, though this time of year, it reaches its lowest point, called nadir (NAY-der). That spot is due north directly under Polaris the North Star. If you have trees in your neighborhood, it’ll be hard to see, but out on an open road at night or gazing skyward from an open field, it’s easy to see. Just like real bears, this one’s hibernating in an out-of-the-way spot: the nether regions of the northern sky.

The Dipper's nearly gone this time of year seen from the far southern U.S. Even the North Star is low in the sky.

From here in Duluth, Minn. at latitude 47 degrees north, the Dipper is a good “fist” above the northern horizon at nadir, which occurs around 8 p.m. local time. As the night deepens, the Bowl slowly climbs higher in the northeastern sky, dragging the Handle along with it. The further south you live, the lower the Dipper appears. From Kansas City, Missouri, (latitude 39 degrees), the burly creature scrapes the northern horizon. And if you’re watching from Miami, all you’ll see from the beach is Dubhe (DUB-ee), which marks the upper right corner of the Bowl.

Traveling south, we drive (or fly) along the curvature of the Earth. Looking ahead, we see stars that were once hidden from us emerge over the southern horizon. Looking back, we bid farewell to those far northern stars – like the Dipper – as they’re hidden by Earth’s curve. While folks in New Orleans and Miami can’t see the Big Dipper in November during mid-evening hours, they’re compensated with things that Northerners can’t get their eyes on. Like Orion WAY up in the sky or the brilliant star Canopus in Carina the Keel, located due south of Sirius in Canis Major the Greater Dog.

If you extend the Earth's poles and equator into space, you get their celestial equivalents. Folks in Australia see southern stars we can't and we see northern stars they can't, but there is a good degree of overlap, too. Any star or constellation near the celestial equator is visible in nearly everyone's sky across the globe.

Astronomers extend familiar landmarks on Earth up into the sky, add the word celestial to their description and use them as way points to navigate the heavens. Hence we have the north and south celestial poles and the celestial equator. Polaris sits near the north celestial pole, the sun is on the celestial equator on the first days of spring and fall, and the starry sky in Australia appears to pivot around the south celestial pole. All these points of reference lie on the celestial sphere, an imaginary sphere centered on the Earth encompassing the heavens.

From mid-northern latitudes we can see all the stars down to about 45 degrees below the celestial equator (CE). Below that, the bulk of the planet cuts off our view of the deep southern sky. From southern Florida, sky watchers can peer down to 65 degrees below the CE, while at the earthly equator, all stars in both hemispheres are visible, although those near the north and south celestial poles are very low in the sky. In the southern hemisphere, it’s the reverse of the north – Earth’s bulk gets in the way once again, but this time the northern stars are below the horizon and invisible, while new ones from the south come into view.

In your travels hither and yon across the planet, you’ll also discover you’ve traveled across the celestial sphere as well. If you look up of course.

Cool stuff to see while you’re out tonight

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This annotated photo shows the moon as it will appear this evening. The most prominent maria are labeled with numbers; craters and other features are lettered. Photo credit: copyright David Haworth www.stargazing.net/david

I know you’ll all be out there moon gazing tonight in celebration of International Observe the Moon Night. You can use the photo and key above to help you identify some of the gibbous moon’s most prominent features. The seas or “maria” (MAH-ree-uh) are visible with the naked eye, while sharp-eyed sky watchers can pick out the larger rayed craters like Copernicus and Tycho. All the other features are visible in binoculars and small telescopes.

* 1-6: The maria are those largish gray spots that make up the face of the “man in the moon”. They’re ancient impact basins created when asteroids struck the moon some four billion years ago. At that time, they looked like enormous craters, but lava from the mantle bubbled up through cracks and later filled them.
* A: Copernicus is 58 miles across and one of the most magnificent lunar craters. It looks like a bulls-eye surrounded by its bright rays of ejecta.
* B: Kepler is similar to Copernicus in appearance but smaller.
* C: Sinus Iridium or Bay of Rainbows is a large crater, the right half of which was flooded by Mare Imbrium lavas. As a result, we see only half the crater which resembles a bay.
* D: Plato is 68 miles across and a nice even gray color. It’s also been flooded by lavas from within, making it look like a miniature lunar sea.
* E: Gassendi crater is the same size as Plato. Its proximity to the moon’s day-night line, called the terminator, will bring its walls, rough interior and central peak into beautiful relief tonight.
* F: Tycho is 53 miles in diameter and one of the freshest, large lunar craters. Its extensive system of rays has no equal on the moon.
* G: Proclus is a small crater with a brilliant, asymmetric ray system.
* H: Langrenus, at 84 miles across, looks like a smooth white oval. Its “flat” appearance is due to lack of shadows (which show relief) from a high sun.
* I: Directly below or south of Tycho, you’ll see Clavius, one of the largest craters on the near side of the moon. It’s 140 across and home to lots of additional craters within its walls.
* J: The arc-shaped Apennines Mountain range lies along the southeastern border of Mare Imbrium. Peaks here reach to 2.8 miles.

Jupiter and its four bright moons: Io (I), Europa (II), Ganymede (III) and Callisto (IV) as seen around 9:30-10 p.m. tonight in binoculars and telescopes. Uranus is directly above the planet. North is at top, east to the left. Maps created with Stellarium

Jupiter quickly catches the eye low in the southeastern sky after 9 o’clock. There’s nothing else that comes close to its brightness in that region. Binoculars will not only show several of its brightest moons, which happen to be lined up left-to-right in order of increasing true distance from the planet, but also the planet Uranus. It’s the “star” directly above Jupiter and about as bright as the moon Io. Jupiter and Uranus are in conjunction with each other tonight and less than one degree apart. If you’re using a small or medium-sized telescope at its lowest magnification, both planets will fit comfortably in the same field of view. As you look at the pair, consider that Jupiter is 367 million miles from Earth, while Uranus is deep in the background at 1.8 billion miles or four times as distant.

The Summer Triangle is directly above the moon tonight. This map shows the sky looking south about 9 p.m.

Above the moon, stands the Summer Triangle, composed of the three luminaries Deneb, Vega and Altair. Vega is the brightest and will occupy the sky’s overhead spot called the zenith around 8:30 p.m.

The west-northwest is not without its celestial booty. Find the Big Dipper, which is leveling out low in the northwestern sky at nightfall, and follow the arc of its handle to the brilliant, papaya-colored Arcturus. No matter where you look tonight, there’s something for the eye to marvel upon.

As a reminder, members of the Arrowhead Astronomical Society will have telescopes set up for looking at the moon and Jupiter in Canal Park in Duluth – weather permitting – between 8 and 11 tonight. Look for us near the Lakewalk at the east end of the parking lot. See you there.

Use the handle of the Big Dipper to guide you to Arcturus, a bright spring star which is now dropping off into the western sky.