Monthly Archives: November 2011

Breathe deeply, life’s a gas

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The moon photographed on July 31, 2011 out the window of the space station. Seen near setting, the moon appears to hover at edge of outer space. The lowest layer of air, tinted orange by twilight, is the troposphere. A brownish layer called the tropopause separates it from the higher stratosphere. Credit: NASA

By convention, outer space starts at 100 km or 62.1 miles above the Earth’s surface, but to get there, a plane or ship must first pass through five layers of atmosphere. The recently released photo was taken from about 230 miles up by an astronaut on board the International Space Station. It’s not only beautiful to look at but clearly shows several layers of our planet’s atmosphere. The lowest region, which contains 80 % of the atmosphere’s mass and 99% of its water vapor, is called the troposphere after the Greek tropos meaning ‘turning’ or ‘mixing’.

Mixing is the word in the lower atmosphere thanks to high and low pressure regions, winds and turbulence. Home to clouds, aerosols and weather, the troposphere is by far Earth’s most colorful air layer. Think of all the pinks, oranges, red, blues and even the occasional green we pass through and breathe in during a year.

Different phenonomena occur in different layers of Earth’s atmosphere. The troposphere is characterized by clouds and weather; the mesosphere by the aurora borealis. Satellites and the space station orbit at the extreme edge called the exosphere. Credit: NASA with my own additions

Up above about 10 miles we enter the stratosphere, a calm region of thin, cold, clear air. If you take a cross-country plane trip, you’ll be cruising through its lower reaches. Unlike the troposphere, temperature increases as you ascend the approximately 30 miles from the bottom to the top due to the absorption of UV light from the sun by the ozone layer. This crucial region was created by life through photosynthesis and in turn protects life by absorbing much of the dangerous, short-wave UV radiation.

To get beyond the stratosphere into the gaspingly-thin air of the mesosphere, you’ll need to be an astronaut. Despite its tenuousness, the mesosphere’s one of the most action-packed places around, hosting everything from flaming meteors to the aurora borealis to fondue parties. Just wanted to see if you were paying attention. Things get chilly again as we ascend this layer. The bottom can be as toasty as the low 20s while the top dips to around 200 below, making it the coldest region of the atmosphere.

Higher up, the air continues to thin out but the temperature rises once again through the thermosphere reaching over 4,500 degrees F during the daytime. Since heat is a measure of the motion of atoms or molecules, the few remaining oxygen atoms at these altitudes dart about rapidly as they absorb energetic radiation from the sun. Yet the air is so rarefied, we’d never feel the heat; there are just too few atoms to bounce off of us to create a sensation of warmth. The sun’s energy also electrifies atoms at these heights making them capable of reflecting radio waves beamed from the Earth long distances from one station to another.

A setting last quarter crescent moon and the thin line of Earth’s atmosphere are photographed by the Expedition 24 crew on the space station on Sept. 4, 2010. Click to enlarge. Credit: NASA.

Once we’ve climbed the 250 miles into the exosphere, Earth falls away as we penetrate deeper into outer space. While 250 miles sounds like a lot of air, and illustrations make the atmosphere appear like a deep pool, the reality is much more stark. If our planet were shrunk to the size of an onion, the Earth’s atmosphere would only be as thick as the onion’s outermost skin. The second Earth-moon photo, also taken by astronauts, hints at how fragile that fuzzy layer really is. Breath deeply and enjoy.

Northern lights – now you see ‘em, now you don’t

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Aurora smoulders in green and reds low in the northern sky around midnight last night near Duluth, Minn. Details: 24mm lens at f/2.8, ISO 1600, 25 second exposure. Photo: Bob King

Why can’t we all live in northern Norway or Finland when northern lights are forecast? Not only are those regions closer to the auroral oval and more likely to see a display when the sun sends a shower of plasma our way, but the long fall and winter nights at those northern latitudes guarantee abundant darkness.

That’s what happened last night as you compare pictures taken from Duluth, Minn. (latitude 47 degrees north) to those made by Helge Mortensen at latitude 65 degrees north near Kvaløya on an island in northern Norway.

Here’s what the aurora looked like from Kvaløya, Norway. Very nice! Lights from a city in the distance color a low cloud pink. Credit: Helge Mortensen

The predicted blast from the sun called a coronal mass ejection arrived during late afternoon hours for North America, but its effects were weaker than anticipated. If the Arctic is your home, you had a fine show just the same, but for observers in the northern U.S. the display was minor. I noticed a glowing arc very low in the northern sky around 10 o’clock. By midnight it spanned from the Big Dipper in the northeast to the Northern Cross in the northwest about one “fist” high above the horizon. The rays that show clearly in the photo were visible but subtle with the naked eye.

The full span of the aurora visible from near Duluth, Minnesota last night. The colors are created by oxygen atoms high in the atmosphere giving off light after being excited by high speed particles arriving from the sun. Photo: Bob King

Many of you probably didn’t see the northern lights because they were low and faint, but I encourage you to keep looking all the same. It never hurts to monitor the Kp index, a measure of magnetic activity in the ionosphere. When you see a yellow or especially a red bar on the graph, that’s a good sign aurora could be dancing outside your door. The space weather forecast continues to call for more minor aurora storms both tonight and tomorrow with quiet conditions returning on Thursday.

Another wonderful image by Helge Mortensen of last night’s aurora.

Meet Jupiter’s new friend plus the mystery of Vesta’s dark rays

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Jupiter, Aries and planet-bearing Hamal are all high up in the southeastern sky around 7 o'clock local time in late November. Aries is only one fist held at arm's length above Jupiter. Created with Stellarium

Not far from Jupiter in the fall sky is a newly discovered planet with a mass nearly twice as large. Granted it’s 66 light years away, but you can look up anytime it’s clear and imagine another hitherto unknown world up there. Called Alf Ari b, it revolves around Hamal (HAM-al), the brightest star in the little constellation Aries, and was discovered just this year using the radial velocity method of detection.

A team of astronomers employed a spectrograph on the 71-inch Bohyunsan Optical Astronomy Observatory reflecting telescope in Korea to precisely measure the minute tugs on the star from the gravity of an orbiting planet. Based on changes in Hamal’s speed toward and away from Earth (radial velocity) they determined how much matter was doing the tugging.

The new planet tips the scales at 1.8 Jupiter-masses and orbits 111 million miles from its host star with a period of 381 days. That’s only a little more than Earth’s distance from the sun. Most extrasolar planets are of the “hot Jupiter” variety – large planets orbiting very close to their host stars. This one is a little further away and perhaps might be called a “warm” Jupiter. Assuming it has a solid surface, which is by no means certain, if you weigh 100 lbs. on Earth, the additional gravity of this massive planet would pump that number up to around 425 lbs. – most uncomfortable. For a bit of fun, click HERE to see what you’d weigh on other planets.

Hamal is 15 times larger than the sun or about 13 million miles in diameter. If put in the sun's place, it would reach more than 1/3 the way to Mercury. Illustration: Bob King

Hamal is an orange giant star 1.5 times the sun’s mass and 15 times larger. A trained eye might detect a hint of warmth in its hue compared to stars of similar brightness. At magnitude 2.0, which is as bright as the stars in the Big Dipper, Hamal is the second brightest star in the night sky to sport an extrasolar planet. While no one can yet see Alf Ari b, it revealed itself through gravity and now shares a place in our mind’s eye.

A fresh 4.3 mile diameter crater on Vesta displays both bright and dark rays as well as blocks of debris (in its center) from the impact. Click to enlarge. Credit: NASA/ JPL-Caltech

I was browsing the Dawn Mission website the other day to see what’s new with the asteroid Vesta and came across an interesting photo of a fresh, small crater with a splatter of both light and dark rays around it. Rays are formed from secondary impacts of rock blasted from the crust that land in a radial pattern around the crater. What’s unusual is that the impact excavated both light and dark layers of material.

A 1-mile-diameter Vestan crater with dark rays. Credit: NASA/JPL-Caltech

Pale rays systems are much more common across the solar system because falling impact debris digs up fresh materials from beneath the crust that have yet to be exposed to the darkening effects of sunlight.  Dark rays are uncommon except it seems on Vesta, which has a surprisingly large share of them. Clearly the asteroid has layers of different kinds of rocks, but exactly what they’re made of is not yet known. Dawn will use its gamma ray and neutron detector to map the elemental composition of the surface in the weeks and months to come, hopefully shedding light on this dark matter.

Solar bling plus auroras possible tomorrow, Tuesday

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The sun photographed in ultraviolet light late yesterday by the Solar Dynamics Observatory displays a beautiful “necklace” of sunspot regions (bright yellow patches) surrounded by loops of hot gas that trace out the powerful magnetic fields above the spots. They’re similar to the arcs formed by sprinkling iron filings around a magnet. Credit: NASA/SDO

A storm is gathering. The good kind, that is. Space weather forecasters at NOAA’s Space Weather Prediction Center expect the effects of a coronal hole on the sun, combined with a recent coronal mass ejection (CME), to fire up possible auroras Monday and Tuesday nights Nov. 28 and 29.  A coronal hole is an open region in the sun’s atmosphere or corona where hot plasma from lower down near the surface can stream away into space. Coronal holes can last for several months and cause repeat auroras approximately every 27 days, when the sun’s rotation brings them into Earth’s line of sight.

This picture was taken at the same time as the top photo but in visible light. The view is similar to what you’d see through an amateur telescope equipped with a safe solar filter. No fewer than seven sunspot groups are in line across the sun’s northern hemisphere. Credit: NASA/SDO

A CME is a large, high-speed burst of solar plasma – a ‘soup’ of electrons and protons bound up in magnetic fields – blasted into space. Many are directed away from the Earth and don’t affect us, but those that are, like the coming blast, can compress our planet’s cushy magnetic bubble and stimulate the production of auroras, affect radio communications and even overload power grids. This particular CME occurred in the wee hours of Saturday morning and is headed our way at nearly 2 million miles per hour.

Since we’ll miss the core of the eruption, only minor storming is forecast for Monday and Tuesday, so I wouldn’t expect a dramatic display of the sun’s muscle. Be on the watch for greenish glows and rays in the northern sky. With the moon still only a crescent, if we do get something, we’ll at least have a dark stage as a backdrop.

With sunrises get later and later as November rolls toward December, you might find yourself up and around during morning twilight. Guess what? That’s just when the International Space Station (ISS) will be making favorable passes over North America in the upcoming week or so. The times below are when to watch for the Duluth, Minn. region. For times for your city, go to Spaceweather Flybys or log in to Heavens Above. Remember that the ISS will appear as a brilliant star, unblinking star traveling from west to east across the sky. It’s currently orbiting 230 miles above our heads.

* Tomorrow Nov. 28 starting at 6:05 a.m. across the northern sky
* Tuesday Nov. 29 at 6:43 a.m. high across the top of the sky and passing near the Handle of the Big Dipper. A brilliant show!
* Wednesday Nov. 30 at 5:49 a.m. in the north and northwest
* Thursday Dec. 1 at 6:27 a.m. high across the south. Another brilliant pass!
* Friday Dec. 2 at 5:32 a.m. Reappears from Earth’s shadow in the Big Dipper high in the northeast and then descends eastward passing the bright star Arcturus
* Saturday Dec. 3 at 6:10 a.m. Another nice, bright pass across the southern sky

(By the way, I want to thank our readers for the inspiration to check out why picture captions were so faint and hard to read. I contacted the blogs management team and explored every internal setting to no avail. Today by pure chance I stumbled upon a well-hidden solution. I hope you’ll enjoy the new legibility.)

We’re on our way to Mars!

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The Mars mission rockets skyward after this morning's successful launch. Credit: NASA

Curiosity Rover is on its way to Mars! The Mars Science Laboratory mission launched successfully right on schedule this morning at 9:02 a.m. CST. The Atlas V rocket sent the probe a parking orbit around Earth; a second firing of the upper stage then propelled the probe on its 352 million mile journey to Mars. It will arrive August 6, 2012, enter the Martian atmosphere and deploy parachutes and a special descent stage that will gently lower the rover onto the surface.

The rover begins its studies a short distance from a mountain in the center of Gale Crater in the planet’s equatorial region. There it will zap rocks with lasers and scoop up samples of soil and analyze them in a miniature laboratory looking for water and organic compounds.

Mars on Nov. 18 shows the dark, Africa-shaped marking called Syrtis Major (right of center) and the North Polar cap made of mostly "dry ice" or frozen CO2. Credit: Damian Peach

During its nearly two-year prime mission after landing, Curiosity will use 10 science instruments  “to investigate whether the region has ever offered conditions favorable for microbial life, including the chemical ingredients for life,” according to NASA.  Mission control is in communication with the probe. Over the next few weeks they’ll be checking out the instruments and performing a planned course correction maneuver. For more about the mission, click HERE. You’ll find additional updates HERE.

Meanwhile the Russian Mars craft Phobos-Grunt remains stuck in Earth orbit with only sporadic communications with ground control. No word yet on why the rockets that would have sent it to Mars failed to fire. The Phobos mission window has closed, but there is hope the probe can be re-purposed for another mission.

The tender lunar crescent and planet Venus this evening. Created with Stellarium

We’ve got a rainy-snowy day here in Duluth, Minnesota, but if it were clear tonight, I’d be watching the very thin crescent moon woo Venus in the southwestern sky at dusk. Let’s hope you have better weather. Look very low in the southwest about 15 minutes or so after sunset. Once you’ve found the moon, Venus is just a few degrees to the left or east. The pairing will be even closer for folks living on the West Coast and Hawaii.


Mars Science Lab mission blast-off and rocket separation

Alien planet family portrait

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This illustration shows nearly all of the 1,235 potential alien planet candidates NASA's Kepler mission has found to date. The planets are shown crossing front of their host stars, which are to scale. The position of each dot gives you an idea of the path each planet takes. Click image to see the full family portrait. Credit: Jason Rowe and Kepler team

704 and counting. So stands the latest tally of extrasolar planet discoveries. And that’s not all. An additional 1,235 planet candidates found by NASA’s Kepler space telescope are awaiting confirmation. Soon we’ll know of more planets than the number of naked eye stars visible on a clear, dark night.

Kepler was launched in 2009 and has been monitoring the brightness of 156,000 stars in the constellation Cygnus the Swan looking for telltale dips in their light that would indicate a passing planet. Only planets in the line of sight between Earth and a star can be found with this method, but with such a large sample, the detections have been many. If a planet is present, its passage will dim the star at repeated intervals by an amount that depends on its size. Larger planets mean bigger dips.

While only 25 Kepler planets  have been confirmed, the majority should be soon. Among its finds is Kepler-7b, one of the lightest planets known, with a density similar to styrofoam. It’s half the mass of Jupiter but 1.5 times its size. Light and airy as they come, this alien world would float on water or blow away in a suitably titanic windstorm. At the other end of the spectrum Kepler-10b is just 1.4 times the size of Earth and dense as iron.

Kepler-16b is the most "Tatooine-like" planet yet found in our galaxy and is depicted here in this artist's concept. It's a cold world, with a gaseous surface, but like Tatooine, it circles two stars with a period of 229 days. Credit:NASA/JPL-Caltech/R. Hurt

Kepler-16b may be one of the most fascinating. It’s the first world found circling two stars, an orange star similar to but smaller than our sun, and a tiny red dwarf. This Saturn-sized world been compared to Luke Skywalker’s home planet Tatooine in the “Star Wars” movies. Unlike Tatooine however, it’s not friendly to humans and giant ant-lion creatures, because it orbits outside the stars’ “habitable zone” where liquid water might exist on its surface. Cold and desolate, Kepler-16b is a planet with awe-inspiring views where science fiction is a daily reality.

Tatooine's two suns. Credit: George Lucas, 20th Century Fox

The pace of alien planet discovery doesn’t appear to be slowing down either. Take a look at the Exoplanet Encylopedia when you get a chance and watch the tally tick higher and higher. The website is loaded with information about the particulars of each exoplanet including discovery dates, locations, brightness of the host star, orbit and mass. For additional information graphics on Kepler planets, you can also check HERE.

If you’d like to participate in a citizen science project sieving Kepler data to hunt for new planets, then Planet Hunters wants you! Sign up and you can search the data for those “dips” we talked about earlier that might indicate the presence of a new planet. With the long winter ahead, what could be more fun than staying warm while tracking down alien worlds?

Wishing you a cosmic Thanksgiving

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Today is the Thanksgiving holiday in the U.S. and a time for feasting and gratitude. Here’s my own short list of things – some little and some very big – that make life a pleasure to live:

* The sun shining in my face on late November afternoons
* The silence of a clear, dark night far from the city
* All the composers and musicians who’ve labored to create great and memorable music
* My job as a photojournalist
* The sound of water tinkling in a creek in a remote wood
* People passionate about everything from highway maintenance to whales. Their intense focus illuminates many an unlit corner of the world.
* Walking up and down the Superior Hiking Trail from ridge top to river bottom
* Kettle-cooked barbecue potato chips
* A steady paycheck
* The compact camp stove given to me by my friend Rick. With it I can brew a cup of tea anywhere in 3 minutes.
* The way birch bark hangs in peelings on a tree
* Nature’s continual reworking of matter through evolution without really trying.
* Seeing across the universe by the simple act of stepping outside
* Bacon

Gosh, I could go on and on, but I’ll save the best for last – my wife, my daughters, family and friends. Without their love and support, the universe would be a much smaller place.

I also want to thank you who read this blog for your interest and for posing questions that have stimulated lots of lively discussion this past year. And now you’ve probably heard enough from me. May your own list never end.

Comet Garradd still going strong; Russian Mars probe contacted!

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Comet Garradd on November 19 shows a classic dual tail. The longer, blue streak is the ion tail. The dust tail is shorter and glows pale yellow from reflected sunlight. Credit: Michael Jaeger

Remember Comet Elenin? Hopes were high it would become the best comet of 2011, but instead it dissolved into a cloud of dust. Amateur astronomers are still tracking its fading remnants as the comet passes the Pleiades star cluster in Taurus this week.

Use this finder chart to track down Comet Garradd. It inches slowly northward only a few degrees in the coming month. The map shows Hercules at around 6 p.m. at the end of evening twilight in the western sky. M13 is a bright globular cluster and stars are shown to 7th magnitude. Created with Chris Marriott's SkyMap software.

The brightest comet of the year never received the dire publicity that stuck with Elenin to the end. Comet Garradd was well-placed and easily visible in binoculars this summer as it crossed the Milky Way en route to its current residence in the sprawling constellation Hercules. Underdog Garradd remains a 7th magnitude fuzzball in binoculars this month. I looked it up recently on one of the few clear nights we’ve had in November and was thrilled to see two tails sticking out of the comet’s bright, fuzzy head or coma. Both show wonderfully in Michael Jaeger’s photo and were just as pretty in my 15-inch scope though much more subtle.

Comet Garradd is 195 million miles away or about twice our Earth’s distance from the sun. That gap will close to 118 million miles by early next March, when the comet will brighten by a magnitude, placing it within naked-eye range from the countryside. Take a look now before it drops too low in the western sky and the moon returns. The best viewing time is right at the end of evening twilight as soon as the sky gets dark.

Binoculars still show a soft, puffy glow and perhaps a hint of a tail. A modest-sized telescope will show the dust tail and maybe even a hint of the ion tail. Dust tails are formed of smoke-sized particles of dust embedded in cometary ice. Heat from the sun vaporizes the ice and releases the particles which fall behind the comet in the form of a tail measuring between 600,000 and 6 million miles long. Comet dust reflects light just like good old house dust or cigarette smoke. Ion tails fluoresce blue when ultraviolet light in sunlight breaks down carbon monoxide jetted by the comet and are often much longer – up to 100 million miles.

The European Space Agency's Perth, Australia radio telescope that contacted Russia's Phobos-Grunt craft yesterday. Credit: ESA

Just got the news this morning that contact was re-established with the Phobos-Grunt mission that’s been stuck circling the Earth since its November 8th launch. You might recall the probe’s engines failed to fire and send the ship to Mars. Yesterday at 2:25 p.m. CST, the European Space Agency’s (ESA) tracking station at Perth, Australia, picked up a radio signal from the probe. ESA is now working with engineers in Russia on how best to maintain communications with the spacecraft. Another contact will be attempted tonight.

There’s no information on what might have gone wrong with Phobos-Grunt or how it might be remedied. If engineers can establish a solid communications link with the craft and learn how to correct the engine-firing problem, it might still be sent on its Mars-Phobos mission, but probably not anytime soon. The next launch window opens in 2013. Full story HERE.


A well-narrated and illustrated summary of how we’ll study Gale Crater with the Curiosity Rover.
Meanwhile the Mars Science Lab Mission (Curiosity Rover), which was originally scheduled for a Nov. 25 launch, has been delayed one day to replace a battery on the rocket. Blastoff is scheduled for 9:02 a.m. Central time this Saturday. Click this Mars Exploration Family Portrait by Jason Davis for a really cool graphic showing all missions to Mars to date.

Stargazing with Santa Claus at the North Pole

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The North Pole photographed in June 2006. There is no land at the pole, only shifting sea ice in the Arctic Ocean. Credit: NOAA/PMEL

With Thanksgiving and the Christmas season just around the corner, Santa and the elves have been laboring mightily at the North Pole assembling everything from X-boxes to rocking horses. Above their heads the stars twinkle in a sky that’s dark 24 hours a day. That’s right. Neither sunshine nor the faintest blush of twilight mar what must seem like eternal night. As I write, the temperature at the pole is -27 F with an expected high today between 10 and 20 below under mostly cloudy skies.

At the North Pole, the sun sets for good on the first day of fall, and the last sign of its presence occurs in early November, when a sharp-eyed elf might see the faintest hint of dusk in the southwestern direction. True and utter night settles in for good on November 13. Not until the end of January will dawn return by slow degree until the sun finally rises again on March 20. The season’s lightning bill alone must weigh heavily on Santa’s back.

Before packing up all those binoculars and telescopes intended for good little girls and boys, the elves undoubtedly check them out under the stars for quality assurance purposes. Any clear night would do as would any clear day. Imagine the freedom to go out and look at the sky anytime you wanted without having to worry about daylight. OK, there are a few downsides, but I’d love a taste of seamless polar darkness.

The Big Dipper is low in the northern sky during November evenings. Maps created with Stellarium

So what would you behold on looking up? You’ll recall yesterday’s discussion about the Big Dipper and how low it sinks in the sky for mid-northern latitudes this time of year. To see it in November, you either have to live in the northern U.S. and peer along the northern horizon or wait until just before dawn, when the Earth’s rotation finally carries the constellation back up in the eastern sky.

From the North Pole, the Dipper not only never sets, it pivots about the North Star near the very top of the sky. Earth’s imaginary north polar axis extends into space in the direction of the North Star (Polaris). As the planet spins, all the stars describe arc-like paths across the sky, a reflection of our spinning motion. All except Polaris. It alone remains in one spot in the sky, because Earth’s axis points directly and unflinchingly at it.

For observers north of the equator, Polaris is as high in the sky as your latitude. That translates to 47 degrees high for Duluth, Minn., 42 degrees for Chicago, 24 degrees for Key West and directly on the horizon for an observer standing on her tiptoes in Quito, Ecuador. If you stepped outside to share a hot cocoa with Santa at the Pole this week, you’d see the North Star 90 degrees high or directly overhead at the zenith point. Any star groups near Polaris like the Big Dipper and Cassiopeia would circle around it and never set.

A 45-minute time exposure of the northern sky reveals how Earth's rotation causes the stars to describe arcs around the North Star (left of center). The Earth's axis points to the north celestial pole located very close to Polaris. That's why it remains nearly motionless in the sky. Photo: Bob King

Stars that never set are called circumpolar. They’re close enough to the North Star that they don’t get cut off by the horizon as Earth’s rotation spins them about. To be precise, any star that’s within the latitude of the observer from Polaris never set. For Duluth, that means stars within 47 degrees of the North Star never set, for Key West, where Polaris is much lower in the sky, only stars within its latitude of 24 degrees are circumpolar. At the equator, where Polaris sits on the horizon, there are no circumpolar stars.

Polaris is at the zenith at the North Pole while stars we associate with all the different seasons like Orion (far right), Leo and the Summer Triangle are always visible and never set. They cycle round and round the North Star.

Guess what’s in store for observers at the North Pole? ALL stars are circumpolar. The sky never changes at the Pole. Nothing rises, nothing sets. Only the moving planets and sun make appearances and change positions, otherwise the same group of constellations are ALWAYS visible. There’s no such thing as the seasonal star groups we experience in the mid-latitudes: Virgo in spring, the Summer Triangle in summer and Orion in the winter. No matter what time of year you go out – whether for real or in your imagination – Polaris will always be overhead, the Big Dipper always visible and the Belt of Orion forever below the horizon. In a sense, all star seasons are visible simultaneously. What you see is what you get.

Can you see any of the southern stars from the North Pole? In a word, no, but let’s first define what we mean by southern stars. Just as Earth’s equator divides northern and southern hemispheres, the celestial equator  defines the boundary between northern and southern stars. Picture the celestial equator as an imaginary extension of Earth’s equator out into the sky. From mid-northern latitudes the celestial equator cuts midway across the southern sky, which means most of us see a mix of both northern and southern stars when we look up at night.

As seen from the North Pole (left) all stars circle the sky parallel to the horizon and never set. The horizon is the same as the celestial equator, so no southern stars are visible. From mid-northern latitudes, stars track through the sky along tilted circles, Polaris is as high as an observer's latitude. Illustration: Bob King

An observer’s horizon is that great circle located 90 degrees from the zenith. From the North Pole, the horizon is 90 degrees from the North Star and coincides with the celestial equator. Santa and his staff would be forever denied a look at brilliant Sirius and constellations like Scorpius and Sagittarius, because they’re south of the celestial equator and always below the horizon. Only the top half of Orion clears the horizon – two of the three famous Belt stars are invisible. The uppermost star in Orion’s Belt might be seen on a favorable night via atmospheric refraction (bending of light), since it lies directly on the celestial equator.

So yes, it might be nice to have 24 hours of night days on end, but never seeing cool stuff like the Orion Nebula (located below the Belt of Orion) would soon have me yawping for points south. Surely Santa must smile at the sight of Sirius ascending in the sky as he speeds south on his sleigh every December.

Beauty at dawn plus tips for happier satellite watching

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An aureole of light surrounds Jupiter as it shines through low clouds last night north of Duluth, Minn. Photo: Bob King

The ailing Russian Phobos probe was a no-show for me last night. You may have had the same luck. Unless satellite flyby engines are updated with the latest orbital changes, the times and paths listed aren’t always reliable. This morning I posted a request to the visual satellite observers group known as Seesat-l for a more reliable, accurate source of satellite predictions. Several people got back to me with two other online flyby calculators that look like excellent, up-to-date tools. One of the easiest to use is CalSky.

When I clicked on the link, it instantly knew my location and plotted a list of Phobos-Grunt passes for the upcoming week. Talk about effortless! Included for each day are links to the satellite’s ground track (overflight path) and a star chart to show its path through the sky.

The second is a very nice, interactive site created by Simone Corbellini called Visual Sat-Flare Tracker 3D. Once you key in your location, it shows predicted passes for the next 24 hours. The big star map is a big plus! Try them out and let me know how they work. And if you have questions on terminology, etc., just use the Comment section in the blog to ask for help.

Last night’s stars didn’t sparkle any less despite Phobos-Grunt’s absence. The fresh snow cover added cheer to the darkness as the Big Dipper settled in for a nap behind the leafless trees. The familiar constellation ebbs lowest in late November and for many disappears altogether until the wheeling of the Earth brings it back into view in the early morning hours. In the south, Jupiter rose to dominate the sky until clouds attempted to quench its radiance. They never succeeded. The planet blasted through even when all the other stars were gone. No one puts Jupiter down.

Look low in the southeastern sky about an hour or so before sunrise Tuesday morning for the delightful trio of moon, Spica and Saturn. Created with Stellarium

Tomorrow morning there will be a very attractive gathering of the thin crescent moon, Virgo’s brightest star Spica and the planet Saturn. If you’ve had any difficulty finding the planet after its recent emergence into the November dawn sky, this is your chance to see it with ease. The map shows the sky around 6 a.m. or about and an hour and 15 minutes before sunrise. Telescope owners are encouraged as always to tote our their instruments and check out one of nature’s more unique creations – the rings of Saturn. I can never seem to get enough of them. The dim, earth-lit portion of the moon to the right of the sun-illuminated crescent should be especially striking. Binoculars will allow you to see darkened lunar seas and even the shapes of several larger craters.