Monthly Archives: October 2011

A flood that would make even Noah turn and run

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The orange band is a small-scale volcanic dike that filled a crack between older lavas about a billion years ago. This one is located at the mouth of the Lester River in Duluth, Minn. Photo: Bob King

Massive floods are not only common on Earth but 3.5 billion years ago they raged across the Martian landscape. One of the most dramatic issued from a breach in a rift called Mangala Fossae. ‘Mangala’ is the Sanskrit word for Mars and ‘fossae’ is Latin for ditch or trough.  This striking linear crack is located 16 degrees south of the Martian equator north and east of the edge of the vast volcanic plateau called the Tharis bulge.

What’s now a wide valley began as a narrow fault in the crust. Scientists believe that a surge of molten rock (magma) beneath the fault caused it to widen into a long, linear valley seen in the photo below. Surges of magma that squeezed between cracks in earlier lava flows are called volcanic dikes. Many can be seen along the rivers and rock outcroppings of Lake Superior’s North Shore.

The large crack in Mars crust at left is Mangala Fossae. Water beneath the surface burst forth when the crack widened, flooding nearly everything you see to the right or north. Multiple bursts of floodwaters carved a huge channel 550 miles long called Mangala Valles. The area in the yellow oval is shown in closeup below. Click photos to enlarge. Credit: NASA/JPL-Caltech/Arizona State University

But there’s more, much more. The cracking released a vast reserve of subsurface water that had been capped and contained either by frozen ground or thick layers of rock. Once the surface was broken, water gushed forth in a fashion similar to shaking a pop bottle and then untwisting the cap. After filling the trough, it breached the wall and flowed with cataclysmic fury across hundreds of miles of desert Martian landscape scouring everything in its path. What a terrifying sight to have seen if eyes had been around back then. The floodplain is named Mangala Valles (valley).

The yellow arrow points to the remains of the volcanic dike that caused the water flow leading to the creation of Mangala Valles. When the dike widened the valley, it broke into a subsurface reservoir of water, causing floods that opened the breach seen here. The blue arrow (right) points to water-cut terraces that suggest the valley saw multiple episodes of floods. This scene is about 6 miles wide. Credit: NASA/JPL-Caltech/Arizona State University

The breach measures five miles wide and 1,600 feet deep. Think of the power it must have taken to tear through all that rock. By counting craters, scientists have estimated that the first and largest flow happened 3.5 billion years ago. Crater-counting has been used across the solar system to get a handle on a body’s age. The more craters, the more ancient the landscape; the fewer the younger.  Judging by the terraces in the downstream walls of rock, smaller floods recurred 1 billion, 500 million and as recently as 200 million years ago, each leaving its own ‘water level mark’ on the hillsides.

Downstream in the valley floor, the floods thinned the material covering an underground aquifer. As the subsurface waters broke out, they joined the main flood. Scene is 4.1 miles wide. Credit: NASA/JPL-Caltech/Arizona State University

Even more evidence for floods are found in the quilted patterns of mesas and valleys in what’s termed ‘chaotic terrain’.  The crazy shapes are believe to form when powerful floodwaters scrape away much of the overlying rock in the floodplain. Without the confinement of that upper layer or rock (or ice), water may have bubbled out all over the place creating this strange scene of jumbled valleys and hilltops.

The Mangala flood scoured the channel deeper and carved hills and knobs into graceful streamlined shapes. This scene 9 miles wide. Credit: NASA/JPL-Caltech/Arizona State University

The Mangala flood tells us that despite current conditions, where liquid water can’t exist on Mars for long because of bitter cold temperatures and low atmospheric pressure, it once did pour across the landscape, creating vast floodplains as well as narrow, branching riverbeds. Since a growing crack in its surface was enough to liberate a flood, I wonder if a well-placed large meteorite strike might someday do the same. Will some future amateur astronomer catch an impact flash on Mars followed by a darkening of the surface as pressurized water once again seeks the light?

(Photos taken by Mars Reconnaissance Orbiter and the infrared camera on the Mars Odyssey orbiter. Thanks to NASA for the background information used to create this piece.)

Join me for a spot of tea at one hellacious overlook

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A welcome sign after a long uphill hike on the Superior Hiking Trail yesterday. Photo: Bob King

After 2 1/2 hours of hiking in the boreal wilderness yesterday, I finally reached my goal – a high point on a ridge line nicknamed the Hellacious Overlook. I sat down to enjoy the spectacular view of hills, beaver ponds and Lake Superior, fired up my small stove and heated water for tea. When I turned back to look again at the scene, to my great surprise, two tiny white poodles stared quizzically at me from the trail. Now where did THEY come from? Not exactly the moose I’d been hoping to see.

Soon their owner appeared along with his friends and family. I joked that had I known they were coming, I would have brought more cups so we all could enjoy an afternoon tea. We passed our time together on that hilltop remarking on the view, the weather and even the recent northern lights show. Honest, I wasn’t the one who brought up the aurora. Still (scratching my head) why does astronomy always seems to come up whenever I’m in a group of people?

Cloud shadows and afternoon sunlight stripe Lake Superior near Hovland, Minnesota late yesterday. Photo: Bob King

Something about the way sunlight fell on Lake Superior reminded me of pictures of Saturn’s rings sent back to Earth by the orbiting Cassini space probe. From the hilltop, the oblique view of sunlight and cloud shadows over the lake made a stack of alternating dark and light stripes.

Another wonderful Cassini photo of Saturn's rings and four of its moons. The largest is Titan (3,200 miles across), while hovering in the foreground is brighter Dione (698 miles). Pandora (50 miles) is at right and tiny Pan (17 miles) in the ring gap at left. Credit: NASA/JPL-Caltech/SSI.

Sure enough, I ran across a lovely image this morning released in the past week showing a quartet of moons against the backdrop of the nearly edge-on ring plane. So many of these Cassini images are artistic masterpieces not only because their subject matter is alien and beautiful, but also because the team, under the leadership of Dr. Carolyn Porco, has a great feel for what makes an excellent photo. Porco describes the Saturn system as “splendid beyond compare”. See here here in this video talking about her two favorite Saturnian moons, Titan and Enceladus.

The moon tonight will be located at the same place tonight that the sun will be on the winter solstice. Created with Stellarium

October’s been a good month in northern Minnesota for sky watching. Every clear night gives us the opportunity to see a celestial version of the Hellacious Overlook. Tonight the thick crescent moon will float in front of the stars of Sagittarius the Archer better known as the “Teapot”. Although it will be difficult or impossible to see due to moonlight, the Milky Way flows like a wide stream across the western side of the constellation in the manner of steam from boiling water in the pot. Since the sun and moon (planets, too) follow the same highway in the sky called the ecliptic, we can use the moon to see where the sun will be in advance. Because the moon revolves around the Earth much faster than the Earth revolves around the sun, the moon mimics a full year of the sun’s movement in the celestial sphere in the same time it takes to orbit Earth -  just under a month.

This particular evening, the lunar crescent will lie almost exactly where the sun will be on the first day of winter on December 22. So if you want to picture in your mind’s eye where the sun will be at its lowest ebb, give the moon and the stars of the Teapot a look tonight. If the thought sends a chill down your back, may I suggest a hot cup of tea?

Hey Pluto, come meet your new brother

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Geese fly toward the crescent moon at dusk last night. Photo: Bob King

I was surprised how easy it was to see Venus and the moon last night. 20 minutes after sundown the crescent stood out sharp as scythe in the west. Well off to the moon’s right Venus was unmistakeable. I got the camera out to take a few exposures when a flock of geese came honking from my left. About half the crew flew near enough in the moon’s direction to create the scene above. Things unexpected are often the greatest of life’s little joys. Honk on!

The moon and Venus (tick mark, far right) a half-hour after sunset last night in the southwestern sky. Photo: Bob King

News came this week that astronomers had accurately measured the diameter of the distant dwarf planet Eris and found it to be nearly identical to that of the dwarf planet Pluto. Last November, astronomers predicted Eris would pass in front of distant background star, briefly blocking it from view in an event called an occultation. When a star is occulted or eclipsed, you’re literally standing in its shadow much like standing in the moon’s shadow during a solar eclipse. By precisely measuring how long the star dims as seen from locations around the globe, scientists can determine an asteroid’s diameter and shape.

Artist impression of the distant, frost-covered dwarf planet Eris located 9 billion miles from sun. That's three times farther than Pluto. Credit: ESO/L. Calçada

Observations were attempted from 26 locations along the predicted path of the dwarf planet’s shadow but only two sites with three telescopes total were able to observe the event. All three recorded the sudden drop in brightness as Eris crossed in front of the distant star. Later analysis of the data showed that the dwarf planet was nearly spherical and 1,445 miles (2326 km) in diameter. Pluto is likewise spherical and between 1,429 and 1,491 miles (2300-2400 km) across. Pluto’s diameter is not known as exactly as Eris’s because its atmosphere gives it a fuzzy edge adding a bit of uncertainty during occultation timings. Still, they’re close enough to be twins.

This diagram shows the path of a faint star during the occultation of the dwarf planet Eris in November 2010. Two sites in South America saw the faint star briefly disappear as its light was blocked by Eris and another recorded no change in brightness. Credit: ESO/L. Calçada with editing

It was also discovered that Eris is one of the most reflective objects in the solar system on par with Saturn’s icy moon Enceladus. The bright surface of Eris is most likely composed of a nitrogen-rich ice mixed with frozen methane coating the dwarf planet’s surface in a thin and very reflective icy layer less than one millimeter thick. To determine a distant object’s surface composition astronomers use spectroscopes that identify minerals and compounds by the sunlight they reflect back to us.

“This layer of ice could result from the dwarf planet’s nitrogen or methane atmosphere condensing as frost onto its surface as it moves away from the Sun in its elongated orbit and into an increasingly cold environment,” said Emmanuel Jehin, who contributed to the study. The ice could then turn back to gas as Eris approaches its closest point to the Sun, at a distance of about 3.5 billion miles. The surface temperature of Eris is about -296 degrees Fahrenheit … on the day side!

Interestingly, Eris was the object that got the ball rolling on Pluto’s demotion from planet to dwarf planet back in 2006. When Eris was discovered in 2005, astronomers realized it was big and just one of a number of large asteroids – many awaiting discovery -  in the distant outer asteroid belt beyond Neptune called the Kuiper Belt. This realization led to the creation of a new class of dwarf planets. Five dwarf planets are currently recognized: Pluto, Eris, Haumea, Makemake and Ceres (located in the main or inner belt of asteroids).

Will the Ghost Nebula ring your doorbell this Halloween?

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Let the newly-minted crescent moon be your guide to Venus tonight. Created with Stellarium

Was finding Venus a little too challenging earlier this week? I thought so. Maybe tonight it will be easier with the help of the crescent moon. If you have an open view to the southwest, look about 15-20 minutes after sunset for the fingernail moon. Venus is just one fist-width at arm’s length to its right and a little below. Venus also has phases just like the moon. Tonight through a telescope it’s 95 percent illuminated or nearly a “full moon”. Over the coming months, the planet will slowly wane to half and then crescent while growing larger and brighter as it approaches the Earth.

Now that's what I call scary. The Ghost Nebula, also known vdB 141, was included in a catalog compiled by astronomer Sidney van den Bergh. Stars embedded in the nebula cause it to glow. Click to enlarge. Credit: T.A. Rector/University of Alaska Anchorage, H. Schweiker/WIYN and NOAO/AURA/NSF

With Halloween coming up, scary creatures will soon be roaming the night in search of sweet treats. Answer that knock at your door or else. Fearful forms are plentiful in the sky overhead, though unlike children, they expect nothing in return.The eeriest are found among the many clouds of starlit gas and dust called nebulae that riddle our galaxy’s spiral arms. The Ghost Nebula in the constellation Cepheus the King is one of the best when it comes to inspiring fear in its viewers.

A week ago astronomers announced the discovery of the youngest planet yet found named LkCa 15b. It's forming in a disk of dust and gas around a young star 450 light years away. In a similar way, planets formed around our sun 4.5 billion years ago. Click image to read more.

Spooky forms reach from this giant cloud of dust that’s two light years across and some 1,200 light year away. The nebula’s curious shape is made visible by dust that reflects the light of several stars buried within the cloud. The brownish-yellow tint is there for the same reason sunsets are red and orange — as starlight streams through the fine dust, the blues and violets in the stars’ light are scattered away, leaving only the warmer yellows to reach our eyes.

Nothing is at rest in the universe. In the coming millenia, the Ghost Nebula will stretch and shrink in ways we can only imagine as pockets of cold dust and gas fall together under the force of gravity to form new stars and perhaps new planetary systems. Something similar happened 4.5 billion years ago when the sun and solar system took shape from a similar nebulous cloud. From stardust to treat-or-treaters – the thought of such a miraculous transformation is almost frightening … in a good way.

Aurora spectacle from outer space

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The Midwestern U.S. at night with a bright display of the aurora borealis over Canada as seen from 220 miles high through a cupola window of the International Space Station. The "Sickle" of Leo the Lion is at top. Click the photo for a larger, unlabeled version. Credit: NASA

Just this week, NASA’s Earth Observatory released a timely photo of the northern lights over the U.S. Midwest and Canada in their weekly e-newsletter. It was photographed by one of the Expedition 29 crew members on board the International Space Station (ISS) on September 29. Grid-like roads and sprawling cities are illuminated by the familiar orange of sodium vapor streetlights, while the aurora is bright enough to make the cloud tops glow green. If you really want to have fun, take a look at this video compiled with multiple still images from the flyover. You’ll feel like you’re flying through space – it’s breathtaking. Since the ISS tracks northeast, the aurora gets closer and closer as the video plays. Give it a minute to load and you won’t be disappointed. I also found a youtube version, but the resolution’s not as good.

Photo taken today by the Solar Dynamics Observatory of the coronal hole that might spark more auroras. Credit:NASA

As for upcoming auroras, there’s a chance for some for the northern U.S. and Canada Friday and Saturday nights as a hole in the sun’s corona or outer atmosphere rotates to face our planet’s direction. Coronal holes are literally holes or openings in the corona where high speed streams of electrons and protons can escape the sun unfettered by the magnetic fields that would otherwise contain them. Some holes can last several months. Every 27-day rotation brings them back in view, giving us a repeat chance for northern lights. In my personal experience, coronal hole auroras are typically “quieter” and less dramatic than what many of you saw two nights ago.

A thick, brilliant band of northern lights crosses Canada and the northern U.S. this past Tuesday evening as recorded by Defense Meteorological Satellite Program's polar orbiting satellite operated by the U.S. Dep't of Defense. It's amazing to see this section of the larger aurora oval expand southward into the states. Credit: Created by Paul McCrone

As long as we touched on the space station, here are some additional times for watching it the next few evenings for the Duluth, Minn. region. For times for your town, log on to Heavens Above or type your zip code in at Spaceweather’s Satellite Flybys site.

* Tonight Oct. 27 starting at 6:14 p.m. in bright twilight across the northern sky moving west to east. Second pass at 7:50 p.m. in the northwest. Watch for the ISS to fade out as it enters Earth’s shadow just below the North Star about three minutes later.
* Friday Oct. 28 at 6:52 p.m. across the northern sky.
* Saturday Oct. 29 at 7:30 p.m. Enters Earth’s shadow and fades away below the familiar W of Cassiopeia. Use binoculars to watch the station’s color change from pale yellow to deep red as it races through another sunset.
* Sunday Oct. 30 at 6:32 p.m. Fades out right next to Jupiter low in the eastern sky about five minutes later.
* Monday Halloween at 7:09 p.m. An ideal time to show the kids while you’re out with them trick-or-treating. The ISS will make a high, brilliant pass across the top of the sky.

Jupiter closest to Earth this week and a splendid sight

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Jupiter and friends as you face east around 9:30 p.m. local time. The Pleiades or Seven Sisters star cluster is about 3 outstretched fists to the lower left of the planet. A fist below it is another star cluster in the shape of the letter V called the Hyades. Further off to the north (left), look for the big "pentagon" of Auriga the Charioteer. Maps created with Stellarium

By now many of you have seen the big, bright, blazing “star” in the eastern sky at nightfall or perhaps noticed it low in the west at dawn. Either way, you’re looking at Jupiter, the brightest planet easily visible in the sky this month. Jupiter owes it brilliance to its giant size (88,000 miles or 11 Earths) and perpetual cloud cover. Like Venus, when we look at Jupiter, we see only clouds and atmosphere. Whatever solid surface this world has is hidden beneath thousands of miles of hydrogen, helium, ammonia and water vapor.

Every 13 months Jupiter and the Earth line up together on the same side of the sun at opposition. This year Jupiter is very near perihelion or closest to the sun around this time. That extra closeness to Earth will make it appear bigger and brighter in the sky than at more distant oppositions. Illustration: Bob King

This Friday evening the 28th Jupiter is at opposition to the sun in the constellation Aries the Ram. When a planet’s at opposition, it lines up with Earth on the same side of the sun. All the outer planets from Jupiter to Neptune reach opposition once a year, when the speedier Earth laps the
slower-orbiting outer planet. As seen from our planet, Jupiter is directly opposite the sun in the sky, rising in the east at the same time the sun sets in the west. It passes due south around 1 a.m. daylight time, when it’s highest in the sky, and then descends in the west, setting at sunrise.

Jupiter photographed on October 22. The two most prominent bands are the South (bottom) and North Equatorial Belts. Also seen are the Great Red Spot and two dark red cyclonic storms in the North belt. Credit: Damian Peach

Not all oppositions are created equal. Because the planets orbit in ellipses with the sun off to one side rather than perfectly concentric circles centered on the sun, Jupiter’s distance from the sun varies around its orbit. At closest, it’s 461 million miles from Sol and 507 million at farthest.

Now it just so happens that Jupiter was at perihelion or closest to the sun this past March. Since Earth is pulling up alongside the planet just 7 months after its perihelion, this opposition will be one of the best ever, with Jupiter blazing at magnitude -2.9, about the same intensity as the International Space Station. That’s not all. Close means big. Jupiter will grow to a diameter of nearly 50 arc seconds or almost 1/30 the size of the full moon. I know that sounds small, but it’s large for a planet, and means you see more detail and color compared to more distant oppositions.

With all that atmosphere to play with, Jupiter’s famous for its colorful and changeable cloud bands. The dark stripes you see in photos and small telescopes are called belts. The North and South Equatorial Belts are thick and dark, making them easy to spy. Separating the belts are the lighter zones. Because the planet is primarily gas and spins rapidly – an entire Jovian day is just under 10 hours long – it bulges noticeably at its equator. Try your hand at seeing this in a small telescope. Once you know what to look for, you’ll might be surprised that Jupiter looks slightly “flattened” instead of spherical. The difference between equatorial and polar diameters is significant – 6,322 miles or 80 percent the size of Earth!

View of Jupiter and its four moons tonight around 9 p.m. CDT as seen in a typical small telescope. South is up and west to the left.

Finally, Jupiter’s four bright moons provide endless fun and interest as they cycle around the planet like a solar system in miniature. Depending how close or far each is from the planet at the time of observation, binoculars will show from one to four moon as tiny stars lined up very close by. Any small telescope magnifying 20x and higher will easily show them all provided they’re not hiding in front of or behind the planet. Medium-sized telescopes from 6-inches and up under steady skies and higher magnifications (200x) will show each moon as a tiny disk.

Comet Elenin fades further as it glides through Gemini and into Auriga today Oct. 26 through Oct. 30. Created with Chris Marriott's SkyMap software

One last note – I was asked for a chart showing where Comet Elenin can be found. Be aware that it’s extremely faint and to my knowledge has been seen by only two expert comet observers. Still you might like to know that Elenin is still there as a faint remnant dust cloud. It travels from Gemini into Auriga this week.

WOW! Aurora sparks excitement across the country

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"With my friend Tony we drove into the country hoping to find some aurora away from city lights. What we found blew us away, it was a once in a lifetime experience, and was by far my best aurora experience ever." Photo by Malcolm Park of Whitby, Ontario, Canada

First off, I want to thank everyone who sent along a comment or observation of the aurora last night. It was thrilling to read how spectacular the display was and how far and wide it was seen. People wrote from Arkansas, Kansas, Maryland, Ontario and Tennessee and even Minnesota, where most of the state was under a heavy blanket of clouds. I stepped outside and checked the sky often during the night, but the clouds never budged. Just the same, your excitement was so palpable, it almost felt like being there.

According to the folks at the National Oceanic and Atmospheric Agency or NOAA, the geomagnetic storm that gave rise to the northern lights was a class G2 or moderate storm. Disturbances to Earth’s magnetic field caused by the sun are rated from G1 – minor with aurora visible in along the borders of northern U.S. states – to G5, which can seriously affect power grids, cause damage to satellite components, blank out radio communications and send auroras all the way down to Florida and southern Texas.

Red, the most exciting color in auroras and not often seen, was widespread in last night's display. This photo was taken by Shawn Malone of Marquette, Michigan. His reaction to the display was similar to what many people felt who saw it -- "WOWOWOWOW! Incredible!"

In last night’s storm, a stream of plasma shot connected to a solar flare or other activity on the sun belted a cloud of high-speed electrons and protons in the Earth’s direction. The average speed of one of these clouds or sprays is over 300 miles per second. When it reached the Earth’s vicinity yesterday afternoon, it strongly compressed the big magnetic bubble around the planet called the magnetosphere, squeezing billions of electrons straight into our atmosphere  some 60 to 200 miles overhead.

Fisheye-lens view of the incredible red auroral rays taken by John Chumack in Yellow Springs, Ohio.

When the electrons strike the oxygen and nitrogen atoms at that altitude, they excite them into a higher energy state. As the atoms return to their normal “ground” state, they emit light of different colors. The most commonly seen hue is green from excited oxygen. Because many auroras are faint, this color frequently appears pale white to the eye, but a time exposure with a camera will clearly reveal their green color. Red also stems from oxygen but it occurs higher up, which is why green rays are often topped by red. The strongest color emissions from nitrogen are in the deep violet end of the rainbow spectrum and invisible to the human eye. Another nitrogen excited state creates the red lower border to the aurora.

Artist rendition of Earth's protective magnetic bubble called the magnetosphere. As material from the sun streams toward the Earth, much is deflected away, but sometimes we take a hit. Subatomic particles like electrons and protons find their way in, where the magnetic field lines guide them into the upper atmosphere to spark auroras. Credit: NASA

Once inside the bubble and on their way down, electrons follow the invisible lines of magnetic force in Earth’s magnetic field. They’re the same ones you see when you sprinkle iron filings around an ordinary magnet. Electrons spiraling around the many approximately parallel field lines in the polar regions create the multiple parallel rays that are so characteristic of the northern lights.

Another colorful view of last night's northern lights from Shawn Malone of Marquette, Michigan

After a big auroral display, there will often be some “leftovers” the next night or two. I checked the NOAA space weather forecast this morning to see what might be in store. Although solar activity is presently low, lingering effects of the sun’s coronal mass ejection should continue through today and possibly into tonight. Keep an eye on the forecast and the Kp index, which is a gauge of changes in Earth’s magnetic field as measured by surface instruments. Make note of the rightmost bar in the graph at the Planetary Kp-index Monitor. This is the most recent plot of activity. If it’s green, meaning the index is below 4, no storm is in progress. A yellow bar at K = 4 indicates activity is picking up and a red bar (K = greater than 4) signals that’s it’s time to put on your coat and go out for a look!

Aurora alert for tonight Oct. 24-25

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Plot of auroral activity in Earth's northern hemisphere taken based on observations by the POES satellite at 6:49 p.m. CDT. Red indicates high activity. Credit: NOAA

A coronal mass ejection (CME) or plasma spray from the sun bumped into Earth’s magnetic field starting around 1 p.m. Central time today and is likely to stimulate auroras for northern latitudes including the northern U.S. and Canada. CMEs are not uncommon, so this is not an extraordinary event, but it could mean aurora borealis in the northern sky overnight. Keep your eyes peeled and let us know if you see any. We’re cloudy here in Duluth, Minn. so mine eyes will not see the glory.

To monitor activity, click this link to the Kp index. If you see a red bar or a series of red bars on the site, it’s worth your while going out for a look.  They indicate high magnetic activity and likely auroras.

UPDATE 9:40 p.m. CDT: We’re getting dozens and dozens of reports of vivid red, blue and green auroras as far south as Missouri, Oklahoma and Tennessee. The display is spectacular! Don’t miss it.

** Please see current Oct. 25 blog at www.astrobob.areavoices.com for pictures and more information

Venus returns at dusk and how water helped us to see

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Venus is not easy to find but with a good horizon and determination you will succeed. The map shows the planet as seen from mid-northern latitudes about 15 minutes after sunset this evening. Mercury will require binoculars. Created with Stellarium

If you’ve been pining for Venus, the goddess of beauty, your days of anguish will soon be ending. Venus has returned to the evening sky after a long daytime engagement with the sun. Put plainly, it’s been too near the sun to observe, but beginning now and continuing for the remainder of the year, the brightest planet will part ways with the keeper of the light and inch its way into the night.

Venus won’t easy … at first. Tonight it will be visible for a brief time starting about 15 minutes after sunset. Look very low in the southwestern sky some 3 degrees above the horizon a little more than one outstretched fist to the left of the sun. Binoculars will help you spot this single bright “star”. If your skies are very transparent, you might even get to see Mercury just 2 degrees below Venus and very close to setting. Over the next few evenings, Venus and Mercury will remain near one another and remain a challenging duo. Of course, if you live in the southern U.S., the two planets are tipped are at a steeper angle to the horizon and noticeably easier to see.Come November, Venus will set later and gradually become easier to see.

The lunar crescent -- just 2 1/2 days before new -- cuts a sharp figure in the sky before sunrise this morning. Photo: Bob King

My daughter came up to visit from college over the weekend. She always marvels at how dark it is where we live and how many stars she can see compared to the Big City. When I helped her scrape frost from her car windows early this morning, the waning crescent moon sent us a small smile. There are only two days left to see the moon at dawn before it new moon on the 26th and its return as a crescent in the evening sky.

Dewdrops not only focus the sun into tiny bright images, they also magnify the veins of the leaf. Photo: Bob King

The other morning while dashing off to work, I was stopped by the sight of a dew-dabbed leaf in my front yard. Looking closely, you can see how the curved surfaces of the drops act like the curved lenses in a pair of glasses, binoculars or telescope to focus the sun’s image into tiny brilliant spots on the leaf’s surface. The convex drops also serve as ephemeral magnifying glasses, too. Take a look at the enlarged view of the leaf vein under the second drop to the left of the big one at top.

I wonder if raindrops or dewdrops were our ancestor’s first inspiration for using rounded, clear objects to magnify, focus and clarify both distant and nearby scenes. While raindrops aren’t very handy when you need a lens, the same principle of curved surfaces can be applied to glass-making, an art discovered around 5000 B.C. The earliest known lens to currently be unearthed was made in the year 750 B.C. and found at the Assyrian palace of Nimrud in modern-day Iraq. It’s believed to have been used as a  magnifying glass or as a burning-glass to start fires.

The infamous Nero, who become Roman Emporer in 54 A.D., watched gladiator fights through a monocle apparently made of emerald crystal. It’s unclear if it was ground out to correct nearsightedness or if he simply was following a popular belief at the time that vision is improved and refreshed when seen through the green gem.

Reading stone from the Middle Ages

During the same era, glass globes filled with water were used to magnify written documents to make them more legible to those like me whose near-vision declines with age. Later, hemisphere-shaped glass lenses called reading stones were used to magnify text for easier reading. Around 1284, the Italian Salvino D’Armate is credited with inventing the first wearable pair of eyeglasses. More than 300 years would pass before Dutch spectacle makers in the late 16th century would place two different lenses one behind the other to create the first telescope.

In researching this information, I came across a fascinating early reference to a telescope from the works of Roger Bacon, the English philosopher and Franciscan friar who was one to advocate the modern scientific method as a tool to understand the world.

This from his Opus Majus: “For we can so shape transparent bodies, and arrange them in such a way with respect to our sight and objects of vision, that the rays will be reflected and bent in any direction we desire, and under any angle we wish, we may see the object near or at a distance … So we might also cause the Sun, Moon and stars in appearance to descend here below.”

And that was in the year 1268!

The ghost of Comet Elenin haunts the morning sky

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Comet Elenin is a very faint, elongated streak as photographed through a 4-inch refracting telescope early this morning from the GRAS network in New Mexico. The picture covers about 2 degrees from side to side. Credit: Rolando Ligustri

For those of you who checked yesterday’s blog, you already know that the German ROSAT (Roentgen X-ray satellite) burned up in the atmosphere last night between 8:45 and 9:15 p.m. CDT. To the best of my knowledge, after digging around various websites, it appears to have come down over the Indian Ocean north of the coral atoll Diego Garcia. Too bad there’s so much water on this planet otherwise we’d have lots more satellite parts and meteorites in our collections.

I wanted to share the most recent pictures of Comet Elenin with you. Amateur astronomers have been busy the past few mornings losing sleep photographing and trying to see the comet through their telescopes. The moon is out of the way and Elenin is presently high up in a dark sky after about 3 a.m. These are the conditions we’ve been waiting for for months! And finally, enough pictures have been taken to confirm that the comet is really there.

Another view of Comet Elenin taken this morning with a 10-inch wide-field telescope in Austria. Credit: Michael Jäger

The photos show a faint, elongated cloud of spreading comet dust, the last gasp of what was to be fall’s best bet for a bright comet. Its ghostly appearance hints at how difficult it’s been to see with one’s own eyes in a telescope. To date, only one observer – Juan Jose Gonzalez – has spotted this wispy remnant from his mountaintop observing site in northern Spain using an 8-inch telescope. Jacob Cerny of the Czech Republic is the second person to observe it, but it was so challenging, he listed his observation as “uncertain”.

Take a look at Elenin’s morphology or form. It reminds me of the Headless Horseman from The Legend of Sleepy Hollow. Indeed, the head of the comet is no longer a separate entity as it was before the August breakup. All is one galloping streak of light.

Comet Elenin will continue along its orbit as it slowly moves farther from Earth with each passing day, fading and expanding as it does and likely to never return. Even though this demure object has been wrongly credited with causing earthquakes and other mayhem, the bright side has been a lively discussion of comets and other topics astronomical. These are good things.

Several readers have mentioned or made reference to Arcturus in recent days. I thought it would be an opportune time to give the star – the 4th brightest in the sky after Sirius, Canopus and Alpha Centauri – one last evening farewell before we get up 11 hours later at dawn to welcome it back. What?

Use the handle of the Dipper to "arc" your way to Arcturus during the early evening. This map shows the sky facing northwest around 7:30 p.m. local time. Maps created with Stellarium

Arcturus, an orange giant star with a distinctive warm tint, hovers low in the northwestern sky off the handle of the Big Dipper on late October evenings. It’s best to catch it an hour or so after sunset during evening twilight when the star is high enough to see relatively easily. As dusk melts into darkness, try looking two outstretched “fists” directly above Arcturus for the little horseshoe-shaped constellation Corona Borealis the Northern Crown.

If you have an open view to the northeast during early dawn, you can watch Arcturus return to view - truly, a star for all seasons! This map shows the sky facing northeast around 6:15 a.m. tomorrow morning.

Arcturus makes its first evening appearance in late winter in the northeastern sky. By May and June, it’s high in the south at twilight’s end; its warm light has come to be associated with warming temperatures and the arrival of summer. In fall, the star drops off into the northwest and finally sets, but because nights are better than 12 hours long in late October, Earth’s rotation carries it back into view for observers in mid-northern latitudes. Watch for its winking red light in the northeast at dawn. In a sense, we never lose Arcturus.

The star’s northern location on the celestial sphere is also responsible for its continuous visibility. The closer a star is to the North Star – the pivot-point star due north that remains in one spot in the sky – the longer it remains visible. All stars within a circle with a radius the same as your latitude never set at all. They’re called circumpolar stars because they circle around the North Star day and night without ever touching the horizon. While Arcturus is not quite circumpolar for Duluth, Minn., the fortuitous combination of northerly location and long nights allow it to be seen every month of the year.