5 hours, 48 minutes and 46 seconds … nothing but trouble

Earth revolves around the sun in a bit more than 365 days, the reason for all the Leap Year fuss. Illustration: Bob King

We got hit with a blizzard in Duluth, Minn. Wednesday and my planned blog on Leap Day was delayed – to say the least. So let’s get to it before February 29 comes to a quick end.

While we normally think of Earth revolving around the sun in 365 days, it actually does so in 365 1/4 days. Those extra quarter days add up to one full day in four years, which is added into the calendar every fourth year as February 29. The Leap Day was introduced by none other than Julius Caesar in 46 B.C.

If we ignored the quarter day and carried merrily along, we’d soon discover the calendar would fall behind by one day after four years. No big deal, right? But after only 100 years the slip would amount to about 24 days. Instead of the first day of spring starting on March 21, it wouldn’t begin until mid-April.

Two men who helped straighten out our calendar so it synchronizes with the Earth's orbit around the sun - Julius Caesar (left) and Pope Gregory XIII

To keep everything tidy, so that our calendar year, which is based on a whole number of days, matches up with the true time it takes Earth to orbit the sun, we add a Leap Day every four years. Problem solved, right? Well not quite. Earth’s precise orbital period is 365 days, 5 hours, 48 minutes and 46 seconds. That’s 11 minutes and 14 seconds shy of a quarter day. So that we don’t overcompensate with Leap Days, we omit them three times every 400 years based on this simple formula:

* Leap year occurs in years divisible by four, except for those divisible by 100 and not divisible by 400. This means that 2000 and 2400 are leap years, while 1800, 1900, 2100, 2200, 2300 and 2500 are not leap years. That last adjustment to the calendar was made by Pope Gregory XIII in 1582. Our calendar and Earth’s orbital period will now be congruent for a very long time – 3,300 years to be exact – when they’ll diverge again by one full day. Come that time, who knows if we’ll still even be using calendars. Something to think about as March tiptoes in after February’s long-winded exit.

Auroras way up north plus the moon visits a famous star cluster

Andy Keen, who lives in Northern Lapland in Finland, had a great view of the northern lights last night. "The colours were fabulous - green, red, pink, turquoise, neon blue - the full works," he said. Details: 14mm lens at f/2.8, ISO 800 and 4-second exposure. Click image to see more photos and a video on Keen's website.

Bright auroras have dressed up the Arctic sky the past two nights after the sun’s wind of charged particles – electrons and protons – pried an opening in Earth’s magnetic field and spiraled down into the upper atmosphere. There’s still a possibility for aurora tonight primarily for those living in the far north. Take a look if clear skies are in your forecast. We’ve had clouds in my town and a now a blizzard on its way, so my eyes will be blinkered for a while.

The moon will be near the Seven Sisters star cluster tonight (Feb. 28) and the Hyades cluster tomorrow night. Created with Stellarium

Tonight the quarter moon is tucked under everyone’s favorite naked eye star cluster called the Pleiades (PLEE-uh-deez) or Seven Sisters. The cluster is shaped like a tiny dipper, and when the moon’s not quite so close to it, most of us see six or seven stars with ease. Binoculars show dozens more. The Pleiades, located about 400 light years from Earth, is a relatively young group of stars compared to our sun; their birth from a massive cloud of dust and gas happened during the age of the dinosaurs a mere 100 million years ago. It’s also the brightest star cluster in the sky.

The Hyades form a distinctive V-shape that represents the face of Taurus the Bull. The bright star at left, called Aldebaran, is a foreground star and not a member of the cluster. It's often referred to as the bull's eye. Photo: Bob King

One outstretched fist to the left or east of the Seven Sisters is a larger, looser star cluster called the Hyades (HY-uh-deez). It’s the closest star cluster to our solar system at a distance of 151 light years. That’s one of the reasons it appears larger and more spread out than the neighboring Pleiades. The Hyades occupy a volume of space some 30 light years across and are moving through space together like a school of fish.

Despite its closeness, the Hyades are fainter than the Pleiades because its stars are more than six times older with ages around 625 million years.

Clusters are born with stars of all different masses. Mass or the amount of stuff a star has determines its temperature, color and how fast it devours the nuclear fuel in its core. The biggest, brightest ones burn up their fuel fastest, either ending their lives as supernovas or evolving into dim white dwarfs. Because of the Hyades rather advanced age, its brightest stars have either blown up or faded away, leaving the smaller, fainter but more frugal fuel users – basically stars with masses similar to or less than the sun – dominating the herd.

Astronomers uses the "eyes" of the Earth on a particular date and then again six months later to measure a nearby star’s parallax or shift against the more distant background stars. Illustration: Bob King

The Hyades are probably the most famous star cluster in the world of astronomy, even eclipsing the Pleiades in importance. Why? Because they were a key steppingstone into deep space as astronomers looked for ways to determine distances to remote stars.

Astronomers use parallax, the apparent shift of nearby stars against the distant background stars when seen from two widely-separated points of view, to measure the distance to the closer stars. You can see a parallax shift when you hold a finger at the end of your nose while opening and closing your right and left eyes in a blinking pattern. Your finger will appear to shift back and forth against the distant background. Measure the distance between your eyes and the angle your finger makes, and you can find the distance to your finger with simple trigonometry.

In this illustration, you can see how a star shifts against the background ones when photographed through a high powered, professional telescope on opposite sides of Earth’s orbit. Illustration: Bob King

To measure the distance to  a star using parallax, astronomers need a super-wide set of eyes, because even the closest ones are so incredibly far away, they show only minute shifts.

That’s where Earth’s orbit comes in (see above). We measure the star’s position against the background stars on one side of our orbit and then again six months later when we’re on the other side. Since we know the baseline length – 180 million miles – and can measure the parallax shift, we can easily calculate the star’s distance. It works beautifully -  at least out to about 300 light years. After that, the shifts are too small to measure directly.

That’s where the Hyades come in. The cluster contain lots of stars of many different types, and since it’s so close, we can use parallax to measure its distance. Next we find a cluster with similar stars but too far away to show a shift and measure the brightnesses of those stars. Since we’ve determined that its stars are the same types as those in the Hyades but say, 100 times fainter, we know they must be 10 times farther away or approximately 1,500 light years from Earth. Bingo! We’ve taken another step deeper into the cosmos.

(Just an FYI – The intensity of light falls off as the square of the distance. It’s known as the inverse square law. 100 times fainter = 10 times farther. 10,000 times fainter = 100 times farther.)

Using the Hyades stars this way, astronomers have hopscotched into the depths of the galaxy. A most clever way to “expand” our universe, don’t you think? To learn more about parallax, please click HERE, and don’t forget to send the Hyades a “thank you” this week.

Milky Way from a hilltop and the starry gazelle leaps again

The view yesterday from atop a hill in the my neighborhood. You can clearly make out the branches on the foreground trees. The background ones are little more than brown haze. Photo: Bob King

Yesterday afternoon I stood atop a hill with snow coming down and the trees all fuzzy in the distance. Then it hit me like a snowball on the back of the neck – the forest helps us understand the appearance of the Milky Way. Forget the snow for a minute and think about the trees. Up close you can distinguish individual trees and their branches, but as you gaze into the distance the trees stack up until they form a nearly uniform haze of branches and trunks. To the unaided eye, it looks like a fuzzy grey-brown carpet, but in binoculars, you can again distinguish individual trees – up to a certain distance.

Brighter and closer stars are visible spread across the sky and even in front of the Milky Way, but the majority are so far away - tens of thousands of light years - their light blends into a hazy band. Photo: Bob King

So it is with the Milky Way. The brightest and closest stars stand out clearly, but when we look into the Milky Way band into the greatest thickness of stars in our galaxy, they stack up to form a nearly uniform, unresolvable haze. That’s when binoculars and telescopes make a difference just as they do in distinguishing fine details in a distant landscape. Optical aid helps us separate and see individual stars and star clusters. Just something to think about the next time you’re out enjoying a vista.

Three pairs of stars between the Big Dipper and Leo represent hoofprints of a gazelle in the sky. Created with Stellarium

Mars is now up in the eastern sky in Leo in the early evening. My neighbor asked about that “bright star” in the east around dinnertime, and it was easy to answer his question. Not far from Mars is 1st magnitude Regulus, which heads up the constellation Leo the Lion. Well above and north of Leo is the Big Dipper, familiar to nearly everyone, and between them a delightful asterism or star pattern named the Three Leaps of the Gazelle.

The tracks are composed of stars belonging to Ursa Major, the sky's Great Bear. Credit: William Jamieson /Urania's Mirror

The three leaps, which you’re free to envision as deer tracks,  is an older Arabic star group composed of three sets of paired stars that resemble starry hoof prints in the sky. None of the pairs is especially bright, but the six stars are stand-outs because they form a striking repetitive pattern. All of them belong to Ursa Major or the Great Bear which itself contains the sky’s most famous asterism: the Big Dipper. Yes, the Big Dipper is not a constellation but rather the brightest stars in Ursa Major the Great Bear.

Legend has it that the gazelle was startled by the lion as it drank from a pond near the lion’s lair. It sprang up and leapt across the sky from east (left) to west leaving impressions in the mud. Seeing these stellar tracks is a reminder that soon the ground will be softening as February slowly gives way to March later this week.

Put your stamp of approval on a new Pluto stamp

Families look at the moon and planets through telescopes last night at Hartley Nature Center in Duluth, Minn. Photo: Bob King

“It looks like the moon cut in half,” said the little boy after he looked at Venus through the telescope last night. And so it did. We had some interference from high clouds, but it was clear enough to see the bright alignment of Venus, Jupiter and the moon.

Members of our local Arrowhead Astronomical Society set up telescopes and gave presentations to a nice group of kids and parents. We had a blast. The moon was near Venus last night and will pull up alongside Jupiter tonight, so if you didn’t have a chance to see the show yesterday, check out the sky tonight.

Overhead view showing how far New Horizons has come (in green) and how far it has yet to go (red). An A.U. or astronomical unit is 93 million miles. Credit: NASA

In 2006 NASA launched the unmanned New Horizons probe to the dwarf planet Pluto. Now 2.1 billion miles along on its 3 billion-mile-journey, the craft will fly by Pluto and its four known moons on July 14, 2015.

Today it’s out beyond the orbit of Uranus. That’s so far that a radio signal sent to the craft traveling at the speed of light takes 6 hours and 43 minutes to make the roundtrip back to Earth. Forget about pizza delivery.

While Pluto is no longer classified as a planet, but instead one of the many icy asteroids in the Kuiper Belt beyond Neptune, this will be our first opportunity to study an “ice-teroid” up close.

Clyde Tombaugh at the telescope he used to discover Pluto at Lowell Observatory in 1930. Credit: AP

Pluto was discovered by American astronomer Clyde Tombaugh in 1930 while working at Lowell Observatory near Flagstaff, Arizona. He was looking for the so-called “Planet X”, a postulated planet beyond Neptune thought to be responsible for irregularities in the orbital motion of Uranus. Later calculations showed that there was no need for Planet X once Neptune’s mass and its effects on Uranus were accurately calculated. Tombaugh was so thorough, he turned up the faint, star-like Pluto among the myriad of stars in his photographs and determined that it lay well beyond Neptune. Astronomers at the time thought Planet X had finally been found.

Pluto and three of its moons. A 4th moon called S/2011 P1 was discovered last summer. Pluto is composed of a mixture of ice and rock with a surface temperature of 380 below F. Credit: NASA/ESA

But the more we learned about Pluto, the less it looked like a planet. Its orbit was tipped at a much steeper angle than the other planets and it was puny – only 1,412 miles in diameter or just 12 % bigger than Earth’s moon. Then in the late 20th and early 21st centuries, astronomers using large telescopes with sensitive electronic detectors, discovered many more Pluto-like asteroids. Some of these, like Eris, with a diameter of 1,460 miles, are even larger than the “9th planet”.  That’s why the International Astronomical Union revised the definition of a planet in August 2006. Pluto, along with Eris, Ceres (in the main asteroid belt between Mars and Jupiter), Haumea and Makemake are now classified as dwarf planets.

New Horizons stamp design by Dan Durda

There’s a lot of sentiment to keep Pluto a planet, and who knows, maybe one day it will rejoin their ranks. In the meantime, NASA is petitioning the U.S. postal system this year to commemorate the upcoming Pluto flyby on a new stamp. The previous Pluto stamp in 1990 described the dwarf planet as “Not Yet Explored”.

If you’re a Pluto fan, I encourage you to sign the petition by the March 13 deadline, the date of the 82nd announcement of Pluto’s discovery. The postal service service considers both the merit of a stamp design proposal and the amount of public support for the idea, so your vote counts. Since it can take up to three years to get a new stamp into circulation, NASA is acting now, so it will be available at the time of the flyby.

Moon and planets align this weekend – don’t miss it

What a sky show tonight! Venus and the moon are joined by Jupiter and Mercury in the western sky during evening twilight. Maps created with Stellarium

If it’s clear in the west tonight, your eyes will twinkle with extra added sparkle. The crescent moon slides just a few degrees to the right of Venus, while Jupiter shines above and Mercury below. You’ll want to be out about a half hour after sunset to see Mercury glowing ember-like in the pale orange of dusk just eight degrees above the western horizon. The other three luminaries are much higher in the sky and visible  up to 3 hours after sunset.

I’ve drawn in the ecliptic, the line that defines the path of the planets, just so you can see how flat our solar system is. If it wasn’t, the planets might be all over the sky and never line up as they will be tonight.  In order of brightness, Venus at magnitude -4.2 ranks first by a significant margin, Jupiter does its level best at -2.2 and tiny but feisty Mercury manages a very respectable -1.1, rivaling the star Sirius (-1.4).

See if you can find Venus even before the sun sets tonight. With help from the moon, it's not too difficult to spot.

Have you ever seen a star or planet in the daytime? You’ll have a shot at it this evening thanks to the moon. If the sky is clear and free of haze, you’re ready to go.

Face toward the sun around 4:30-5 p.m. and look high up to the left to find the crescent moon. Now look a little (about 3 degrees to be exact) to the lower left of the moon for a tiny star-like spot of light against the blue. That’s Venus! Feel free to cheat a little by using binoculars first. Make sure you focus them sharply on the moon, then place the crescent in the upper right of the field of view. You should easily spot Venus to the lower left. Lower the binoculars from your eyes and stare at that spot without optical aid. If you can see what looks like a tiny white spark against the blue sky, you’ve nailed it.

The map above shows the moon and Venus for the U.S. Midwest around 5 p.m. For sky watchers in the western states, the moon will be more directly above the planet and the two slightly farther apart. For European viewers, the the moon will lie almost directly to the right of the planet. The moon’s position with respect to Venus changes depending on your time zone, because it’s moving upward and to the east as it orbits the Earth.

How our four bright, shiny objects will appear through the telescope tonight. C=Callisto, E=Europa, Io and G=Ganymede. Illustration: Bob King / Moon photo by Frank Barrett

If you have a telescope that magnifies around 50x and up, Mercury will look like a very tiny gibbous moon, Venus a little more than half-full and all four of Jupiter’s brightest satellites will be beautifully displayed on either side of the planet. And don’t forget the moon. Lots of craters and other interesting features will greet your eye. As always, I hope it’s clear over your neighborhood tonight.

February fireballs really shake things up

Security video captured the Canadian fireball over Saskatchewan, Alberta, Canada

Meteorites seem to be dropping everywhere. First China and now today comes word of fresh cosmic booty on the ground north of the town of Rockhaven (a wonderfully appropriate name) left in the wake of a brilliant fireball that appeared over Alberta, Canada this past Tuesday evening.

The meteor was described as blue-white and as bright as the moon. Some went even further and compared it to the sun. Observers reported hearing low rumbling noises for several minutes after it broke up and disappeared. These are all good signs that material survived the fiery, high pressure flight through Earth’s atmosphere. The first specimens of what appears to be a very fresh meteorite were picked up not long after the fall on a road north of Rockhaven and can be viewed HERE. Yes, one of them is already up for sale!

Another fireball, this time recorded by NASA’s All-Sky Camera in Georgia on Feb. 13

The Rockhaven fall is just one of about a half dozen bright fireball sightings in North America this month. While that number isn’t unusual, their very slow speed and deep penetration into the atmosphere is. Their incoming speed has been around 32,000 mph followed by a rapid deceleration and burnout at some 31 miles high.

A fireball streaks through the sky. Fireballs are defined as meteors brighter than the planet Venus. Credit: John Chumack

“This month, some big space rocks have been hitting Earth’s atmosphere,” says Bill Cooke of NASA’s Meteoroid Environment Office. “There have been five or six notable fireballs that might have dropped meteorites around the United States.” The first one briefly lit up the sky over Dallas-Ft.Worth, Texas on February 1, wowing thousand with a sputtering light as bright as a full moon.

The incoming meteoroids – as they’re known before breaking up and potentially landing as meteorites on the ground – range in size from “basketballs to buses”. When astronomers analyzed their orbits based on photos and eyewitness observations, they all trace back to various locales in the asteroid belt between Mars and Jupiter. Most meteorites are thought to originate from collisions between asteroids that ultimately send fragments toward the Earth and other planets.

Because of this year’s numerous sightings as well as those made by both amateurs and professionals in Februaries past, some astronomers suspect that a stream of meteors they’ve nicknamed the “February Fireballs” intersect Earth’s orbit this time every year. Some studies show a correlation, some don’t. We may soon get a more definitive answer thanks to a network of night eyes.

One of NASA's all-sky cameras keeps watch on the night sky. Credit: NASA

There are currently six all-sky cameras operated by NASA’s All-Sky Fireball Network in north Alabama, northwest Georgia, southern Tennessee and southern New Mexico with many more in the planning stages. Like the ever-watching eye of Sauron in the Lord of the Rings story (sorry for the dark analogy), the cameras photograph the sky with fisheye lenses all night long. When a fireball is seen by more than one camera, astronomers can triangulate its height, speed and even determine an orbit. And once you know an orbit, you can trace the cosmic rock back to its ancestral home.

Scientists estimate that 37,000 to 78,000 tons of meteorite material falls to Earth each year. That number sounds huge, but remember that most meteoroids are broken up into dust from the profound heating and pressure experienced during atmospheric entry and never make it to the ground.

According to NASA astronomer Dr. Steve Odenwald, the Earth intercepts 19,000 meteoroids weighing over 3.5 ounces every day. Of these, only about 10 are recovered by human hunters each year. Our planet is big, very big, and much of what falls does so in the oceans unseen by nearly everyone. That’s what makes finding a meteorite – especially one from a fresh fall – so rare.

Faster than light neutrino result flawed, loose cable to blame

Tracks made by neutrinos in an experiment at CERN. Credit: CERN

Remember last September’s Italian experiment that supposedly detected faster-than-light neutrinos?  Neutrinos, which come in several varieties, are neutral subatomic particles that have a very minute mass and rarely interact with matter. When hydrogen is fused into helium in the sun’s core to produce the light and heat that make Earth a pleasant abode, zillions of neutrinos are created in the process. Most pass right through the sun, speed outward and fly right through the planets as if they weren’t even there. 50 trillion electron neutrinos zip through your body every second!

When the Italian team discovered that their neutrinos completed the journey from CERN Laboratory near Geneva, Switzerland to Gran Sasso Laboratory near Rome 60 nanoseconds faster than a beam of light, even they were skeptical of the result and encouraged others to repeat their experiment. According to one of the key tenets of Einstein’s Theory of Relativity, no material object in the universe can travel faster than the speed of light.

The Gran Sasso National Laboratory is located nearly a mile below the surface of Gran Sasso mountain some 60 miles from Rome. The massive array detects tiny particles called neutrinos. Credit: Paolo Lombardi INFN-MI Rome

And indeed a flaw in the experiment was uncovered this week. Come to find out that a loose cable between a GPS receiver and a computer was to blame. The GPS was used to synchronize the start and arrival times of the neutrinos. When the cable was tightened, the 60 nanoseconds difference disappeared. An additional nail-in-the-coffin was delivered by another group of experimenters working in the same lab in a repeat of the experiment. They failed to detect the radiation that would be emitted by particles traveling faster than the speed of light.

The sun produces trillions of neutrinos as it cooks up hydrogen in its core. Photo: Bob King

One more interesting sidelight about neutrinos. Lest you think they all get away without turning everything and everybody into Swiss cheese, scientists have built special neutrino detectors like Super Kamiokande in Japan to spot their tracks. Detectors there pick up tiny flash of blue light when a neutrino has a rare interaction with a water molecule in a stainless steel tank filled with 50,000 tons of ultra-pure water. Besides being useful for studying the sun’s neutrino output, Super Kamiokande can also detect neutrinos shot out when a star collapses and explodes as a supernova. Because they travel at nearly the speed of light, they escape the star before anything else, giving astronomers a heads-up on what’s happening inside the explosion. Pretty cool.

Einstein can still rest comfortably in his grave that the speed of light – at least for the time being – will remain the ultimate speed limit in the universe. I encourage you to check out the full story for more information.  And before we leave the subject, here’s a  joke I think you’ll enjoy:

“We don’t allow faster than light neutrinos in here”, said the bartender. A neutrino walks into a bar.

* Source for some of the info in today’s blog comes from space.com

Mercury makes its move into the evening sky

Three planets and a crescent moon will light up the western sky shortly after sunset this evening (Feb. 22). Created with Stellarium

Move over Jupiter. Move over Venus. It may be the smallest planet, but Mercury is on its way up into the evening sky. Beginning tonight – and with the help of a very young crescent moon – observers with clear skies and a wide open western horizon can seek the innermost planet alongside the 1-day-old moon. As always, take your binoculars to help in case the sky is less than ideal.

The duo will be well below the Venus-Jupiter line just five degrees or three fingers held together at arm’s length above the west-southwest horizon. The best time to look is starting about 20 minutes after sunset.  Don’t wait too long or they’ll set before you get the chance to see them.

As we move into late February and early March, the moon will move up and away from Mercury and pass near Venus  on the 25th and Jupiter on the 26th. Mercury also moves up and away from the sun and will soon become much easier to see. I’ll keep you posted on good viewing opportunities coming up.

Two nearly complete maps of the planet Mercury made from pictures taken by the MESSENGER spacecraft in orbit around the planet. The black and white map is more detailed than the color version, which highlights different types of minerals and terrains. Credit: NASA

NASA’s Mercury MESSENGER (Mercury Surface, Space ENvironment, GEochemistry, and Ranging) mission has nearly completed its initial mission goal of mapping the planet in color and black and white. It’s also made quite a few discoveries including:

* Most of Mercury’s mass – 60-70% vs. 32% for Earth is in the form of metal in its core. Lighter materials were either boiled away from intense solar heat and solar wind bombardment or from heating caused by a major impact long ago.  Mercury is 36 million miles from the sun or 2.5 times closer than the Earth. Surface temperatures are as hot as 800 degrees and sunlight 6.5 times more intense than on Earth.

Shallow, flat-bottomed pits on Mercury may be caused by subatomic particles from the sun zapping away at sulfur-laden minerals. Credit: NASA

* Like Earth, Mercury is surrounded by a magnetic field, but it’s offset far to the north of the planet’s center and fluctuates over time. Compared to the planet’s small size (3032 miles or about 1.5 times the size of the moon), this offset is far more than any other planet. Scientists are still at a loss to explain why.

* A vast expanse of volcanic plains with lavas as thick as 1.2 miles surround the north polar region. According to James Head of Brown University, the deposits appear to be flood lavas or huge volumes of solidified molten rock similar to those  in the Columbia River basin in the northwest United States. “Those on Mercury appear to have poured out from long, linear vents and covered the surrounding areas, flooding them to great depths and burying their source vents,” said Head.

* New, unexpected landforms called ‘hollows’ have been discovered inside some of the planet’s craters. The shallow, rimless pits range from about 100 feet to 2 miles wide are often seen in clusters. They’re very reflective and appear quite fresh. Scientists believe the intense solar wind felt at Mercury’s distance may be eating away at exposed sulfur deposits on the surface to create the depressions.

* Mercury’s surface may look like the moon, but its rocks contain lots more potassium and sulfur than the lunar variety.

If you’d care to learn more about the new findings and see additional photos of Mercury, check out the MESSENGER website. And don’t forget to go out and see the planet with your own eyes in the next few weeks.

Rocket launches into aurora plus a new meteorite falls in China

A two-stage Terrier-Black Brant rocket arced through aurora 200 miles above Earth as the Magnetosphere-Ionosphere Coupling in the Alfvén resonator (MICA) mission investigated the physics of the northern lights. Photo by Terry E. Zaperach, NASA

As some of us stood amazed at the haphazard dance of northern lights last Saturday night, a team of scientists and graduate students from New Hampshire’s Space Science Center watched with equal amazement night as a rocket laden with sensors arced 200 miles into the sky over the Poker Flat Research Range in Fairbanks, Alaska. Its purpose – to learn how Earth’s magnetic bubble (magnetosphere) couples with the upper atmosphere to deliver displays of the northern lights.

Magnetic waves are in part responsible for the multiple arcs of northern lights in Saturday's display. Photo: Bob King

Instruments on board sampled changes in the magnetic and electric fields stimulated by a barrage of electrically charged particles streaming into Earth’s ionosphere from the sun. Scientists hope the information gathered and relayed back to the ground station will help them better understand magnetic waves called Alfvén waves in our upper atmosphere. The waves are thought to be the driving force in the creation of the thick arcs of northern lights often seen spanning the northern sky from east to west during auroral displays. We saw some of these arcs in last Saturday’s aurora.

According to Marc Lessard, an associate professor at the UNH Institute for the Study of Earth, Oceans, and Space (EOS) and department of physics, the Alfvén resonator is a channel in the ionosphere several hundred miles tall and only about six miles wide that acts like a guitar string when “plucked” by energy delivered by the solar wind to Earth’s magnetosphere high above. It’s thought that electrons from the sun’s solar wind (or delivered by flare or coronal mass ejection) are pumped into the channel to create a column of aurora. Complicated physics for sure.

We’ve come a long way since the days when people once thought the aurora was sunlight reflecting off polar ice!

A meteorite fell to the ground in China last week. Click to watch the 3-minute TV report. Credit: CNTV

In other news, a meteor flared over Huangzhong County, Qinghai Province, China on the afternoon of Saturday February 11 leaving several meteorites scattered across the landscape and gouging out at least two small craters. To date four pieces have been recovered. The largest, weighing over 25 lbs., fell on a snowy mountaintop. Clicking on the picture above will take you to an excellent report on the fall by a Chinese TV station.

Take a good look at the fresh meteorite. It’s very typical – pale, cement-like interior with a matte-black fusion crust of melted rock from its high speed burn through the atmosphere. From the appearance alone, the new Chinese meteorite looks like a very primitive but common type of stony chondrite from the outer crust of an asteroid.  For photos of some of the smaller pieces and villagers searching for more, click HERE.

A partial solar eclipse of the sun was photograph in ultraviolet light by the Solar Dynamics Observatory earlier today. Credit: NASA

By the way, did you see the partial eclipse of the sun earlier today? No? Neither did I, since the eclipse wasn’t visible from the ground, but NASA’s Solar Dynamics Observatory did from geosynchronous orbit some 22, 369 miles away. That can only mean that today is new moon. Watch for the moon to scoot away from the sun and return to the evening sky tomorrow.

The Great Twilight Planet Show rolls into town

Venus (lower planet) and Jupiter vie for attention in the western sky yesterday during twilight. Photo: Bob King

Have you been watching the light show in the western sky these past few weeks? Jupiter and Venus has been ever-so-slowly drawing closer together during evening twilight. Like two lovers in a lengthy courtship, these two planets were clearly meant for each other. They’ll prove it come March 12-14 when they’re closest together for the year at just three degrees apart. The time of closest approach occurs on the night of the 13th. Watch the show unfold from your front yard or from downtown Chicago – these two luminaries are bright enough for anyone to see.

Watch Venus and Jupiter move together and then glide past each other in the western sky at dusk over the next several weeks. Mercury joins the scene later this month. Created with Stellarium

There are two reasons the planets are approaching one another. Earth’s revolution around the sun causes the stars to drift westward with time. For example, we first see Orion in the morning sky in the east in late summer. By mid-winter, it’s straight up south during the early evening, and when April rolls around the Hunter soon disappears below the western horizon. The same westward slide applies to all the outer planets from Mars to Neptune. That’s why Jupiter has been inexorably moving westward in Venus’ direction. It was only a matter of time when they’d meet.

Venus will move farther to the left of the sun all the way through March 27, the date of its greatest elongation east as seen by an observer on Earth. After that date, it will appear to change direction and head back to the west (right) toward the sun. At the same time Venus' phase changes because the viewing geometry changes. Illustration: Bob King

The inner planets Venus and Mercury are different because they orbit between the sun and Earth. Take a look at our illustration above and you’ll see that Venus moves to the left or east of the sun when it’s in the evening sky, defying the western drift. For observers on Earth, the planet appears to move up and away from the sun until reaching its greatest separation on March 27. With Jupiter headed west and Venus east, the two planets are on a collision course. OK, not really. It only looks that way. Jupiter is several hundred million miles in the background “behind” Venus.

After greatest elongation, Venus will appear to move closer to the sun, reversing its direction of travel from our perspective, and dropping down to the western horizon late this coming spring. Notice that the planet’s phase changes throughout. Today it’s a “gibbous moon”, in late March a half moon and by May a crescent. The phases are caused by the ever-changing viewing geometry between Earth and Venus as each orbits the sun.

One great thing about the planets is how easy they are to see. Just a casual look now and again will keep you in touch with who’s doing what in the evening sky.