Mercury and Mars twist it up at dusk

Mars and Mercury have a quick tete-a-tete tonight Feb. 7 and Friday Feb. 8 low in the western sky in the direction of sunset. The scene shows the sky about 1/2 after sunset at which time Mercury will be about 8 degrees high. That’s just shy of one fist held at arm’s length against the sky. Created with Stellarium

It’s a long shot for some, but if you’ve got a wide open western horizon and clear sky tonight (Feb. 7) and tomorrow, you can watch a very close conjunction of Mercury and Mars. Mercury is just beginning its trek into the evening twilight, so it’s still low and soaked in solar glare. That will change next week when the planet climbs farther from the sun and becomes considerably easier to see.

Mars has been hanging around in twilight for months. Being on the faint side, it’s been a binoculars-only planet for many weeks. Mercury shines two magnitudes brighter at -1 and should just be visible with the naked eye in the darkening sky. Just the same, I’d bring binoculars if I were you. Scan a little ways above the west-southwest horizon about 30 minutes after sundown to locate Mercury. Once you see it, you’ll spot Mars about 3/4 degree (1.5 moon diameters) to its upper left tonight and 1/2 degree to its lower left Friday evening.

Good luck!

Move over Orion, it’s the Big Dog’s turn

The sky facing south around 9-9:30 p.m. local time in mid-February. Canis Major lies to the right and below the constellation Orion and represents a large dog. Created with Stellarium

Orion the Hunter claims the southern sky as his own during evening hours in early February, but the times are changing. Nipping at his heels is the Dog Star Sirius and the rest of the stars that comprise the constellation Canis Major the Greater Dog. ‘Greater’ because there’s also a ‘lesser’ dog in the neighborhood called Canis Minor.

Truthfully, this constellation’s so small, it looks more like a dog bone treat for the bigger Canis.

Open your door and look outside at 8 o’clock and you can’t miss Orion’s three belt stars. If you shoot a line downward through the belt toward the southern horizon, you’ll soon arrive at scintillating Sirius, flashing like a silent firecracker in the turbulent air common at lower elevations.

Dangling below Sirius are some half dozen stars in the shape of a musical triangle. These form the legs, tail and head of Canis Major. Connect the dots the next clear night and you’ll see they do form the likeness of a dog jumping at your feet.

Mythological depiction of Canis Major and nearby Lepus the Hare. That rabbit better watch out. Credit: Urania’s Mirror atlas

Canis Major has been described in myth as Orion’s hunting companion and also as Laelops, “a dog so swift that no prey could outrun it”, according to Ian Ridpath, author of Star Tales. The Big Dog doesn’t have to look far for a snack -  just beneath Orion, Lepus the Hare munches contentedly in the stellar garden.

It wasn’t too many weeks ago that you had to stay up late to catch the canine constellation, but now I see it’s nudging Orion from its top spot by 9:30 p.m. As the Earth spins, stars appear to rise in the east, reach their greatest height when due south and set in the west. By month’s end, Canis Major will be due south around 8 p.m. and Orion will have taken a hike to the west.

The Greater Dog constellation topped by Sirius, nicknamed the “Dog Star” for obvious reasons. The star cluster M41, located just a short distance below Sirius, is a very pretty sight in binoculars and very easy to find. Photo: Bob King

If the nightly east-west drift of stars is due to Earth’s rotation, what causes the seasonal drift of the stars? Why doesn’t Orion always stay in the same place week after week, month after month? Blame it on Copernicus. He made the claim, outrageous for his time, that the Earth moved around the sun. Throughout antiquity and into the Middle Ages people thought that if the Earth moved, every time you jumped off the ground, the planet would rush away and leave you behind. Since that didn’t happen, it was obvious the Earth must stand still.

Few understood that EVERYTHING – the Earth, the jumper, birds and atmosphere – were all moving at the same speed and so appeared to be at rest relative to each other. The same thing happens when you’re flying at 550 mph in a plane. Once the plane has reached a constant speed, you’re hardly aware you’re moving. And since you, your laptop and that ginger ale are all traveling at 550 mph, they don’t go flying around the plane. This habit of things to stay put as long as they’re all moving at the same speed is called inertia.

Because our planet orbits the sun, we see into different directions in space over the weeks and months of a year. In January (right), Orion dominates the southern sky; in April it’s Leo and in June, Scorpius. The whole cycle repeats every year. Illustration: Bob King

OK, back to the Big Dog. As the Earth orbits the sun, our perspective on the nighttime sky changes over the weeks and months. At 10 p.m. in mid-January Orion stands straight up in the southern sky, but at 10 p.m in February, he’s been replaced by Canis Major. Come 10 p.m. in April, Leo the Lion will be high in the south and Orion will have set in the west.

As the weeks and months go by, we peer into a different direction of sky just as a runner sees different groups of fans as she runs the 1500-meter on a race track. Like many good things in skywatching, the cycle repeats anew every year.

Tadpole comet swims under Deep Impact’s gaze

Video of Comet C/2012 S1 ISON compiled from images taken by NASA’s Deep Impact spacecraft on Jan. 17-18, 2013.

Comet ISON looks like a tadpole in the video, but we all know that tiny tadpoles grow into big green frogs. So will the comet when it brightens to naked eye visibility later this year. Well, not a frog exactly. A great comet is more like a colossal tadpole with a long, bright tail that can stretch many degrees across the sky.

NASA’s Deep Impact probe, the one that gave us amazing closeup pictures of comets Tempel 1 and Hartley 2, is back in the business of comet watching. NASA directed the spacecraft to track and image Comet ISON as part of a campaign to learn all we can about this frozen ball of ice and dust during its first trip to the inner solar system.

Comet ISON photographed on Jan. 20, 2013 using the Vatican Observatory’s 72-inch telescope. A short tail, fuzzy coma (comet atmosphere) and bright nucleus are visible. Inside the nucleus is the comet body itself, believed to be about 2 miles across. We can’t see it directly because it’s shrouded by its own gas and dust. Click photo to learn more. Credit: Carl Hergenrother

Like Comet C/2011 L4 PANSTARRS, ISON is believed to come from the Oort Cloud, a gigantic, spherical reservoir of comets in the distant outer solar system that reaches a third of the way to the nearest star system, Alpha Centauri. As the sun travels around the center of the Milky Way galaxy, gravitational nudges from neighboring stars can give an Oort Cloud comet a little push and send it falling toward the inner solar system.

The ensuing sun-bound voyage is THE definition of a slow boat to China. It takes millions of years for a comet like ISON to inch toward the inner sanctum, but when these first-timers finally get a taste of the sun’s heat, pristine, dust-laden ices are quick to vaporize.

Artist depiction of Oort Cloud, sphere filled with millions of inactive comets extending some 9 trillion miles from the sun. In 1932 and again in 1950 astronomers Ernst Opik and Jan Hendrik Oort postulated the existence of the cloud to explain where comets with long orbital periods originate.

When the photos were taken, ISON was 493 million miles from the spacecraft or about as far as Jupiter is from the sun. Despite this vast distance, we can already see a haze of gases called the coma from vaporizing ice and a short tail more than 40,000 miles long pointing southeast. Amateur astronomers have recorded a similar appearance with telescopes and cameras here on Earth.

Comet ISON is a hot topic whether you’re a professional astronomer, amateur or brand new to skywatching because it belongs to a special group of comets called sungrazers. As the name implies, these comets passed exceptionally close to the sun before swinging back out into the depths of space. ISON will arc only 130,000 miles from the sun or a little more than half the Earth-moon distance on November 28, 2013. Assuming the comet doesn’t break to pieces under the intense heat and gravitational stress, we should see a long-tailed spectacle with the naked eye both before and after closest approach.

Comet McNaught (C/2006 P1) was our most recent “Great Comet”. As the photo attests, it was a spectacular sight in mid-January 2007 for skywatchers in the southern hemisphere. Some predict Comet ISON has what it takes to become the next great comet. Credit: NASA

Although I don’t have the details on the comet’s size, many astronomers believe ISON is big enough to survive intact and make for a great show this fall and winter in both northern and southern hemispheres.

Have no fear about any effects on Earth except for jaws dropping in wonder (assuming predictions hold true); Comet ISON will only come as close as 40 million miles on Dec. 26, 2013.

New nova erupts in Cepheus

The new nova in Cepheus is just below the W of Cassiopeia near the attractive open star cluster NGC 7510. To find Cassiopeia, look halfway up in the north-northwestern sky around 7 p.m. local time. Created with Stellarium

No, I’m not talking about that Chevy Nova you muscled around town years ago. This one’s a tiny star of a thing in the constellation Cepheus the King not far from the W of Cassiopeia. Japanese amateur astronomers Koichi Nishiyama and Fujio Kabashima discovered the “new” star on Feb. 2 shining where no star had been noticed before. They reported their observation and the object was soon given the unwieldy working name of PNV J23080471+6046521.

PNV stands for ‘possible nova’ and the numbers are its celestial coordinates, akin to latitude and longitude. A day later the discovery was confirmed and the new star received the nifty official name Nova Cephei 2013 – our first of the new year.

Want to see the nova in your scope? Click and go to the AAVSO page where you can print a larger version. Just copy and paste the name PNV J23080471+6046521 into the star name box there. Credit: AAVSO

Before you get too excited, this nova is not visible with the naked eye, but a 6-inch telescope will show it. The Japanese astronomers found it shining around magnitude 10.3, plenty bright for a a small telescope, but the star has faded to around 11.7 in the past few days.No worries. Even if you’re not equipped with the right instrument and the burning desire to freeze finger tips in the cold, you can still enjoy what novas are all about.

About half a dozen novae (NO-vee) are found each year along the star rich byways of the Milky Way. These days they’re usually picked up during deliberate photographic patrols of the night sky by amateur astronomers.

Though a nova can happen anywhere in the sky, they’re more likely to be found along the band of Milky Way because that’s where the majority of stars are. Amateurs hunt there to you increase their odds of finding one.

Now that I’ve been blabbing on about the topic for four paragraphs it’s probably time to tell you a nova is NOT a new star despite it hopeful name. It’s an old star really, a very old star, but one that gets an occasional, if explosive, face lift. While we’ve been eating breakfast, lunch and dinner all our lives, a tiny white dwarf star in Cepheus has been dining on the gas of a close companion star for centuries.

A white dwarf with the mass of the sun is about the same size as Earth. Its surface temperatures is about 180,000 degrees (16x hotter than the sun). Unlike the sun, a white dwarf shines by residual heat. Nuclear fusion in its core has ended. Credit: Prof. Richard Pogge

Picture the sun with all its mass compressed to the size of the Earth and you’ve got a white dwarf. Gravity is some100,000 times stronger there than on our “fluffy” planet, so that a teaspoon of matter scooped from a dwarf’s surface weighs 5 tons.

When a white dwarf happens to be in a very close orbit about a normal star, it siphons gas from that star into a swirling accretion disk like cotton candy wound around a paper cone. From there, the material spirals down to the dwarf itself.

Hydrogen gas – the primary ingredient of most stars – gradually builds up on the dwarf’s blazing surface and becomes heated and compressed by gravity until it’s hot enough to burn or fuse. Normally nuclear fusion happens inside of stars; the energy released gradually works its way to the surface and becomes sunshine. On a white dwarf’s surface fusion happens all at once everywhere, created a powerful burst of light and energy as now-incandescent hydrogen is blasted into space. That’s a nova.

Novae happen only in very close binary star systems where a white dwarf pulls matter off its companion. The material spirals down to the dwarf’s surface and eventually ignites. Credit: NASA

We look up and see a star that was otherwise much too faint to notice suddenly become bright enough to spot in a 3-inch telescope. Some novae are brighter or closer and flare to naked eye brightness.

Novae usually flare brightest earliest and then gradually fade back down, but sometimes additional bursts are seen, so it’s fun to keep an eye on them for changes.

The out-of-the-way open cluster NGC 7510 in Cepheus isn’t far from the nova. The cluster’s about 2,400 light years away. Credit: Jim Misti

For amateur astronomers who plan to seek Nova Cephei, you’re in for a treat. Not half a degree away is the rich, box-shaped star cluster NGC 7510. I stumbled on it two nights ago when I got my first look at the nova. It’s worth a look if you’re in the neighborhood.

First drilling photos from Mars

Closeup of one of the holes drilled taken by the MAHLI (Mars Hand Lens Imager) camera taken on Feb. 3, 2013.  Grey powdery dust – could it be clay-related – lines the hole. Credit: NASA/JPL-Caltech/Malin Space Science Systems

The first pictures of the Curiosity rover’s drill in operation appeared in the raw image archive this weekend and show a gray powder piled up around the holes. Much red dust covers the Red Planet, but once you get below the surface, the true rock color is revealed.

Curiosity is test drilling at the John Klein site in Yellowknife Bay inside Gale Crater. Once it’s cleaned its sample containment container mounted above the drill with grit from the drilling process, actual sampling and analysis will begin. That’s probably still a few days away.

In this quick animation, pre-drilling and drilling photos show pebbles shifting position due to vibration from the drill. Credit: NASA

Look closely at test drill animation above and you’ll see small pebbles about a foot away shift position as the slabby rock they’re on shakes with each percussive jab of the drill. Almost like being there.

Picture of the robotic arm with the drill in position taken by Curiosity’s Mastcam on Feb. 1, 2013. Click for hi-res image. Credit: NASA/JPL-Caltech

Bizarre green meteorite NWA 7325 may be from Mercury

Wow, that’s what I call green! Green, glassy fusion crust coats one side of Ralew’s new meteorite. This is the largest of the 35 fragments, weighing just over 100g. Cube at right is 1 cm across. Click for larger version. Credit: Stefan Ralew

In April 2012 Stefan Ralew, a meteorite collector from Berlin, found himself staring at a spread of 35 green meteorite fragments for sale by a dealer in Morocco

“It was offered as a Martian (meteorite) but for me it was simply far too green,” said Ralew. Moroccan meteorite always keep an eye out for green rocks in the belief that they’re of Martian origin. Sometimes however they turn out to be nothing more than Earth rocks. Since this one was expensive, Ralew would have normally declined, but he noticed that the pieces had fusion crust, that frothy, typically dark coating of melted rock that forms when a meteorite is heated during its fall through the atmosphere.

Stefan Ralew Credit: Mirko Graul

“It was a big risk because of the high price,” said Ralew, but he sealed the deal and mailed off a piece to Dr. Tony Irving at the University of Washington, well-known for his expertise in meteorites from other planets.

After chemical analysis, Irving discovered that Ralew’s green rock was a completely new type of achrondrite (ay-KON-drite), a class of igneous meteorite that forms deep within the crust of larger asteroids and planet-sized bodies. In fact, Ralew’s green meteorite shared similarities with the planet Mercury, making it a one-of-a-kind.

Many of the more familiar achondrites that scientists and meteorite hunters have picked up here on Earth were blasted from the surface of Vesta by meteorite and asteroid impacts. Still others have been liberated from the moon and Mars. They drift through space until swept up by the ceaseless Earth. Scientists have done the math and arrived at the conclusion that meteorites from Mercury impacts should also by lying around in the deserts of the world, preserved by arid air and lack of rain. But no one had definitely identified a rock from Mercury until the green meteorite entered the scene.

A closeup of a polished, cut face of NWA 7325 shows striking green crystals of chromium diopside (a silicate mineral with chromium) and gray crystals of plagioclase, a rock also common in Earth’s crust. Click for larger version. There are a total of 345 grams (about 12 ounces) mostly in small fragments. Credit: Stephan Ralew

Other classes of achondrites called aubrites and angrites were once believed to have originated on the innermost planet, but further research points to their home on a yet-unknown asteroid or planet.

Mercury photographed by MESSENGER. The planet’s crust lacks iron and is pockmarked by countless craters. One of these impacts possibly sent NWA 7325 our way. Credit: NASA

Stefan’s meteorite, now classified as NWA 7325 (NWA=Northwest Africa, its find location), is a near-match for rocks examined from orbit by Mercury MESSENGER space probe. NWA 7325 is rich in magnesium, calcium and a silicate material laced with chromium that lends it an emerald sparkle, but it lacks iron. And that’s the key. Surface rocks on Mercury are likewise igneous and depleted in iron.

The match isn’t perfect. NWA 7325 has more calcium than it should and lacks the silicate mineral enstatite (common on Mercury), but that doesn’t worry scientists too much. Because the rock was excavated from deeper down in the crust, it would be expected to have its own unique qualities.

Mars meteorites show evidence of shock from impact in their crystal structures, and the same would be expected for rocks delivered to us from Mercury. Plagioclase, a very common mineral in Earth’s crust, and found in abundance in NWA 7325, has been completely melted, likely due to shock from the impact that sent it flying from the planet long ago.

Bubbly fusion crust on another fragment of Stefan’s meteorite. Click for larger version. Credit: Stefan Ralew

While the evidence points to a Mercury origin, we won’t really know for certain whether Ralew’s rock originated from the innermost planet until further studies are done. Scientists are still working to determinewhen those gorgeous green crystals formed as well as how long the rock coasted through space before arriving on Earth.

“Ultimately, only a sample return from Mercury may provide an answer,” wrote Irving in his group’s recent report on NWA 7325. In the meantime, Stefan’s meteorite stands as one of the most singular finds to date. It couldn’t have happened to a better guy. Ralew has a been a great friend of meteorite collectors and the scientific community for years. You can check out his website HERE.

Saturn and moon match up tomorrow morning

Saturn and last quarter moon hang together in the southern sky tomorrow morning Feb. 3, 2013 at dawn. Time shown is 6 a.m. local time facing south. Farther east, the summer star Antares and Scorpius are visible. Created with Stellarium

We’ve only had one bright planet adorn the evening sky this winter – Jupiter. He’s certainly generous with his moons, clouds belts and brilliant display, but he’ll soon have company. The planet Saturn edges 4 minutes closer to the evening sky every night.

The ringed one rises around 12:45 a.m. tomorrow morning but by month’s end pops up at 11 o’clock. Either time may be too late for many, but if you’re an early-riser, consider peeking out your window at dawn tomorrow. Like fruit hanging from a twig, the last quarter moon will dangle below Saturn. Although not a particularly close conjunction, the two will be near enough to catch your attention. Closest approach of 3.4 degrees occurs around 1 a.m. (CST).

Saturn photographed on Dec. 27, 2012. The planet is covered in clouds of ammonia ice crystals, some of which are arranged in colorful bands. The rings are composed of countless, individual icy “moonlets”. The dark Cassini’s Division separates the A and B rings. Credit: Damian Peach

If you’re feeling brave, take your scope out for a look at its marvelous tipped rings in the dawning sky. Some of my favorite views of planets have been at dawn or dusk. Seen against a deep blue sky, Saturn’s natural glare is lessened and the view more natural and satisfying. Examine the rings closely and you may be able to spot the hairline gap between the outer, narrower A ring and broader interior B ring. The apparently empty space is named Cassini’s Division in honor of 17th century Italian astronomer Giovanni Cassini who discovered the gap in 1675. Under good conditions even a small 3-inch telescope will show the 3,000-mile-wide vacancy. Gravitational interactions by the moon Mimas clear out ring particles to create the gap.

Giovanni Cassini (1624-1712) was an Italian astronomer but moved to France to become director of the Paris Observatory in 1671.

Cassini has many firsts to his credit. He discovered four of Saturn’s moons, co-discovered Jupiter’s Great Red Spot and determined the rotation periods of Jupiter and Mars by careful study of their surface and cloud features. With the help of his assistant Jean Richer, he triangulated the distance to Mars in 1672. Once Mars’s distance was known, Cassini could easily calculate the distances to all the other planets, since the ratio of their distances to the sun was already known through geometry.

He did well. His measurement of the Earth-sun distance was off by just 7%.

It’s no wonder then why his name was chosen for the Cassini mission to Saturn which has been orbiting that planet and its family of moons since July 1, 2004. New pictures are taken all the time, many of which I’ve featured in this blog. Like Cassini himself, his namesake continues blazing a path of discovery.

This set of images from NASA’s Cassini mission shows the evolution of a massive thunder-and-lightning storm that circled all the way around Saturn and fizzled when it ran into its own tail. The storm was first detected on Dec. 5, 2010. Click to see more photos. Credit: NASA/JPL-Caltech

Recently NASA released a series of photos showing Saturn’s monster storm, the biggest ever recorded in the planet’s northern hemisphere, that began around Dec. 5, 2010 and finally ran out of steam 267 days later. It’s been compared to a hurricane on Earth with its powerful winds, lighting and thunder though on a far grander scale.

Earthly hurricanes derive their energy from warm oceanic waters, while Saturn funnels its power from warm, rising gases in its enormous atmosphere. But there the similarity ends. With no land masses to get in the way and sap the storm of its fury, the leading edge of Saturn’s “hurricane” circled the full 190,000 miles of the planet’s circumference and met up again with its tail! Some have compared it to the mythical serpent Ouroboros eating its own tail. An apt image if there ever was one.

Of course, Cassini was there snapping away the entire time. To read more about the big storm and see additional photos, I invite you to click HERE.

How to get the best views of Comet Panstarrs this March

Comet C/2011 L4 PANSTARRS with its dusty tail photographed on January 27, 2013 from Australia, where it’s well placed for viewing before dawn. Taken with an 11-inch telescope. Credit: Michael Mattiazzo

Even if Comet L4 PANSTARRS doesn’t become the spectacle many of us hope it will be, it will almost certainly be visible with the naked eye and a fine sight in binoculars, with a sweeping tail pointing away from the sun.

The latest predictions by knowledgeable amateur comet observers peg it at between magnitude 2 and 3 when far enough from the glare of the sun to see. That compares well with the brightness of the stars in the Big Dipper. Not too shabby as comets go.

Comet PANSTARRS won’t make its first appearance for northern hemisphere skywatchers until the first week of March during evening twilight. That’s only 5 weeks from now. For the U.S. the comet will appear in the western sky very near the horizon. Observers in the southern states will have a slightly better view with the comet standing a degree or two higher through the 12th; after that all locations across the country will be equally blessed. If you want to see it from the start when the comet’s also brightest, you’ll need an observing spot with a view as far down to the western horizon as possible.

Look for an observing site with a wide view down to the horizon to ensure a good view of Comet L4 PANSTARRS. Photos: Bob King

Scout your neighborhood or take a drive away from home to a nearby soccer field, park or other place with an open view to the west. Once you’ve found your ideal location, go out on the next clear, moonless night and scan that direction for city light pollution. Unless you live in the countryside, a small amount of city glow is inevitable. That’s OK. Few places are light-pollution free these days.

But if your western sky is filled with a star-swamping, foggy miasma on what is otherwise a dark, clear night, consider putting another 10, 15 or 20 miles between you and your town for a better view. If you need help finding a good site or need additional expertise, contact your local astronomy club. Here’s a directory of clubs across the U.S.

Comet L4 PANSTARRS keeps low to the horizon when its brightest from early to mid-March. The map shows the comet’s position and approximate tail direction each night from March 7-25 about 30 minutes after sunset from the mid-section of the U.S. (around latitude 42 degrees N). Created with Chris Marriott’s SkyMap software

Because of L4 PANSTARRS’s low altitude during the first half of March, light pollution, natural horizon haze and twilight itself will compromise the view. From first appearance near the sun in the west-southwest around March 7, the comet never gets higher than about 10 degrees (one fist held at arm’s length) between March 8-20, the time during which it’s expected to put on the best show. While the bright head of the comet will still be visible, much of its tail could well be masked by city light or haze. A dark site is best.

Later, as the comet moves northward and higher, it will fade but may become easier to see as it moves into a dark sky. Binoculars should show it through early May and perhaps even later. From mid-May onward, L4 PANSTARRS becomes circumpolar for observers at mid-northern latitudes and remains visible all night long. At that time it will shine around 8th magnitude and require a small to medium-sized telescope to view.

Comet L4 PANSTARRS reaches perihelion (closest to the sun) on March 10 at a distance of 27.9 million miles or about 6 million miles closer to the sun than Mercury is on average. Intense solar heating will cause the comet to grow a fine dust tail that could stretch for many degrees away from the sun. Closest approach to Earth happens on March 5 at 102.3 million miles – hardly a close shave but good enough for a nice show.

8×40 (left) and 10×50 binoculars are excellent for bright comet viewing. You can pick up a decent pair for around $50-100. Photo: Bob King

As far as the best instrument to use, we’re all hoping PANSTARRS will be bright enough to see plainly with the naked eye. Based on its predicted brightness and tail development, a binoculars will probably provide the best view.

Get a pair that magnify between 7x and 10x with an aperture (lens diameter) of 40 to 60mm. 10×40, 10×50 and 7×50 models are perfect, and they’re reasonably priced, too. Avoid binoculars that magnify 20x or 30x. While more power sounds tempting, anything above 10x will narrow the field of view and make the binoculars nearly impossible to hold steady.

My favorites are the 10×50 wide field variety with lots of eye relief. Large eye relief lets us unfortunates who must wear glasses see the entire field of view instead of getting the equivalent of looking through a straw.

Uwe Pilz of Germany wrote a program that follows the path of dust particles in comets and created these excellent simulations of PANSTARRS’ dust tail. The aqua blue line points away from the sun; the black line is 0.9 degrees long so you estimate tail length. Click image to see the larger complete set. Credit: Uwe Pilz

Comet PANSTARRS is what astronomers term a dynamically new object, making its first visit to the inner solar system after millions of years in the deep cold of the comet repository known as the Oort Cloud. Such comets make a bright appearance at great distance because their rarefied ices are ripe to vaporize. This can lead one to think that the comet will continue to brighten into negative magnitudes as it approaches the sun and Earth. But after those virgin ices have sublimed away, new comets often settle down and lag behind predictions. The old hats who’ve been around the block a few times brighten and fade more reliably.

Whatever happens with PANSTARRS is worth watching. As we’ve encountered with previous comets, unpredictability is their charm. The comet could be brighter, fainter, experience a sudden outburst of brightness or disintegrate into clods of dust. I hope we’re all fortunate enough to witness such revelatory moments in nature.

Deneb and Mu, farthest stars of a winter’s night

Deneb in the Northern Cross and Mu in Cepheus are the most distant, easily visible stars you can see with the naked eye. Deneb’s a snap to see. To find Mu, stick out your arm and look a little more than one vertically-held fist above and to the right of Deneb to Alpha Cephei. Mu is “two fingers” to the left of Alpha and shines at 4th magnitude. Created with Stellarium

Yesterday we looked at the obscure yet up-close-and-personal Wolf 359. Today I thought it would be fun to touch the other extreme and visit with two of the most distant stars visible with the naked eye. That jaunt takes us to a pair of stellar supergiants – Deneb in the Northern Cross and Mu Cephei (SEF-ee-eye) in the constellation Cepheus the King. Happily, both are near one other in the northwestern sky during early evening hours in February.

Deneb will be familiar to many of you as the star at the head of the Northern Cross also known as Cygnus the Swan. To our best knowledge, Deneb lies between 1,550 and 2,600 light years from Earth. The wide range of values has to do with different methods for estimating its distance, the first based on satellite observations and the other on computer modeling and direct measurement of star’s size.

Size comparison of the sun and the supergiant star Deneb.

We know it shines at least 54,400 times brighter than our sun with a diameter 114 times larger. Size-wise, the sun is to Deneb as Earth is to the sun.

Despite the vast gulf separating us, Deneb still shines at first magnitude. But what fun we’d have if it were moved to a distance of 7.7 light years, the same as terribly faint Wolf 359. From there Deneb would be a commanding sight at magnitude -11, glowing as brightly as the gibbous moon.

I came across Mu Cephei, better known as the Garnet Star, when looking up the most distant star visible with the naked eye. In a previous blog post, I’d written that V762 Cassiopeia, a variable star in Cassiopeia, held the record at 16,308 light years. While that distance is a best estimate, V762 lies at the naked eye limit of 6th magnitude. Most of us will probably never see it from our light-polluted towns and cities.

Both Mu and Deneb are classified as supergiant stars because of their stupendous girth and luminosity, but while Deneb is young, hot and white, Mu is older, cooler and red. As supergiants age, they puff out their outer layers, cool and redden. Betelgeuse in Orion’s shoulder is another example of a red supergiant. Both stars are unstable and routinely shrink and expand, which causes their brightness to vary over periods of months and years.

The sun is no match for Mu Cephei’s vast starscape. Illustration and photo: Bob King

With a diameter 1,650 times greater than the sun, Mu would dazzle our eyes off if it weren’t so far away. Distance estimates vary widely but 2,400 light years is often cited. If we could haul Mu to our solar system and put it in place of the sun, its surface would reach all the way to Saturn’s orbit.

To the eye, Mu is a dim and undistinguished 4th magnitude star, but binoculars show its orange-red color clearly. Astronomer William Herschel, who discovered the planet Uranus, described its color as “a very fine deep garnet”, hence its nickname the Garnet Star.

With the moon now out of the early evening sky, go out the next clear night and face northwest at nightfall to see this pair of bloated beauties. They’re the most distant stars within easy naked eye range. If only we could haul them closer to Earth, we’d better appreciate their true splendor.

Dwarf star Wolf 359 endures after fictional Borg battle

Wolf 359 photographed several years apart so you can see its movement across the sky. The star travels 0.4 arc seconds per year – the moon’s diameter in 4,500 years – against the distant starry background. Credit: ESO, Digitized Sky Survey, U.K. Schmidt Telescope, PPARC and the Association of Universities for Research in Astronomy, Inc. (AURA).

The Borg were probably the most frightening and evil of all the alien races in Star Trek: The Next Generation. Outside of their collective group, nothing mattered. It was just kill, kill, kill and assimilate. If you were captured, the Borg hooked you into the network, sucked every thought from your brain and used the knowledge to destroy the next heroic attempt to snuff them out.

A famous fictional battle took place between the good guys and the Borg happened in the year 2367 near the star Wolf 359. Why Wolf 359 was chosen I don’t know, but it is a real star and a special one at that. Perhaps the writers wanted a star near Earth to bring home the impending threat to our own solar system.

Wolf 359 is a very faint star located in the southern half of Leo the Lion. This map shows the sky facing east in late Jan. – early Feb. around 9 p.m. local time. Created with Stellarium

Wolf 359 was the 359th star of more than a thousand found discovered by German astrophysicist Max Wolf to have a large motion across the sky, what astronomers refer to as proper motion. All stars are moving around the center of the Milky Way galaxy. Nearby stars generally appear to move more quickly across the sky than distant ones because they’re closer to us. Kind of like driving along the freeway where a service station quickly recedes into the distance while the distant mountain ahead appears nearly still for many miles.

Astronomers are able to measure distances to stars with large proper motions, and once you know distance, you know how big and bright a star really is. What we learn from them can then be applied to more distant stars, the movements of which are nearly impossible to detect. That’s why Wolf cataloged as many of these stellar midges as he could.

The size of our sun and Wolf 359 compared. Illustration: Bob King

Outside of the sun, Wolf 359 is the third closest star to Earth after the Alpha Centauri system and Barnard’s Star. Just 7.7 light years away, it’s one light year closer than the sky’s brightest star, Sirius. You’d think something so close would outshine Sirius or at least be visible with the naked eye. I wish. Wolf 359 shines at a paltry 13.5 magnitude, requiring at least an 8-inch telescope to see.

Unlike Sirius, which is both hotter and nearly twice as large as the sun, Wolf 359 is a red dwarf only about 16% the size of the sun or approximately 140,000 miles across. That’s hardly twice the size of Jupiter. If Wolf 359 were at the center of our solar system, you’d need binoculars to see it as a disk. Not only that, but with an energy output of 1/10th of 1% of the sun, it would only be as bright as ten full moons squished into a tiny dot.

Astronomer Max Wolf

Red dwarfs are red because their surfaces are cool, and like an ember, emit more red light than green or blue. They’re also small. Wolf 359 is about as small as star can be and still fuse hydrogen atoms together in its core to create energy the way the sun does. Its surface cooks at at a tepid 4,000-4,700 degrees F, cool enough to allow molecules like water and carbon monoxide to form. You won’t find that happening on old Sol.

Despite its diminutive persona, Wolf 359 will outlast the sun and nearly every star we see in the night sky. Being cool, red dwarfs burn their hydrogen fuel frugally compared to larger stars that devour theirs at prodigious rates. Not only that, but hydrogen is continually recycled throughout the interior of red dwarfs and available for burning. In sun-sized and larger stars, hydrogen is converted into helium ash, which settles in the core. The sun will continue to burn hydrogen in its old age, but only in a thin shell around the core.

When the sun runs out of fuel in another 5 billion years and evolves into a white dwarf star, Wolf 359 will keep the home fires burning for up to 10 trillion years. No matter what happens in science fiction, Wolf 359 will endure.