Tag Archives: planets

NASA’s Kepler spies 3 new “Goldilocks” planets

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Relative sizes of the newly discovered habitable-zone planets and Earth. Left to right: Kepler-69c, Kepler-62e, Kepler-62f and Earth (except for Earth, these are artists’ renditions). Image credit: NASA Ames/JPL-Caltech

NASA’s Kepler Mission proves once again that Earth has relatives or at least good friends. The agency announced the discovery today of three new super-Earth-size planets around two different stars. All three are rocky planets orbiting within their host stars’ “Goldilocks Zone”, a region neither too hot nor too cold but just right for liquid water to exist on a planet’s surface.

The diagram compares the planets of the inner solar system to Kepler-62, a five-planet system about 1,200 light-years from Earth in the constellation Lyra. The three inner planets orbit so close to the host star, they’re too hot to be in the Goldilocks Zone. Credit: NASA Ames/JPL-Caltech

Two of the new planets – Kepler-62e and 62f – circle the star Kepler-62 along with three other planets for a total of five in the system; Kepler-69c, the third super-Earth, orbits Kepler-69 along with one additional planet. Kepler-62 is only 2/3 the size of the sun, 1/5 as bright and resides 1,200 light years away in the constellation Lyra the Harp. Kepler-62 is slightly smaller and less luminous than the sun and lies 2,700 light years from Earth in Cygnus the Swan.

The diagram compares the planets of the inner solar system to Kepler-69, a two-planet system about 2,700 light-years from Earth in the constellation Cygnus. The two planets of Kepler-69 orbit a star that belongs to the same class as our sun, called G-type. Credit: NASA Ames/JPL-Caltech

Here are the specs on the super-Earths, defined as planets with masses greater than Earth but less than that of the planets Uranus and Neptune which are about 15 times more massive than Earth:

* Kepler-69c – 70% larger than Earth, the smallest yet found in the habitable zone of a sun-like star. It circles its sun in 242 days with an orbit similar to that of Venus.

* Kepler-62e —  60% larger than Earth, orbits every 122 days in the the habitable zone’s inner edge.

* Kepler-62f – 40% larger than Earth, the smallest known habitable zone exoplanet, orbits every 267 days.

Although some 871 exoplanets have been discovered to date only 10 have been found in their host stars’ habitable zones. Since mission start on April 8, 2009, Kepler has detected 2,740 candidates of which 122 have been confirmed. Planets are becoming as common as rabbits it would seem.

Kepler watches for dips in a star’s brightness when a planet transits or crosses in front of it.

Kepler uses the transit method to spy its new planets, keeping a constant eye on more than 150,000 stars in Cygnus and Lyra just waiting for a planet to transit or pass in front of one of them. The resulting dip in the brightness of the star reveals the planet’s size relative to its host. Based on information we read in a star’s light using a spectrograph, we can estimate the star’s size and then calculate the planet’s size. Three successful transits are required to become a planet candidate. Earth-based telescopes then perform follow-up observations to confirm Kepler’s results.

The significance of today’s announcement is simple. With every new potentially habitable planet discovered, we learn more about how Earth fits in. How long will our blue globe remain unique as planet finding turns from trickle to torrent?

Click HERE for more details.

A painting in the western sky

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Tonight's gathering of Moon, Jupiter, Venus and transcontinental airliner in the western sky in mid-twilight Sunday. Details: 35mm lens at f/4.5, ISO 400 and 6 seconds. Photo: Bob King

I hope you had a chance to see the spectacle of moon and planets in the western sky Sunday evening. The full circle of the moon is visible alongside Jupiter. The bright part of the circle (crescent) is illuminated by the sun, while the remainder of the moon shines by sunlight reflected from Earth’s clouds, water and land. Earthshine is much fainter than direct sunlight, which is why that portion of the moon glows only weakly.

Not far above the pair is Venus and the Seven Sisters star cluster. Very eye-catching all!

Tonight the moon will be next to Venus and even closer than it is to Jupiter tonight, but you don’t have to wait till dusk to see the pair. Why not try and spot them in binoculars before sunset?

See if you can spot Venus in the daytime today using the moon as your guide. All you need is a pair of binoculars. If your sky's really clear, Venus will be visible with the naked eye. Time shown is CDT. Created with Stellarium

The moon is fairly easy to see in a clear sky by late afternoon and early evening. Once you find it, take a look through binoculars and you’ll have no problem seeing Venus not far to its upper right. Seeing Venus in a sunlit sky can be challenging, but with the moon nearby you’ve got the cosmos on your side. Give it a try. I think you’ll be surprised how easy it is. And once you’ve spotted the duo in binoculars, take the next step and try to pick out Venus with your naked eye.

The maps show the pair for the central U.S. If you live on the East Coast, Venus will be a tad higher to the right; for the West Coast they’ll be more “level” or in line with each other.

Excellent cloud details show up in this photo of Venus taken on March 24, 2012. Credit: George Tarsoudis

George Tarsoudis of Greece took a wonderful image of Venus that shows far more detail than what you’d see with your eyes through any telescope. Using a digital camera and ultraviolet filters on his 10-inch scope, he captured textures in the planet’s clouds not visible in everyday “visual” light.

Even to the most seasoned observers rarely see detail in Venus’ clouds due to their extremely low contrast. His photo reminds me of the images taken by the Pioneer Venus Orbiter spacecraft in 1979.

Alien planets for May nights

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While 522 exoplanets have been discovered so far, we only have photos of about a half-dozen. The star pictured above is HR 8799. It's 130 light years from Earth and 1.5 times more massive than the sun. It's been obscured to better show the three planets - b,c and d - in orbit about it. Credit: C. Marois et. all, NRC Canda

I’ve been reading a great new book about the history of discovery of exoplanets – planets revolving around stars beyond the sun – called Strange New Worlds – The Search for Alien Planets by Ray Jayawardhana.

The three primary ways astronomers detect other planets is by measuring the small gravitational tugs they produce on their host stars revealed through the shifting patterns of light in the stars’ spectra, transits or mini-eclipses across the face of their host stars that cause a tiny but measurable drop in the star’s light and microlensing.

We examined microlensing last week when the topic of ‘free-floating’ planets came up. When a star lines up precisely with a distant background star, the foreground star acts like a lens and magnifies the light of the distant one, briefly making it much brighter. A planet orbiting the foreground star will cause deviations in the light that betray its presence.

To date, 522 alien planets have been discovered, most them through gravitational tugging, better known as the ‘radial velocity’ method. The planet in effect tugs the star forward and then backward during it orbital revolution causing a small change in the star’s velocity toward and away from Earth. Jupiter, the biggest planet in our solar system, shifts the sun to and fro by 40 feet per second, a very tiny amount.

"Hot Jupiters" are the most common type of alien planet discovered. They're big enough - and close enough - to produce measurable tugs on their host stars. Most orbit closer in than Mercury does to the sun, making their sun-facing sides exceedingly hot.

It should come as no surprise that the larger and closer an extrasolar planet is to its host star, the greater its gravitational pull will be and the larger it will appear during a transit. That’s why most of the new planets are Jupiter-sized or larger and located very close to their host suns. They’re the easiest planets to see because their effects are the most obvious. Although our instruments are extremely sensitive, exoplanet detection is still in its infancy. The first planet around a sun-like star was only discovered in 1995.

The smallest exoplanet found so far is Kepler 10-b which is only 1.4 times the size of Earth. As methods and instrumentation improve, we’ll soon be finding more earth-sized rocky planets. Already, astronomers have come up with clever ways to detect chemicals in a planet’s atmosphere. During a transit, a bit of the star’s light passes through the planet’s atmosphere and leaves a ‘fingerprint’ on its light. When the planet has finished its pass in front of the star, astronomers then measure the star’s light alone. Subtracting the two tells them what chemicals the planet’s atmosphere contribute to the light. Sodium, carbon monoxide and hydrogen are some of the materials they’ve found.

Four stars with planets are visible in the southern sky at nightfall. The brightest and easiest in the spring sky is the star Gamma in Leo the Lion. It's orbited by the planet Gamma 1 Leo b that packs nine times the mass of Jupiter and goes around once in 428 days. Maps created with Stellarium

With all these new planets popping up, I thought it would be fun to comb through the list to see which planet-hosting stars are visible with the naked eye on late May nights. I was pleasantly surprised to find 11 stars – two with multiple planets – that were brighter than the standard rural sky limit of magnitude 6.0.

Turning to face the northwest at nightfall, Gemini, Cancer and Ursa Major (UMa) all sport exoplanets. The planet 47 UMa b is a triple planetary system, while 55 Cancri has five in all!

While the planets themselves are utterly invisible – like trying to see a firefly next an arc light 1,000 miles away – we can see the stars well enough. One of them, Gamma Leonis, is even bright enough to see from a city. All the others are visible to varying degrees depending on your sky. Binoculars will show them all with ease.

Four additional stars greet sky watchers facing north in late May. The second brightest planet-bearing star in the spring sky is Gamma Cephei, located below the North Star.

The next time it’s clear and you have a chance to go outside, see how many of these planet-bearers you can see for yourself. To help you picture the invisible worlds in orbit, consult the list below for details. Planets take their star’s name with the letter ‘b’ appended for the first planet discovered followed by ‘c’, ‘d’, etc. if additional ones are found.

Southern sky
* Gamma 1 Leo b  / 8.8 Jupiter-mass planet orbits 1.2 x Earth’s distance in 428 days / Star brightness or magnitude is 2.0 – bright!
* 70 Vir b / 6.6 Jupiter-mass planet orbits 0.5 x Earth’s distance in 117 days / Star mag. = 5.0
* Tau Boo b / 4 Jupiter-mass planet orbits 0.046 x Earth’s distance in 3.3 days / Star mag. = 4.5
* Kappa CrB b / 1.8 Jupiter-mass planet orbits 2.7 x Earth’s distance in 1191 days / Star mag. = 4.8

Western sky
* Tau Gem b / 18 Jupiter-mass planet orbits in 305 days / Star mag. = 4.4
* 55 Cnc b, c, d, e, f / range of 0.03 to 3.8 Jupiter-mass planets orbiting from 0.02 to 5.8 x Earth’s distance in 0.7 to 5218 days / Star mag. = 6.0
* 47 UMa b, c, d / 0.5 to 2.5 Jupiter-mass planets orbiting from 2 to 11.6 x Earth’s distance in 1078 to 14,002 days. / Star mag. = 5.0

Northern sky
* 4 UMa b / 7 Jupiter-mass planet orbiting 0.9 x Earth’s distance in 269 days. / Star mag. = 5.8
* 11 UMi b / 10.5 Jupiter-mass planet orbiting 1.5x Earth’s distance in 516 days / Star mag. = 5.0
* Gamma Cep b / 1.9 Jupiter-mass planet orbiting 2x Earth’s distance in 903 days / Star mag. = 3.0
* 42 Dra b / 3.9 Jupiter-mass planet orbiting 1.2x Earth’s distance in 479 days / Star mag. = 4.8

C. Marois et al., NRC Canada

Saturn’s violent storm rages on

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If you're an early riser like some runners I know, see how many of the planets you can spot before sunrise. Jupiter is easiest, followed by Venus, Mercury and faint Mars. Binoculars help! Map: Stellarium

It’s still a traffic jam of planets in the morning sky, the longest I can recall in years. Depending on your latitude, it’s more or less easy to see up to four planets gathered in the eastern sky about 1/2 hour before sunrise. The map at left shows the scene tomorrow morning.

For folks living in the northern U.S., Europe and Canada, they’re all quite low, requiring haze-free skies and a clear horizon view to see. In Duluth in particular, I can happily recommend Lake Superior as the place for a.m. planet watching. The farther south you live, the better placed Mars, Mercury, Venus and Jupiter become. Best is the southern hemisphere, where the four planets line up almost straight up in the east before sunrise.

The 'Spring Triangle' is high in the south at nightfall in late May. One fist held at arm's length separates Spica and Saturn. The other two sides of the triangle are about '3 fists' long. Photo: Bob King

Saturn is still the only evening planet. Along with its bright neighbors Spica and even brighter Arcturus, it’s part of a ‘spring triangle’ that dominates the southern sky at nightfall. Without interference from moonlight, I was pleasantly surprised last night to see how bright this trio appeared.

We’ve followed the progress of Saturn’s monster northern hemisphere thunderstorm on several blogs since it exploded on the scene in December 2010. Super storms like these are rather rare with only six recorded since 1876. But what they lack in frequency they make up in intensity.

The current storm now reaches completely around the planet, measuring some 223,000 miles long. To put that in perspective, imagine a line of swirling clouds, blizzards of ammonia ice crystals and torrential winds stretching from Earth almost to the moon!

“Our new observations show that the storm had a major effect on the atmosphere, transporting energy and material over great distances – creating meandering jet streams and forming giant vortices – and disrupting Saturn’s seasonal [weather patterns],” according to Glenn Orton, based at NASA’s Jet Propulsion Laboratory and co-author of a recent paper about the upheaval.

This colorized picture of Saturn taken in three wavelengths of infrared light by the orbiting Cassini probe shows large amounts of ammonia ice particles dredged up by the storm, shown in yellow. Credit: NASA/JPL/Univ. of Arizona

Yeah, this is a biggie. Powerful updrafts from the storm pulled ammonia gas from 30 miles beneath the visible cloud deck into the bitter cold upper atmosphere, where it condensed into large ice crystals. Winds and associated storm clouds punched through the cloud tops with such force they penetrated Saturn’s normally serene stratosphere.

“On Earth, the lower stratosphere is where commercial airplanes generally fly to avoid storms which can cause turbulence,” says Brigette Hesman, a scientist at the University of Maryland in College Park and second author on the paper. “If you were flying in an airplane on Saturn, this storm would reach so high up, it would probably be impossible to avoid it.”

In this May 18 photo, the storm is the white band near the top split in two by a thin darker cloud belt. The warmer-toned belt below the storm is Saturn's North Eq. Belt. Credit: Efrain Morales

According to NASA, it’s the most violent event ever observed at Saturn by an orbiting spacecraft. Seeing this violence in amateur telescopes takes persistence because its appearance is subtle and requires high magnification (200x and up) and a night of very calm, steady air to see. Look for a pale white zone bordering the length of Saturn’s grey-toned North Equatorial Belt.

To help you find it, use this much smaller version of Efrain’s photo at right. I’ve taken and flipped it, so south is up the way you’d see it in most telescopes. The view simulates about how the planet appears on a steady night when magnified around 250x. Good luck telescopic observers!

Does the Milky Way harbor billions of orphaned planets?

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This week's full moon provided the illumination for a photo of the Big Dipper (top) above a stand of poplar trees. Details: 16mm lens at f/2.8, ISO 400 and 20-second exposure. Photo: Bob King

How many planets do you think are in this photo? At least hundreds of thousands according to a new joint Japan-New Zealand survey that scanned the center of the Milky Way in 2006-2007 looking for spikes in the brightness of distant stars that reveal the presence of planets.

A planet or other large body passing directly between the Earth and a distant star acts like a lens and briefly causes the star to surge in brightness. Credit: U. of Notre Dame

The gravity of a passing planet or star warps the light of the background star, causing it to magnify and brighten. Stars warp the light of the background star to a greater extent, resulting in brightening events that can last weeks. Small planet-size bodies will cause less of a distortion, and brighten a star for only a few days or less. By measuring the the range and change in brightness over time, astronomers can estimate the size and mass of the object. It’s called gravitational microlensing and related to the warping effects of matter on space that we explored in a blog last month.

Astronomers used the 5.9-foot telescope at the Mount John University Observatory in New Zealand to regularly scan the star-rich center of the galaxy for microlensing events as part of the Microlensing Observations in Astrophysics or MOA survey. The more stars it could stare at, the greater probability of finding lensing events caused by free-floating planets.

These ‘free agents’ roam the galaxy unattached to a parent star. Either they were kicked out at birth by tortuous gravitational interactions with other planets orbiting their birth star or they formed freely by themselves, condensing from dust and gas into planet-sized brown dwarf stars or giant Jupiter-sized planets.

Free-floating planets might be common in the galaxy. Rather than orbit a host star, each would follow its own track around the center of the Milky Way. Credit: NASA/JPL-Caltech

Scientists detected 10 probable free-floaters in the survey with roughly the mass of Jupiter at distances of 10,000 to 20,000 light years from Earth.  Based on their results and theories that predict even more Earth-sized planets being ejected than large ones, the group estimates that loner planets are as common as the more familiar orbiting variety. That adds up to hundreds of billions of orphaned planets in our galaxy alone -  twice as many as the stars themselves!

The question naturally arises whether a solo planet without a star to warm it up might still potentially harbor life. All depends. If it’s large enough, the heat created during its formation through gravitational contraction could persist for billions of years. Though their cloud tops are bitter cold, deep down, the distant giants Jupiter, Saturn and Neptune are still hot enough to emit more heat than they receive from the sun. Even solo orbs might offer a foothold for life in their deep interiors. Life’s insidious that way.

Planet blast climaxes this week

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Follow the peregrinations of the planets in the dawn sky 20-30 minutes before sunrise as seen from mid-northern latitudes. Venus and Jupiter are about 3 fists to the right of the sun. Use binoculars to help you find Mercury and Mars, both considerably fainter. Created with Stellarium

The ecliptic makes a low angle to the horizon in the spring morning sky for sky gazers in mid-northern latitudes. Maps made with Chris Marriott's SkyMap

The next few mornings will see the two brightest planets – Venus and Jupiter – coming together for a close conjunction in the morning sky. Joining them will be two fainter orbs, Mercury and Mars. From mid-northern latitudes the show takes place very low in the eastern sky not long before sunrise. You’ll need a wide open horizon to see them.

Even Venus and Jupiter, the best-placed of the four, will be only 5 degrees high in a bright sky some 20 minutes before sunrise. The climax of the display will be Wednesday morning, when the two planets are closest at just 0.6 degrees or about a ‘full moon’ apart. Bring your binoculars to make sure you see them all. Only Venus is likely to be visible with the naked eye.

The planetary parade will be much easier to see from the southern hemisphere because the ecliptic tilts up steeply from the horizon.

Because the planets’ path, called the ecliptic, is making a very shallow angle to the horizon this time of year in the morning sky, they barely clear the horizon before the sun comes up. Further south in places like Miami and Phoenix, Venus and Jupiter are more than twice as high – 12 degrees – and from Alice Springs, Australia (latitude 24 degrees south), they climb to 22 degrees or two fists high 20-30 minutes before sunrise. Very easy to see!

If the sky is clear, especially for the big event Wednesday morning, I’ll be out there watching with eye and camera. Let’s hope for clear skies.

Yesterday’s Astronomy Day here at the University of Minnesota-Duluth (UMD) was a great success. Something like 500 people dropped by, mostly families with lots of kids. We all looked at the sun and its several sunspots, which people variously described as dots, bugs, freckles and cookie crumbs.

Kids really enjoyed the Touch the Planets exhibit at yesterday's Astronomy Day at the Marshall Alworth planetarium on the UMD campus. Photo: Bob King

Inside there were nonstop talks and lectures, telescope displays and an imaginative ‘Touch the Planets’ exhibit created by Eric Norland. He set up a boxes you could stick your hands into with different textured materials for each planet. Earth had spongy stuff and spruce boughs, Pluto was ice and Jupiter soft and foamy. Thanks to the Arrowhead Astronomical Society and the UMD Astronomy Club for a fantastic time!

May meteors and a brush with the aurora

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Clouds are silhouetted against the green glow of the aurora around 11 p.m. last night. The 'W' of Cassiopeia is visible above. Details: 35mm lens at f/2.8, ISO 1600 and 30-second exposure. Photo: Bob King

We had a brush with the aurora last night here in northern Minnesota. Not much to see, just a fringe of green along the northern horizon. The recent storm of particles from the sun’s coronal holes have been subsiding, and the four sunspot groups currently dotting the sun’s face have been well-behaved.

What surprised me was how easy it was to see the aurora’s color despite being so low in the sky. All auroras are worth watching. You never know when a small display might puff up into a life-changing experience.

Four planets are stretched across the eastern sky shortly before sunrise in early May. You can use the bright glow at the horizon where the sun will rise to help you find them. Venus is about two fists to the right of the sun. Be sure to use binoculars. Maps created with Stellarium

Four planets continue to dance about in bright morning twilight. If you have a completely level, open horizon to the east, grab your binoculars and look two fists held at arm’s length to the right of where the sun rises to find Venus, Mercury, Jupiter and Mars.

For observers in the northern U.S., they’re challenging to see because even Venus, brightest of the gang, is only half a fist high 20 minutes before sunrise. In the southern U.S. the four are slanted up at a higher angle and easier to see. And if you live in South Africa or Australia, you’ll have no problem at all finding them.

Beginning tomorrow and continuing through the weekend, another event favoring those living at more southerly latitudes is happening. It’s the annual Eta Aquarid (AY-tuh ah-QWAR-id) meteor shower. The radiant, or location in the sky from which the meteors appear to radiate, is in the constellation Aquarius, which is very low at dawn for mid-northern latitudes like Duluth and Chicago. We might see a few per hour during the Friday morning (May 6)  peak of the shower.

This map shows the sky facing east at the start of dawn the next few mornings. The meteors appear to radiant from near the star Eta Aquarii, hence the shower's name.

Further south, Mississippians might spot 10 per hour. But if you live south of the equator, this is one of the best meteor showers of the year, with rates up to one a minute.

It’s all about how high the radiant gets. A low radiant means most of a shower’s meteors are out of view, streaking away below the horizon. Like the current string of planets in the morning sky, the Aquarid radiant is tilted higher and much better placed for sky watchers below the equator than above.

If you’d like to try anyway, perhaps combining your meteor watching with an attempt to see the dawn planets, face east about two hours before sunrise. The radiant is to the right of the boxy Great Square of Pegasus. There will be no moon, so conditions are good for seeing any meteors at all, even faint ones.

The Eta Aquarids are grains of ice and rocky material shed by Halley’s Comet as it orbits the sun. Twice a year, the Earth crosses Halley’s orbit. When it does, we see a meteor shower as the grains collide with our atmosphere and burn up. In mid-October we encounter Halley’s orbit again and re-visit the comet’s dust trail in the form of the Orionid meteor shower. Good luck!

One last tidbit to update you on the progress of repairs of the space shuttle Endeavour. The earliest next launch date is now Tuesday, May 10. Click HERE for more information.

 

Morning moon and planet party begins

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You'll see the moon low in the eastern sky the next two mornings when it will join a pack of planets. Bring binoculars! The Jupiter-Mars combo is only 1.5 degrees high, the moon about 15 or 1 1/2 'fists'. Maps created with Chris Marriott's SkyMap software

Tomorrow and Saturday mornings we begin a grand round of moon and planet conjunctions that lasts into mid-May. Last week we looked at the ‘invisible planetary alignment’ to the right or west of the sun. Those same planets are sorting themselves out and finally becoming visible in the dawn sky shortly before sunrise. Meanwhile, Saturn is the only planet shining in the evening sky.

A word of warning. From mid-northern latitudes, all the planets will be very low in the sky, and except for Venus, require binoculars to see. Those of you living in the southern U.S. and farther south will have a clear advantage. The path of the moon and planets – called the ecliptic – is tipped at a low angle to the horizon on spring mornings. This means the planets never get very high before the sun rises and they become impossible to see.

Things improve the farther south you go. From the latitude of Phoenix, Ariz. (33 degrees north), the planets and moon will be higher and easier to see.

Further south, the ecliptic tips up at a steeper angle, enabling the planets to climb higher and be more easily visible before they’re overtaken by daylight. The ideal place to watch the show is near the equator, where the ecliptic is nearly vertical to the horizon. Any equatorial observers out there?

If your lucky enough to have clear, haze-free skies and the ability to see right down to the horizon, you might be able to see all four planets with the moon the next few mornings using binoculars. In order of difficulty from easiest to hardest they are: Venus, Mercury, Jupiter and Mars. Consider yourself an “A” class sky watcher if you find Venus, Mercury and the moon. Find all and you get an A+!

The moon leaves the scene by next Monday, but the planets continue to scoot by one another in the coming two weeks. We’ll have more information on when and how to watch in upcoming posts.

The space shuttle Endeavour moves along the crawlerway from the Vehicle Assembly Building to the launch pad last month. Credit: NASA/Terry Zaperach

Excitement is building as NASA prepares to launch the second-to-last space shuttle mission. Endeavour will blast off tomorrow at 2:47 p.m. Central time from Kennedy Space Center’s Launch Pad 39A. The crew of six will be under the command of Mark Kelly, whose wife, Arizona Congresswoman Gabrielle Giffords, will be there to watch the spectacle. So will President Obama and his family. Stay tuned to the latest news by stopping by the NASA Space Shuttle website.

Tomorrow we’ll take a look at a most interesting piece of equipment the astronauts will deliver to the International Space Station (ISS) – an Alpha Magnetic Spectrometer. With it, astronomers hope to probe dark matter, antimatter and a theoretical form of matter called strangelets.

Comet Elenin update and an invisible planetary alignment

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Comet Elenin is the little blob between the tick marks in this negative image (black stars, white sky) taken on April 20 through a 10-inch telescope. Notice the bit of fuzz around it - that's part of the comet's gaseous envelope called the coma. The galaxy NGC 3376 is at right. Credit: Jean-François Soulier

Comet Elenin continues to inch its way through the asteroid belt en route to the inner planets. Seen from Earth, it recently moved from the constellation Sextans the Sextant into the more familiar Leo the Lion. Today it’s 242 million miles from the sun and 171 million miles from Earth. Based on its brightness in late March, the comet was estimated to be between 4 and 15 miles across. That figure may change. Over the past month, Elenin hasn’t brightened up as expected; it’s still stuck at around magnitude 16 – very faint! That’s according to photos taken this past week. A couple dedicated amateur astronomers have reported seeing the comet a magnitude brighter at 15, still very dim.

Why would I even bother you with an update on such a faint object? While the comet appears like an innocent hunk of dusty ice to me, if you search its name on the Internet, most of the links point to websites involving cover-ups, collisions with Earth, reversals of the Earth’s poles, earthquakes and a connection with Nibiru, an imaginary brown dwarf star on an imaginary collision course with our planet.

Comet McNaught R1, with its long skinny tail, was faintly visible with the naked eye but a beautiful sight in binoculars last June. Photo: Bob King

While it’s inevitable that sometime in the future, after you and I are long gone, an asteroid or comet will strike the Earth and cause untold devastation, Comet Elenin doesn’t fit the bill. Its orbit’s been nailed down, and Earth’s in the clear by millions of miles. How about a meteor shower from a side swipe of the tail? Extremely unlikely if not impossible. The comet and tail are simply too far away to touch us.

If anything, the latest news leans to the disappointing side. The comet may not live up to its original expectation of reaching naked eye visibility. Recent estimates suggest we’ll need to keep our binoculars handy. That’s OK. Even a binocular comet is worth staying up late to see.

I’ve been asked by several people when Comet Elenin will first show in our backyard telescopes. Assuming Elenin follows predictions based on its current brightness, it won’t be visible in large amateur telescopes until late June. That’s according to Seiichi Yoshida’s excellent Weekly Information about Bright Comets. Bad news as the comet will be low in the western sky at the end of twilight at that time. Observers in the southern U.S. (and especially the southern hemisphere) should spot it in small telescopes and binoculars later in July and early August before it’s lost in the twilight glow. The comet then passes between us and the sun in late September.

Once it reappears in the morning sky in October, sky watchers across much of the world should see a nice tail and bright coma through binoculars.

I forget exactly how many comets have drawn me out at night over the years, but it’s upwards of 250. One of reasons I love following them is that unlike many other objects in the sky, they change. Comets get brighter and fainter, grow and lose tails, and sometimes do unexpected things like break into pieces or suddenly fade out. The best surprise Elenin could give us would be to grow brighter than expected. Maybe it’ll even spall to pieces, giving ‘birth’ to several smaller comets. We’ll just have to wait and see.

The International Space Station slowly fades as it's eclipsed by Earth shadow during a pass through Leo the Lion earlier this week. Although difficult to see in the picture, the color of the ISS changed from pale yellow to orange as it experienced orbital sunset. Sunsets happen about every 90 minutes for the astronauts on board as they circle Earth at 17,500 mph. Photo: Bob King

We’ve sure had lots of nice space station passes this week, and more are coming the week next. I hope you’ve caught one or two of them. I was out earlier trying to photograph a pass into Earth’s shadow (above). Sometimes the station fades quickly – depending on its angle to the sun – and sometimes more slowly. This was a slow fade across the constellation of Leo the Lion. I’ve drawn in his ‘head’ which is shaped like a question mark written backwards. Tomorrow I’ll update the blog with times to watch in the coming evenings.

Too bad the atmosphere gets in the way, otherwise we'd see five planets lined up west of the sun this week. Created with Stellarium

There’s another interesting thing happening this week – five of the eight planets are lined up to the west of the sun this week making it easy to visualize how flat the solar system is. Too bad you can’t go out and see them with your eyes. Only Venus is visible very low near the sun during morning twilight. The rest are too close to the sun or too faint to see. Late this month, Mercury, Mars and Jupiter will pull away from the solar glare and make for some nice pairings in binoculars.

A little tilt is all it takes

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I hope the first couple days of spring have lived up to seasonal expectations where you live. They have here, but now a howling snowstorm is on its way, threatening to repave all the lovely, exposed ground with a foot of wet, white concrete.

The sun is shown at noon on the first day of spring (left) and 10 days later. The arrow shows the direction it's moving. Notice that the sun's path, called the ecliptic, intersects the imaginary arc of the celestial equator on the first day of spring. By the 30th, the sun has moved noticeably north of the equator and is higher in the sky. Created with Stellarium

In Sunday’s blog we discussed that the reason for the seasons has to do with the tip or inclination of Earth’s axis, rather than our planet’s distance from the sun. The tip causes first one hemisphere and then the other to alternatively face toward and away from the sun. This makes the sun’s apparent path across the sun swing from low to high to low in the year-long cycle of four seasons. Spring began when the sun crossed the imaginary projection of Earth’s equator – called the celestial equator – on its march northward.

This diagram shows the various tilts of the planets and dwarf planet Pluto. Credit: Image courtesy of Courtney Seligman / cseligman.com

What about the other planets in the solar system? Do they have seasons too? Well, to have seasons, you need to be tipped on your side. You can see that Mercury, Venus and Jupiter have little to no axial tip, so it follows they don’t experience the seasons. The sun follows the same path across the sky, neither dipping low nor ascending to the heights, the entire year round on these planets.

On Earth, and sometimes in Duluth, liquid water returns as winter transitions to spring. Photo: Bob King

Venus is a bit of an oddball. It’s tipped so far over – 177 degrees – that its north pole is where the south pole should be. This extreme tip means Venus is actually rotating backwards or clockwise as seen from above the plane of the solar system. From the same perspective, most of the other planets rotate counterclockwise.

Because Earth, Mars, Saturn and Neptune have similar inclinations, they all experience similar seasons. For instance, right now it’s late spring in Mars’ northern hemisphere and early spring in Saturn’s northern hemisphere.

Keep in mind that seasons on these outer planets last longer than those on Earth, because they take longer to orbit the sun. A typical season on Mars last twice as long as the equivalent on Earth. Neptune takes takes 165 years to journey once around the sun, making spring a tedious 41 years in length. Well, maybe you like spring more than I do.

Pluto and Uranus also have seasons, but surprising things happen when you’re rolling around the sun on your side.

The Hubble Space Telescope photographed Uranus and its rings between 2003 and 2007. The rings, which lie above the planet's equator, went from open presentation in 2003 to edge-on in 2007. Credit: NASA/ESA/M. Showalter

Uranus orbits the sun every 84 years. As the north polar regions face the sun for 21 years, the sun hugs the horizon at the equator and the south pole is in complete darkness. During the next 21 years, the equator faces the sun and all parts of the planet experience sunlight. The poles see sunlight too, but just barely, as the sun circles the horizon for years on end. This is followed by 21 years of sunlight at the south pole and an equally long night at the north pole. The Uranian year wraps up with the equator once again facing the sun with sunlight across the whole planet. Just weird.

Seasons on Earth keep life interesting, but when you add in the rest of the planets, you really get a feel for how much variation is possible from a simple little thing like tilt.