Astronomy & Science

A Star’s Closest Flyby to the Sun

Sky&Telescope -

A red dwarf and its brown dwarf companion buzzed through the outer Oort Cloud some 70,000 years ago, around the time when modern humans began migrating from Africa into Eurasia.

An artist's conception of Scholz's star. The Sun can be seen as a bright background star to the left. Michael Osadciw / University of Rochester.

An artist's conception of Scholz's star. The Sun can be seen as a bright background star to the left.
Michael Osadciw / University of Rochester.

Most of space is empty. So in a galaxy bustling with hundreds of billions of stars, there’s too high a separation between them for any physical run-ins. Even close encounters are few and far between.

But studies of a nearby, low-mass star hiding among the confusion of the galaxy’s disk shows that space might be a little less empty than previously thought.

A year ago, astronomer Eric Mamajek (University of Rochester) heard about a faint star, while chatting with his colleague. This star, nicknamed Scholz’s star, sparked his interest: it was close — only 20 light-years away — yet its proper motion was surprisingly slow, meaning that it inched sluggishly across the sky.

The latter doesn’t mean that the star isn’t moving, but that much of its movement is hidden in its radial velocity, the motion along our line of sight and into the plane of the sky. It became clear that the star had recently passed close to the Solar System and was now moving rapidly away.

Putting the star’s approximate distance and velocity into a “toy code,” Mamajek had a rough answer within 20 minutes: the star had almost certainly sped near the Sun tens of thousands of years ago.

To calculate the star’s trajectory more precisely, and to see just how close it had come, Mamajek needed data on the star’s current position and its motion, both along and into the plane of the sky. A team led by Adam Burgasser (University of California, San Diego) gathered the necessary data.

The star’s proper motion along the plane of the sky can only be measured by waiting long enough for the star to change its position appreciably. Luckily, images as far back as a photographic plate from 1955 had serendipitously captured the star. Between 1955 and 2014, the star had moved roughly 6 arcseconds. (For comparison, your little finger held up to the sky covers a full degree, or 60 arcseconds.)

Burgasser’s team measured the star’s parallax — that tiny back-and-forth motion we see as Earth moves from one end of its orbit to the other — to give the star’s current distance. And spectroscopy showed the slight Doppler shift in the star’s spectral lines as it moves away from us, providing the star’s radial velocity.

Most surprisingly, Burgasser’s team showed that Scholz’s star, a red M-class star, actually has a smaller brown dwarf companion.

With all the pieces of the puzzle, Mamajek and his colleagues were able to trace all the possible paths Scholz’s star may have taken. The team simulated 10,000 orbits for the star to take into account the uncertainties in the star’s position, distance and velocity, as well as the effect of Milky Way’s gravitational field.

Of all those simulations, 98 percent show that the star had passed through the outer Oort Cloud. Its closest approach was probably between 0.6 and 1.2 light-years away, when it scraped the Oort Cloud 70,000 years ago at 83 kilometers per second.

Until now, the top candidate for the closest flyby had been the so-called “rogue star” HIP 85605, discovered by Coryn Bailer-Jones (Max Planck Institute of Astronomy) in a study that analyzed the trajectories of 50,000 nearby stars. That star was predicted to pass 0.13 to 0.65 light-years from our Sun in 240,000 to 470,000 years.

Mamajek and his colleagues, however, demonstrated that the original distance to HIP 85605 was likely underestimated by a factor of ten. At its more likely distance, its newly calculated trajectory would not bring it within the Oort Cloud at all.

Bailer-Jones agrees with the team’s assessment of the rogue star. But he also warns that even though Scholz’s star currently holds the record, it doesn’t hold it by much. A second star, known as Gliese 710, has a more precisely calculated trajectory that shows it flying by almost as close as Scholz’s star. Both close approaches come within each other’s uncertainties.

Nonetheless, the discovery of another close-pass star proves an interesting point. “This is by no means a statistical survey,” says Mamajek. But, he continues, it’s an example of what are likely many more undiscovered nearby stars, whose trajectories might bring them close to the Sun.

The European Space Agency recently launched the Gaia satellite to map out the distances and velocities of billions of stars, bringing low mass stars into focus.

Close encounters could perturb comets in the Oort cloud, shaking them up and sending them our way. “But there is no need to worry,” says coauthor Henri Boffin (European Space Observatory). “Even if the Oort cloud was perturbed, it takes millions of years for a comet in the cloud to reach the Earth.”


Adam Burgasser et al. " WISE J072003.20-084651.2: An Old and Active M9.5 + T5 Spectral Binary 6 pc from the Sun." Astrophysical Journal. February 19, 2015.

Eric Mamajek et al. “The Closest Known Flyby of a Star to the Solar System.” Astrophysical Journal Letters. February 12, 2015.

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Tele Vue’s 3-Inch Paracorr

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Dennis di Cicco with Paracorr telescope

The author with his Meade 12-inch LightBridge used to test Tele Vue’s Big Paracorr. Because the scope was quickly modified as a temporary test bed for the Paracorr it wasn’t planned to be entered in any beauty contests (nor was the author, for that matter).
Dennis di Cicco

As is usually the case for S&T Test Reports involving imaging products, there were more photographs made with Tele Vue’s new 3-inch Big Paracorr coma corrector than would fit in the review that appears in the April 2015 issue. Furthermore, pictures appearing with a review are often selected to emphasize aspects of the product rather than be aesthetically pleasing. Thus we’re presenting here some of the images that remained on the cutting-room floor when the review was prepared for publication.

All the images were made with the Meade 12-inch f/5 LightBridge Dobsonian reflector described in the review and pictured here with the author. As explained in the review, the scope was modified to accept the Paracorr, which requires a 3-inch focuser.

The images were made with an Apogee U16M CCD camera equipped with a KAF-16803 sensor, and, except where noted, all were made through a 3-nm Astrodon hydrogen-alpha filter. They were assembled from 10-minute subexposures that were calibrated with dark and flat-field frames and stacked with MaxIm DL software. The images are reproduced full frame, and with only minimal processing to enhance image contract. No special sharpening or star-enhancement algorithms were used during the processing.

My love of black-and-white deep-sky photographs, especially long-exposure images made through hydrogen-alpha filters, goes back to my earliest days as an astrophotographer shooting Kodak’s “astronomical” emulsions 103a-E, 103a-F, and, later, hypersensitized Tech Pan 2415.

And it’s been my good fortune that this work can be done from the light-polluted backyard of my suburban home less than 20 miles from the heart of downtown Boston. Digital cameras and image processing raised the level of my results far beyond even my wildest expectations in the days of film.

Lightbridge modifications - before & after

The LightBridge modifications included adding a 3-inch focuser that would accept the Big Paracorr and upgrading the original 2.6-inch secondary mirror to a 4-inch mirror, which provided better field illumination for the large-format CCD camera. Parts of the focuser and secondary support were scavenged from the author’s earlier telescope-making projects, making them seem overly built for what was a temporary test setup.

Initially I planned to modify my 12-inch LightBridge only as a temporary test bed for the Paracorr. I didn’t seriously consider the modified scope as a permanent astrograph. Nevertheless, as I mentioned in the review, that wouldn’t have been such a crazy idea.

Lightbridge test set-up

As with the first tests with a 16-inch f/3.2 mirror mentioned in the magazine review, the first-light tests with the modified LightBridge were done with the scope propped up in the author’s driveway to shoot the field around Polaris.

I was initially worried that the front end of the LightBridge wasn’t rigid enough to handle the weight of my heavy CCD camera, filter wheel, the Paracorr, and my homemade focuser, not to mention the 4-inch secondary mirror and heavy spider assembly. I was especially concerned about all the added weight flexing the thin-wall steel used for the scope’s upper tube assembly.

As it turns out, there was some flexure, but it probably could be fixed with minimal reinforcing. The LightBridge’s well-designed truss structure is more than strong enough to handle the extra load. Had I made the LightBridge modifications with a bit more care, and made provision for squaring the focuser/camera to the scope’s optical axis, the setup would be an excellent permanent astrograph.

If it weren’t for my current project of resurrecting the 12-inch f/4 scope that I started building some years ago (it’s mentioned in the review), I would certainly consider re-working the LightBridge for permanent astrophotography with the Big Paracorr and large-format CCD cameras.

The Results North America Nebula

This view of the southern half of the North America Nebula was captured with 90 minutes of exposure. Additional details for all the images are given in the text above.

Elephant Trunk Nebula

One of the first tracked images made with the modified LightBridge was of the region around the Elephant Trunk Nebula within the large emission complex IC 1396 in Cepheus. The image was assembled from seven unguided 5-minute exposures through a red filter. Unlike the other images here, this one was processed without flat-field calibration frames. The review published in the April 2015 issue includes a color image of the Elephant Trunk made this telescope and an SBIG STT-8300 CCD camera.

Horsehead Nebula

80 minutes of total exposure were used for this view of the famous Horsehead Nebula in Orion. Despite the extraordinarily bright star Alnitak (Zeta Orionis) at the eastern end of Orion’s Belt, there are no objectionable haloes or reflections introduced by the Paracorr optics.


IC 443

There are also no reflections due to the bright star Eta Geminorium adjacent to the unusual nebula IC443 in Gemini captured in this 170-minute exposure.

Rosette Nebula

One of the most-photographed objects in the northern winter Milky Way is the Rosette Nebula in Monoceros. This view is a 110-minute exposure.

A wealth of nebulous detail surrounds the Christmas Tree asterism nicknamed by the 20th-century astronomy popularizer Leland Copeland. Prominent near the bottom of this 190-minute exposure is the appropriately named Cone Nebula.

A wealth of nebulous detail surrounds the Christmas Tree asterism nicknamed by the 20th-century astronomy popularizer Leland Copeland. Prominent near the bottom of this 190-minute exposure is the appropriately named Cone Nebula.

The post Tele Vue’s 3-Inch Paracorr appeared first on Sky & Telescope.

Inside the April 2015 Issue

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FC_Apr2015_172pxApril Pilgrimages: To Ceres, Deep-Sky Wonders, and Beyond!

"Whan that Aprille with his shoures soote..." April is the month when heading out at night gets a little less chilly and a lot more fun. So it's the perfect month, as Geoffrey Chaucer wrote, to go on pilgrimages. Join S&T contributing editor Emily Lakdawalla as she guides us through the journey of the Dawn spacecraft to the largest asteroid, Ceres. Then follow the historical footprints of William and Caroline Herschel and relive their legendary night of discovery: on April 11, 1785, exactly 230 years ago, they recorded 74 new galaxies, nebulae, and star clusters. Then take that history and science with you (and the magazine too!) as you head outdoors. April's evenings feature five bright planets and deep-sky jewels aplenty, perfect for after-dinner expeditions through the cosmos.

Feature Articles Dawn

The Dawn spacecraft

Dawn Arrives at Ceres
NASA's spacecraft enters into orbit around the largest asteroid in the main belt.
By Emily Lakdawalla

WorldWide Telescope
Take a virtual and interactive tour of the universe.
By Alyssa Goodman & Curtis Wong

William Herschel's Extraordinary Night of Discovery
Recreating the legendary sweep of April 11, 1975.
By Mark Bratton

Astronomy Aboard SOFIA
After two decades of trial and tinkering, the Stratospheric Observatory for Infrared Astronomy (SOFIA) is finally flying high.
By J. Kelly Beatty

Backyard DSLR Imaging
Get the most out of your deep-sky imaging from any location with these helpful tips.
By Richard Jakiel

Beyond the Printed Page Fig6_VallesMarineris

The WorldWide Telescope hovers over Valles Marineris on Mars.

The Herschel Sprint by JR
Experience the Herschels' "Night of Discovery" for yourself.

How to Use the WorldWide Telescope by Monica Young
Learn how this interactive software can be used to research and educate.

Follow the Dawn Spacecraft
Keep up to date on Dawn's visit to Ceres by following posts from chief engineer Marc Raymond.

Lunar Librations by Sean Walker
Librations and other lunar data for April 2015.

ALSO IN THIS ISSUE Image of red Moon during lunar eclipse April 15, 2014

The total lunar eclipse on April 15th, 2014.
Joel D. Tonyan (Sky & Telescope's Online Photo Gallery)

The Pilgrim's Way
Venus and Jupiter lead us on a journey through spring skies.
By Fred Schaaf

A Barely Total Lunar Eclipse
On the morning of April 4th, the Moon skims just inside Earth's umbra.
By Alan MacRobert

Spring's Hit Parade
A blood-red gem and a misty bird of prey top the charts.
By Sue French

Table of Contents
See what else April's issue has to offer.

The post Inside the April 2015 Issue appeared first on Sky & Telescope.

Donald C. Parker, 1939-2015

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A planetary imaging pioneer passed away in Miami, Florida.

Parker It is with a profound sense of loss that we announce the passing of long-time planetary observer and Sky & Telescope contributor Donald C. Parker on the evening of February 22, 2015. Parker was a pioneer of planetary astrophotography and an inspiration to generations of imagers around the world.

Born in 1939, Parker was raised in Highland Park, Illinois, where he caught the astronomy bug at a young age. He built several telescopes during the 1950s, including an 8-inch f/7.5 Newtonian reflector that was featured in the November 1957 issue of Sky & Telescope.

Donald earned a medical degree from Northwestern University and served as a medical officer in the United States Navy, where he conducted research into diving physiology.

After relocating to Florida to begin a career in anesthesiology, Donald resumed his fascination with observing the planets, particularly Mars. He became Mars Section Coordinator for the Association of Lunar and Planetary Observers (A.L.P.O.) in 1977. There, he became acquainted with the Lowell Observatory astronomer Charles F. Capen, who encouraged Don to refine his observing skills and introduced Don to advanced planetary photographic techniques. Don quickly mastered the extensive darkroom technique of stacking images and rose to the forefront of amateur planetary photography. In 1988 he co-authored the book “Introduction to Observing and Photographing the Solar System” with Capen and fellow amateur Thomas A. Dobbins.

He continued to be a pioneer at the forefront of planetary observing and imaging techniques, and played a role in developing many of the methods used in digital planetary imaging today, as well as being credited with the discovery of features on Mars and Jupiter. Many of his 20,000+ images of the planets have supported professional researchers at NASA, JPL, and other institutions.

Don Parker (4th from right, front row) surrounded by family and friends at the Winter Star Party on February 18, 2015. Photo courtesy of Manuel R. Padron.

Don Parker (4th from right, front row) surrounded by family and friends at the Winter Star Party on February 18, 2015. Photo courtesy of Manuel R. Padron.

Parker co-authored scores of papers in scientific journals, popular magazines, and news sites worldwide, including a paper in Nature published only weeks ago. In 1994, the International Astronomical Union named asteroid 5392 Parker in his honor for his contributions to solar system science. A frequent speaker at amateur conventions, he delighted audiences with his colorful and often self-deprecating humor.

As an astrophotographer myself, I had the honor of befriending Parker more than a decade ago. We traded imaging techniques and discussed the latest developments in camera technology and software. Parker was my inspiration to begin imaging the planets after seeing his series of images recording the impact scars of comet Shoemaker-Levy 9 in the cloud tops of Jupiter in 1994. He was never guarded about his techniques and gladly shared them with anyone who was interested. He maintained his razor-sharp intelligence, wit, and an unfailingly kind disposition to the end. It’s difficult to convey in words just how funny and entertaining Don was. I’m certainly going to miss our frequent conversations about the latest discoveries in the solar system, which often focused on how amateurs contributed to them.

The post Donald C. Parker, 1939-2015 appeared first on Sky & Telescope.

Cepheids Map Milky Way – and Beyond

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Cepheid variable stars are helping astronomers see what our galaxy looks like from within.

Cepheids on Milky Way map

This annotated map of the Milky Way galaxy shows the rough location of the Cepheid stars discussed in three independent studies: Dekany et al. (purple), Chakrabarti et al. (red arrow, since they lie far off the galactic disk), and Feast et al. (green). Click image to enlarge.
NASA / JPL-Caltech

How many spiral arms does the Milky Way have? How far does its disk extend? Even the simplest questions about the galaxy we call home are still up for debate. Now, in what is likely only the beginning of a larger effort, three independent studies are using a famous class of pulsating star to map out hidden reaches of the Milky Way.

Classical Cepheid variables are aging massive stars whose fame derives from their bid to avoid gravitational collapse. Having run out of hydrogen to fuse in their cores, they struggle to burn shells of helium instead, puffing up and deflating at a rate directly tied to their intrinsic luminosity.

That deceptively simple relation, which Henrietta Leavitt discovered in 1908, has led to profound revisions in everything from the shape and extent of our galaxy to the fate of the universe.

Now astronomers are increasingly studying Cepheids in near-infrared light, and they are beginning to pierce the veils of dust and gas that enshroud the Milky Way.

“Our knowledge of galactic structure is rather unsatisfactory . . . no consensus exists,” says Daniel Majaess (Saint Mary’s University and Mount Saint Vincent University, Canada).

That’s what motivates surveys such as VISTA Variables in Vía Láctea (VVV). The VISTA telescope at Paranal Observatory in Chile has already cataloged about a billion point sources. Since 2010, it has returned again and again to look at their variability over time. The VVV survey is expected to turn up hundreds of classical Cepheids — an incredible number when you consider the importance of just two Cepheids on the far side of the Milky Way.

The Twins Two Cepheids on Milky Way's far side

Seeing through the Trifid Nebula, Dekany et al. glimpsed two Cepheids on the far side of the galaxy.
ESO / VVV consortium / D. Minniti

István Dékány (Millenium Institute of Astrophysics, Chile, and Pontificia Universidad Católica de Chile), Majaess, and colleagues announced the discovery of two Cepheids 37,000 light-years from Earth and 11,000 light-years from our galaxy’s center. The pair is remarkably close, separated by only 3 light-years, and both are between 45 million and 51 million years old.

Given their similarities, these Cepheids were most likely born in the same star cluster in the “Far 3 kpc Arm,” a spiral arm thought to circle the far side of the galaxy’s star-packed bulge. But deeper observations will need to confirm this — the intense amount of dust and the sheer number of stars in the bulge prevent the authors from identifying any other members of the alleged cluster. For now, they dub it the “Invisible Cluster.”

The Quadruplets

Just two weeks after Dékány’s team published their results, another study (now accepted to Astrophysical Journal Letters) reported an additional four Cepheids in VVV data. But the pulsing stars found by Sukanya Chakrabarti (Rochester Institute of Technology) and colleagues were nowhere near the bulge — they appear to be almost 300,000 light-years from the Sun.

You read that right. These stars lie far beyond the Milky Way’s disk, which is about 100,000 light-years across. And this find is all the more interesting because Chakrabarti had predicted the existence of a dwarf galaxy at that exact location six years ago.

Astronomers had previously detected ripples in the outer part of the Milky Way’s gas disk, which can’t be explained in an isolated spiral galaxy. Instead, such ripples might come from gravitational interactions with smaller, dwarf galaxies. Chakrabarti ran simulations that showed a dwarf one-hundredth the mass of the Milky Way could have passed through our galaxy to create the mysterious ripples. The dwarf would have escaped detection until now because it’s dim and lies right behind the Milky Wayplane from our perspective. She even predicted its orbit and structure.

“I had hoped that because the prediction was very specific, observers would try and search for this dwarf galaxy,” Chakrabarti adds. “I finally decided to look for it myself.”

And she seems to have found exactly what she was looking for. But there’s a catch.

The classical Cepheids researchers tend to look for are the more common variable stars: massive, young (even as they near the end of their lives), and pulsating. But a second type of Cepheid variable, called Type II, are actually much less massive stars (half the mass of the Sun or so) and about 100 times older, so their intrinsic luminosity is much fainter.

Trouble is, Type II Cepheid light curves masquerade as classical Cepheids pretty well, with the same general shape of pulsations. And if Chakrabarti’s Cepheids are of the Type II variety, then they lie only 160,000 light-years away. They’d still be an interesting (and puzzling) find, but one that wouldn’t match the precise prediction for the dwarf galaxy.

But Chakrabarti’s money is on these Cepheids being of the classical variety. For one, Type II Cepheids are less common, and therefore less likely. And Chakrabarti and colleagues also see red clump stars, luminous giant stars that in aggregate serve as another kind of standard candle, at the same location in the sky and at the same distance.

Spectroscopy will cinch the matter, though it will be a challenge for these faint stars. If the team can get radial velocity observations, they can see whether the clump of Cepheids moves together, and if they move in the way predicted for the dwarf’s passage through the Milky Way.

Still More Cepheids

All of these results come after a study published last year in the May 15th Nature. Michael Feast (University of Cape Town, South Africa) and colleagues followed up on 32 possible Cepheids discovered in the Optical Gravitational Lensing Experiment (OGLE), using the South African Large Telescope (SALT) and the Infrared Survey Facility. The spectroscopy and near-infrared images allowed the team to more definitely determine the “classical” status of five Cepheids.

These five Cepheids again lie in the outer reaches of the Milky Way’s disk, though at distances less extreme than those found in Chakrabarti’s study, between 42,000 and 72,000 light-years from the galaxy’s center.


Five Cepheids in Milky Way's flared disk

The five classical Cepheids discussed in Feast et al. lie above and below our galaxy's plane as pictured here, so the authors suggest they could be part the outer Scutum-Centaurus arm, which flares on the very outer edge of the disk. The Sun is the yellow circle on the right side, surrounded by local Cepheid variables known at the time.
Robin Catchpole (University of Cambridge, UK)

Since classical Cepheids are massive and young, they are typically associated with spiral arms. It would be odd to see one of these stars sitting out in the galactic halo. So Feast’s team suggested that these Cepheids lie in the Outer Scutum-Centaurus arm, which would have to flare to account for the Cepheids’ spread above and below the galactic plane.

“Clearly, these Cepheids are just the tip of the iceberg,” Feast and colleagues write. The VVV survey and others are well on their way to revealing the rest.

Sukanya Chakrabarti et al. "Clustered Cepheid Variables 90 Kiloparsecs from the Galactic Center." Accepted for publication in Astrophysical Journal Letters.

István Dékány et al. "Discovery of a Pair of Classical Cepheids in an Invisible Cluster Beyond the Galactic Bulge." Astrophysical Journal Letters, 19 January 2015.

Michael Feast et al. "Cepheid Variable in the Flared Outer Disk of Our Galaxy." Nature, 15 May 2014.

Do you teach astronomy? You might be interested in Sky & Telescope's lab exercises, such as "Cepheid Variables and the Cosmic Distance Scale."

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Introducing Sky & Telescope’s Earth Globe

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Satellite imagery and other datasets come together to show our home planet from mountaintop to ocean bottom.

Earth is our home. It's the planet we know best, our terra cognita. And for centuries, cartographers have attempted to portray what we've learned about this world — first as maps (some more fanciful that others) and eventually as round globes.

Having produced globes of the Moon, Venus, Mars, and Mercury, the Sky & Telescope staff thought it was high time to add a version of Earth to our growing collection. However, rather than mimicking the usual geopolitical format, with lines identifying national boundaries and labels for countries and major cities, we opted for a version that shows our planet's best features: its mountains, valleys, and other major geologic structures.

The project began with a search for the best portrayals of both land and sea. The goal was to show land masses very close to their natural color, while simultaneously depicting the fascinating topography hidden beneath the oceans and seas.

Himalaya Close-up

To preserve the natural beauty and underlying detail of the base map, only a limited number of geologic features are labeled.
Sky & Telescope illustration

Data for the land portion comes from a mosaic of thousands of images, known as the Blue Marble, acquired by MODIS instruments (short for Moderate Resolution Imaging Spectroradiometer) aboard NASA's Terra and Aqua satellites. The MODIS instruments make their observations in 36 spectral bands at a resolution of 500 meters (0.3 mile) per pixel and with consistent solar illumination. Our globe depicts Earth as it appears in September — the transition from summer to autumn in the Northern Hemisphere and the onset of spring in the Southern Hemisphere.

For the 71% of the globe not involving land, we turned to bathymetry from the British Oceanographic Data Centre. BODC scientists amass these data using "acoustic radar" — by generating sound waves at the surface that travel through the water, bounce of the seafloor, and return upward to waiting detectors. These acoustic echoes also reveal details about the size and shape of seamounts (underwater mountains) and seafloor roughness. Darker blue shadings indicate greater depths.

No sea ice is shown, which makes it easy to distinguish water from land. Nor are there clouds — though at any given moment they hide about 70% of our planet.

Earth globe daisy

Before it can be wrapped into its final shape, each hemisphere (north and south) must first be projected into this unique shape — a combination of azimuthal equidistant projection near the poles and polyconic projection for each 30°-wide longitude gore.
Sky & Telescope illustration

S&T illustration director Gregg Dinderman then combined these databases into a single base map. But a big rectangle doesn't conform to a sphere seamlessly — a special projection was needed. For that we turned to cartographer Michael Zeiler of, who created a unique "daisy-shaped" projection for each hemisphere using Esri's ArcGIS software.

"I received the map in a Plate-Carree projection, a rectilinear portrayal that treats geographic coordinates (latitude and longitude) as Cartesian (x,y) coordinates," explains Zeiler. Then he transformed the map's gores, each 30° of latitude wide, in a polyconic projection, while utilizing azimuthal equidistant projections for the arctic and antarctic areas (latitutdes above 80°).

Sky & Telescope's Earth Globe

Sky & Telescope's Earth Globe has a diameter of 12 inches, which corresponds to a scale of 1:42,000,000.
Sky & Telescope illustration

"These were quite large files," Zeiler adds, "because we wanted to work at a very high resolution so that the stretching and compressing of pixels from the Plate-Carree to the polyconic projection would not be visible." Dinderman then assembled the pieces, added labels for key features, and delivered the huge files to Replogle Globes for printing and globe production. (Here's a fascinating 5-minute video showing how Replogle assembles its globes.)

We're pleased with how it all turned out. Our hope is that, by scrutinizing our custom Earth Globe — and especially by comparing it with those of other worlds — you'll gain a deeper appreciation for our planet's geologic features and its unique status among the solar system's many diverse worlds.

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This Week’s Sky at a Glance, February 20 – 28

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Some daily sky sights among the ever-changing Moon, planets, and stars. Venus, Mars and the Moon form a tight bunch as twilight fades on Friday, Feb. 20, 2015.

Venus, Mars, and the Moon form a tight bunch as twilight fades. (The Moon here is positioned for an observer near the middle of North America. It's drawn three times its actual apparent size.)

Conjunction of Mars and Venus, Feb. 21, 2015.

A day later Mars and Venus appear closest, with the thickening crescent now above them.

Friday, February 20

Venus, the thin crescent Moon, and little Mars form a tight bunch in the west-southwest during and after dusk, as shown at right. They fit in a circle just 2° across at the times of dusk for most of North America. Think photo opportunities! See our article, Venus and Mars Pair Tightly at Dusk.

We have just a few more days to follow Comet Lovejoy, still 5th magnitude, high in a moonless evening sky this month.

Saturday, February 21

Venus and Mars are in conjunction 0.4° apart at dusk, with the Moon now looking on from above.

Two mutual events among Jupiter's moons. Watch Europa pass in front of Io this evening, from 9:05 to 9:11 p.m. EST. Their combined light dims by 0.6 magnitude (not quite half) at the center of this time.

Then less than an hour later, Europa casts its shadow onto Io from 9:41 to 9:49 p.m. EST, dimming Io by 0.9 magnitude at the mid-time.

Watch Christopher Go's highly magnified videos of Europa occulting Io and then Europa eclipsing Io on February 18th. (The gray spot at the center of each satellite is a processing artifact.)

Sunday, February 22

Jupiter blazes in the east after dark this week. High above it are Pollux and Castor. Look about half as far to Jupiter's right for the dim head of Hydra, the Sea Serpent, about the width of your thumb at arm's length.

Before the Moon starts brightening the evening sky too much, take a telescopic tour through some of the Melotte star clusters with Sue French's Deep-Sky Wonders column, charts, and photos in the March Sky & Telescope, page 58.

Monday, February 23

Spot the Pleiades high above the Moon after dark. Look to the Moon's right, just a little less far, for the brightest stars of Aries lined up nearly vertically.

Tuesday, February 24

Soon after nightfall, look upper right of the Moon for the Pleiades and upper left of the Moon for Aldebaran and the Hyades.

One of the most famous challenge objects for amateur astronomers is Sirius B, Sirius's white-dwarf companion. The pair has been widening for the last two decades, and now Sirius B stands a good 10.7 arcseconds to Sirius's east. To try to extract it from the dazzlement of the 10,000-times-brighter primary star, see the tips and tricks in the March Sky & Telescope, page 50.

A much easier white dwarf is Omicron2 Eridani B, also described there and also now in the evening sky.

Wednesday, February 25

Look for Aldebaran shining near the first-quarter Moon.

Thursday, February 26

Watch Jupiter's satellite Europa reappear from eclipse out of Jupiter's shadow at 10:23 p.m. EST (7:23 p.m. PST), just off Jupiter's eastern limb.

Mercury is at greatest elongation low in tomorrow's dawn, 27° west along the ecliptic from the Sun.

Friday, February 27

Venus and Mars in the western twilight have widened to be 2.7° apart. Find faint little Mars beneath Venus not.

Saturday, February 28

Early this evening, the dark limb of the waxing gibbous Moon will occult (cover) the 3.6-magnitude star Lambda Geminorum for North America east of the Mississippi and north of the deepest South.

Some times: central Massachusetts, 8:00 p.m. EST; Washington DC, 7:56 p.m. EST; Chicago, 6:31 p.m. CST (in twilight); Kansas City, 6:21 p.m. CST (in twilight). See map and detailed timetables of both the disappearance and the (unobservable) reappearance; be careful not to mix these up when scrolling down the table.

Want to become a better astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby; for an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).

Pocket Sky Atlas

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but it's still less than one per square degree on the sky. Also plotted are many hundreds of telescopic galaxies, star clusters, and nebulae.

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The standards are the little Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger and deeper Sky Atlas 2000.0 (stars to magnitude 8.5); and once you know your way around, the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, the bigger Night Sky Observer's Guide by Kepple and Sanner, or the beloved if dated Burnham's Celestial Handbook.

Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (able to point with better than 0.2° repeatability, which means fairly heavy and expensive). As Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."

This Week's Planet Roundup

Jupiter on February 18th, by <a href=

Mercury (magnitude 0.0) glimmers just above the east-southeast horizon in early dawn. As the sky brightens toward sunrise, you'll need binoculars.

Venus (magnitude –3.9) and Mars (less than 1% as bright, at magnitude +1.3) appear very close together in the west-southwest during evening twilight.

On Friday the 20th the crescent Moon joins them to make a beautiful bunch-up. On Saturday the 21st Venus and Mars are in conjunction, 0.4° apart with Mars just to Venus's upper right as seen from North America. In the following days, Mars moves down and away from Venus.

Jupiter (magnitude –2.6, in Cancer) is two weeks past opposition. Watch for it coming into view in the eastern sky early in evening twilight. As night falls, look to its left and lower left for the Sickle of Leo. By 9 or 10 p.m. Jupiter is nearly as high as it will get. In a telescope Jupiter is still a big 45 arcseconds wide at its equator.

Saturn (magnitude +0.5, at the head of Scorpius) rises around 2 a.m. It's best placed in the south as dawn begins. Below Saturn by 8° or 9° is orange Antares.

Look 1.6° to Saturn's lower right in early dawn for Beta Scorpii, magnitude 2.5, a showpiece double star for telescopes. Look much closer just below Saturn for fainter Nu Scorpii, a wider telescopic double.

Uranus (magnitude 5.8, in Pisces) is getting low in the west just after dark, to the upper left of Venus and Mars. Finder chart.

Neptune is hidden in conjunction with the Sun.

All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.

Eastern Standard Time (EST) is Universal Time (UT, UTC, or GMT) minus 5 hours.

“This adventure is made possible by generations of searchers strictly adhering to a simple set of rules. Test ideas by experiments and observations. Build on those ideas that pass the test. Reject the ones that fail. Follow the evidence wherever it leads, and question everything. Accept these terms, and the cosmos is yours.”

— Neil deGrasse Tyson, 2014.

The post This Week’s Sky at a Glance, February 20 – 28 appeared first on Sky & Telescope.

The Kavli Foundation Q&A: Insights Into Cosmic Inflation

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Recently, two high-profile experiments released new data and analyses of the universe’s earliest light. Watch a live discussion of the latest results, what they mean for the theory of cosmic inflation, and what we can expect to learn about the very early universe in the coming decade.

The oldest light in the universe, called the cosmic microwave background, is a fossil from the Big Bang that fills every square inch of the sky. It provides a glimpse of what the universe looked like 14 billion years ago, and can shed light on everything from the evolution of the universe to how much dark matter and dark energy the universe contains.

Recently, two high-profile experiments released new data and analysis of this early light. These data support the theory of cosmic inflation, which posits that the universe underwent an enormous expansion in the moments following the Big Bang. During this time, space grew monumentally, swelling from smaller than a proton to an enormity that defies comprehension.

Courtesy of The Kavli Foundation, Sky & Telescope is featuring an in-depth Q&A that took place on February 18, 2015. Three preeminent scientists came together to discuss these latest results, what they mean for the theory of inflation, and what we can expect to learn about the very early universe in the coming decade.

About the Participants

GEORGE EFSTATHIOU is a cosmologist with a leading role in the Planck mission, which studies the oldest light in the universe. He is the Director of the Kavli Institute for Cosmology at the University of Cambridge and Professor of Astrophysics at the University of Cambridge.

CLEMENT PRYKE is an experimental cosmologist and Associate Professor at the University of Minnesota. He has played a leading role in the construction and operation of a series of telescopes that study the universe's first light from the South Pole, and in analyzing the data they produce.

PAUL STEINHARDT is the Albert Einstein Professor in Science and Director of the Princeton Center for Theoretical Science at Princeton University. His research spans particle physics, astrophysics, condensed matter physics and cosmology, and he shared the 2002 P.A.M. Dirac Medal for his role as one of the architects of inflationary theory.

KELEN TUTTLE (moderator) is a freelance journalist with more than a decade of experience in science communications. Most recently, she served as Editor in Chief of Symmetry, a magazine dedicated to the science and culture of particle physics. Her fields of expertise also include astrophysics, biology and chemistry.

The post The Kavli Foundation Q&A: Insights Into Cosmic Inflation appeared first on Sky & Telescope.

The Kavli Foundation Q&A: What Has Planck Taught Us About the Early Universe?

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The latest data release from the Planck space telescope offers insight into everything from the fabric of space to dark matter — and may even have a shot at detecting gravitational waves, says Kavli Institute for Cosmology Director George Efstathiou.

From its orbit 930,000 miles above Earth, the Planck satellite spent more than four years detecting the oldest light in the universe, called the cosmic microwave background. This fossil from the Big Bang fills every square inch of the sky and offers a glimpse of what the universe looked like almost 14 billion years ago, when it was just 380,000 years old. Planck’s observations of this relic radiation shed light on everything from the evolution of the universe to the nature of dark matter.

Earlier this month, Planck released new maps of the cosmic microwave background supporting the theory of cosmic inflation, which posits that the universe underwent a monumental expansion in the moments following the Big Bang. During this time, space expanded faster than the speed of light, growing from smaller than a proton to an enormity that defies comprehension.

Courtesy of The Kavli Foundation, Sky & Telescope is featuring a conversation with Dr. George Efstathiou, director of the Kavli Institute for Cosmology at the University of Cambridge and one of the leaders of the Planck mission, to better understand Planck’s latest results and their implications for the theory of inflation.

The following is an edited transcript of a roundtable discussion, which took place via teleconference on February 10, 2015. The participants have been provided the opportunity to amend or edit their remarks.

THE KAVLI FOUNDATION: In 2013 and now this year, Planck provided very strong experimental evidence supporting the theory that the universe went through a mindbogglingly rapid expansion in its very first moments. Can you elaborate on the latest findings and why they’re important?

GEORGE EFSTATHIOU: Inflation – the theory that the early universe expanded incredibly rapidly in its first moments – makes a number of generic predictions. For example, the geometry of the universe should be very close to flat, and this should be reflected in fluctuations we see in the cosmic microwave background light. With the first Planck data, which we released in 2013, we verified some aspects of this model to pretty high precision by looking at the temperature of the cosmic microwave background across the sky. With the 2015 release, we improved the precision of those temperature measurements and also added accurate measurements of a twisting pattern in the cosmic microwave background called polarization. These polarization measurements are really important in telling us what the fabric of space was like in the early universe.

You see, there are several possibilities. For example, in some models motivated by higher-dimensional theories such as string theory, “cosmic strings” can be produced in the early universe, and these would generate a different type of fluctuation pattern. We see no evidence for cosmic strings or other types of cosmic defect. What we found is that everything is consistent – with a very high precision – with simple inflationary models. So, for example, we now can say that the universe is spatially flat to a precision of about half a percent. That’s a substantial improvement over what we knew before Planck.

BeckmanUCIThe European Space Agency’s Planck satellite was launched into space in 2009. During its 4-year mission, it observed variations in the cosmic microwave background across the entire sky. The first all-sky map was released in March 2013 and the second, more detailed map was released in February 2015. The mission’s successes include determining that the universe is slightly older than thought; mapping the early universe’s subtle fluctuations in temperature and polarization, which eventually gave rise to the structure we see today; and confirming that 26 percent of the universe comprises dark matter. (Credit: ESA)

TKF: You’ve called the theory of cosmic inflation a cartoon of a theory. What did you mean by that?

EFSTATHIOU: We don’t yet understand the fundamental physics that drove inflation, and we certainly don’t understand the details of how it worked. The simplest model of inflation requires that the early universe contained what’s called a scalar field. This field permeates all of space and is responsible for causing space to expand faster than the speed of light. And, as with all quantum fields, it contains quantum fluctuations. It’s those tiny quantum fluctuations that, once they were stretched in size during inflation, generated the structure that we see across the Universe today – all of the galaxies and stars and planets. That’s a simple model of inflation.

Now, what is that field exactly? We don’t know. There are many theories out there, but really they’re all just guesses. That’s why I called it a cartoon of a theory – because we don’t understand how inflation works in any fundamental sense. What we need is better experimental data that tells us what the early universe looked like and hopefully this will point us toward a fundamental theory of inflation.

TKF: Does that mean the next steps are experimental as opposed to theoretical?

EFSTATHIOU: That is a very interesting question. In my mind, real progress will require experiments, because the very early universe involves energy scales so much higher than anything we’ve been able to test in laboratory experiments here on Earth. When you make such a very big leap, you don’t really know what things look like. That leaves open lots and lots of possibilities. For example, the extra dimensions predicted by string theory are hidden from us – so we don’t experience them. They must be very small and “compactified” in some way – but how, we don’t know. So from the theory point of view, there are just too many options right now. Also, in cosmology, we’re talking about highly dynamic situations. Everything is changing very rapidly and that’s also difficult to analyze theoretically. There’s always the possibility that some tremendous new theoretical insight will narrow down the options.

But I think that we need to do experiments – if we can – that narrow down the options experimentally. If we detected gravitational waves, which are ripples in the curvature of space-time, that measurement would narrow down the options a lot. It would tell us the energy scale of inflation. What’s more, any detectable level of gravitational waves would establish an empirical link with quantum gravity. Quantum gravity, which would align the force of gravity with the principles of quantum mechanics, is a very important experimental target, one that is possible to reach with high precision experiments. I think that would be the most likely experimental development that could actually make contact with physics at the very high energy scales of the early universe.

TKF: One of the most publicized new revelations from Planck is evidence the first stars in the universe started to shine about 550 million years after the Big Bang – which means they are younger by about 100 million years than previously thought. How could we have gotten this so wrong? 

EFSTATHIOU: You know, I’m not so keen on claiming this as a great scientific achievement by Planck – but it is interesting. To explain why, I need to give you a little background. At the end of inflation, we know that the universe became very, very hot. Since then, as the universe expanded, it cooled down. And when the universe was 400,000 years old, the temperature was low enough that electrons and protons could combine to form neutral hydrogen. So at that time, the universe was neutral and pretty uniform.

We can see quasars – very bright compact regions at the centers of distant galaxies – that existed back when the universe was about 840 million years old. That’s really very young compared to its 13.8 billion years today. Back then, if the universe had been filled with neutral hydrogen, that hydrogen would have absorbed quasar light at short wavelengths and we wouldn’t be able to see it in our measurements today. So because we can see this light from these quasars, we know that when the universe was 840 million years old, it was no longer neutral. Sometime between the Universe being 400,000 years old and 840 million years old, energy must have been injected into the gas to change this. So the question is, where did that energy come from?

Well, it must be that stars formed and started to release energy. Now, looking at the deepest images from the Hubble Space Telescope, we can see some of these very early stars. But from the stars we see, it wouldn’t be possible to release enough energy to ionize the hydrogen by the time the universe was 420 million years old – as was suggested by previous measurements of the cosmic microwave background made with the Wilkinson Microwave Anisotrophy Probe – or WMAP – satellite. Now, with the Planck measurements, we’re saying that it happened a bit later, at 560 million years. That difference of about 140 million years may not sound like a lot, but it now brings all of our observations into alignment.

This is a very, very difficult measurement to make – it’s a very small signal hidden behind a lot of contamination from our own Milky Way. You have to dig out the real signal from all this noise. With Planck, we were for the first time able to make this measurement using the Planck data in two different ways. Why I’m not so keen on it as a real highlight from Planck is that there’s absolutely nothing wrong with the previous measurements. The WMAP observations are perfectly fine, but if you take their maps, and correct for contamination by the Milky Way, then you get the same answers as the Planck results. So everything is consistent in the end.

BeckmanUCIThe Background Imaging of Cosmic Extragalactic Polarization 2 (BICEP2) experiment, shown here in the foreground, studies the cosmic microwave background from the South Pole, where cold, dry air allows for clear observations of the sky. In March 2014, the BICEP2 team announced that they had seen evidence of gravitational waves, offering what seemed to be “smoking gun” evidence of inflation. Although a Planck-BICEP2 joint analysis has since shown that dust in the Milky Way mimicked the signal expected from gravitational waves, future experiments may yet discover these long-sought features of the early universe. (Credit: Steffen Richter, Harvard University)

TKF: The Planck results are also helping us understand dark matter, the mysterious substance that makes up 20 percent of the universe yet has yet to be well understood. What exactly have we learned about dark matter from Planck?

EFSTATHIOU: What do we know? Really, we’re still a long way from understanding dark matter. The leading candidate is a type of particle predicted by supersymmetry. That theory predicts a partner particle for each particle that we already know. But if that theory is true, supersymmetric particles should appear in collisions at the Large Hadron Collider. So far, they haven’t. So dark matter is still unknown.

Planck has detected no signal of dark matter. Supersymmetry predicts that dark matter particles should occasionally interact with other dark matter particles and produce a flash of energy – a process called annihilation. But we don’t see it. That’s really not all that surprising. It’s easy to hide. So that’s something that future cosmic microwave background experiments might be able to see. But we haven’t seen any signs of annihilating dark matter from Planck.

We have looked also very carefully at neutrinos – tiny, ubiquitous particles we know come in three types. As far as well can tell, there are no other types of neutrinos that could help account for some of the dark matter. People are also still trying to determine the mass of these three neutrinos. We know from other experiments the least mass that these three particles could have. Planck has now set a limit on the most mass that they could possibly have. We’re narrowing down the options, and will hopefully soon learn their exact mass. Neutrinos are some of the most mysterious particles in the universe, so this would be an important step toward understanding them.

Some theorists have also suggested that dark matter and dark energy could interact in some way. As far as we can tell, dark energy is completely constant – so there’s no evidence that it interacts with dark matter.

TKF: We would be remiss if we didn’t talk a bit more about gravitational waves. Last March, another experimental team called BICEP2 announced that they had seen evidence of gravitational waves in their observations of the very early universe. Then, just a few weeks ago, joint analysis of that data carried out by members of both Planck and BICEP2 revealed that unidentified gas and dust had contaminated the data, and that gravitational waves remain undiscovered. What does this mean for future hopes of discovering gravitational waves?

EFSTATHIOU: When the BICEP2 team announced their result, I was really shocked. The signal they detected was really big. We had already done an analysis based on the Planck 2013 data, and we had set a limit on how big the signal could be. And BICEP2’s measurements were about twice as big as that. So if BICEP2 really had detected gravitational waves,  there would need to be some really strange and unexpected physics at work for us to get such different results.

The BICEP2 group knows what it’s doing – these guys are as good as any group in the world. And they’ve been working on various versions of this experiment for 7 or 8 years. So from the experimental side, the data is beautiful. They clearly detected something.

BeckmanUCIThis map, captured by ESA's Planck space telescope, reveals the Milky Way galaxy.  Gas appears in yellow, radiation in blue and green, and several types of dust in red. (Credit: ESA/NASA/JPL-Caltech)

That something could have been gravitational waves, or it could have been intervening dust that confused their data. The BICEP2 experiment looks at a very small field of view, and Planck’s signal to noise is not very big. So we arranged to collaborate. Essentially, we improved the signal to noise on dust by cross-correlating their maps with ours. That showed that, as of yet, we still have no statistically significant evidence of gravitational waves. That resolves the conflict with the original Planck results. And, in the big picture, that’s a good thing. No really strange physics is needed to reconcile the two experiments.

So now we’re in a situation where we have a limit on the size of a gravitational wave signal, and that number is consistent with the Planck results. It doesn’t rule out gravitational waves by any means. If you look at the joint analysis, you see that there’s plenty of room for gravitational waves to be lurking there, just below the level we’ve set by combining the BICEP2 and Planck data. If that’s true, it shouldn’t take a very long time to dig it out. So there could be a very important development coming.

The post The Kavli Foundation Q&A: What Has Planck Taught Us About the Early Universe? appeared first on Sky & Telescope.


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