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Peaks of “Eternal” Light

Sat, 06/24/2017 - 06:00

If we ever try to live on the Moon, the best locations will be polar mountains bathed in nearly continuous sunlight.

This is the time of year when we become keenly aware that Earth’s equator is inclined 23½° to the plane defined by its orbit around the Sun. The solstice fell on June 21st at 4:24 Universal Time (12:24 a.m. Eastern Daylight Time), and that’s when the northern pole of our planet’s spin axis is maximally tilted toward the Sun.

In addition to causing seasons, this axial tilt (known as obliquity) allows sunlight to fully illuminate the poles — periodically even at midnight — so that over a year, remote-sensing satellites can image the entire surface of our planet.

The Moon, however, is tilted only 1½° with respect to the ecliptic, and hence the Sun is always near or just below the horizon as seen from its poles. In fact, the Sun never rises above the rims of some deep polar craters, and so their floors receive very little direct sunlight, if any at all. Thermal maps created by the Diviner instrument on NASA’s Lunar Reconnaissance Orbiter (LRO) show that the always-dark floors of these craters are some of the coldest locations in the solar system.

Offsetting this absence of light are some nearby polar mountains that nearly always bask in sunlight. The pioneering German lunar mapper Johann Heinrich von Mädler was the first to realize this, but it was French astronomer and author Camille Flammarion who, about 40 years later in 1879, romanticized the idea by calling these always-sunlit places pics de lumière éternelle – peaks of eternal light.

Actually, no lunar real estate is 100% illuminated, though a few peaks are lit by the Sun more than 90% of the time. In any case, these locations are always difficult to observe and identify. Even when seen with favorable lunar libration, the extreme foreshortening created by looking sideways at the lunar poles compresses circular crater rims into apparently straight ridges.

Spacecraft-borne laser altimeters have mapped the topography near the Moon's south pole. High points on the rims of Malapert and Shackleton receive sunlight about 90% of the time.
NASA/Goddard Space Flight Center

However, using images from the lunar-orbiting Clementine, Kaguya, and LRO spacecraft, which have been able to look straight down on the poles, scientists have disentangled these distortions and mapped lunar locations that are nearly permanently shadowed and, conversely, rarely so.

Take the Polar Challenge

For a telescopic observer, identifying the “pics” near the lunar south pole is especially difficult because the area is heavily cratered. The most continuously sunlit peaks typically occur as small pieces of rim crests and ridges around Shackleton, a 21-km-wide crater located right at the pole. But I have yet to come across an Earth-based image of Shackleton.

Instead, peaks on the rims of the craters Cabeus and Malapert are the most southerly named features that can usually be identified telescopically when librations tip the south pole toward Earth. They’re both in view in the image at the top of the facing page.

South is up in this view of the south-polar terrain seen during an extremely favorable libration. Malapert Massif and other high-standing peaks in this region receive nearly constant sunlight.
Avani Soares

Most conspicuous are informally named Malapert Massif (a 5-km-high crest along that crater’s southwestern rim) and other isolated high points that are parts of the rim of the enormous farside basin called South Pole-Aitken. Cabeus is a little easier to spot. In 2009, NASA’s LCROSS probe crashed onto its permanently shadowed floor, discovering near-surface deposits of water and other volatiles (S&T: Feb. 2010, p. 28).

Observing pics near the north pole is far easier because the topography is much flatter and appears less cluttered with craters and mountains. The view at lower right shows the longest and easiest-to-see peak of eternal light. The bright ray crater at far left is Anaxagoras — ignore it. Instead, look toward the right at Scoresby, a fresh, somewhat larger (56-km-wide) but not-as-bright crater at 78° north. A distinguishing feature is the small bright crater on its inner rim.

Thanks to smoother terrain overall, you'll have an easier time "crater-hopping" to the Moon's north pole when favorable libration permits. The far rim of Peary enjoys nearly constant sunlight.
George Tarsoudis

Immediately poleward are the overlapping, flat-floored twins Challis and Main. Continuing north, look for another flat-floored crater Gioja (42 km wide, 83°N). Beyond that are prizes not often seen: Byrd (94 km, 85°N) and Peary (70 km, 89°N). The actual north pole is on the brightly illuminated far wall of Peary — it is nearly constantly draped with sunlight.

A very favorable north-polar libration — just under 7° — occurs on May 24th. Unfortunately, the Moon is then a hair-thin waning crescent only 1.3 days from new. You might try one day earlier, May 23rd, when the libration is closer to 6°.

In Flammarion’s day, the pics de lumière éternelle were romantic oddities, but they could soon become valuable real estate. Their summits are washed with nearly constant grazing sunlight that solar-cell arrays could use to generate electricity for lunar bases. The temperature would stay nearly constant at roughly –50°C (–60°F), which is a brutally frigid winter day in Alaska but rather temperate for a lunar location. The deep, permanently shadowed craters nearby likely contain enough water to drink, irrigate crops, and break down into hydrogen and oxygen for use as rocket fuel. They could be the oases in an otherwise completely arid land.

A recent investigation by Martin Elvis (Harvard-Smithsonian Center for Astrophysics) and two colleagues suggests that the uniqueness of these pics might lead to a rush to claim them. The Outer Space Treaty of 1967 states that the Moon is the “province of all mankind” and prohibits nations and corporations from claiming ownership of lunar land.

But 50 years ago we had no detailed knowledge of these polar peaks. Elvis and his co-authors speculate that their value as both energy and water resources could lead to creative interpretations of the Treaty. For example, one provision states that any lunar station’s “delicate scientific experiment” would require others to keep away so as not to interfere. So you might want to get out your telescope and take a look at this polar property before the “no trespassing” signs go up.

This article originally appeared in print in the June 2017 issue of Sky & Telescope.

The post Peaks of “Eternal” Light appeared first on Sky & Telescope.

Categories: Astronomy Headlines

NEAF 2017 Astronomy Equipment Videos

Fri, 06/23/2017 - 10:34
Panorama of NEAF 2017 Exhibit Floor

A panorama of the exhibition hall at NEAF 2017. Sean Walker (S&T)

Several thousands of amateur astronomers flocked to the 2017 Northeast Astronomy Forum, held every year in Suffern, New York, to see some of the hottest new telescopes, mounts, cameras, eyepieces, and other astronomy equipment at one of the world's largest astro trade shows.

Former S&T editor Dennis di Cicco interviewed several vendors about their newest products.

Browse vendors below and click to watch these in-depth conversations and find full details on new product lines and featured equipment.

Video Interviews on Astronomy Equipment

Video Interview with Finger Lakes Instrumentation

 

 

 

 

 

Video Interview with iOptron

 

 

 

 

 

Video Interview with Meade Instruments Corp.

Meade

See our entire library of video interviews.

The post NEAF 2017 Astronomy Equipment Videos appeared first on Sky & Telescope.

Categories: Astronomy Headlines

Meade Instruments Corp. at NEAF 2017

Fri, 06/23/2017 - 10:33

MeadeDennis di Cicco and Meade’s Scott Byrum look at many of the products Meade had on display at this year’s Northeast Astronomy Forum. With an eye toward the upcoming total solar eclipse, they take a detailed look at the Coronado line of affordable hydrogen-alpha solar scopes, and the company’s new EclipseView line of entry-level instruments. In addition to featuring removable white-light solar filters for observing the Sun, the EclipseView telescopes are great for viewing the heavens at night.

 

See additional videos from the 2017 Northeast Astronomy Forum.

Return to our Product Videos page.

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Categories: Astronomy Headlines

iOptron at NEAF 2017

Fri, 06/23/2017 - 10:21

Sky & Telescope’s Dennis di Cicco talks with iOptron’s Roger Rivers about some of the newest products in the company’s expanding line of mounts and telescopes. They give special emphasis to the new, highly versatile and extremely portable Sky Tracker Pro mount designed for cameras and small telescopes.

 

See additional videos from the 2017 Northeast Astronomy Forum.

Return to our Product Videos page.

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Categories: Astronomy Headlines

Finger Lakes Instrumentation at NEAF 2017

Fri, 06/23/2017 - 10:15

Gary McAnally of Finger Lakes Instrumentation shows Sky & Telescope’s Dennis di Cicco some of FLI’s newest imaging equipment, including the Kepler line of cooled, scientific-grade CMOS cameras, which feature high sensitivity, extremely low read noise, and high frame rates.

See additional videos from the 2017 Northeast Astronomy Forum.

Return to our Product Videos page.

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Categories: Astronomy Headlines

This Week’s Sky at a Glance, June 23 – July 1

Fri, 06/23/2017 - 02:40

 

Moon, Pollux, Castor on June 25, 2017

Binoculars will help you pick out Pollux and Castor to the right of the crescent Moon low in bright twilight on Sunday evening the 25th. Their visibility in a bright sky is exaggerated here.

Moon and Regulus, June 27, 2017

Two days later the thickening Moon passes Regulus . . .

Moon, Jupiter, Gamma Virginis June 30, 2017

. . .and then on the 30th at first quarter, the Moon puts on a show with Jupiter and especially Gamma (γ) Virginis. (The Moon's position in these scenes is always plotted exact for latitude 40° N, longitude 90° W, near the middle of North America. The Moon is always shown three times its actual apparent size.)

Friday, June 23

• This is the time of year when, after dark, the dim Little Dipper floats straight upward from Polaris (the end of its handle) — like a helium balloon on a string escaped from a summer evening party. Through light pollution, however, all you may see of the Little Dipper are Polaris at its bottom and Kochab, the lip of the Little Dipper's bowl, at the top.

• New Moon (exact at 10:31 p.m. EDT).

Saturday, June 24

• This is the time of year when the two brightest stars of summer, Arcturus and Vega, are equally high overhead soon after dark: Arcturus in the southwest, Vega toward the east.

Arcturus and Vega are 37 and 25 light-years away, respectively. They represent the two commonest types of naked-eye stars: a yellow-orange K giant and a white A main-sequence star. They're 150 and 50 times brighter than the Sun, respectively — which, combined with their nearness, is why they dominate the evening sky.

Sunday, June 25

• By the time it's fully dark this week, Altair is shining well up in the east. A finger-width above it or to its upper left is its little sidekick Tarazed (Gamma Aquilae), actually an orange giant that's far in the background. Altair is 17 light-years from us; Tarazed is about 460.

Look left of Altair, by hardly more than a fist width, for the compact little constellation Delphinus, the Dolphin.

Monday, June 26

• The tiny black shadow of Io crosses Jupiter's face tonight from 10:23 p.m. to 12:33 a.m. EDT, when it leaves Jupiter's western limb. Then just three minutes later Europa exits from in front of Jupiter's western limb, moving in the same direction.

Tuesday, June 27

• This evening, look for 1st-magnitude Regulus within 1° or 2° of the waxing crescent Moon.

Wednesday, June 28

• Do you know about the dark Propeller in the M13 star cluster in Hercules? With no Moon in the sky, take advantage of the dark to visit Sue French's six favorite summer deep-sky objects, which she features in the July Sky & Telescope, page 54.

Thursday, June 29

• The central stars of the constellation Lyra, forming a small triangle and parallelogram, dangle to the lower right from bright Vega high in the east. The two brightest stars of the pattern, after Vega, are the two forming the bottom of the parallelogram: Beta and Gamma Lyrae, Sheliak and Sulafat. They're currently lined up vertically. Beta is the one on top.

Friday, June 30

• First-quarter Moon (exact at 8:51 p.m. EDT). The "star" left of the moon is Jupiter.

• And this evening, the Moon's dark limb will occult (cover) the bright, tight double star Gamma Virginis (Porrima) for much of the U.S. and Canada. The event happens in daylight for the West, twilight for the central longitudes of the continent, and later in darkness for the East.

See more in the July Sky & Telescope, page 50. Here are detailed timetables for hundreds of cities and towns. (The UT date of the event is July 1st.) Plan ahead!

Saturday, July 1

• The Moon forms a broad triangle with Jupiter and Spica in the southwest this evening.

________________________

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.

Pocket Sky Atlas, jumbo edition

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but it's less than one per square degree on the sky. Also plotted are many hundreds of telescopic galaxies, star clusters, and nebulae. Shown above is the Jumbo Edition for easier reading in the night. Larger view. Sample chart.

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or Jumbo Edition), which shows stars to magnitude 7.6.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many. The next up, once you know your way around, is 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, or the bigger Night Sky Observer's Guide by Kepple and Sanner.

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 (meaning heavy and expensive). And 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 Saturn on June 11, 2017

This just might be the sharpest image of Saturn even taken from the ground. Damian Peach and six colleagues acquired it on June 11th using the 1-meter Pic Du Midi reflector high in the French Pyrenees. "Rarely seen details are observed, such as small ringlets within Ring C, including the Maxwell and Colombo divisions," writes Peach. "The Encke division is easily observed around the entire [outer] A ring. Note the strong blue colouration of the southern hemisphere shining through the Cassini division." South is up.

Jupiter with Io and Europa in transit, June 16, 2017

If you've wondered why you can't see Io and Europa in your scope when they're crossing Jupiter's face, it's because they're about the same brightness and color as Jupiter itself. The top tick points to Io, the bottom tick to Europa. Christopher Go took this image at 10:55 UT June 16, 2017. South is up.

Mercury and Mars are buried deep in the glow of sunset this week.

Venus (magnitude –4.2) shines brightly in the east before and during dawn.

Jupiter (magnitude –2.1, in Virgo) shines brightly in the southwest during evening. Spica, magnitude +1.0, glitters 11° left of it. In a telescope, Jupiter has shrunk to 38 arcseconds wide.

Saturn (magnitude 0.0, in southern Ophiuchus) glows pale yellowish in the southeast to south during evening. Fiery Antares, less bright, is 15° to Saturn's right or lower right. Delta Scorpii, the third brightest object in the area, catches the eye half that far to the upper right of Antares.

Uranus (magnitude 5.9, in Pisces) is well up in the east before the beginning of dawn, and Neptune (magnitude 7.9, in Aquarius) is higher in the southeast at that time.

__________________________

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 Daylight Time (EDT) is Universal Time (UT, UTC, or GMT) minus 4 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

"Objective reality exists. Facts are often determinable. Vaccines do stop diseases. Carbon dioxide does warm the globe. Science and reason are no political conspiracy; they are how we discover reality. Civilization's survival depends on our ability, and willingness, to do so."
— Alan MacRobert, your Sky at a Glance editor

"Facts are stubborn things; and whatever may be our wishes, our inclinations, or the dictates of our passions, they cannot alter the state of facts and evidence."
— John Adams, 1770

 

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Categories: Astronomy Headlines

NASA Closes Out Its Asteroid Redirect Mission

Thu, 06/22/2017 - 12:43

Following the release of the 2018 budget, the space agency has ordered an “orderly closeout” for the Asteroid Redirect program.

NASA's boulder-retrieval mission

NASA's Asteroid Redirect Mission would have retrieved a boulder from the surface of an asteroid.
NASA

After years of study, NASA announced recently that its plan to retrieve an asteroid and place it in lunar orbit, known as the Asteroid Redirect Mission (ARM), will be shut down due to lack of congressional support in the proposed FY2018 budget. The NASA ARM program director Michele Gates made the announcement on June 13th, during the recent meeting of the Small Bodies Assessment Group held at the Goddard Space Flight Center in Greenbelt, Maryland. The focus will now turn shutting down the program while salvaging key technologies and lessons learned for other possible future applications.

“The agency remains committed to the next human missions to deep space, but we will not pursue the Asteroid Redirect Mission (ARM) with the Fiscal Year 2018 budget proposal,” says Kathryn Hambleton (NASA). “The ARM team is in the process of documenting its activities to ensure key knowledge from the mission concept is archived as part of an orderly closeout.”

Asteroid redirect mission EVA

This artist's concept shows an astronaut examining the returned boulder while in lunar orbit.
NASA

ARM was an ambitious plan from the start. First proposed in 2013, the project called for an automated rendezvous and capture of a small near-Earth asteroid, which would then be placed in orbit around the Moon. Astronauts would then rendezvous with the asteroid in lunar orbit, study the asteroid, and collect and return samples to Earth. NASA ARM would have relied on the new Orion crewed capsule and the new Space Launch System (SLS) heavy lift rocket, both still under development.

Politically, the mission had detractors from the start, and it failed to find support in Congress, even though the plan was often touted as a stepping stone between leaving low-Earth orbit and heading to Mars in the 2030s. From an engineering perspective, the plan plan was complex, requiring an automated spacecraft to retrieve an SUV-sized boulder from a larger asteroid moving slowly relative to Earth's orbital motion, a scenario that significantly limited the potential targets.

Bennu

Our best look at Bennu, one of the asteroid candidates for the boulder retrieval concept of ARM. The image at right shows radar reflectivity as measured by Arecibo, with the radar beam shining from the top. At right is a reconstruction of Bennu's shape using those data.
NASA / Arecibo

But even as the ARM mission closes out, research and development will still continue in some key areas. The solar electric propulsion system, initially envisioned to fly on the robotic segment of ARM, is still being developed for future deep-space use. And the search for near-Earth asteroids involving observatories worldwide will go on.

“While our long-term Mars architecture is still in development,” Hambleton says, “we've recently unveiled a concept using SLS and Orion to build a deep space gateway and transport in cis-lunar space to help us prepare for human deep space missions, including Mars.”

NASA FY18 Budget Break Down NASA FY2018 Budget Request Changes

Changes expected from the president's budget request for NASA.
AAAS

The end of NASA ARM is also part of a larger picture: a time of transition amid the new presidential administration. NASA overall actually makes out pretty well in the proposed FY2018 budget: $19.1 billion dollars, a 3% drop from the $19.7 billion budget of FY17, though still slightly above where NASA funding levels have stalled for the past decade. Planetary sciences was the big winner in the FY18 NASA budget, getting a proposed $1.9 billion dollars, the division's highest annual funding to date. This will support the Mars 2020 rover and the Mars InSight lander, as well as the Europa Clipper and Lucy and Psyche asteroid missions planned for the 2020s.

A lion's share of NASA's proposed budget will go towards continued support of the International Space Station, the James Webb Space Telescope (set to launch in late 2018), and development of the Orion capsule and the SLS, though the latter face significant cuts. The first flight of Orion aboard the SLS is slated for 2019 and will carry an uncrewed capsule around the Moon and back. NASA studied the idea of putting a crew on the first Orion/SLS flight but nixed the idea last month.

Along with NASA ARM, NASA's Earth sciences division will take a hit under the proposed budget, losing $170 million dollars for a nearly 9% drop from FY17 to FY18. This puts several crucial Earth observing missions, including the Orbiting Carbon Observatory (OCO-3) and the Deep Space Climate Observatory (DSCOVR), in jeopardy. However, 18 Earth-observing missions will remain in orbit, according to NASA acting administrator Robert Lightfoot.

NASA's Office of Education also faces closure with this budget, with just $37 million set aside for transitional and closing costs.

However, while some changes appear to be set, such as the ARM close-out, it's important to remember that the president's budget request often changes before it becomes signed into law later in the year. The Planetary Society offers their take on NASA's new budget here. To learn how the NASA budget comes about, watch this explanation from The Planetary Society's Casey Dreier:

When it comes to NASA funding, it's an uncertain time of crisis and opportunity. As ever, the phrase “no bucks, no Buck Rogers” applies. We're also now farther away from the end of the U.S. Space Shuttle program in 2011 than the first shuttle flight in 1981 was from the end of Apollo in 1975.

Perhaps, the lessons from NASA ARM will get paid forward, as U.S. astronauts once again venture out of low-Earth orbit in the next decade.

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Categories: Astronomy Headlines

A Partly Cloudy Exoplanet

Thu, 06/22/2017 - 11:42

Artist’s illustration of a cloudy exoplanet. A new study suggests that the Jupiter-like exoplanet 51 Eri b may have partly cloudy skies.
Mark Garlick/University of Warwick

Direct imaging of exoplanets was once only possible for the brightest of planets orbiting the dimmest of stars — but improving technology is turning this into an increasingly powerful technique. In a new study, direct-imaging observations of the Jupiter-like exoplanet 51 Eridani b provide tantalizing clues about its atmosphere.

Direct Imaging of 51 Eri b

Images of 51 Eri b from GPI (top) and Keck (bottom).
Rajan et al. 2017

While transit detections remain the best way to discover large quantities of new exoplanets, direct imaging provides a unique advantage: you can measure the light from the exoplanet itself. With proper constraints on the host star, it therefore becomes possible to measure the spectrum of the planet’s atmosphere.

One target for this technique is 51 Eri b, a Jupiter-like exoplanet located roughly 100 light-years away. This object was the first exoplanet directly imaged by the Gemini Planet Imager Exoplanet Survey, a project that used the Gemini Planet Imager (GPI) instrument in Chile to search for exoplanets around 600 young nearby stars.

A team of scientists led by Abhijith Rajan (Arizona State University) has now made new near-infrared observations of 51 Eri b: spectroscopy in the K band using GPI, and photometry in the Ms band with a camera on the Keck I telescope in Hawaii. Rajan and collaborators combined this new data with past observations and modeling to better characterize the 51 Eri b’s properties.

Cloudy Transition

Color–magnitude diagrams for brown dwarfs and imaged exoplanets (click for a closer look). The color of 51 Eri b (marked with red star) places it among late T dwarfs, but it is redder than most comparable-temperature brown dwarfs. The tracks for the L–T transition for two different planet masses are shown.
Rajan et al. 2017

One intriguing aspect of 51 Eri b is the challenge of determining its spectral type. Though its spectrum is consistent with that of a T dwarf, photometry shows that it’s unusually red for this spectral type. There may be a reason for this, however: clouds.

Rajan and collaborators find that the best fitting models for 51 Eri b’s spectra all have an atmosphere consisting of patchy clouds. This result holds true both for models with the salt and sulfide clouds expected to condense in the atmospheres of mid-to-late T dwarfs, and for models with the iron and silicate clouds common in atmospheres of redder L-dwarfs.

The authors hypothesize that 51 Eri b may be in the process of transitioning from a warmer L-type body to a cooler T-type body. As an L-type planet cools, holes and low-opacity patches appearing in an initially uniform cloud deck could cause the transition of the planet’s spectrum to T-type.

An Unusual Start?

The ten best-fitting cloudy (red) and cloudless (blue) atmospheres over the wavelength range of JWST, illustrating that JWST will likely be able to differentiate between atmospheric models for 51 Eri b.
Rajan et al. 2017

In addition to examining 51 Eri b’s atmosphere, Rajan and collaborators use its luminosity to explore how it may have formed. They demonstrate that 51 Eri b is one of the only directly imaged planets that’s consistent with what’s known as the cold-start scenario, in which planets slowly grow via accretion onto a solid core.

While much remains to be learned about 51 Eri b, these new results provide an excellent step in the right direction. The authors also show that future observations — such as with the James Webb Telescope — will allow us to further differentiate between models describing this planet. 51 Eri b’s intriguing atmosphere makes it a prime target to revisit as our observational capabilities continue to improve.

Citation

Abhijith Rajan et al 2017 AJ 154 10. doi:10.3847/1538-3881/aa74db

Related Journal Articles

This post originally appeared on AAS Nova, which features research highlights from the journals of the American Astronomical Society.

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Categories: Astronomy Headlines

New Wrinkles in the Search for “Planet X”

Wed, 06/21/2017 - 20:42

Are astronomers being misled by the quirky alignment of orbits that they’re finding in the distant Kuiper Belt?

Even as the count of known planets around other stars continues to climb, a small group of observational astronomers and dynamicists are fixated on something much closer to home: tantalizing clues that a super-Earth-size planet lurks undiscovered somewhere beyond the Kuiper Belt in our own solar system.

Some have dubbed it "Planet X," others "Planet Nine," and right now observing teams are using some of the world’s largest telescopes in a race to track it down. One big problem is that they’re not sure where to look — or if it even exists.

Planet Nine orbit plots

Orbits for the six most distant known objects in the solar system as of early 2016, whose orbits (shown in magenta) remain beyond Neptune, all aligned in one direction. A hypothesized massive "Planet Nine" (orange orbit) could be responsible for their perplexing alignment.
Caltech / Robert Hurt

The evidence so far is purely circumstantial. To recap, observers have started to accumulate discoveries of a class of far-flung objects in a kind of dynamical "no man's land." They have very eccentric orbits that average at least 150 astronomical units from the Sun (five times Neptune’s distance) but never come closer to the Sun than Neptune’s 30 a.u.

Orbit elements diagram

The intersection of an object's orbit with the ecliptic plane (reference plane) is called the line of nodes, as it connects the center of mass with the ascending and descending nodes. This plane, together with the vernal point (♈), establishes a reference frame that defines the orbit uniquely in three-dimensional space.
Lasunncty / Wikipedia / CC BY-SA 3.0

Chadwick Trujillo (then at Gemini Observatory) and Scott Sheppard (Carnegie Institution for Science) were the first to realize that the initial 12 such discoveries all had perihelia, the point of their orbits closest to the Sun, near the ecliptic plane (the argument of perihelion for each was near 0° or 180°). Although they initially thought this arrangement might be due to a distant, massive planet, an analysis last year by Ann-Marie Madigan (Univ. of California, Berkeley) and Miochael McCourt (Harvard) concluded that one big planet wouldn’t do — but that a massive disk of Kuiper Belt objects in eccentric orbits would.

Meanwhile, Konstantin Batygin and Michael Brown (Caltech) realized that the longitude of these perihelia also cluster on one side of the Sun. Such an alignment wouldn’t happen by chance: The elongated orbits of these objects should gradual precess (pivot) around the Sun at different rates, deconstructing the convergence in perhaps 10 million years. But a single, massive planet — itself in a highly eccentric orbit — could impose the observed orbital order via subtle, long-term gravitational perturbations.

All along, the nagging question has been whether a sample of just a dozen objects, however tightly their orbits might be clustered, is enough of a sample to make a robust statistical case for a massive unseen planet. Is their orbital congregation real, or is it just a quirk outcome due to how observers searched for them? Two recent analyses offer opposing answers to this crucial question.

A team led by Cory Shankman (University of Victoria, Canada) argues that observational bias is skewing our perception of reality. Made public on June 18th and due to appear in the Astronomical Journal, the the analysis details how the Outer Solar System Origins Survey discovered (beginning in 2013) eight new Kuiper Belt objects that average at least 150 a.u. from the Sun and never come closer than 30 a.u. One find, 2013 SY99, ranges in its solar distance from 50 a.u. to an incredible 1,420 a.u.

At face value, some of these eight objects have orbits roughly aligned with the dozen earlier finds, but others do not. More importantly, simulations of the project’s observing strategy suggest that “the orbital distribution in the OSSOS sample could have resulted from a randomly oriented population of objects — it doesn’t require the clustering that others have claimed.” More broadly, Shankman and his colleagues argue that the apparent clustering is an artifact of how these challenging observations — by OSSOS and others — are being made.

First, because these objects have such strongly elongated orbits, they’re far more likely to be discovered when close in (near perihelion). And if observers consistently look for them along the ecliptic or far from the congested plane of the Milky Way, as has often been the case, then the outcome is a cluster of objects in these preferred directions. The OSSOS team acknowledges this observational bias and concludes it could have preferentially swept up objects from an otherwise random distribution that have orbital characteristics.

But does that logic apply to the clustering reported by Trujillo/Sheppard and Batygin/Brown? In an analysis posted just last week as well, Brown concludes that observational bias can’t explain the clustering of the original 12 distant, eccentric KBOs. "Shankman et al. make the unwarranted conclusion that 'If our survey is biased, everyone else's must be too,'" says Brown.

"[The OSSOS survey] was done at only a few longitudinal locations, which makes it hard to say much about the areas they didn’t survey," Sheppard says. Still, he adds, "It’s great that more extreme objects are being found," because up to this point everyone has been grappling with statistical probabilities based on a very limited sample.

Where to Find Planet Nine

Black lines show the range of possible locations and observing characteristics for the putative "Planet Nine." (Red lines delineate the Milky Way.) It could be anywhere along its orbit, which could have a period of 10,000 to 20,000 years.
Konstantin Batygin & Mike Brown

One sure way to end all the speculation, of course, would be to find this hypothesized planet. Batygin and Brown estimate that it must have at least 10 times Earth's mass and a few times bigger around. But their simulations say it also needs to be in a highly elongated orbit that averages maybe 700 a.u. (100 billion kilometers) from the Sun. In that kind of orbit, it’s going to spend most of its 10,000- to 20,000-year orbital period very far from perihelion. Maybe it’s no brighter than magnitude 22 — a challenge to spot even in the best telescopes.

So both Brown and Trujillo/Sheppard will be looking in the months ahead, and both are using the 8.2-meter Subaru Telescope on Mauna Kea. "Either we will find it, or we will not," Brown says. "My money is still on finding it."

Meanwhile, a third analysis of distant orbits also argues that the Kuiper Belt harbors a planet, though this one isn’t nearly so massive or far away.

Kathyrn Volk and Renu Malhotra (University of Arizona) analyzed the orbits of more than 600 Kuiper Belt objects and found that those relatively close in have orientations that, collectively, match the average plane of our planetary system (known as the invariable plane) to within 2°.

However, more distant ones, those averaging 50 to 80 a.u. from the Sun, deviate from the invariable plane by roughly 9° and create a kind of warp in the overall distribution of orbits. "There is not more than a 1% or 2% chance that this warp is merely a statistical fluke," Volk points out. Instead, she and Malhotra suspect that the warp is due to something at least as massive as Mars situated roughly 60 a.u. from the Sun in an orbit 8°.

Planet-size object in Kuiper Belt

If a new analysis is correct, a hypothesized "planetary mass object" makes its existence known by altering the orbital planes of distant Kuiper Belt objects.
Univ. of Arizona / Heather Roper

So wouldn’t such a body have been spotted by now? Maybe not. As she notes in a university press release, there’s a 30% chance that Kuiper Belt surveys to date would have overlooked an object of the right brightness and distance. If it really exists, the Large Synoptic Survey Telescope should sweep it up quickly once it starts scouring the sky in a few years.

The post New Wrinkles in the Search for “Planet X” appeared first on Sky & Telescope.

Categories: Astronomy Headlines

Eclipse 2017: T-Minus Two Months and Counting

Wed, 06/21/2017 - 14:15

It’s officially two months until this summer’s total solar eclipse, the first eclipse to sweep across the entire contiguous United States in 99 years. Totality will pass through 14 states over the course of an hour and an half on August 21st.

http://www.skyandtelescope.com/wp-content/uploads/eclipse2017usa_360p30.mp4

NASA/Goddard Space Flight Center Scientific Visualization Studio. The Blue Marble data is courtesy of Reto Stockli (NASA/GSFC).

There are loads of resources to help you plan for the total solar eclipse. If you haven’t already planned where you’ll be on eclipse day, think about it now or you may find that there’s nowhere left to sleep (or use the restroom). Do not wing this! The Department of Transportation is asking that people DO NOT pull off to the side of the interstate. Visit the DoT website where you can see how traffic may be affected by the eclipse.

If you can’t make it out to the path of totality, or if weather prevents you from viewing the eclipse, NASA will be streaming live video through the eyes of satellites, aircrafts, and balloons during the entire eclipse as it passes from coast to coast. You can even commemorate the event with an awesome heat sensitive stamp from the U.S. Postal Service.

Once you know where you’re watching the eclipse, whether from the path of totality or only a partial eclipse, you’ll need to think about how you’ll watch the eclipse. Of course, there are always handy solar glasses, so that you can observe with your eyeballs, but if you’d like a more zoomed-in view, or if you plan to take pictures with your smartphone, you’ll need to think about which filters are right to protect your eyeballs and your equipment.

PRO TIP: do not point binoculars, telescopes, finder scopes, cameras, and cell phones directly at the Sun, even during an eclipse, without solar filters. At minimum, you could damage the optics of your camera or telescope. At maximum, you could cause yourself immense pain and permanent blindness. Take it from someone who tried to set paper on fire with a telescope in college: a telescope will focus the light enough to burn through paper, and it’s painful to put soft tissue at the focal point. (Good news: the soft tissue in question was a hand, not an eyeball.) Always block the light before it gets to the focusing apparatus, not after.

Whether you have a solar telescope or just a smartphone, the solar eclipse also offers a great opportunity to do some science. While professional scientists are conducting some of the research, other projects are being carried out by enthusiastic volunteers. The Citizen CATE project will use identical setups across the country to help determine what accelerates the solar wind, and the Megamovie Project will give us a closer look at the solar corona. You can even help scientists observe how the eclipse affects plants and animals with the Life Responds project.

Image of the total eclipse taken Mar. 20, 2015 at Svalbard, Norway.
S. Habbal, M. Druckmüller and P. Aniol

If you’re planning to photograph the eclipse, you’ll probably want to plan your shots down to the sub-minute, and you might want some pro tips to help you do that. Start planning your sequence now, so you’re prepared when the moment comes. Because in the short minutes of totality, you’ll be too overwhelmed with awe and wonder as you realize our place in the universe — as bit players in the cosmic dance between the Moon, Earth, and Sun.

 

 

 

The post Eclipse 2017: T-Minus Two Months and Counting appeared first on Sky & Telescope.

Categories: Astronomy Headlines

Citizens Uncover a Cold World 100 Light-years Away

Wed, 06/21/2017 - 09:29

Citizen scientists have discovered a brown dwarf 100 light-years from the Sun, and more finds are sure to come from the Backyard Worlds citizen-science project.

Brown dwarf discovered by citizen scientists using Backyard Worlds

The "flipbook" in which citizen scientists identified the new brown dwarf, seen as a faint speck inside the red circle.
NASA

Believe it or not, there are exotic celestial objects hiding closer than we think — just a short distance from the Sun. And we want to find them. That’s why, last February, I helped launch Backyard Worlds. The citizen-science project invites anyone in the world to join the search for new worlds close to our own Sun. We’ve already found one — a brown dwarf just 100 light-years away.

To get started in Backyard Worlds, all you need is access to a computer and an Internet connection. We ask users to create a username that links to your email so if you do end up finding something interesting; we know how to give you proper credit. Once you’re logged in, the exploration begins: you begin flipping through images taken by a NASA spacecraft called WISE, the Wide Field Infrared Survey Explorer, and scan for objects that appear to move over time.

All celestial bodies in our galaxy are moving. A planet orbits its parent star, which in turn can be found moving with other stars in an association, and all of those are moving around the galaxy. Stars, planets, comets, and other objects all move at different speeds. If an object is close enough, you can look at two images taken a few years apart, flip between them, and catch the object "jumping" relative to the background stars. Within the Backyard Worlds, more than 39,000 volunteers have been examining more than 4 million such "flipbooks" of the sky .

Six days after the project launched, a user alerted our science team to one such object that appeared to be nearby and cold — in other words, not a star. In all, four citizen scientists alerted our team to the source: a science teacher in Tasmania initially reported the faint object, and volunteers from Russia, Serbia, and Sweden tagged it as well. After some excitement and investigation, we decided that this was the kind of object that we wanted to follow up: Its fast motion in the flipbooks was exciting, but to truly understand the nature of the source we needed to obtain a spectrum.

Typically, telescope time requires several months of lead time and an evaluation by a time allocation committee, but under these special circumstances, we were able to request a small window of discretionary time on NASA's Infrared Telescope Facility. After a few hours of observing the target, its nature became clear. This was a brown dwarf, just a few hundred degrees warmer than Jupiter, that had previously been hidden from sight. It lies only 100 light-years away, but it’s so faint, previous surveys had missed it in their searches of the sky.

Artist's illustration of brown dwarf

Backyard Worlds volunteers are helping astronomers find the coldest isolated celestial objects in our galaxy. These brown dwarfs are far more similar to Jupiter than stars and are abundant near the Sun.
NASA / JPL-Caltech / R. Hurt (SSC)

Brown dwarfs are abundant in the Milky Way, though their dimness makes them hard to find. They lack the mass to keep hydrogen burning, but they’re hot enough to glow faintly at infrared wavelengths. They’re also strikingly similar to Jupiter, so we study their atmospheres in order to understand what weather on other worlds might look like.

While the Backyard Worlds project is ultimately hoping to find the infamous Planet 9 hiding in our own solar system, these new brown dwarfs are also exciting discoveries. It's possible that one of these cold worlds might lie even closer to us than Proxima Centauri, the star nearest the Sun. If it does, one of our citizen scientists is going to find it.

So far, volunteers have given our research team several great targets for telescopic follow-up. Given enough time, I think our volunteers are going to map out our whole solar neighborhood. Anyone can participate and join the search party at backyardworlds.org.

The post Citizens Uncover a Cold World 100 Light-years Away appeared first on Sky & Telescope.

Categories: Astronomy Headlines

Does the Milky Way Live in a Void?

Wed, 06/21/2017 - 09:01

A sparse galactic neighborhood could clear up certain problems with our understanding of the universe.

Cosmology has a minor problem on its hands. The universe is getting bigger over time, that much we know for sure. But measurements of how fast the universe is currently expanding depend on what you measure.

Hubble constant measurements

This plot shows some representative measurements of the expansion rate of today's universe, known as the Hubble constant. The figure includes three values derived from measurements of the cosmic microwave background (left side of the plot) and four values derived from "nearby" objects (right side of plot). The values presented here are the bare-bones results from each study; any of these values can be made more precise by combining information from multiple datasets.
Ana Aceves / Monica Young

Observations of the cosmic microwave background, the afterglow of the Big Bang, suggest that today’s universe is expanding at a rate between 66.3 and 67.6 kilometers per second per megaparsec. But studies of relatively local objects, like variable Cepheid stars or Type Ia supernovae in nearby galaxies, point to a faster expansion rate: between 71.5 and 75 km/s/Mpc. Granted, one measurement comes from photons released 370,000 years after the Big Bang and the other measurement from photons released billions of years later. Nevertheless, the two methods should be getting the same answer for today’s expansion rate — and they aren’t.

At the 230th meeting of the American Astronomical Society, Benjamin Hoscheit and Amy Barger (both at University of Wisconsin, Madison) presented a possible workaround. What if, they proposed, the Milky Way lives in a cosmic void? That could skew the measurements of local stars and supernovae, but it wouldn’t affect the faraway CMB.

The Relative Emptiness Around Us Large-scale structure

This frame from a computer simulation shows the foamy large-scale structure of the universe, in which long filaments of galaxy clusters surround immense voids. The image measures 300 million light-years on a side.
Virgo Project

In 2013 Barger and two colleagues, Ryan Keenan (then at the Academia Sinica Institute of Astronomy and Astrophysics, Taiwan) and Lennox Cowie (University of Hawai‘i) counted some 35,000 galaxies from multiple surveys. What they found is that the Milky Way appears to live in a relatively empty area. Per unit volume, there’s half again as much light reaching us from galaxies 1.5 billion light-years away as there is from galaxies right around us.

It’s as if we’re living in the suburbs, and the skyglow we see in our backyard comes more from distant cities than from our neighbors.

If this sparse region that we live in is a true cosmic void, then at 1.5 billion light-years in radius, it’s well above average in size, says Hoscheit. Typical voids have radii between 90 million light-years and 450 million light-years, he says. But this void would be so big, it would encompass the Laniakea Supercluster, which the Milky Way and its Local Group of galaxies call home, as well as the Tully Local Void, which Laniakea borders. “It would be the largest void known to science,” he says.

A Void by Any Other Name

But Radek Wojtak (University of Copenhagen, Denmark) isn’t so sure that the KBC region (for Keenan, Barger, and Cowie) is a void at all.

First, he notes, the galaxy counts that define the potential void aren’t taken from the whole sky — and the surveys the team used look away from the Laniakea Supercluster.

Moreover, Wojtak adds, “A change in density by factor of 1.5 is not enough to call it a void — but this is of course a matter of definition.” Observational cosmologists will sometimes call any big, underdense region a void, he says, but typical cosmic voids have densities 5 times smaller than the universe’s average density.

So, does the Milky Way live in a void? It’s really too soon to say. Measurements from nearby standard-candle supernovae are too scattered to confirm or rule out the existence of the KBC void, Hoscheit points out. What could clear up the situation, Wojtak says, is more data: counting galaxies across the whole sky instead of just certain regions could help determine whether the KBC void is real.

The post Does the Milky Way Live in a Void? appeared first on Sky & Telescope.

Categories: Astronomy Headlines

Fun in the Sun: A White-Light Guide to Our Nearest Star

Wed, 06/21/2017 - 08:21

We examine the fascinating solar phenomena that anyone with a small scope and safe solar filter can see, whether the Sun's in eclipse or not.

Nibble and a big crumb

You never know what kind of bonus sights will accompany a solar eclipse. Giant sunspot region 2192 was a highlight of the October 23, 2014, partial solar eclipse.
Bob King

With the August 21st total solar eclipse fast approaching, the Sun's on everyone's mind. And having just passed the solstice, it stands highest in the sky and makes a powerful impression on June afternoons. Those planning to be within the path of totality can expect incredible views of Bailey's Beads, pink prominences, stars in the middle of the day and the coup de grâce — the magnificent solar corona. Others not inside that licorice strip of darkness will watch the Moon take a bite from the Sun and then give it back.

More people than ever will have safe solar filters for both naked eye and telescopic viewing. Why not put them to good use in getting to know our local star better? Plus, solar observing is just fun. No mosquitos, dropped flashlights or driving miles to escape light pollution. The Sun's signature features — sunspots, faculae, granulation and limb darkening — are all accessible in instruments as small as 3-inches.

Observing the Sun: Granulation Solar porridge

A time lapse video shows solar granules bubbling up from beneath the photosphere. When they reach the surface, the gases expand, cool, and drain back into the interior along the dark intragranular lanes.
University of Alabama

Sunspots get the most attention, and we'll get to them in a moment, but even when spots are absent, we can always look for the subtle, granular appearance of the Sun's photosphere, called granulation. Older astronomy guides describe it as resembling ground glass.

As long as the seeing's good, I can discern this exquisitely fine texture across the entire solar disk even at 28x in my 80mm University Optics refractor. It's amazing to think that each granule is a cell of convective gas about 930 miles (1,500 km) across (a bit bigger than the state of Texas) rising up from the Sun's interior like a bubble in a pot of boiling water.

Oh, but that pot has a lot of bubbles. At any given time, there are 4 million granules bumping heads in the photosphere. Their brighter cores are filled with hot plasma on the rise, while darker outlines mark where cooling gas is descending back below the surface. These churnin', burnin' rings of fire make the photosphere jumpier than a school busload of kids in a McDonald's ball pit. Granules live brief lives, only 8 to 20 minutes, before they're replaced by the rising minions from below.

Observing the Sun: Limb Darkening

If you take in a low power view of the full solar disk, you'll notice that it's not evenly illuminated but brightest in the center and dimmest around the limb. Limb darkening shows up better in photos, but once you know to look for it, it's unmistakable.

Digging beneath the surface

This photo, taken in June 1989, two solar cycles ago, dramatically illustrates limb darkening. Notice that faculae (described below) appear much more obvious in limb-darkened areas. Like Earth, the Sun rotates on its axis from east to west but takes 24.4 days at the equator to complete one full spin. Sunspots move westward with the rotation.
Bob King

When we look to the edge of the Sun (or any star), we can't see to the same depth as we can when looking squarely at its center because our line of sight slices through the disk at an oblique angle. Basically, at the edge we just don't see as deeply into the solar gases. With less material for our gaze to penetrate, the solar rim looks dimmer. A second reason for limb darkening concerns the difference in temperature of the gases in the Sun's core compared to those in its exterior — temperature decreases outward from the core. When you look at the Sun in your telescope, the center is hottest because you're seeing deeper into the core, while limb views are closer to the Sun's cooler surface.

Taken together, these two factors offer us a vision of the Sun that's transformative. Despite appearances, our star has no solid surface. Through a filtered scope, the solar disk looks as hard-edged as a dinner plate. But the reality is we're seeing into a fiery ball of plasma at different depth and temperature wherever we rest our gaze. Almost like having X-ray vision!

Observing the Sun: Sunspots (Sun) Spot on

Sunspot activity moves up and down the disk across the 11-year solar cycle. We're headed toward solar minimum in a historically low cycle, so spots have been infrequent of late. This photo was taken by NASA's Solar Dynamics Observatory on June 16th and shows two currently visible active regions. Region 2663 is a bipolar sunspot group with the west end having south magnetic polarity and the east end north polarity. The group is a knot of magnetic energy that rose up and broke through the surface. Limb darkening is also evident. North is up.
NASA / SDO

Following the parade of sunspots that pops up on the photosphere daily, weekly and sometimes by the hour makes for an easy and informative daytime activity. Sunspots form in what are called active regions, and their numbers wax and wane with the Sun's 11-year solar cycle. Cycle 24, the current one, is the weakest since Cycle 14, which peaked in February 1906. Cycle 24 officially began in 2008, peaked in April 2014, and will bottom out sometime in 2020. So far this year, spots have speckled the Sun on 76% of the days, so your chances of seeing at least a few a week are good. As you'd expect on the downside of the cycle, large groups are becoming scarce.

Magnetic behemoth

Sunspot groups can grow large enough to become easily visible to the naked eye with a safe solar filter. Clouds filtered the view in this photo taken of region 1967 on Feb. 2, 2014. The Chinese were the first to record the appearance of sunspots, with records going back to 800 B.C.
Bob King

Sunspots are the most obvious manifestation of the Sun's magnetic energy and form when differential rotation winds up and intensifies magnetic fields below the surface. The fields become buoyant and break through the surface, creating a sunspot group. Sunspots aren't physical spots per se, but regions of strong magnetic energy that hinder heat from rising from below the surface. As such they're several thousand degrees cooler than the rest of the photosphere and appear dark in contrast.

Magnetic manifestations

Sunspots, their filamentary penumbrae, and solar granulation are sharply resolved in images like this one from Hinode's Solar Optical Telescope.

A sunspot often begins life as a tiny, black pore not much bigger than a granule. Should it continue to grow, it develops a dark core (or cores) called an umbra, surrounded by a pale, skirt-like penumbra. The umbra is cooler than the penumbra and makes a dimple some 250 to 500 miles (400 to 800 km) below the surface.

What sunspots lack in heat, they make up in magnetic energy. Many groups resemble bar magnets, where the leading spot has one magnetic polarity and its followers have the opposite. Magnetic fields surrounding the spots resemble the looped patterns of iron filings sprinkled around an ordinary magnet.

Temper, temper

A powerful X-class flare and CME erupted from near the Sun's limb on March 7, 2011.
NASA / SDO

Sometimes multiple polarities crowd close together inside the umbra making for complicated and downright messy magnetic fields. When fields of opposite polarity cross paths, they can reconnect, releasing tremendous amounts of energy in the form of solar flares or as outbursts of solar plasma called coronal mass ejections (CMEs). We can't see the heated plasma with our eyes, but multiple times a day, NASA's Solar Dynamics Observatory (SDO) photographs these radiant swirls in far-ultraviolet light. Rarely, an extremely powerful flare can appear as a white spot in white light but most radiate at H-alpha and other wavelengths and require special filters to see.

Subatomic particles released in these explosive events travel outward at more than a million miles an hour and can spark space-weather events at Earth including brilliant auroras.

Watch the growth of sunspot group 1158 in Feb. 2011:

It's fascinating to see the day-to-day changes in sunspot size and complexity. Some last hours, others months. Sunspots can range from 3,500 km to 60,000 km across. A typical group is often bigger than Earth, and the larger ones are plainly visible to the naked eye when viewed through a safe solar filter.

To keep track of trends, try your hand at this traditional way of counting sunspots. First, count the individual spots in all groups, then count each individual group as 10. Add the two together to arrive at the total. There are now more refined methods, but for beginners this method works well.

Observing the Sun: Faculae Near edge-on granules with faculae

In this high-resolution image, individual faculae are bright spots where we see through the walls of solar granules, the cells of hot plasma bubbling up from below.
Courtesy Goran Scharmer / Royal Swedish Academy of Sciences

Sunspot groups are often accompanied by small, white flecks called faculae, after the Latin for "little torch." Sunspots may come and go, but faculae often linger longer or even presage the appearance of new spot groups. Faculae are much smaller spots of concentrated magnetic energy; they fleck a granules' walls and are best seen in the outer quarter of the solar disk. Here we view them in profile, their light stacking up to appear more intense than when seen broadside. Limb darkening also enhances their visibility.

Current Sun

SDO took this white light image on June 20th, showing three sunspot groups, granulation, and faculae.
NASA / SDO

But wait. Why are faculae bright when sunspots are dark? Small but strong magnetic fields dilute the gases along the granules' walls, letting us see into their hotter, brighter cores. Like sunspots, faculae appear to be a thing, but they're more of a phenomenon — an invisible hand painting the Sun with a magnetic brush.

The closer I look at the Sun I thought I knew, the stranger it becomes. Join me in my happy befuddlement by snapping on a filter and having a look yourself.

Resources:
Observers' Guide to the H-alpha Sun
* Solar Dynamics Observatory daily images

The post Fun in the Sun: A White-Light Guide to Our Nearest Star appeared first on Sky & Telescope.

Categories: Astronomy Headlines

waning crescent and planet

Wed, 06/21/2017 - 07:07

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Categories: Astronomy Headlines

Carina Nebula – DSLR Cooled

Tue, 06/20/2017 - 17:48

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Categories: Astronomy Headlines

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