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Partial Solar Eclipse Roundup

11 hours 56 min ago

Readers share their experiences of the October 23, 2014 partial solar eclipse.

I hope everyone enjoyed the late afternoon/early evening show yesterday. Did you see AR 2192, the giant sunspot group? If not, break out the eye protection again — it's moving quickly across the Sun's disk and you don't want to miss it. This was the last eclipse opportunity for awhile for those of us in the United States (already planning my western desert viewing for the total solar eclipse in 2017!); that might explain the explosion of photos in my twitter feed yesterday evening.

Image of partial solar eclipse as seen through clouds

Partial solar eclipse through thin cloud clover, Houston, Texas, October 23, 2014.
Greg Penner

As Greg Penner's photo demonstrates, clouds aren't always a problem when it comes to viewing solar events (even the sunspots are visible in the image he captured at 5:26 CDT). The skies were clear in Rancho Cucamonga, California, as evidenced by the image taken by Alson Wong at almost the same time. And Michael D. Radenich shows us what the scene looked like for most of the viewers in the central region of North America: a setting Sun with a nice bite taken out of it courtesy of the Moon.

My pick for "best use of old technology" goes to Sarah Ballard and Woody Sullivan at the University of Washington. Using an old Sloan Digital Sky Survey (SDSS) plate, they projected 640 images of the eclipse — simultaneously.

If you'd like to share your photos of the partial solar eclipse with S&T, feel free to submit them to our online gallery and view additional photos as they come in.

Partial solar eclipse, October 23, 2014, Rancho Cucamonga, California.Alson Wong

Partial solar eclipse, Rancho Cucamonga, California, October 23, 2014.
Alson Wong

Sunset during partial solar eclipse, Weatherby, Missouri, October 23, 2014.Michael D. Radencich

Sunset during partial solar eclipse, Weatherby, Missouri, October 23, 2014.
Michael D. Radencich

Repurposing an old SDSS plate to make a solar projection system.Sarah Ballard and Woody Sullivan (University of Washington)

Repurposing an old SDSS plate to make a solar projection system, October 23, 2014.
Sarah Ballard and Woody Sullivan (University of Washington)


640 simultaneous projections of the partial solar eclipse, October 23, 2014.
Sarah Ballard and Woody Sullivan (University of Washington)

The post Partial Solar Eclipse Roundup appeared first on Sky & Telescope.

Categories: Astronomy Headlines

Teepee Lodge Poles n Milky Way

12 hours 34 min ago

The post Teepee Lodge Poles n Milky Way appeared first on Sky & Telescope.

Categories: Astronomy Headlines

Lunar Eclipse in Taiwan

12 hours 45 min ago

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Categories: Astronomy Headlines

This Week’s Sky at a Glance, October 24 – November 1

17 hours 39 min ago
Some daily sky sights among the ever-changing stars and planets

The monster sunspot continues in view; see "This Week's Planet Roundup" below.

The waxing crescent Moon passes Mars in twilight, Oct. 27-28, 2014.

The waxing crescent Moon passes Mars in the Monday and Tuesday twilight. (The Moon in these scenes is always drawn three times its actual apparent size.)

Friday, October 24

As the stars come out, Deneb is nearly straight overhead for skywatchers at mid-northern latitudes. Brighter Vega is west of the zenith. Altair is farther from the zenith toward the south.

Saturday, October 25

A half hour after sunset, spot the thin waxing crescent Moon very low in the west-southwest. Look to its lower right to see whether you can still detect Saturn, which has been sinking lower every day. Binoculars help.

Sunday, October 26

As autumn proceeds, the Great Square of Pegasus shines ever higher in the east at nightfall. It's still balancing on one corner. Later in the night and the season, it turns to rest upright very high when you face south.

Monday, October 27

Spot Mars to the left of the waxing crescent Moon at nightfall, as shown here.

Tuesday, October 28

This evening Mars is below the Moon at nightfall, as shown above.

Wednesday, October 29

The Ghost of Summer Suns. Halloween is approaching, and this means that Arcturus, the star sparkling low in the west-northwest in twilight, is taking on its role as "the Ghost of Summer Suns."

What does this mean? For several days centered on October 29th every year, Arcturus occupies a special place above your local landscape. It closely marks the spot there where the Sun stood at the same time, by the clock, during warm June and July — in broad daylight, of course. So, in the last days of October each year, you can think of Arcturus as the chilly Halloween ghost of the departed summer Sun.

Thursday, October 30

First-quarter Moon (exactly so at 3:33 p.m. EDT). As twilight fades out, use binoculars to look a bit right of the Moon for Alpha Capricorni, a wide, lovely yellow double star. Look to Alpha's lower left for Beta Capricorni, a wide but more difficult double for binoculars; the secondary star in this case is much fainter.

Mercury in its best dawn display for 2014 (Nov. 1)

Mercury is now in its best dawn display for 2014. (The blue 10° scale is about the width of your fist held at arm's length.)

Friday, October 31

Mercury is coming into fine view at dawn, as shown here. Can you make out fainter Spica below it?

For Halloween after dark, the quarter Moon shines in the south. It's between Altair, very high to its upper right, and Fomalhaut, down to its lower left.

Saturday, November 1

This evening at nightfall, look for Fomalhaut almost straight below the Moon. Vega is the brightest star very high in the west-northwest. Capella, similarly bright, is rising in the northeast.

Daylight-saving time ends at 2 a.m. Sunday morning for most of North America. Clocks fall back an hour.


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

The Sun. This week, the huge sunspot group AR2192 will be rotating from near the center of the Sun's disk around to the Sun's western limb. Solar flares within it strong enough to affect Earth's near-space environment remain likely. See our article Huge Sunspot Group Now in View and updates at Follow near-real-time images from space at the Solar Dynamics Observatory site.

Mercury is coming into its best morning apparition of 2014 for skywatchers at mid-northern latitudes. It brightens rapidly from magnitude +0.7 to –0.6 this week, hanging low above the eastern horizon in mid-dawn. It'll probably be in best view about 60 to 45 minutes before sunrise, depending on the clarity of your low eastern sky. Don't confuse Mercury with twinklier Arcturus far to its left in the east-northeast.

Venus is close to the Sun, hidden its glare.

Mars (magnitude +0.9) remains low in the southwestern sky as twilight fades into night.

Jupiter (magnitude –2.0, at the Cancer-Leo border) rises in the east-northeast around 1 a.m. By dawn it shines brightly high in the southeast. Spot Regulus about a fist-width below or lower left of it.

Saturn is sinking away into the sunset. Scan for it with binoculars just above the west-southwest horizon, very far to the lower right of Mars, as twilight deepens.

Uranus (magnitude 5.7, in Pisces) and Neptune (magnitude 7.9, in Aquarius) are high in the southeast and south, respectively, in early evening. See our finder charts for Uranus and Neptune online or in the September Sky & Telescope, page 50.

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.

The post This Week’s Sky at a Glance, October 24 – November 1 appeared first on Sky & Telescope.

Categories: Astronomy Headlines

Spacecraft Observe Comet Siding Spring

Thu, 10/23/2014 - 13:56

Although flight controllers were worried that Mars-orbiting spacecraft might be harmed by the comet's close approach, nothing happened — and unique scientific observations are now streaming back to Earth.

Six months ago, flight controllers on both sides of the Atlantic were worried about how close Comet Siding Spring (C/2013 A1) was coming to Mars and what might happen when it got there.

Close call at Mars

Comet Siding Spring passed roughly 85,000 miles (137,000 km) from Mars at 16:29 Universal Time on October 19, 2014.
NASA / JPL / Horizons

NASA's teams decided to take the proactive route by altering the paths of their three orbiting spacecraft: Mars Reconnaissance Orbiter, Mars Odyssey, and the just-arrived the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. These tweaks put all three on the opposite side of the planet during the window of greatest danger, which computer models suggested would occur 90 to 100 minutes after the comet came closest to Mars.

Meanwhile, dynamicists at the European Space Agency took a wait-and-see approach. A plan was drawn up to have the agency's Mars Express orbiter briefly duck behind Mars as well.

However, because spacecraft is low on fuel and spends most of its orbiter relatively far from Mars, and because the comet's activity waned as the encounter neared, no adjustment was necessary. In fact, earlier this month mission managers decided not to turn the spacecraft so its big dish antenna could serve as a partial shield to protect the craft from cometary particles.

Instead, the good news is that all five Martian orbiters (including India's Mars Orbiter Mission) survived the comet's encounter without incident. Here are NASA's post-encounter status reports for MRO, MO, and MAVEN. Here's the latest word about Mars Express. (There's no word yet on the status of MOM or the observations it gathered.)

How NASA spacecraft will observe Comet Siding Spring

A summary of the observations of Comet Siding Spring planned with the five NASA spacecraft currently at Mars. Click on the image for a larger version.

Early Results from the Comet Encounter

Now that the comet has come and gone, at least in the neighborhood of Mars, planetary scientists are eager to analyze all the data these and other spacecraft are gathering about the unprecedented close flyby.

One of the most anticipated results came from the powerful HiRISE camera aboard MRO. Alfred McEwen, the University of Arizona researcher who heads the camera team, described the picture-taking attempt as "like imaging a speeding bullet while riding a roller coaster." Concern heightened when, 12 days before the encounter, test images showed that the comet wasn't quite in its predicted location.

HiRISE image of Comet Siding Spring

NASA's Mars Reconnaissance orbiter had the best camera for capturing Comet Siding Spring as it swept past Mars on October 19, 2014. The view at top left shows that the comet's nucleus was large enough to be resolved, but just barely. Below that is an enhanced version of the same image, showing gas and dust in the comet's outer coma.
NASA / JPL / Univ. of Arizona

But everything worked just fine, and HiRISE images taken during the encounter show that the nucleus of Comet Siding Spring is only two or three pixels across. So it can't be more than 0.5 km (about 1,500 feet) across — about half the size estimated from earlier observations. Still, this is the first time anyone has seen the nucleus of an Oort Cloud comet. McEwen and his team hope to derive the albedo, or reflectivity, of the icy nucleus (likely very, very dark) and its rotation rate.

The high-resolution camera on ESA's Mars Express wasn't able to resolve the nucleus, but its images of the comet's coma and tail will still be valuable. Word is that those data are on the ground but will take a few days for a quick-look analysis.

A very different perspective came from NASA's enduring rover, Opportunity, which looked up into the Martian night and spotted the comet from its perch in Merdiani Planum. Curiosity took some snaps too, but those haven't been released yet.

Hydrogen atoms from Comet Siding Spring

Two days before Comet Siding Spring swooped past Mars, an ultraviolet imager aboard NASA's MAVEN spacecraft mapped the distribution of hydrogen atoms in the comet's coma. This image, about 1½° across, records Lyman-alpha emission from hydrogen up to 93,000 miles (150,000 km) from the nucleus.
NASA / LASP / Univ. of Colorado

Another intriguing result is to what extent, if at all, gases from the comet's coma impinged on the upper Martian atmosphere, effectively contaminating it. Here's where the recent arrival of MAVEN and MOM, both equipped to make such observations, proved serendipitous. Earlier today the MAVEN team released an ultraviolet image that recorded a vast cloud of hydrogen atoms (derived from water molecules) in the comet's coma.

Other MAVEN results might not emerge so quickly. Measurements of hydrogen (and its heavier isotope deuterium) in the planet's upper atmosphere must take into account a pulse delivered recently by a strong coronal mass ejection from the Sun. "It's our first data taken in mapping mode, and we'll have to understand our instruments," explains MAVEN principal investigator Bruce Jakosky (University of Colorado). "The bottom line is that I can't promise yet when we'll have results — it may be very quickly, or it may take a while."

Meanwhile, lots of cameras here on Earth were pointed in the planet's direction, and amateurs (as usual) came up with many dramatic views of the Red Planet and its cometary companion. Two of the better ones are below.

The Hubble Space Telescope also recorded the comet as it neared Mars. But, frankly, the composite image that NASA pulled together looks very unnatural, especially the simulated starfield. Have a look and see if you agree.

Mars and Comet Siding Spring

Veteran astrophotographer Damian Peach recorded Mars (upper right) and Comet Siding Spring (lower left) under excellent conditions from Siding Spring, Australia, using a robotic 20-inch telescope. It was 11:07 Universal Time on October 19, 2014, just 5½ hours before the two were closest together. Mars outshines the 12th-magnitude comet by roughly 10,000 times.
© SEN / Damian Peach.

Mars and Comet Siding Spring

From the ultra-dark sky of Tivoli Farm in Namibia, Gerald Rhemann captured Comet Siding Spring just below brilliant Mars at 19:04 Universal Time (about 1&frac12: hours after the two were closest) on October 19, 2014. This is a composite of four 4-minute exposures through single-color filters.
Gerald Rhemann / Sky Vistas

Our special issue, "Mars: Mysteries & Marvels of the Red Planet," is loaded with spectacular photos and a must-read for anyone interested in this intriguing neighboring world.

The post Spacecraft Observe Comet Siding Spring appeared first on Sky & Telescope.

Categories: Astronomy Headlines

See a Partial Solar Eclipse — Today!

Thu, 10/23/2014 - 06:54

Find everything you need to enjoy today's partial solar eclipse — where to go, what you'll see, weather forecasts, and just in case, an online backup plan.

Need an excuse to take a mid-afternoon coffee break? Try this one: “Back in a few minutes, boss. There’s a partial solar eclipse going on right now!” Grab your coffee, your appropriate eye protection, and your supervisor, then head outdoors to watch to the show.

What will you see?Partial Solar Eclipse

Partial solar eclipse as viewed from "Amiral Vasile Urseanu" Public Observatory in Bucharest, Romania.
Alex Conu

This is a partial solar eclipse, and your location will determine how much of the Sun appears darkened by the Moon’s silhouette. Action begins near the Kamchatka Peninsula and edges eastward, deepening as the Moon moves along its orbit. The farther north you are, the deeper the eclipse you’ll see; the farther west, the higher the Sun and Moon will be in the sky.

The eclipse may seem modest for viewers in southern Mexico, but viewers in the northern half of the country could see 30-40% of the Sun “go dark” in the late afternoon. On the west coast of the United State — in San Francisco, for instance — about half of the Sun by covered by mid-afternoon. For viewers in northern Canada (Yukon and western Northwest Territories), the Moon will eat 70-80% of the Sun. From the central region of North America — Alabama, Michigan, Ontario, eastern Nunavut — the deepest point of the eclipse will coincide with setting of the Sun; you may have the most interesting view of all!

If you’re east of the imaginary line that runs from the Florida panhandle through the center of Hudson Bay, you should be able to see some of the eclipse, but the Sun will set before it reaches maximum. If you live in the east — New England, the Maritimes — you’re out of luck. Sunset will spoil your show.

Clear Skies

Your view of the solar eclipse depends as much on the weather as it does your position on Earth. Most of the weather apps and websites get their data from the National Weather Service (NOAA). The interface looks a bit old school, but a single click on the weather map will provide a good look at your regional weather. This can be helpful if you want to seek out nearby cloud breaks. Weather Underground supplements NOAA data with reports drawn from a system of personal weather stations. Their real-time weather updates may be also useful to eclipse chasers.

Watch Online

Here at Sky & Telescope, we’re suffering through a nor’easter; even if we were positioned perfectly to view the eclipse (we're not), we’d be rained out. So we’re watching online instead. Join us!

Need More Information?

Have questions about the eclipse? We have answers. Not sure if you’ll be able to see it? We can help you figure it out. And remember: never look at the Sun without appropriate eye protection!

Use the 2015 Sky & Telescope Observing Wall Calendar to plan your next skywatching session!

The post See a Partial Solar Eclipse — Today! appeared first on Sky & Telescope.

Categories: Astronomy Headlines

Sky Watchers Association of Bardhaman

Thu, 10/23/2014 - 06:46

Sky Watchers Association of Bardhaman


West Bengal  713101  India 


SWAB Admin. 





Affiliated to the Confederation of Indian Amateur Astronomers (CIAA) and Astronomers Without Borders (AWB)

Exceptional of exception, thinks beyond boundaries . It was just the thought of some school going children and some vital citizens of the city, which got a perfect blend to step out towards the heavens. It got crystallized to form a minor group, unknown to most. The year 2013, the coming of Comet ISON, made a swift way out to do something extraordinary with an extravagant feeling. The Sky and Telescope newsletters as guide, thrilled our nerves and we started our adventure with our unaided eyes and a pair of binoculars. Clear skies of the summers and the crystal pure heavens in winters, pushed us , to stretch our boundaries and conquer the unattained. Sky Watchers Association of Bardhaman, operates from the Rice Bowl of West Bengal, the city of Bardhaman.


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Categories: Astronomy Headlines

NASA’s IRIS Finds Solar Tornadoes, Bombs, and More

Wed, 10/22/2014 - 18:38

New IRIS results show a Sun rife with twisting and snapping magnetic fields, data that will elicit clues on what bakes the puzzlingly hot corona.

Eruption on the Sun

NASA's IRIS spacecraft provides a new window on the region between the Sun's visible surface and its outer atmosphere, the corona. The outer image comes from the Solar Dynamic Observatory, imaging the same eruption from the surface of the Sun on May 9, 2014.
NASA / Lockheed Martin Solar & Astrophysics Laboratory

The Sun’s visible surface gives off the radiation that governs our daily life. And during the rare occasion of a total solar eclipse, we can glimpse the tenuous, white-hot corona. But only if our eyes are very good can we see the red flame of the chromosphere, a thin layer sandwiched between the Sun’s surface and its extended atmosphere.

Even using spacecraft, it’s difficult to study the so-called interface region, which contains the chromosphere and the transition region right above it. But this is where the party’s at. Here, magnetic fields snap and pop, accelerating and heating particles a thousandfold — a party trick that scientists still don’t understand — before they reach the million-degree corona.

Now, first results from NASA’s sungazing spacecraft IRIS (Interface Region Imaging Spectrograph), published in the October 17th Science, are shedding light on this complex region. “Even seeing this part of the solar atmosphere at all in this detail is amazing!” says Louise Harra (UCL Mullard Space Science Laboratory, UK), who wrote a perspective piece accompanying the science results.

Launched in June 2013 to an earthbound orbit, IRIS views the Sun in ultraviolet light through an 8-inch scope, capturing detailed images and spectra at high frame rates. The data effectively point a magnifying glass on a scarcely studied, yet crucial region of the Sun’s atmosphere.

Perhaps the best illustration of this general statement is the IRIS work of Bart de Pontieu (Lockheed Martin Solar and Astrophysics Laboratory and University of Oslo) and his team. They found that the entire interface region, including active and quiet regions alike, is writhing. Plasma races around small loops of twisted magnetic field lines at 20,000 to 70,000 mph (10 to 30 km/s). The mini-tornadoes are everywhere, even in regions where nothing much (such as sunspots, flares, or the like) is happening.

The video below shows these features in succeeding images from NASA’s IRIS. The spacecraft observed the same area of the Sun in different wavelengths, measuring how fast and in what direction the solar material is moving.

Credit: NASA / IRIS / Pereira

“We have to re-evaluate how this can possibly be, and how it produces energy,” says Harra.

There’s a lot to chew on in the five Science papers, but here’s a look at two other results that intrigued me.

Solar Bombs

In another set of observations, a team led by Hardi Peter (Max Planck Institute for Solar System Research, Germany) discovered several round, bright features (see video below) in the photosphere. These silent explosions, which last roughly 5 minutes, represent pockets of gas heated suddenly to 80,000 K, despite their relatively cool (6000 K) surroundings — a temperature difference that reminds me of the tongue-burning cheeseballs in an otherwise frozen Hot Pocket.

Credit: NASA / IRIS / Peter

These features could be a hot analog of Ellerman bombs, microflares discovered almost 100 years ago. To create an Ellerman bomb, an undulating magnetic field line straddles the cooler photosphere and the hotter chromosphere. The motions of the hot and cold plasma reshape the line into a U-shaped loop that pinches off. The ensuing release of magnetic energy heats two pockets of plasma, one driving down into the dense photosphere and the other rocketing upward, visible as a solar bomb.

But typical signatures of Ellerman bombs, such as a change in the shape of the Hα line, don’t show up for the bombs discovered by Peter’s team. They may yet find these Ellerman signatures, or it's possible that these bombs could be a brand-new blast, one that defies current explanation.


Like solar bombs, flares ignite when two oppositely aligned magnetic field lines touch. But instead of exploding into the high-density region near the Sun’s visible surface, flares accelerate particles into the rarefied corona.

Back in 1988, Eugene Parker first suggested that many millions of nanoflares, flares beyond the reach of telescopes at the time, could heat the corona. But in their size lies the quandary ­— nanoflares are too small to observe directly. Astronomers don’t necessarily doubt that nanoflares exist, but they argue plenty about whether they are capable of heating the corona.

With IRIS’s exquisite spatial resolution, astronomers are now getting closer and closer to resolving the smallest flares that ought to exist.

Coronal loop

This SDO image shows a coronal loop. IRIS imaged the same coronal loop, showing flickering plasma at the loop's footprints.

Paola Testa (Harvard-Smithsonian Center for Astrophysics) and colleagues report that nanoflares might explain plasma churning and flickering near the footprints of coronal loops in IRIS data.

Using simulations to make their point, the team proposes that the magnetic energy released in nanoflares accelerates the corona’s electrons. Some electrons may escape into the corona or solar wind, but a sizable fraction dives back into the interface region, heating its plasma through collisions.

Although the observations and simulations make a powerful argument, these results won’t convince everybody.

“There’s no unique observation where someone can say, ‘I found it!’”, says Samuel Krucker (University of Applied Sciences Northwestern Switzerland and Space Sciences Laboratory, University of California). “We always rely on assumptions, and assumptions are debatable.”

Krucker suggests hard X-ray data might help bolster the scenario proposed in Testa’s paper. Observations with NASA’s NuSTAR X-ray satellite are in the works, he says, but they’ll have to wait for a quiet Sun, when solar activity doesn’t pose a danger to the instrument’s electronics.

For more information about IRIS’s results, read this introduction by three of the Science papers’ authors.

Keep up on the latest astronomy news and observations with a Sky & Telescope subscription!

The post NASA’s IRIS Finds Solar Tornadoes, Bombs, and More appeared first on Sky & Telescope.

Categories: Astronomy Headlines

How Many Pleiades Can YOU See?

Wed, 10/22/2014 - 07:46

Most of us are familiar with the Seven Sisters, but have you met their brothers? Learn how to find more Pleiades than first meet the eye.

Seven Sisters rise again this month

The Pleiades star cluster is located in Taurus and dominated by hot blue stars that formed within the past 100 million years.
Bob King

They're called the Seven Sisters, but can you see all seven? Better known as the Pleiades star cluster, this lovely group in the shape of a miniature Big Dipper enchants the eye on autumn nights. I love watching the Pleiades. There’s nothing quite like it in the heavens. Most stars are single and separate from each other, but the Pleiades packs more than a handful into a compact bunch that stands apart from nearly everything else in the sky.

The Pleiades is one of brightest star clusters in the sky. It contains some 3,000 stars and lies about 444 light-years from Earth. Side to side the group spans 13 light-years, or about halfway from Earth to the bright star Vega. Like a school of fish, its members move together as a gravitationally-bound swarm through space.

In late October the group clears the treetops around 9:30 p.m. local time and remains visible the rest of the night.

Like a cluster of grapes on the vine

The Pleiades (upper left) rises for easy viewing around 9:30 p.m. local time in late October. A distinctive knot of naked-eye stars, the cluster catches our eye whenever it's in the sky.
Bob King

When asked how many stars they see in the cluster, beginning observers will usually say five. That's what most of us see at a glance, and it makes sense because the five brightest Pleiades — Alcyone, Atlas, Electra, Maia, and Merope — range from magnitude 2.9 to 4.2, well within the grasp of most observers from a reasonably dark sky site. But can we do better?

To find 7 Pleiads we work from 5

The brighter of the Pleiades stars with names are shown along with their magnitudes. After spotting the five easy ones, try Taygeta and then Pleione to make seven.
John Lanoue

According to Agnes Clerke, a late 19th-century/early 20th-century astronomer and writer: "Carrington and Denning (British amateur astronomers) counted fourteen." Robert Burnham, in his 3-volume Celestial Handbook, writes that "there are at least 20 stars in the group which might be glimpsed under the finest conditions."

Wow! Really? Let's start with the next two easier targets. Extend a line from Alcyone through Maia to find Taygeta. Most amateur astronomers can spot this one with ease. A touch of averted vision, a technique of looking "around" the object of interest instead of directly at it, should make this a snap. It's the next one, Pleione, that gives many observers trouble. Not only is it dimmer, but the star nestles against brighter Atlas. For me, seeing it requires good dark adaption, patience, and a mix of averted and direct vision.

Time to track down the  the cluster's dimmer denizens

This view shows the bright central cluster plus additional fainter members and several unrelated but helpful guide stars nearby along with their magnitudes. In addition to the core cluster, stars circled in red are Pleiades members. Click to enlarge.
Source: Stellarium

That's seven. Ready to move on to the challenge round? We now go deep, pinging stars ranging from magnitude 5.4 to the inky sky limit of 6.5. Fully dark-adapted eyes and a moonless, transparent sky are musts. The dim Asterope duo and Celaeno beckon near the Pleiades core, but that's the problem. They're so close to other member stars, they're difficult to distinguish on their own.

I've caught tantalizing hints of both with averted vision when the cluster's high in the sky. Asterope presents a special challenge as the pair is separated by only 2.4 arc minutes — more than one arc minute closer than the famous Double-Double Epsilon Lyrae, itself no easy split, and nearly two magnitudes fainter. At best, you might see them as a single elongated star.

Once we move beyond the distraction of the central cluster, hunting gets easier. The magnitude 5.4 star (HD 23753) below the "dipper handle" is relatively easy, but the 6.0 (HD 23950) will place greater demands on your visual cortex. 18 Tauri likewise is relatively easy with averted vision, but beware of the 6.1 and 6.5 members south of Atlas. They'll push your vision to the limit. But that's where you want to be, right? Limits tempt us to go that extra step.

And now for the really big picture

Find the Pleiades cluster by facing east and looking 2-3 fists above the eastern horizon in late October around 10 p.m. local time.
Source: Stellarium

By the way, I keep a pair of binoculars at my side to not only verify Pleiades star sightings, but to help me know just where to look if I'm having difficulty finding a star. They also provide a splendid and visually refreshing look at the cluster after straining to see its fainter members.

So let's add up our starry gems. The bright five plus two not-so-difficult core cluster stars make seven. Add in seven more faint hanger-ons (we'll count Asterope as one) and you've got 14. Not bad, not bad at all.

New to stargazing? Let us help you with the Secrets of Stargazing!

The post How Many Pleiades Can YOU See? appeared first on Sky & Telescope.

Categories: Astronomy Headlines

Huge Sunspot Group Now in View

Tue, 10/21/2014 - 19:33

A gigantic cluster of sunspots, emerging into view on October 17th, could become the trigger point for potent solar storms.

Active Region 2192 rotates into view

Active Region 2192 rotates into view in this daily image sequence taken October 17th to 22nd by the Solar Dynamics Observatory.

As soon as it rotated into view on October 17th, perched on the Sun's eastern limb, it was clear that Active Region 12192 meant business. Since then this enormous sunspot group (abbreviated AR 2192) has only gotten larger and more impressive — even menacing. Today's spacecraft images revealed a huge disturbance as large as Jupiter.

"It continues to grow in size and complexity," observes C. Alex Young, a solar specialist at NASA's Goddard Space Flight Center.

While sentry spacecraft like the Solar and Heliospheric Observatory and Solar Dynamics Explorer continue to track AR 2192, now nearing the middle of the Sun's disk, high-resolution instruments on Japan's Hinode spacecraft and at ground-based observatories have zeroed in on the big group.

Active Region 2192 on October 22, 2014

A sunspot group as big as Jupiter is currently crossing the solar disk. NASA's Solar Dynamics Observatory obtained this white-light view early on October 22, 2014.

It's already been the source of several outbursts, including an X-class flare two days ago. Indeed, a group of solar physicists (colorfully dubbed the Max Millennium Chief Observers) has issued a "major flare watch" for this region.

Their expectation is that AR 2192 will erupt at a level of at least M5, and perhaps X1 or greater, in the days ahead. In fact, as this was being written, an M8.7 flare erupted from this location early on October 22nd.

Extreme-ultraviolet view of the Sun

The footprint of AR 2192 is obvious in this October 22nd view taken at the extreme-ultraviolet wavelength of 304 angstroms.

Space-weather forecasting is a tricky business. Just last month a powerful flare was propelled directly toward Earth, only to fizzle upon arrival. (Blame the blast's magnetic field, which wasn't oriented in a way that could readily couple with Earth's magnetosphere and allow easy entry for solar-wind particles.)

Given that AR 2192 is situated near the solar equator, a strong outburst over the next few days could send a solar blast wave squarely in Earth's direction. Is a major geomagnetic storm in our future? Wouldn't you like to have a nice auroral display in dark, Moonless skies this weekend?

Could Earth ever fall victim to a "solar superstorm"? Gets the odds of that happening — and the consequences if it does — in the February 2011 issue of Sky & Telescope.

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Categories: Astronomy Headlines

Targeting Crisis Averted for New Horizons

Tue, 10/21/2014 - 12:35

NASA scientists have found three potential Kuiper belt objects in the nick of time, saving the Pluto-bound probe from missing out on half of its mission.

An artist's conception of New Horizons reaching its designated KBO. Alex Parker, SwRI

An artist's conception of New Horizons reaching its designated KBO.
Alex Parker, SwRI

In July 2015, the New Horizons space probe will whiz past Pluto just 10,000 kilometers from its surface. This long-awaited flyby will provide unprecedented views of the dwarf planet, its moons, and the environment around it.

But scrutinizing the Pluto system is only half of New Horizons’s mission.

Soon afterward, the spacecraft will fire thrusters to set itself on a course to fly past a Kuiper belt object, or KBO. Because planning for that redirection must begin soon, project managers have worked hard to find a KBO worthy of such a visit. Yet, despite 3 years of searching, by mid-2014 a suitable candidate had not been found.

But now, the science team can breathe easier. NASA’s Hubble Space Telescope has uncovered three KBOs viable for a quick visit. “The story of the discovery is one of persistence, ingenuity, uncertainty, and a bit of a gamble,” says team member Keith Noll (NASA Goddard Space Flight Center).

Hubble Saves the Day

In a perfect world, project scientists would have identified a suitable KBO long before the space probe’s launch in 2007. But they postponed their main search until 2011 for multiple reasons.

By waiting longer, all possible KBOs began converging on the narrow cone of space that New Horizons will be able to reach after its Pluto encounter. With less sky to search, detecting suitable KBOs should — in principle — be easier, even if done at a later date.

Pluto has been crossing the constellation Sagittarius, home of our star- and dust-filled galactic center. The crowded field makes finding any intrinsically faint object extremely challenging. Fortunately, Pluto is moving in front of dark clouds, allowing the search to continue without so much background confusion.

The team members were also hoping that, by waiting, they could utilize bigger telescopes and much better instruments than were available 10 years ago. And in fact, they’ve used the 10-meter Keck Telescopes and 8.2-meter Subaru Telescope in Hawaii, the 8.1-meter Gemini telescopes in Hawaii and Chile, and the 6.5-meter Magellan Telescope in Chile.

But, despite using some of the best ground-based telescopes in the world, the search turned up only 50 new KBOs, none of which were close enough for New Horizons to reach. So the team turned to Hubble and was awarded roughly two weeks of observing time — a large chunk on the most sought-after telescope. And it paid off. Hubble quickly picked up three potential targets.

“The Hubble Space Telescope has rescued the exploration of the Kuiper Belt,” says principle investigator Alan Stern (Southwest Research Institute).

But Stern also argues that having dedicated project scientists was equally important. “This team did about two years of work in four months,.” he explains. “It was night and day, seven days a week. They wrote crazy amounts of code. They did crazy amounts of rapid-fired data reduction, analysis, and follow-up.”

Uncharted Territory

The Kuiper Belt is a vast ring of primordial debris encircling our solar system. Its objects are so intrinsically faint, small, and distant that they’re nearly impossible to study from Earth. And yet they contain crucial clues about the formation of the solar system. Because KBOs have not been heated by the Sun, their ices are therefore a sample of what the early solar system was like 4.6 billion years ago.

The first target, designated “Potential Target 1,” was discovered on June 27th — just 11 days after the search team was awarded time on Hubble. Since then, the object has been imaged four times. These follow-up images allowed the team to constrain its orbit and size (roughly 30 to 45 km across) and provided assurance that New Horizons will reach it in January 2019.

Five Hubble Space Telescope Wide Field Camera 3 images of a faint, distant object that will be visited by New Horizons in January 2019. The photos were taken on June 24, 2014. The object has a magnitude of 26.8, too faint to be observed by ground-based telescopes. NASA, ESA, SwRI, JHU/APL, and the New Horizons KBO Search Team

Click above to see the five HST images of PS1.
NASA, ESA, SwRI, JHU/APL, and the New Horizons KBO Search Team

Even better, PT1 is reachable with only two-thirds of the spacecraft’s remaining fuel supply, says Stern. So if the project scientists need to make slight adjustments to the spacecraft’s orbit, once PT1 comes into view, they can.

But PT1 is incredibly faint, roughly 200 million times fainter than the naked eye can see. So although PT1 is the most likely of the Hubble-discovered objects to be targeted, it’s possible that follow-up observations might make PT2 or PT3 more desirable. They’re both slightly brighter and therefore bigger than PT1, which will make targeting them easier.

Their larger surfaces also have a huge advantage. “By looking at their surfaces we can learn about how battered they have been by collisions over the years — how violent or quiet things have been in the outer region of our solar system,” says team member Susan Benecchi (Planetary Science Institute).

But the project scientists still don’t know what to expect. “What we’ve found in planetary science is that when we send a spacecraft for the first time to a new place, we’re often wrong,” says Stern. “For example, no one expected river valleys on Mars, volcanoes in the outer solar system, and oceans on the inside of worlds.”

A typical KBO is about 10 times larger than 67P/Churyumov–Gerasimenko (Rosetta’s comet), and about 100 times smaller than Pluto. So they serve as great stepping-stones from smaller cometary objects to larger dwarf planets.

“We’re either going to confirm conventional wisdom, which would be important, or we’re going to find a big surprise,” says Stern. “Either way it’s a data point — and one we can’t get unless we go there.”

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Categories: Astronomy Headlines