Stars Archives

May 2, 2016May 3, 2016 by Jason Major

Three New Earth-sized Planets Found Just 40 Light-Years Away

Artist's impression of rocky exoplanets orbiting Gliese 832, a red dwarf star just 16 light-years from Earth. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org).

Three more potentially Earthlike worlds have been discovered in our galactic backyard, announced online today by the European Southern Observatory. Researchers using the 60-cm TRAPPIST telescope at ESO’s La Silla observatory in Chile have identified three Earth-sized exoplanets orbiting a star just 40 light-years away.

The star, originally classified as 2MASS J23062928-0502285 but now known more conveniently as TRAPPIST-1, is a dim “ultracool” red dwarf star only .05% as bright as our Sun . Located in the constellation Aquarius, it’s now the 37th-farthest star known to host orbiting exoplanets.

The exoplanets were discovered via the transit method (TRAPPIST stands for Transiting Planets and Planetesimals Small Telescope) through which the light from a star is observed to dim slightly by planets passing in front of it from our point of view. This is the same method that NASA’s Kepler spacecraft has used to find over 1,000 confirmed exoplanets.

*Location of TRAPPIST-1 in the constellation Aquarius. Credit: ESO/IAU and Sky & Telescope.*

As an ultracool dwarf TRAPPIST-1 is a very small and dim and isn’t easily visible from Earth, but it’s its very dimness that has allowed its planets to be discovered with existing technology. Their subtle silhouettes may have been lost in the glare of larger, brighter stars.

Follow-up measurements of the three exoplanets indicated that they are all approximately Earth-sized and have temperatures ranging from Earthlike to Venuslike (which is, admittedly, a fairly large range.) They orbit their host star very closely with periods measured in Earth days, not years.

“With such short orbital periods, the planets are between 20 and 100 times closer to their star than the Earth to the Sun,” said Michael Gillon, lead author of the research paper. “The structure of this planetary system is much more similar in scale to the system of Jupiter’s moons than to that of the Solar System.”

Structure of the TRAPPIST-1 exosystem. The green is the star's habitable zone. Credit: PHL. — *Structure of the TRAPPIST-1 exosystem. The green is the star’s habitable zone. Credit: PHL.*

Although these three new exoplanets are Earth-sized they do not yet classify as “potentially habitable,” at least by the standards of the Planetary Habitability Laboratory (PHL) operated by the University of Puerto Rico at Arecibo. The planets fall outside PHL’s required habitable zone; two are too close to the host star and one is too far away.

In addition there are certain factors that planets orbiting ultracool dwarfs would have to contend with in order to be friendly to life, not the least of which is the exposure to energetic outbursts from solar flares.

This does not guarantee that the exoplanets are completely uninhabitable, though; it’s entirely possible that there are regions on or within them where life could exist, not unlike Mars or some of the moons in our own Solar System.

The exoplanets are all likely tidally locked in their orbits, so even though the closest two are too hot on their star-facing side and too cold on the other, there may be regions along the east or west terminators that maintain a climate conducive to life.

“Now we have to investigate if they’re habitable,” said co-author Julien de Wit at MIT in Cambridge, Mass. “We will investigate what kind of atmosphere they have, and then will search for biomarkers and signs of life.”

Artist's impression of the view from the most distant exoplanet discovered around the red dwarf star TRAPPIST-1. Credit: ESO/M. Kornmesser. — *Artist’s impression of the view from the most distant exoplanet discovered around the dwarf star TRAPPIST-1. Credit: ESO/M. Kornmesser.*

Discovering three planets orbiting such a small yet extremely common type of star hints that there are likely many, many more such worlds in our galaxy and the Universe as a whole.

“So far, the existence of such ‘red worlds’ orbiting ultra-cool dwarf stars was purely theoretical, but now we have not just one lonely planet around such a faint red star but a complete system of three planets,” said study co-author Emmanuel Jehin.

The team’s research was presented in a paper entitled “Temperate Earth-sized planets transiting a nearby ultracool dwarf star” and will be published in Nature.

Source: ESO, PHL, and MIT

________________

Note: the original version of this article described 2MASS J23062928-0502285 (TRAPPIST-1) as a brown dwarf based on its classification on the Simbad archive. But at M8V it is “definitely a star,” according to co-author Julien de Wit in an email, although at the very low end of the red dwarf line. Corrections have been made above.

April 15, 2016April 15, 2016 by Evan Gough

A Super-Fast Star System Shrugs Its Shoulders At Physics

This annotated artist's conception illustrates our current understanding of the structure of the Milky Way galaxy. Image Credit: NASA

Astronomers have found a pair of stellar oddballs out in the edges of our galaxy. The stars in question are a binary pair, and the two companions are moving much faster than anything should be in that part of the galaxy. The discovery was reported in a paper on April 11, 2016, in the Astrophysical Journal Letters.

The binary system is called PB3877, and at 18,000 light years away from us, it’s not exactly in our neighborhood. It’s out past the Scutum-Centaurus Arm, past the Perseus Arm, and even the Outer Arm, in an area called the galactic halo. This binary star also has the high metallicity of younger stars, rather than the low metallicity of the older stars that populate the outer reaches. So PB3877 is a puzzle, that’s for sure.

PB3877 is what’s called a Hyper-Velocity Star (HVS), or rogue star, and though astronomers have found other HVS’s, more than 20 of them in fact, this is the first binary one found. The pair consists of a hot sub-dwarf primary star that’s over five times hotter than the Sun, and a cooler companion star that’s about 1,000 degrees cooler than the Sun.

Hyper-Velocity stars are fast, and can reach speeds of up to 1,198 km. per second, (2.7 million miles per hour,) maybe faster. At that speed, they could cross the distance from the Earth to the Moon in about 5 minutes. But what’s puzzling about this binary star is not just its speed, and its binary nature, but its location.

Hyper-Velocity stars themselves are rare, but PB3877 is even more rare for its location. Typically, hyper velocity stars need to be near enough to the massive black hole at the center of a galaxy to reach their incredible speeds. A star can be drawn toward the black hole, accelerated by the unrelenting pull of the hole, then sling-shotted on its way out of the galaxy. This is the same action that spacecraft can use when they gain a gravity assist by travelling close to a planet.

This video shows how stars can accelerate when their orbit takes them close to the super-massive black holes at the center of the Milky Way.

But the trajectory of PB3877 shows astronomers that it could not have originated near the center of the galaxy. And if it had been ejected by a close encounter with the black hole, how could it have survived with its binary nature intact? Surely the massive pull of the black hole would have destroyed the binary relationship between the two stars in PB3877. Something else has accelerated it to such a high speed, and astronomers want to know what, exactly, did that, and how it kept its binary nature.

Barring a close encounter with the super-massive black hole at the center of the Milky Way, there are a couple other ways that PB3877 could have been accelerated to such a high velocity.

One such way is a stellar interaction or collision. If two stars were travelling at the right vectors, a collision between them could impart energy to one of them and propel it to hyper-velocity. Think of two pool balls on a pool table.

Another possibility is a supernova explosion. It’s possible for one of the stars in a binary pair to go supernova, and eject it’s companion at hyper-velocity speeds. But in these cases, either stellar collision or supernova, things would have to work out just right. And neither possibility explains how a wide-binary system like this could stay intact.

Fraser Cain sheds more light on Hyper-Velocity Stars, or Rogue Stars, in this video.

There is another possibility, and it involves Dark Matter. Dark Matter seems to lurk on the edge of any discussion around something unexplained, and this is a case in point. The researchers think that there could be a massive cocoon or halo of Dark Matter around the binary pair, which is keeping their binary relationship intact.

As for where the binary star PB3788 came from, as they say in the conclusion of their paper, “We conclude that the binary either formed in the halo or was accreted from the tidal debris of a dwarf galaxy by the Milky Way.” And though the source of this star’s formation is an intriguing question, and researchers plan follow up study to verify the supernova ejection possibility, its possible relationship with Dark Matter is also intriguing.

April 6, 2016April 14, 2016 by Jason Major

Nearby Supernovas Showered Earth With Iron

Visible, infrared, and X-ray light image of Kepler's supernova remnant (SN 1604) located about 13,000 light-years away. Credit: NASA, ESA, R. Sankrit and W. Blair (Johns Hopkins University).

We all know that we are “made of star-stuff,” with all of the elements necessary for the formation of planets and even life itself having originated inside generations of massive stars, which over billions of years have blasted their creations out into the galaxy at the explosive ends of their lives. Supernovas are some of the most powerful and energetic events in the known Universe, and when a dying star finally explodes you wouldn’t want to be anywhere nearby—fresh elements are nice and all but the energy and radiation from a supernova would roast any planets within tens if not hundreds of light-years in all directions. Luckily for us we’re not in an unsafe range of any supernovas in the foreseeable future, but there was a time geologically not very long ago that these stellar explosions are thought to have occurred in nearby space… and scientists have recently found the “smoking gun” evidence at the bottom of the ocean.

Two independent teams of “deep-sea astronomers”—one led by Dieter Breitschwerdt from the Berlin Institute of Technology and the other by Anton Wallner from the Australian National University—have investigated sediment samples taken from the floors of the Pacific, Atlantic, and Indian oceans. The sediments were found to contain relatively high levels of iron-60, an unstable isotope specifically created during supernovas.

*The Local Bubble is a 300-light-year long region that was carved out of the interstellar medium by supernovas (Source: Science@NASA)*

Watch: How Quickly Does a Supernova Happen?

The teams found that the ages of the iron-60 concentrations (the determination of which was recently perfected by Wallner) centered around two time periods, 1.7 to 3.2 million years ago and 6.5 to 8.7 million years ago. Based on this and the fact that our Solar System currently resides within a peanut-shaped region virtually empty of interstellar gas known as the Local Bubble, the researchers are confident that this provides further evidence that supernovas exploded within a mere 330 light-years of Earth, sending their elemental fallout our way.

“This research essentially proves that certain events happened in the not-too-distant past,” said Adrian Melott, an astrophysicist and professor at the University of Kansas who was not directly involved with the research but published his take on the findings in a letter in Nature. (Source)

The researchers think that two supernova events in particular were responsible for nearly half of the iron-60 concentrations now observed. These are thought to have taken place among a a nearby group of stars known as the Scorpius–Centaurus Association, some 2.3 and 1.5 million years ago. At those same time frames Earth was entering a phase of repeated global glaciation, the end of the last of which led to the rise of modern human civilization.

While supernovas of those sizes and distances wouldn’t have been a direct danger to life here on Earth, could they have played a part in changing the climate?

“Our local research group is working on figuring out what the effects were likely to have been,” Melott said. “We really don’t know. The events weren’t close enough to cause a big mass extinction or severe effects, but not so far away that we can ignore them either. We’re trying to decide if we should expect to have seen any effects on the ground on the Earth.”

Regardless of the correlation, if any, between ice ages and supernovas, it’s important to learn how these events do affect Earth and realize that they may have played an important and perhaps overlooked role in the history of life on our planet.

“Over the past 500 million years there must have been supernovae very nearby with disastrous consequences,” said Melott. “There have been a lot of mass extinctions, but at this point we don’t have enough information to tease out the role of supernovae in them.”

You can find the teams’ papers in Nature here and here.

Sources: IOP PhysicsWorld and the University of Kansas

UPDATE 4/14/16: The presence of iron-60 from the same time periods as those mentioned above has also been found on the Moon by research teams in Germany and the U.S. Read more here.

March 22, 2016April 12, 2016 by Evan Gough

Kepler Catches Early Flash Of An Exploding Star

“Life exists because of supernovae,” said Steve Howell, project scientist for NASA’s Kepler and K2 missions at NASA’s Ames Research Center. “All heavy elements in the universe come from supernova explosions. For example, all the silver, nickel, and copper in the earth and even in our bodies came from the explosive death throes of stars.”

So a glimpse of a supernova explosion is of intense interest to astronomers. It’s a chance to study the creation and dispersal of the life-enabling elements themselves. A greater understanding of supernovae will lead to a greater understanding of the origins of life.

Stars are balancing acts. They are a struggle between the pressure to expand, created by the fusion in the star, and the gravitational urge to collapse, caused by their own enormous mass. When the core of a star runs out of fuel, the star collapses in on itself. Then there is a massive explosion, which we call a supernova. And only very large stars can become supernovae.

The brilliant flashes that accompany supernovae are called shock breakouts. These events last only about 20 minutes, an infinitesimal amount of time for an object that can shine for billions of years. But when Kepler captured two of these events in 2011, it was more than just luck.

Peter Garnavich is an astrophysics professor at the University of Notre Dame. He led an international team that analyzed the light from 500 galaxies, captured every 30 minutes over a period of 3 years by Kepler. They searched about 50 trillion stars, trying to catch one as it died as a supernova. Only a fraction of stars are large enough to explode as supernovae, so the team had their work cut out for them.

“In order to see something that happens on timescales of minutes, like a shock breakout, you want to have a camera continuously monitoring the sky,” said Garnavich. “You don’t know when a supernova is going to go off, and Kepler’s vigilance allowed us to be a witness as the explosion began.”

An artist's concept of a shock breakout. Image: NASA Ames/STScl/G. Bacon — An artist’s concept of a shock breakout. Image: NASA Ames/STScl/G. Bacon

In 2011 Kepler caught two gigantic stars as they died their supernova death. Called KSN 2011a, and KSN 2011d, the two red super-giants were 300 times and 500 times the size of our Sun respectively. 2011a was 700 million light years from Earth, and 2011d was 1.2 billion light years away.

The intriguing part of the two supernovae is the difference between them; one had a visible shock breakout and one did not. This was puzzling, since in other respects, both supernovae behaved much like theory predicted they would. The team thinks that the smaller of the two, KSN 2011a, may have been surrounded by enough gas to mask the shock breakout.

The Kepler spacecraft is well-known for searching for and discovering extrasolar planets. But when some components on board Kepler failed in 2013, the mission was re-cast as the K2 Mission. “While Kepler cracked the door open on observing the development of these spectacular events, K2 will push it wide open, observing dozens more supernovae,” said Tom Barclay, senior research scientist and director of the Kepler and K2 guest observer office at Ames. “These results are a tantalizing preamble to what’s to come from K2!”

(For a brilliant and detailed look at the life-cycle of stars, I recommend “The Life and Death of Stars” by Kenneth R. Lang.)

November 15, 2015December 23, 2015 by Bob King

Sweet Sights for November Nights

A pretty crescent moon will be the first thing you'll see appear in the sky tonight. Look southwest shortly after sunset to spot it. Source: Stellarium

Clear night ahead? Let’s see what’s up. We’ll start close to home with the Moon, zoom out to lonely Fomalhaut 25 light years away and then return to our own Solar System to track down the 7th planet. Even before the sky is dark, you can’t miss the 4-day-old crescent Moon reclining in the southwestern sky. Watch for it to wax to a half-moon by Thursday as it circles Earth at an average speed of 2,200 mph (3,600 km/hr). That fact that it orbits Earth means that the angle the Moon makes with the sun and our planet constantly varies, the reason for its ever-changing phase.

You'll see two and possibly three lunar "seas" tonight (Nov. 15). Only a portion of Mare Tranquilliitatis (Seas of Tranquility) is exposed. The large crater Janssen, 118 miles wide and 1.8 miles deep, is visible in binoculars. Credit: Virtual Moon Atlas / Legrande and Chevalley — You’ll see two and possibly three lunar “seas” tonight (Nov. 15). Only a portion of Mare Tranquilliitatis (Seas of Tranquility) is exposed. The large crater Janssen, 118 miles wide and 1.8 miles deep, is visible in binoculars. Credit: Virtual Moon Atlas / Legrande and Chevalley

With the naked eye you’ll be able to make two prominent dark patches within the crescent — Mare Crisium (Sea of Crises) and Mare Fecunditatis (Sea of Fecundity). Each is a vast, lava-flooded plain peppered with thousands of craters , most of which require a telescope to see. Not so Janssen. This large, 118-mile-wide (190-km) ring will be easy to pick out in a pair of seven to 10 power binoculars. Janssen is named for 19th century French astronomer Pierre Janssen, who was the first to see the bright yellow line of helium in the sun’s spectrum while observing August 1868 total solar eclipse.

Piscis Austrinus, the Southern Fish, has but one bright star, 1st magnitude Fomalhaut. It shines all by its lonesome in the south around 7 p.m. local time at mid-month. The star is located only 25 light years from Earth. Source: Stellarium

English scientist Norman Lockyer also observed the line later in 1868 and concluded it represented a new solar element which he named “helium” after “helios”, the Greek word for sun. Helium on Earth wouldn’t be discovered for another 10 years, making this party-balloon gas the only element first discovered off-planet!

See the fish now? Greek mythology tells us that Piscis Austrinus is the "Great Fish", the parent of the two fish in the zodiacal constellation of Pisces the Fish. Source: Stellarium — See the fish now? Greek mythology tells us that Piscis Austrinus is the “Great Fish”, the parent of the two fish in the zodiacal constellation of Pisces the Fish. Source: Stellarium

Directing your gaze south around 7 o’clock, you’ll see a single bright star low in the southern sky. This is Fomalhaut in the dim constellation of Piscis Austrinus, the Southern Fish. The Arabic name means “mouth of the fish”. If live under a dark, light-pollution-free sky, you’ll be able to make out a loop of faint stars vaguely fish-like in form. Aside from being the only first magnitude star among the seasonal fall constellations, Fomalhaut stands out in another way — the star is ringed by a planet-forming disk of dust and rock much as our own Solar System was more than 4 billion years ago.

The planet Fomalhaut b orbits Fomalhaut inside a circumstellar disk of dust and rock, taking about 1,700 years to orbit. Brilliant Fomalhaut, represented by the small, white dot, has been masked from view, so astronomers could photograph the much fainter disk. Credit: NASA / ESA / Hubble Space Telescope

Within that disk is a new planet, Fomalhaut b, with less than twice Jupiter’s mass and enshrouded either by a cloud of dusty debris or a ring system like Saturn. Fomalhaut b has the distinction of being the first extrasolar planet ever photographed in visible light. The plodding planet takes an estimated 1,700 years to make one loop around Fomalhaut, with its distance from its parent star varying from about 50 times Earth’s distance from the sun at closest to 300 times that distance at farthest.

Shoot a diagonal across the Square of Pegasus to 4th magnitude Delta Piscium. Point your binoculars here and slide east to 4th magnitude Epsilon and 2° south to the planet Uranus shines at magnitude +5.7 and can be glimpsed with the naked eye from a dark sky site. Time shown is around 7 p.m. local time. See detailed map below. Source: Stellarium

Next, we move on to one of the more remote planets in our own solar system, Uranus. The 7th planet from the sun, Uranus reached opposition — its closest to Earth and brightest appearance for the year — only a month ago. It’s well-placed for viewing in Pisces the Fish after nightfall high in the southeastern sky below the prominent sky asterism, the Great Square of Pegasus.

Wide-field binocular view of Uranus' travels now through next April. I've labeled two stars near the planet with their magnitudes - 5.5 and 6.0 - which are similar to Uranus in brightness, so you don't confuse them with the planet. The others are naked eye stars in Pisces. Source: Chris Mariott's SkyMap — Wide-field binocular view of Uranus’ travels now through next April. I’ve labeled several stars near the planet with their magnitudes, which are similar in brightness to Uranus, so you’ll know to tell them apart from the planet. The others are naked eye stars in Pisces. Source: Chris Mariott’s SkyMap

A telescope will tease out its tiny, greenish disk, but almost any pair of binoculars will easily show the planet as a star-like point of light slowly marching westward against the starry backdrop in the coming weeks. Check in every few weeks to watch it move first west, in retrograde motion, and then turn back east around Christmas. For those with 8-inch and larger telescopes who love a challenge, use this Uranian Moon Finder to track the planet’s two brightest moons, Titania and Oberon, which glimmer weakly around 14th magnitude.

We’ve barely scratched the surface of the vacuum with these offerings; they’re just a few of the many highlights of mid-November nights that also include the annual Leonid meteor shower, which peaks Tuesday and Wednesday mornings (Nov. 17-18). So much to see!

November 9, 2015December 23, 2015 by Dan Majaess

Radio waves absent from the reputed megastructure-encompassed Kepler star?

Radio observations were carried out from the Allen Telescope Array of the reputed megastructure-encompassed star KIC 8462852.

Astronomers at the SETI institute (search for extraterrestrial intelligence) have reported their findings after monitoring the reputed megastructure-encompassed star KIC 8462852. No significant radio signals were detected in observations carried out from the Allen Telescope Array between October 15-30th (nearly 12 hours each day). However, there are caveats, namely that the sensitivity and frequency range were limited, and gaps existed in the coverage (e.g., between 6-7 Ghz).

Lead author Gerald Harp and the SETI team discussed the various ideas proposed to explain the anomalous Kepler brightness measurements of KIC 8462852, “The unusual star KIC 8462852 studied by the Kepler space telescope appears to have a large quantity of matter orbiting quickly about it. In transit, this material can obscure more than 20% of the light from that star. However, the dimming does not exhibit the periodicity expected of an accompanying exoplanet.” The team went on to add that, “Although natural explanations should be favored; e.g., a constellation of comets disrupted by a passing star (Boyajian et al. 2015), or gravitational darkening of an oblate star (Galasyn 2015), it is interesting to speculate that the occluding matter might signal the presence of massive astroengineering projects constructed in the vicinity of KIC 8462582 (Wright, Cartier et al. 2015).”

One such megastructure was discussed in a famous paper by Freeman Dyson (1960), and subsequently designated a ‘Dyson Sphere‘. In order to accommodate an advanced civilisation’s increasing energy demands, Dyson remarked that, “pressures will ultimately drive an intelligent species to adopt some such efficient exploitation of its available resources. One should expect that, within a few thousand years of its entering the stage of industrial development, any intelligent species should be found occupying an artificial biosphere which completely surrounds its parent star.” Dyson further proposed that a search be potentially conducted for artificial radio emissions stemming from the vicinity of a target star.

An episode of Star Trek TNG featured a memorable discussion regarding a ‘Dyson Sphere‘.
The SETI team summarized Dyson’s idea by noting that Solar panels could serve to capture starlight as a source of sustainable energy, and likewise highlighted that other, “large-scale structures might be built to serve as possible habitats (e.g., “ring worlds”), or as long-lived beacons to signal the existence of such civilizations to technologically advanced life in other star systems by occluding starlight in a manner not characteristic of natural orbiting bodies (Arnold 2013).” Indeed, bright variable stars such as the famed Cepheid stars have been cited as potential beacons.

The Universe Today’s Fraser Cain discusses a ‘Dyson Sphere‘.
If a Dyson Sphere encompassed the Kepler catalogued star, the SETI team were seeking in part to identify spacecraft that may service a large structure and could be revealed by a powerful wide bandwidth signal. The team concluded that their radio observations did not reveal any significant signal stemming from the star (e.g., Fig 1 below). Yet as noted above, the sensitivity was limited to above 100 Jy and the frequency range was restricted to 1-10 Ghz, and gaps existed in that coverage.

Fig 1 from Harp et al. 2015 (http://arxiv.org/abs/1511.01606) indicating the lack of signal detected for the Kepler star (black symbols). — Fig 1 from Harp et al. (2015) conveys the lack of radio waves emerging from the star KIC 8462852 (black symbols), however there were sensitivity and coverage limitations (see text). The signal emerging from the quasar 3c84 is shown via blue symbols.

What is causing the odd brightness variations seen in the Kepler star KIC 8462852? Were those anomalous variations a result of an unknown spurious artefact from the telescope itself, a swath of comets temporarily blocking the star’s light, or perhaps something more extravagant. The latter should not be hailed as the de facto source simply because an explanation is not readily available. However, the intellectual exercise of contemplating the technology advanced civilisations could construct to address certain needs (e.g., energy) is certainly a worthy venture.

September 29, 2015April 26, 2016 by David Dickinson

Challenge-Watch the Daytime Moon Occult Aldebaran for North America This Friday

How about that total lunar eclipse this past Sunday? Keep an eye of the waning gibbous Moon this week, as it begins a dramatic dive across the ecliptic towards a series of photogenic conjunctions throughout October.

The Main Event: This week’s highlight is an occultation of the bright +0.9 magnitude star Aldebaran (Alpha Tauri) by the waning gibbous Moon on Friday morning October 2^nd.

The occultation footprint for Friday’s occultation of Aldebaran by the Moon, with pre-dawn, dawn and post-dawn zones annotated. Image credit: Occult 4.0 software

This occurs in the pre-dawn hours for Alaskan residents, and under favorable dawn twilight skies along the U.S. and Canadian Pacific west coast; the remainder of the contiguous United States and Canada will see the occultation transpire after sunrise. This is the 10th of 49 occultations of Aldebaran by the Moon worldwide running from January 29th, 2015 through September 3rd, 2018. The Moon will be at 74% waning gibbous phase, and Aldebaran will disappear behind its illuminated limb to reappear from behind its trailing dark limb.

Check out this amazing Vine of the last occultation of Aldebaran by the Moon courtesy of Andrew Symes @FailedProtostar:

It’s interesting to note that the southern graze-line for the occultation roughly follows the U.S./Mexican border. Seeing a bright star wink in and out from behind the lunar valleys can be an unforgettable sight, adding an eerie 3D perspective to the view. A detailed analysis of the event can even help model the rugged limb of the Moon.

Hunting stars and planets in the daytime can be an interesting feat of visual athletics. We’ve managed to spy Aldebaran near the lunar limb with binoculars during an occultation witnessed from Alaska on September 4^th, 1996, and can attest that it’s quite possible to see a +1^st magnitude star near the Moon with optical aid. A clear blue sky is key. The Greek philosopher Thales noted that stars could be seen from the bottom of a well (though perhaps he’d fallen down a well or two too many in his time)… Friday’s event should push your local seeing to its limits. Start tracking Aldebaran before local sunrise, and you should be able to follow it all the way to the lunar limb, clear skies willing.

The occultation path for various locales across the United States Friday morning. Image credit: Dave Dickinson/Stellarium

Here’s a listing of times for key events for Friday from around the U.S. Check out The International Occultation Timing Association’s page for the event for an extensive listing:

Key times for the occultation for the same locales depicted in the graphic above, along with the lunar elevation (altitude) above the local horizon at the time noted. Image credit: Dave Dickinson

And whenever the Moon meets Aldebaran, it has to cross the open star cluster of the Hyades to get there, meaning there’ll be many other worthy occultations of moderately bright stars around October 2^nd as well. Gamma Tauri, 75 Tauri, Theta^1 Tauri, and SAO93975 are all occulted by the Moon on the morning of October 2^nd leading up to the Aldebaran occultation; particularly intriguing is the grazing occultation of +5 magnitude 75 Tauri across the Florida peninsula.

The path of the moon through the Hyades this weekend. Image credit: Starry Night Education software — The path of the Moon through the Hyades this weekend. Image credit: Starry Night Education software

Fun fact: the Moon can, on occasion, occult members of the M45 Pleiades star cluster as well, as last occurred in 2010, and will next occur on 2023.

Chasing the Moon through October

Follow that Moon for the following dates with astronomical destiny worldwide:

The Moon reaches Last Quarter phase on Sunday, October 4th at 21:06 UT/5:06 PM EDT.
A close pass with Venus on October 8^th, with a brilliant occultation visible in the pre-dawn hours from Australia.
A tight photogenic grouping of the Moon, Mars and Jupiter in a four degree circle on the morning on October 9^th;
A close pass of the Moon just 36 hours from New near Mercury on the morning of Sunday, October 11^th, with another occultation of the planet visible from Chile at dawn;
And finally, New Moon (sans eclipse, this time) occurring at 00:06 UT on October 13^th, marking the start of lunation 1148.

Why occultations? Consider the wow factor; light from Aldebaran left about 65 years ago, before the start of the Space Age, only to get ‘photobombed’ by the occulting Moon at the last moment. Four bright stars (Regulus, Spica, Antares and Aldebaran) lie along the Moon’s path in our current epoch. Dial the celestial scene back about two millennia ago, and the Moon was also capable of occulting the bright star Pollux in the astronomical constellation of Gemini as well.

We’ll be running video for the event clear skies willing Friday morning here from Hudson, Florida in the Tampa Bay area. And as always, let us know of your tales of astronomical tribulation and triumph!

September 17, 2015December 23, 2015 by Bob King

Amateur Astronomer Chases Down Barnard’s Star – You Can Too!

It now covers 9 years (9 animation frames) from 2007 to 2015 (July). Nothing much has changed but for its location keeps moving north. For those looking to find it visually the arrowhead asterism to the south seen in the full frame image which is about a half degree wide and a third of a degree high. so fits a medium power telescope field of view. The galaxy near the bottom of the image is CGCG 056-003, a 15.6 magnitude galaxy some 360 million light-years distant and 85,000 light-years across. Credit: Rick Johnson

Tucked away in northern Ophiuchus and well-placed for observing from spring through fall is one of the most remarkable objects in the sky — Barnard’s Star. A magnitude +9.5 red dwarf wouldn’t normally catch our attention were it not for the fact that it speeds across the sky faster than any other star known.

Incredibly, you can actually see its motion with a small telescope simply by dropping by once a year for 2-3 years and taking note of its position against the background stars. For one amateur astronomer, recording its wandering ways became a 9-year mission.

This map shows the sky facing southeast around 10:30 p.m. local time in early June. Barnard's Star is located 1° NW of the 4.8-magnitude star 66 Ophiuchi on the northern fringe of the loose open cluster Melotte 186. Source: Stellarium — This map shows the sky facing south-southwest around 9 o’clock local time in late September. Barnard’s Star is located 1° NW of the 4.8-magnitude star 66 Ophiuchi on the northern fringe of the loose open cluster Melotte 186. Use the more detailed map below to pinpoint the star’s location. Source: Stellarium

Located just 6 light years from Earth, making it the closest star beyond the Sun except for the Alpha Centauri system, Barnard’s Star dashes along at 10.3 arc seconds a year. OK, that doesn’t sound like much, but over the course of a human lifetime it moves a quarter of a degree or half a Full Moon, a distance large enough to be easily perceived with the naked eye.

Barnard's Star would be an undistinguished red dwarf in Ophiuchus were it not for its rapid motion across the sky. It measures 1.9 times Jupiter's diameter and lies only 6 light-years from Eart — Barnard’s Star is a very low mass red dwarf star 1.9 times Jupiter’s diameter only 6 light-years from Earth in the direction of the constellation Ophiuchus the Serpent Bearer. Credit: Wikipedia with additions by the author

This fleet-footed luminary was first spotted by the American astronomer E.E. Barnard in 1916. With a proper motion even greater than the triple star Alpha Centauri, we’ve since learned that the star’s speed is truly phenomenal; it zips along at 86 miles a second (139 km/sec) relative to the Sun. As the stellar dwarf moves north, it’s simultaneously headed in our direction.

Based on its high velocity and low “metal” content, Barnard’s Star is believed to be a member of the galactic bulge, a fastness of ancient stars formed early on in the Milky Way galaxy’s evolution. Metals in astronomy refer to elements heavier than hydrogen and helium, the fundamental building blocks of stars. That’s pretty much all that was around when the first generation of suns formed about 100 million years after the Big Bang.

Generally, the lower a star’s metal content, the more ancient it is as earlier generations only had the simplest elements on hand. More complex elements like lithium, carbon, oxygen and all the rest had to be cooked up the earliest stars’ interiors and then released in supernovae explosions where they later became incorporated in metal-rich stars like our Sun.

All this to say that Barnard’s Star is an interloper, a visitor from another realm of the galaxy here to take us on a journey across the years. It certainly got the attention of Lincoln, Nebraska amateur Rick Johnson, who first learned of the famous dwarf in 1957.

Close-up map showing Barnard's Star's northward march every 5 years from 2015 to 2030. Your guide star, 66 Ophiuchi, is at lower left. Stars are numbered with magnitudes and a 15? scale bar is at lower right. North is up. The line through the two 12th-magnitude stars will help you gauge Barnard's movement. Click for larger map. — Close-up map showing Barnard’s Star’s position every 5 years from 2015 to 2030. Your guide star, 66 Ophiuchi, also shown on the first map, is at lower left. Stars are numbered with magnitudes and a 15 arc minute scale bar is at lower right. North is up. The line through the two 12th-magnitude stars will help you gauge Barnard’s movement in the coming few years. Click for a larger map.

“One of the first things I imaged was Barnard’s Star on the off chance I could see its motion,” wrote Johnson, who used a cheap 400mm lens on a homemade tracking mount. “Taking it a couple months later didn’t show any obvious motion, though I thought I saw it move slightly. So I took another image the following year and the motion was obvious.”

Many years later in 2005, Johnson moved to very dark skies, upgraded his equipment and purchased a good digital camera. Barnard’s Star continued to tug at his mind.

“Again one of my first thoughts was Barnard’s Star. The idea of an animation however didn’t hit until later, so my exposure times were all over the map. This made the first frames hard to match.” Later, he standardized the exposures and then assembled the individual images into a color animation.

This diagram illustrates the locations of the star systems closest to the sun. The year when the distance to each system was determined is listed after the system's name. NASA's Wide-field Infrared Survey Explorer, or WISE, found two of the four closest systems: the binary brown dwarf WISE 1049-5319 and the brown dwarf WISE J085510.83-071442.5. NASA's Spitzer Space Telescope helped pin down the location of the latter object. The closest system to the sun is a trio of stars that consists of Alpha Centauri, a close companion to it and Proxima Centauri. Credit: NASA / Penn State — This diagram illustrates the locations of the star systems closest to the Sun along with the dates of discovery. NASA’s Wide-field Infrared Survey Explorer, or WISE, found two of the four closest systems: the binary brown dwarf WISE 1049-5319 and the brown dwarf WISE J085510.83-071442.5. The closest system to the Sun is a trio of stars that consists of Alpha Centauri, a close companion to it and Proxima Centauri. Credit: NASA / Penn State

“Now the system is programed to take it each July,” he added. I’m automated, so its all automatic now.” Johnson said the Barnard video is his most popular of many he’s made over the years including short animations of the eye-catching Comet C/2006 M4 SWAN and Near-Earth asteroid 2005 YU55.

With Johnson’s wonderful animation in your mind’s eye, I encourage you to use the maps provided to track down the star yourself the next clear night. To find it, first locate 66 Ophiuchi (mag. 4.8) just above the little triangle of 4th magnitude stars a short distance east or left of Beta Ophiuchi. Then use the detailed map to star hop ~1° to the northwest to Barnard’s Star.

Barnard's Star is one of our galaxy's ancient ones with age of somewhere between 7 and 12 billion years — Barnard’s Star, a red dwarf low in metals, is very ancient with an age between 7 and 12 billion years. Like people, older stars slow down and Barnard’s is no exception with a rotation rate of 150 days. Heading in the Sun’s direction, the star will come closest to our Solar System around the year 11,800 A.D. at a distance of just 3.75 light years. Credit: NASA

It’s easily visible in a 3-inch or larger telescope. Use as high a magnification as conditions will allow to make a sketch of the star’s current position, showing it in relation to nearby field stars. Or take a photograph. Next summer, when you return to the field, sketch it again. If you’ve taken the time to accurately note the star’s position, you might see motion in just a year. If not, be patient and return the following year.

Most stars are too far away for us to detect motion either with the naked eye or telescope in our lifetime. Barnard’s presents a rare opportunity to witness the grand cycling of stars around the galaxy otherwise denied our short lives. Chase it.

August 24, 2015December 23, 2015 by David Dickinson

Astro-Challenge: Splitting 44 Boötis

44 Bootis from the Palomar Sky Survey. Image credit: The CDS/Aladin previewer

How good are your optics? Nothing can challenge the resolution of a large light bucket telescope, like attempting to split close double stars. This week, we’d like to highlight a curious triple star system that presents a supreme challenge over the next few years and will ‘keep on giving’ for decades to come.

The location of 44 Boötis in the constellation of the Herdsman. Image credit: Stellarium click image to enlarge

The star system in question is 44 Boötis, in the umlaut-adorned constellation of Boötes the herdsman. Boötes is still riding high to the west at dusk for northern hemisphere observers in late August, providing observers a chance to split the pair during prime-time viewing hours.

Sometimes also referred to as Iota Boötis, William Herschel first measured the angular separation of the pair in 1781, and F.G.W. Struve discovered the binary nature of 44 Boötis in 1832. Back then, the pair was headed towards a maximum apparent separation of 5 arc seconds in 1870. We call this point apastron. A fast forward to 2015 sees the situation reversed, as the pair currently sits about an arc second apart, and closing. 44 Boötis will pass a periastron of just 0.23” from the primary in 2020. Can you split the pair now? How ‘bout in 2016 onward? Can you recover the split, post 2020?

The physical parameters of the system are amazing. About 42 light years distant, 44 Boötis A is 1.05 times as massive as our Sun, and shines at magnitude +4.8. The B component is in a 210 year elliptical orbit with a semi-major axis of 49 AUs (for comparison, Pluto at aphelion is 49 AUs from the Sun), and is itself a curious contact spectroscopic binary about one magnitude fainter. Though you won’t be able to split the B-C pair with a backyard telescope, they betray their presence to professional instruments due to their intertwined spectra. 44 Boötis B and C have a combined mass of 1.5 times that of our Sun, and orbit each other once every 6.4 hours at a center-to-center distance of only 750,000 miles, or only 3 times the distance from Earth to the Moon:

That’s close enough that the pair shares a merging atmosphere. It’s a mystery as to just how these types of contact binary stars form, and it would be fascinating to see 44 Boötis up close. This fast spin along our line of sight also means that 44 Boötis B-C varies in brightness by about half a magnitude over a six hour span.

An artist’s conception of the B-C pair of the 44 Boötis system, using data from the Chandra X-ray observatory. Image credit: NASA/CXC/M.Weiss

Though the visual 44 Boötis A-B pair doesn’t quite have an orbital period that the average humanoid could expect to live through, beginning amateur astronomers can watch as the pair once again heads towards a wide an easy 5” split during apastron around 2080.

Collimation, or the near-perfect alignment of optics, is key to the splitting close binaries, and also serves as a good test of a telescope and the stability of the atmosphere. A well-collimated scope will display stars with sharp round Airy disks, looking like luminescent circular ripples in a pond. We call the lower boundary to splitting double stars the Dawes Limit, and on most nights, atmospheric seeing will limit this to about an arc second.

But there’s another method that you can use to ‘split’ doubles closer than an arc second, known as interferometry. This relies on observing the star by use of a filtering mask with two slits that vary in distance across the aperture of the scope. When the mask is rotated to the appropriate position angle and the slits are adjusted properly, the ‘fringes’ of the star snap into focus. A formula utilizing the slit separation can then calculate the separation of the close binary pair. This method works with stars that are A). Closer than 1” separation, and B). Vary by not more than a magnitude in brightness difference.

44 Boötis near periastron definitely qualifies. As of this writing, our ‘cardboard interferometer’ is still very much a work in progress. We could envision a more complex version of this rig mechanized, complete with video analysis. Hey, if nothing else, it really draws stares from fellow amateur astronomers…

We promise to delve into the exciting realm of backyard cardboard interferometry once we’ve worked all of the bugs out. In the meantime, be sure to regale us with your tales of tragedy and triumph observing 44 Boötis. Revisiting double stars can pose a life-long pursuit!

– Be sure to check out another double star challenge from Universe Today, with the hunt for Sirius B.

August 12, 2015December 23, 2015 by Vanessa Janek

The Journey of Light, From the Stars to Your Eyes

The Milky Way from Earth. Image Credit: Kerry-Ann Lecky Hepburn (Weather and Sky Photography)

This week, millions of people will turn their eyes to the skies in anticipation of the 2015 Perseid meteor shower. But what happens on less eventful nights, when we find ourselves gazing upward simply to admire the deep, dark, star-spangled sky? Far away from the glow of civilization, we humans can survey thousands of tiny pinpricks of light. But how? Where does that light come from? How does it make its way to us? And how do our brains sort all that incoming energy into such a profoundly breathtaking sight?

Our story begins lightyears away, deep in the heart of a sun-like star, where gravity’s immense inward pressure keeps temperatures high and atoms disassembled. Free protons hurtle around the core, occasionally attaining the blistering energies necessary to overcome their electromagnetic repulsion, collide, and stick together in pairs of two.

Proton-proton fusion in a sun-like star. Credit: Borb

So-called diprotons are unstable and tend to disband as quickly as they arise. And if it weren’t for the subatomic antics of the weak nuclear force, this would be the end of the line: no fusion, no starlight, no us. However, on very rare occasions, a process called beta decay transforms one proton in the pair into a neutron. This new partnership forms what is known as deuterium, or heavy hydrogen, and opens the door to further nuclear fusion reactions.

Indeed, once deuterium enters the mix, particle pileups happen far more frequently. A free proton slams into deuterium, creating helium-3. Additional impacts build upon one another to forge helium-4 and heavier elements like oxygen and carbon.

Such collisions do more than just build up more massive atoms; in fact, every impact listed above releases an enormous amount of energy in the form of gamma rays. These high-energy photons streak outward, providing thermonuclear pressure that counterbalances the star’s gravity. Tens or even hundreds of thousands of years later, battered, bruised, and energetically squelched from fighting their way through a sun-sized blizzard of other particles, they emerge from the star’s surface as visible, ultraviolet, and infrared light.

Ta-da!

But this is only half the story. The light then has to stream across vast reaches of space in order to reach the Earth – a process that, provided the star of origin is in our own galaxy, can take anywhere from 4.2 years to many thousands of years! At least… from your perspective. Since photons are massless, they don’t experience any time at all! And even after eluding what, for any other massive entity in the Universe, would be downright interminable flight times, conditions still must align so that you can see even one twinkle of the light from a faraway star.

That is, it must be dark, and you must be looking up.

The incoming stream of photons then makes its way through your cornea and lens and onto your retina, a highly vascular layer of tissue that lines the back of the eye. There, each tiny packet of light impinges upon one of two types of photoreceptor cell: a rod, or a cone.

Most photons detected under the low-light conditions of stargazing will activate rod cells. These cells are so light-sensitive that, in dark enough conditions, they can be excited by a single photon! Rods cannot detect color, but are far more abundant than cones and are found all across the retina, including around the periphery.

The less numerous, more color-hungry cone cells are densely concentrated at the center of the retina, in a region called the fovea (this explains why dim stars that are visible in your side vision suddenly seem to disappear when you attempt to look at them straight-on). Despite their relative insensitivity, cone cells can be activated by very bright starlight, enabling you to perceive stars like Vega as blue and Betelgeuse as red.

But whether bright light or dim, every photon has the same endpoint once it reaches one of your eyes’ photoreceptors: a molecule of vitamin A, which is bound together with a specialized protein called an opsin. Vitamin A absorbs the light and triggers a signal cascade: ion channels open and charged particles rush across a membrane, generating an electrical impulse that travels up the optic nerve and into the brain. By the time this signal reaches your brain’s visual cortex, various neural pathways are already hard at work translating this complex biochemistry into what you once thought was a simple, intuitive, and poetic understanding of the heavens above…

The stars, they shine.

So the next time you go outside in the darker hours, take a moment to appreciate the great lengths it takes for just a single twinkle of light to travel from a series of nuclear reactions in the bustling center of a distant star, across the vastness of space and time, through your body’s electrochemical pathways, and into your conscious mind.

It gives every last one of those corny love songs new meaning, doesn’t it?