Showtime! Aurora makes first appearance – updated

A diffuse double is seen low in the northern sky at 9:30 p.m. CDT this evening September 11, 2014. The Big Dipper is off to the left. Credit: Bob King

(Scroll down for the latest update)

Just came in from a check on the northern lights and they’re out. Just a quiet start, but I can see a classic green arc low in the northern sky. Once my eyes were dark adapted, faint rays streaked the sky above the arc. No doubt they would have stood out more boldly were it not for the rising gibbous moon off to the east. Stay tuned for more updates during the night.

Faint rays streak either side of this photo taken at 9:35 p.m. Moonlight lowered the contrast but they were dimly visible with the naked eye. Credit: Bob King

Here are some links for you to check out to help you plan through the night:

The approximate extent of the auroral oval forecast for 10:30 p.m. CDT from Ovation. Credit: NOAA

* Ovation oval – shows the approximate extent of the auroral oval that looks like a cap centered on Earth’s geomagnetic pole. During storms, the oval extends south into the northern U.S. and farther.

* Kp index – indicator of magnetic activity high overhead and updated every three hours. A Kp index of “5″ means the onset of a minor storm; a Kp of “6″, a moderate storm.

* NOAA space weather forecast

* Advanced Composition Explorer (ACE) satellite plots - The magnetic field direction of the arriving wind from the sun. The topmost graph, plotting Bz, is your friend. When it drops into the negative zone that’s good! A prolonged stay at -10 or lower increases the chance of seeing the aurora.

* UPDATE 8:15 a.m. Saturday Sept. 13: Well, well, well. Yes, the effects of the solar blast did arrive and we did experience a G3 storm, only the best part happened before nightfall had settled over the U.S. and southern Canada. The peak was also fairly brief. All those arriving protons and electrons connected for a time with Earth’s magnetic field but then disconnected, leaving us with a weak storm for much of the rest of the night. More activity is expected tonight but the forecast calls for a lesser G1 geomagnetic storm.

* UPDATE 10:30 p.m. : Although the aurora has died back, I just got the NOAA forecast update which still calls for a strong storm overnight. Crossing my fingers it happens.

Graph of Bz from the ACE spacecraft shows the past 24 hours of solar wind direction changes. Far right is 11 p.m. CDT Credit: NOAA

* UPDATE 9:30 p.m. : Definite aurora seen through breaks in the clouds low in the northern sky here in Duluth, Minn. After a big surge late this afternoon and during early evening, activity’s temporarily dropped off. The ACE plot has “gone north”. Will keep tabs and report back.

UPDATE Friday 7:30 p.m September 12: Wow! Kp=7 (G3 storm). Auroras should be visible now over the far eastern seaboard of Canada including New Brunswick and the Gaspe Peninsula. If I were a betting man, folks in Maine should see at least a low, glowing arc in the northern sky. Still dusk here in Duluth.

UPDATE Friday 3 p.m.: The Kp index is now at “5″ or minor storm. If you live in the Scandinavian countries or Iceland, you’re getting a very good show right now.

* UPDATE Friday 9 a.m. September 12: Auroras did appear as forecast overnight beginning at nightfall and continuing through about 1 a.m. this morning. Then the action stopped. The Kp index reached “5″ during that time leading to a G1 or minor geomagnetic storm. It wasn’t a particularly bright aurora, remained low in the northern sky and had to compete with moonlight, so many of you may not have seen it.

The stronger G3 geomagnetic storm from the second and more Earth-directed solar blast is still forecast for tonight. This should bring a much better display and should begin right at nightfall. Peak is expected between 10 p.m. and 1 a.m. Central Daylight Time.

My forecast is good, so I’ll be updating during the night. Good luck and clear skies!

Twin solar storms may stoke auroras tonight Sept. 11-12

A CME or coronal mass ejection from the sun on September 9 is expected to pass Earth later today and possibly spark auroras tonight. Credit: NASA/ESA

(Click HERE for updates))

Two bursts of solar particles propelled by flares on September 9th and 10th are expected to arrive starting tonight and possibly touch off a moderate G2 geomagnetic storm. Translation: auroras may bloom in the next few nights!

A moderate M4 flare occurred early on September 9th followed by a more powerful X1.6 yesterday afternoon. Provided the magnetic field the particles come packaged in points in the right direction – south – these bursts have good potential for creating auroras tonight and again over the weekend.

A second, Earth-directed CME leaves the sun in the wake of the X1.6 flare on September 10th. Credit: NASA/ESA

The timing is good because the moon is past full and won’t be too bright. During a moderate storm, auroras are often seen across the northern tier of states and Canada. According to the latest NOAA space weather forecast, activity should kick up but remain shy of storm level from 9 p.m.-midnight Central Daylight Time tonight September 11th.

The brunt of the storm is expected from 1-4 a.m. tomorrow morning the 12th with effects lasting until 7 a.m.

This may only be the start of an even stronger storm anticipated Friday night and continuing into the weekend beginning from yesterday’s flare. That one blasted material directly toward Earth. Always a good omen for auroras.

Earth’s magnetic bubble, generated by motions within its iron-nickel core and shaped by the solar wind, is called the magnetosphere. It extends some 40,000 miles forward of the planet and more than 3.9 million miles in the tailward direction. Credit: NASA

As always with northern lights, keep in mind they’re fickle. Most of the time, Earth’s magnetic defense – a humongous, teardrop-shaped bubble of magnetism called the magnetosphere –  acts as a bulwark against strong solar winds, letting them slide by harmlessly. We’ll see what happens on this round, but I’m optimistic.

The Earth weather forecast for my locale is mostly clear tonight, so I’ll be monitoring the sky. Stop back later for an update.

* UPDATE 9 p.m. CDT: Quiet so far. Auroras still holed up in Hudson Bay and Quebec. The magnetic field direction of the arriving wind from the sun shows a lot of variation (see ACE satellite plot, topmost graph showing Bz) rising and falling from positive to negative. Negative is good! A prolonged stay at -10 or lower increase the chance of seeing the aurora.

Struggled to find Uranus? Let the moon take you there tonight

Once you’re done chuckling, we’ll move on. Ahem!

The waning gibbous moon will near the planet Uranus tonight September 10, 2014. From northeastern U.S. it will be covered by the moon. These views show moon and planet from Syracuse (eastern U.S.) and the Midwest at the times shown. Source: Stellarium

If you’ve ever had trouble finding the remote planet Uranus, Luna can help you tonight. The waning gibbous moon will occult or cover up the planet for observers in northeastern North America, Greenland, Iceland and northern Scandinavia around 8 p.m. Eastern Daylight Time this evening.

If you have a small telescope, you’ll be able to watch the bright eastern (left) edge of the moon slowly approach and then hide the planet. Unlike a point-like star, which winks out in a split second when covered by the moon’s edge, Uranus shows a small disk and will fade more gradually over several seconds.

Observers in the wedge-shaped zone that spans the Northeastern U.S., Canada and other northern countries will see the moon cover Uranus. Those living in the U.S. and Canada will spy the planet very close to the moon’s west rim. Credit: USNO

But let’s say like me you live outside the occultation zone. What will we see? From the Midwest, Uranus will be just less than 1° to the west (right) of the moon as it comes up in the eastern sky in late twilight. Over the hours, it will appear to move gradually drift to the west away from the moon as the moon moves eastward in its orbit.

The farther west you live, the farther Uranus will be from the moon’s western edge. But not too far. Even from the California Coast, Uranus strays only about 2° (four moon diameters) to the right of the moon.

The planet may even be easier to see in binoculars from points west because it will be further from the lunar glare. No matter what, it’ll be easy to find the planet, which shines around 6th magnitude.

The view from the U.S. West Coast around 10 o’clock local time tonight. Source: Stellarium

Remember, you’ll need 50 mm binoculars, or better, a small telescope, to view the planet near the moon. Telescope users are encouraged to crank up the magnification and see Uranus’ diminutive disk next the moon, which appears gigantic in comparison. In reality, the 7th planet is nearly 15 times as large.

Uranus only a degree east of the totally eclipsed moon seen from the Midwest on October 8, 2014. Stellarium

Get ready for an even better shot at seeing Uranus. On the morning of October 8th, the full moon will be in total eclipse and the planet will lie very close due east. With no glary moonlight and everyone focused on the eclipse, more people will probably see Uranus at one time than perhaps any time in history.

Harvest Moon glow show / Rosetta captures pieces of a comet

The Full Harvest Moon rises from Lake Superior in Duluth, Minn. as the HR Maria heads down the lake last night September 8, 2014. Credit: Bob King

We luckily avoided the clouds last night to see a big pink moon rise from Lake Superior. The moon languished near the horizon for a long time as if reluctant to meet the deck of clouds waiting for it higher up.

The full moon prepares to enter the cloud deck shortly after moonrise last night. Credit: Bob King

Watch for it to rise tonight about a half hour later. Will you be able to tell it’s no longer a perfect circle? A shadow has crept up along its western edge transforming it from a full to a waning gibbous moon.

Because the moon orbits Earth, we see it from a slightly different angle in relation to the sun each night, causing different parts of the globe to be in sunlight and shadow.

COSIMA catches bits of the comet. Left: an image of the target plate (measuring about 1/2-inch on the side) on which the grains were collected; right: a section of the plate showing it on August 17 when no dust grains were visible and August 24 (bottom) when some large dust grains were detected. The plate is illuminated from the right by LEDs and the length of the shadows is proportional to the height of the dust grains. Credit:  ESA/Rosetta/MPS for COSIMA Team et. all

While you and I may prefer our dust swept away, planetary astronomers feel otherwise. Scientists at the European Planetary Science Conference (EPSC) in Lisbon, Portugal, recently got a look at photos of the first dust grains collected by Rosetta’s COSIMA instrument. The specks were gathered between August 11th and 24th  from a distance of around 62 miles (100 km) from the nucleus of comet 67P/Churyumov-Gerasimenko

Many tiny grains showed up on the plate; the two largest, each about the width of a human hair, stand out in the photo above. Some of the samples will be selected for further analysis on board the probe. Here’s how it works.

Jagged cliffs and prominent boulders are visible in this image taken by the OSIRIS camera on September 5, 2014 from a distance of 39 miles (62 km) from comet. The left part of the image shows a side view of the comet’s ‘body’, while the right is the back of its ‘head’. One pixel corresponds to 3.6 feet (1.1-m). Click for a huge picture! Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

The target plate will be moved to place each selected grain under an ion gun, a device that blasts the particle with a beam of ions. Ions are atoms which have gained or lost an electron and become either positively or negatively charged. The ion beam will ablate or vaporize the grain layer by layer. The material is then analyzed in a secondary ion mass spectrometer to determine its composition.

Several different regions are indicated in this preliminary map, which is oriented with the comet’s ‘body’ in the foreground and the ‘head’ in the background. The brown smooth terrain contrasts with the rugged blue region.
Credits: ESA/Rosetta/MPS for OSIRISTeam/MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Astronomers are quite excited about getting these early dust grains studied as they’re the first to be retrieved from the solar system’s “snow line”, the distance from the sun at which stable ice grains can form.

A new color-coded terrain map of 67P/C-G has also been created based depicting regional variations in the comet’s landscape. Some terrains are smooth, others dominated by cliffs and still others by craters and depressions. The maps will play a key role this weekend (Sept. 13-14) as Rosetta’s Lander Team and the Rosetta orbiter scientists determine primary and backup landing sites for the Philae lander.

Asteroid 2014 RC makes astronomers’ heads spin / Crater appears in Nicaragua

Multiple images of asteroid 2014 RC made with the Lowell Observatory 42-inch Hall telescope showing its motion on September 7, 2014.

Not only did it make a very close approach to Earth yesterday, but astronomers got a better handle on 2014 RC’s size and how fast it spins during the flyby.

The space rock was originally thought to be 60-feet (20-m) across but we now know it’s closer to 40-feet (12-m) or about the size of a school bus and spinning very rapidly. Try one rotation every 15.8 seconds!

That makes 2014 RC the fastest rotating asteroid (by 50%) observed to date. Astronomers using NASA’s Infrared Telescope Facility (IRTF) on September 6 observed the space rock in infrared light to determine its composition. It reflects about much light (25%) as green grass and belongs to the “Sq class” of stony asteroids. Rocky asteroids are the most common kind. Based on its reflectivity, 2014 RC is much brighter than a typical comet and several other classes of asteroids.

The suspect crater near the Managua airport. Credit: AP

In a story begging to be related but isn’t, a purported meteor crater showed up near Managua, Nicaragua’s international airport this weekend. Whatever caused  it, the blast occurred during the early morning of September 6th, 13 hours before 2014 RC’s close flyby, which passed beneath Earth’s orbit anyway. A loud bang was heard and the ground shook, but there are no eyewitness reports or video of a meteor or meteorite fall. The crater is about 40 feet (12-m) across.

The surest way to confirm if a meteorite fell would be to look for fragments in and around the crater. No news yet on that. I’ll update when more information becomes available.

What Makes the Harvest Moon Special

“The Harvest Moon”, a circa 1833 oil painting by Samuel Palmer. Closely spaced moonrises meant extra light to bring in the crops in the days before electric lighting.

Today, September 8, the Harvest Moon will rise the color of a fall leaf and spill its light across deserts, forest, oceans and cities. The next night it rises only a half hour later. And the next, too. The short gap of time between successive moonrises gave farmers in the days before electricity extra light to harvest their crops, hence the name.

The Harvest Moon is the full moon that falls closest to the autumnal equinox, the beginning of northern autumn. As the moon orbits the Earth, it moves eastward about one fist held at arm’s length each night and rises about 50 minutes later. You can see its orbital travels for yourself by comparing the moon’s nightly position to a bright star or constellation.

Around the time of Harvest Moon, the full moon’s path is tilted at a shallow angle to the eastern horizon making with successive moonrises only about a half hour apart instead of the usual 50 minutes. Source: Stellarium

50 minutes is the usual gap between moonrises. But it can vary from 25 minutes to more than an hour depending upon the angle the moon’s path makes to the eastern horizon at rise time. In September that path runs above the horizon at a shallow angle. As the moon scoots eastward, it’s also moving northward this time of year.

This northward motion isn’t as obvious unless you watch the moon over the coming week. Then you’ll see it climb to the very top of its monthly path when it’s high overhead at dawn. The northward motion partly cancels out the eastward motion, keeping the September full moon’s path roughly parallel to the horizon with successive rise times only ~30 minutes apart.

The angle of the moon’s path to the horizon makes all the difference in moonrise times. At full phase in spring, the path tilts steeply southward, delaying successive moonrises by over an hour. In September, the moon’s path is nearly parallel to the horizon with successive moonrises just 20+ minutes apart. Times are shown for the Duluth, Minn. region. Illustration: Bob King

Exactly the opposite happened 6 months earlier this spring, when the moon’s path met the horizon at a steep angle. While it traveled the identical distance each night then as now, its tilted path dunked it much farther below the horizon night to night. The spring full moon moves east and south towards its lowest point in the sky. Seen from the northern hemisphere, that southward travel adds in extra time for the moon to reach the horizon and rise each successive night.

If all this is a bit mind-bending, don’t sweat it. Click HERE to find when the moon rises for your town and find a spot with a great view of the eastern horizon. You’ll notice the moon is orange or red at moonrise because the many miles of thicker atmosphere you look through when you gaze along the horizon scatters the shorter bluer colors from moonlight, tinting it red just as it does the sun.

A series of photos of the full moon setting over Earth’s limb taken by from space by NASA astronaut Don Pettit on April 16, 2003. Refraction causes a celestial object’s light to be bent upwards, so it appears higher than it actually is. The bottom half of the moon, closer to the horizon, is refracted strongest and “pushed” upward into the top half, making it look squished. Credit: NASA

The moon will also appear squished due to atmospheric refraction. Air is densest right at the horizon and refracts or bends light more strongly than the air immediately above it. Air “lifts” the bottom of the moon – which is closer to the horizon – more than the top, squishing the two halves together into an egg or oval shape.

How we perceive the moon’s size may have much to do with what’s around it. In this illustration, most of us seen the bottom moon as smaller, but they’re both exactly the same size. Crazy, isn’t it? Credit: NASA

You may also be entranced Monday night by the Moon Illusion, where the full moon appears unnaturally large when near the horizon compared to when viewed higher up. No one has come up with a complete explanation for this intriguing aspect of our perception, but the link above offers some interesting hypotheses.

Can you see craters with your naked eye? Yes! Try tonight through Wednesday night. Plato is the trickiest. Credit: Bob King

Finally, full moon is an ideal time to see several lunar craters with the naked eye. They’re not the biggest, but all, except Plato, are surrounded by bright rays of secondary impact craters that expand their size and provide good contrast against the darker lunar “seas”. Try with your eyes alone first, and if you have difficulty, use binoculars to get familiar with the landscape and then try again with your unaided eyes.

In contrast to the other craters, Plato is dark against a bright landscape. This one’s a real challenge – I’ve tried for years but still haven’t convinced myself of seeing it. The others are easier than you’d think. Good luck and clear skies!

Glows before dawn / Tomorrow’s close shave with asteroid 2014 RC

A wreath of green aurora capped by a diffuse glow burns just above the northern horizon this morning before dawn. Can you spot the Big Dipper? Credit: Bob King

The moon’s bright and near full, but if you wait until after it sets, there’s still a sliver of dark sky before dawn. This morning a quiet arc of aurora glowed in the north while I did some comet hunting after moonset. Auroral activity has kicked up of late from the combined effects of solar outbursts called CMEs (coronal mass ejections) and coronal holes.

The softly luminous ‘finger’ of zodiacal light (left side) tilts upward this morning in early dawn to meet the Milky Way in northern Orion. You can spot the three Belt Stars at right. Jupiter is the bright “star” at lower left. The zodiacal light is centered on the ecliptic, the path followed by the sun, moon and planets across the zodiac constellations. Credit: Bob King

The aurora wasn’t the only thing setting the sky aglow. As fall approaches, so too the angle at which the ecliptic meets the eastern horizon at dawn. When that angle is steep, as it is now through early November, we get a good look at the zodiacal light. It looks like a fat finger or cone of diffuse light tilting up from the eastern horizon.

Like breadcrumbs dropped to mark a trail, comets shed dust particles each time they cycle about the sun. Asteroid collisions also contribute. The dust accumulates in the plane of the planets and glows by reflected sunlight. To see the zodiacal light while the crickets murmur at dawn is to witness the comings and goings of countless comets across generations of humanity.

With the Full Harvest Moon knocking on the door, we’re done with dark sky after tomorrow morning. Mark your calendar for September 22. Not only is that the first day of fall, but the zodiacal light returns to a dark sky and remains visible for two full weeks.

This graphic depicts the passage of asteroid 2014 RC past Earth on September 7, 2014. At time of closest approach, the space rock will be about one-tenth the distance from Earth to the moon. Based on brightness, astronomers estimate the asteroids’s size at 60 feet. Times indicated on the graphic are EDT or Eastern Daylight Time. Credit: NASA/JPL-Caltech

Something invisible to most of us is one its way to Earth’s skies tomorrow afternoon. That’s when the recently discovered asteroid 2014 RC rips across half the sky in a span of hours while making a very close approach to our planet. The approximately 60-foot-wide, house-sized space rock will skim the outer edge of the geosynchronous satellite belt only 25,000 miles (40,000 km) from the hairs on your head around 2:15 p.m. Eastern Daylight Time. It was discovered on September 1.

Map showing just how fast this asteroid will zip across the sky around the time of closest approach tomorrow Sunday September 7, 2014. 2014 RC moves from Aquarius (lower right) all the way to Puppis in just 12 hours. Created by Gianluca Masi using the SkyX Pro software. Click to enlarge.

Nothing to worry about here as the asteroid will safely pass by Earth. 2014 RC will return in the future, but no threatening passes have been identified. Though most of the really bad-boy 1-km or larger Earth-approaching asteroids have been discovered, many smaller ones remain large. An estimated 1 million NEOs (Near-Earth objects) in the 100-foot (30-meter) are still out there. Surveys like those carried out with the PanSTARRS-1 telescope in Maui, Hawaii and the Catalina Sky Survey are constantly on the lookout for them. At least once a month, a new Earth-approacher is found.

2014 RC will pass along the edge of the geosynchronous satellite belt, home to many weather and communications satellites. The chance of a hit is close to infinitesimal. Click for more information and detailed finder charts for the asteroid. Credit: SatFlare

Because 2014 RC will brush by Earth during daylight hours for the Western hemisphere, we’ll miss it. Observers in other parts of the southern hemisphere where it’s dark might spot it with a 6-inch or larger telescope as an 11.5 magnitude star moving as fast as a slow satellite through the field of view.

While most of us won’t see the asteroid in our own telescopes, plans are underway for radar imaging with the Goldstone dish in California. Italian astronomer Gianluca Masi will also have telescope trained on the space rock and feature it live on his Virtual Telescope Project site beginning today at 6 p.m. EDT. Take a look!

This video’s got it all – sprites, gravity waves and airglow!


Randy Halverson captured rare night lights in this timelapse made on August 20, 2014

On August 20 a thunderstorm rumbled over central South Dakota and Randy Halverson was ready. He set up cameras to capture sprites, bizarre pink electrical discharges that race upward from storm clouds, and picturesque gravity waves. Sprites last only milliseconds. You’ll appreciate their brevity when you watch the video – each outburst lasts just one quick frame.

Sprites are members of a family of energetic, high-altitude phenomena occurring during thunderstorms. Credit: Abestrobi / Wikipedia

Halverson looked over his many still images and found seven with sprites. The jellyfish-like forms occur some 50 miles above active thunderstorms – about the same level as noctilucent clouds – and extend upward from 12 to 19 miles. The name refers to the phenomenon’s spooky, elusive nature like the folkloric fairies of old.

They’re associated with cloud-to-cloud lightning and possibly irregularities in the upper atmosphere created by meteors. Besides a faint red light, sprites also release bursts of radio waves and high energy gamma rays.

A sprite makes its appearance in a single frame at the 27-second mark in the video. Credit: Randy Halverson

But there’s a lot more in Randy’s video. Check out the pale green ripples of airglow in the top half of the frame. Most green airglow comes from oxygen atoms that reside about 60 miles up, the same altitude as the aurora. Ultraviolet light from sunlight during the daytime hours energizes the atoms which then release their energy overnight as they “relax” back to their original state. Airglow also occurs when sunlight breaks apart nitrogen molecules; when the nitrogens combine with oxygen, light is released.

Gravity waves create ripples in the dim greenish airglow in the dark sky above the thunderclouds. To see more of Halverson’s images and videos, visit dakotalapse.com Credit: Randy Halverson

The ripples are created by gravity waves, thought to be caused by powerful updrafts from thunderstorms. Gravity waves are different from gravitational waves which are released by extremely massive objects like neutron stars in orbit about one another.

There’s even a bit of aurora toward the end of the video. Halverson uses a Canon DSLR and exposures of 10-30 seconds to capture his night sky images. If you’re into night photography, I encourage you to read how he keeps dew off his camera lens – a real problem for many of us.

Milky Way settles into its new home, the Laniakea Supercluster

The Milky Way galaxy is an outlier in an enormous, newly designated supercluster of galaxies dubbed Laniakea. The vast assemblage spans some 500 million light years across and contains the mass of one quadrillion suns. The Local Supercluster, centered in Virgo, is only a small part of the much larger Laniakea. The looping lines represent galaxy flows toward large concentrations of galaxies within the supercluster. Credit: SDvision interactive visualization software by DP at CEA/Saclay, France (additions by B. King)

The name fits so well – Laniakea. It means ‘immense heaven’ in Hawaiian, and now it’s home. In the biggest sense of ‘big picture’ you can imagine.

Astronomers using the National Science Foundation’s Green Bank Telescope (GBT), among other telescopes, have determined that our own Milky Way galaxy is part of a newly identified titanic supercluster of galaxies they nicknamed  Laniakea (Lah-nee-ah-KAY-uh).

The Hercules Cluster in the constellation Hercules is a good example of a rich galaxy cluster. It contains about 200 galaxies and is located 500 million light years away. The cluster is a member of the Hercules Supercluster. Credit: Jim Misti

The Milky Way’s always been in one gang or another. It’s a member in good standing of the Local Group, a gravitationally bound small cluster of some 54 neighborhood galaxies. It in turn, along with dozens of other clusters, are drawn by gravity to the granddaddy Virgo Cluster, which contains some 2000 galaxies 53 million light years away.

All these clusters are interconnected, linked into a web through mutual gravitational attraction. Taken together, they’re known as the Local Supercluster, and superclusters are the single biggest structures in the universe. Our Local Supercluster contains at least 100 different galaxy groups and stretches across 110 million light years.

Another view of the Laniakea Supercluster. The outer surface (blue) shows the region dominated by the supercluster’s gravity. The streamlines shown in black trace the paths along which galaxies flow as they are pulled closer inside the supercluster. The historical Local Supercluster in shown in green and the Great Attractor region in orange. Credit: SDvision interactive visualization software by DP at CEA/Saclay, France

Up till now we thought it was the biggest structure of which the Milky Way was a part. Not anymore.

R. Brent Tully from the University of Hawaii’s Institute for Astrophysics and his team studied the motions of galaxies in the Local Supercluster and discovered that we live in a MUCH bigger house than we ever thought.

By using the GBT and other radio telescopes to map the velocities of galaxies throughout our local universe, the team was able to define the region of space where each supercluster dominates. They found that superclusters are involved in a tug of war for galaxies – many are pulled into the supercluster while those near the edge are up for grabs.

By studying these streaming motions, Tully and team discovered that our historical supercluster home was itself part of a much larger supercluster I’m almost tempted to call the Local Superdupercluster (but I won’t). Doubtless the more poetic Laniakea was picked because of Tully’s Hawaii connections.


Meet Laniakea, the Milky Way’s home supercluster

“We have finally established the contours that define the supercluster of galaxies we can call home,” said Tully. He compared it to realizing for the first time that your hometown belongs to a much larger country bordering other nations (superclusters).

Not only do large galaxy clusters dominate the new landscape, but an enigmatic mass of distant galaxies called the Great Attractor is also a bona fide member.

It’s cool being part of something even bigger than we’d ever imagined. I just had a gut feeling the Milky Way needed more space.

To twinkle or not to twinkle, that is the question

Venus passes Regulus on the morning of September 5. Look low in the eastern sky 30-45 minutes before sunrise to see the pair. Bring binoculars in case twilight overwhelms Regulus. Stellarium

Early Friday morning September 5, skywatchers will see Venus and Leo’s brightest star Regulus in a close conjunction. The two will be separated by just 1° and look very nice in binoculars. Find a place with a view down to the eastern horizon and start looking about 40 minutes before sunrise. Jupiter, higher up in a darker sky, can help guide you to Venus.

This will be Venus’ last encounter with a bright star at dawn before it’s lost in the glare of the sun. It’s often said that one way you can tell a planet from a star is that a planet’s light appears steady, while stars twinkle. Not always. Stars only appear as points of light even through the largest telescopes and are easily shoved this way and that by air turbulence. These tiny shifts in position are what cause twinkling.

When we look at stars low in the sky we look across hundreds of miles of air in the lower, densest part of the atmosphere. Air currents across that great distance push a star’s light around causing it to twinkle. It can have the same effect on bright, naked eye planets when they’re far away and show a smaller than usual disk. Credit: Bob King

Planets have measurable disks and are less affected by the flutter of air, so we rarely catch them shimmering. But when the planet is far from Earth and very low in the sky, the rules change. Both Venus and Mars range in size from tiny blips to substantial disks (or in the case of Venus, a substantial half-moon or crescent). When viewed at low altitude, I’ve seen both twinkle lively.

Illustration showing how a planet, with a measurable disk, defeats air turbulence compared to a star which appears as a tiny point of light through a telescope. Credit: Bob King with Jupiter pic by Damian Peach

I witnessed it last Thursday morning with Venus. Jupiter, larger and higher in the sky, was a steady beacon. Venus, now nearly on the opposite side of the sun from Earth and about as small as it ever gets, trembled like a flame in the wind. What will you see Friday morning?

Venus remains visible for another two weeks before it’s lost in the solar glare. We won’t see the planet at all for more than a month until it returns to the evening sky around Thanksgiving in November. Watch for it to shake and shimmy its way up the western sky until fattening up around Christmas.