Asteroid smash-up tells of rocky road to planet formation

This artist’s concept shows the immediate aftermath of a large asteroid impact around NGC 2547-ID8, a 35-million-year-old sun-like star thought to be forming rocky planets. Credit: NASA/JPL-Caltech

NASA’s Spitzer Space Telescope has spotted an eruption of dust around a young star, possibly the result of a smashup between large asteroids. This type of collision can eventually lead to the formation of planets.

Small clumps of material within a disk stick together to form larger clumps. Eventually these clumps grow to become planets. Credit: NASA

Planets form by dribs and drabs within dusty disks around newly-forming stars. Dust sticks to dust to form small clumps. The clumps grow bigger as they which sweep up more material within the cloud until they’re boulder-sized. Gravity now works its wonders, drawing smaller bits of debris to larger until asteroids (also called planetesimals), the seeds of the planets form.

Many asteroids break apart when they collide, but others continue to grow by accumulation until they’ve collected enough stuff to collapse through self-gravity to form a sphere. After 100 million years of bone-crushing impacts, a planet is born!

Astronomers had been regularly observing the star NGC 2547-ID8 located 1,200 light years away in the constellation Vela the Sails with the Spitzer telescope, which can see into the infrared, a color of light just beyond the red end of the rainbow spectrum. We sense infrared as heat, but Spitzer sees it as glowing radiation.

Dust warmed by starlight radiates brightly in the infrared. Previous observations of NGC 2547-ID8 had already shown variations in the amount of dust around the star, hinting at possible asteroid collisions. But astronomers couldn’t believe their eyes when they compared photos made in August 2012 and five months later in January 2013.

The bright summer star Vega – 25 light years from Earth – photographed by the Spitzer Space Telescope shows a huge disk of glowing dust extending at least 76 billion miles from the star. Like NGC 2547-ID8, Vega is a young star that appears to be forming planets much like the sun 4.6 billion years ago. Credit: NASA

“We not only witnessed what appears to be the wreckage of a huge smashup, but have been able to track how it is changing – the signal is fading as the cloud destroys itself by grinding its grains down so they escape from the star,” said Kate Su of the University of Arizona and co-author on the study.

Now a large, thick cloud of dust orbits the star which the team of astronomers is keeping their eye on in hopes of spotting more collisions.

Astronomers were surprised to see these data from NASA’s Spitzer Space Telescope in January 2013, showing a huge eruption of dust around a star called NGC 2547-ID8. In this plot, infrared brightness is shown on the vertical axis and time along the bottom. Credit: NASA/JPL-Caltech/University of Arizona

“We are watching rocky planet formation happen right in front of us,” said George Rieke, a University of Arizona co-author of the new study. Although no one was around to watch out solar system’s planets form, Spitzer offers a glimpse into those lost times through its study of young, dust-cloaked stars in the present.

 

Get cornered by the Summer Triangle tonight

The Summer Triangle comes up in the east-northeast sky around 11:30 p.m. in mid-May. It takes its name from three bright stars – Vega in Lyra the Harp, Deneb in the Cygnus the Swan (a.k.a. Northern Cross) and Altair in Aquila the Eagle. The figure is a signature asterism of the summer sky. View shows the sky facing east around 11:30 p.m. Stellarium

Winter never seems long in coming but summer does. It’s on our doorstep right now. We notice it in later sunsets and lingering twilight. True darkness doesn’t begin for observers in the mid-section of the U.S. until an hour 45 minutes after sundown. For the northern U.S. and southern Canada it stretches from 2 hours 15 minutes to nearly the entire night.

When it comes to walking I love the longer twilights. Instead of black night at the dinner hour, we can watch the stars slowly come out. There’s an ease in that. Mid-May also brings new constellations to the eastern sky.

The Summer Triangle, which has been in hibernation since December, returns to view before midnight. Brightest and the first to rise of the three stars that define its corners is Vega. Look for its hard white sparkle around 10 o’clock in the northeastern sky. Deneb in the Northern Cross and Altair in Aquila the Eagle follow by 11:30 p.m.

The waning gibbous moon will rise along with the Summer Triangle tonight (May 16) but will be out of the way around 11:30-midnight starting tomorrow. The hazy band is the Milky Way, a sidelong view along our galaxy’s midsection. Stellarium

The moon still troubles the sky with glare tonight but will rise late enough beginning tomorrow night to allow many skywatchers their first look this season at the ravishing summertime Milky Way. This silent river of starlight flows across the Northern Cross and over the Eagle’s back. As it rises, you might at first mistakenly think clouds are moving in from the east especially if you live where the sky is very dark.

Naw, that’s just a few tens of billions of stars in our own Milky Way galaxy so distant and so closely spaced (because of their distance) their light blends into phosphorescent haze.

Can you find the three stars that outline the Summer Triangle in this time exposure photo of the Milky Way? Credit: Bob King

The rich star clouds, nebulae and star clusters that comprise our galaxy mirror the approaching season’s nonstop thrum of life. Partake.

Once upon a midnight summer’s dream

The Summer Triangle, outlined by Vega, Deneb and Altair is up in the eastern sky around midnight in early May and by 10 p.m. at month’s end. The band of the Milky Way passes directly between the trio. Stellarium

Midnight. Too late for a look at the sky? Not if you hungry for a token of summer. It’s out there alright – the Summer Triangle. It’s unclear who named this giant triangle formed by three of summer’s brightest stars – Vega, Deneb and Altair – but its usage has been around since at least the 1920s. The first person we know of to connect the three stars in a triangle, even though he didn’t give the figure a name, was the German astronomer Johann Bode back in 1816. Bode created some of the most beautiful star atlases ever made.

Star chart created by Johann Bode in 1805 showing Cygnus the Swan (Schwan) with Deneb and Lyra the Harp (Leyer) with Vega.

Sometime in the late 1920s Austrian astronomer and prolific astronomy popularizer Oswald Thomas described these stars as the “Grosses Dreieck” (Great Triangle) and later in 1934 as the “Sommerliches Dreieck” (Summerly Triangle). Another great name in astronomy, England’s Patrick Moore, who passed away last December, described the trio as the Summer Triangle starting in the 1950s in his many books and lectures.

A short time exposure shows the three bright stars of the Summer Triangle (Vega at top) and bright Milky Way. Photo: Bob King

Tonight you’ll see the famed asterism crest the eastern horizon around midnight. Vega, the westernmost of the three and earliest to rise, sparkles in the northeast by 10 p.m. Deneb’s up by 11 and joined by Altair shortly before midnight. Although tipped on its side and slung low in the east in early May, by month’s end, the triangle stands higher and becomes visible at nightfall.

From July through September the Summer Triangle rules the sky, standing upright in the south balanced on its southermost apex Altair. That’s how it got its name of course, since it’s most obvious in the mid to late summer months. Come October and November, the figure scootches over to the west and by December it’s gone – just in time for winter.

Each of the Summer Triangle stars has its own individual character. Altair (17 light years distant) is about twice the diameter of the sun, Vega (25 light years) about three times and Deneb (~2600 light years) is a supergiant star 200 times as big. Altair and Vega rotate rapidly causing them to bulge out at their equators. Illustration: Bob King

The brightest of the three pivotal stars is Vega in the constellation Lyra the Harp. All Lyra’s stars are dim, but Vega more than compensates with a radiance as pure and white as burning magnesium.

To find Deneb, the brightest star in Cygnus the Swan or Northern Cross, reach your balled fist to the sky and look ‘two fists’ to the lower left of Vega. Altair in Aquila the Eagle is way down to the lower right. Three-plus fists will get you there. Vega, Deneb and Altair are all easy to see even from a middle-sized city and suburban areas.

You can use this map to help you find the constellations belonging to each of the Summer Triangle’s stars. Stellarium

An additional treat awaits the eyes of rural observers or those who make a drive to the country. The Summer Triangle frames a bright section of the Milky Way, and with the moon out of the way for the next couple weeks, it’s worth the time to witness this most impressive sight.

I don’t know about you, but winter was too long in the tooth around here, so every time I see those three bright stars and swirly Milky Way I get jazzed for summer nights ahead.

Vega’s asteroid belts hint at hidden planets

This conceptual illustration depicts an asteroid belt around the bright star Vega. Evidence for the ring of debris comes from NASA and ESA space telescopes. Credit: NASA/JPL-Caltech

Look low in the northwestern sky at dusk in mid-January and you’ll spy a bright, sparkling star. That’s Vega, Lyra the Harp’s most luminous star and the fifth brightest in the sky … after the sun, of course. We’ve known since 1983 that Vega is surrounded by a dusty disk of debris, the first star discovered to have one. Warmed by the star, dust radiates a feeble heat that was detected by the NASA’s orbiting Infrared Astronomical Satellite (IRAS).

Look for Vega above the trees during the early evening. This map shows the sky facing northwest around 6:30 p.m. local time. Maps created with Stellarium

Earlier this week NASA announced evidence for two separate asteroid belts and potential planets around the star. Sound familiar? Our solar system has both an inner, warm asteroid belt located between Mars and Jupiter and a cold, outer belt of “ice”-teroids beyond Neptune. Using NASA’s Spitzer Space Telescope and the European Space Agency Herschel Space Telescope, both of which are optimized to detect infrared (heat) light, astronomers detected two bands of dust created and replenished by collisions of comets and rocky asteroids around Vega.

The amount of dust indicates that Vega’s belts have far more material than our own asteroid belts, no surprise given that our solar system is far older – about 5 billion years – and has had a much longer time to “clean house” through planet-asteroid interactions. Vega, a star with twice the sun’s mass and 36 times more luminous, is thought to be a youthful 600 million years old.

The Vega system, with its own set of asteroid-comet belts, is compared to our solar system in this illustration. The relative size of our system compared to Vega is illustrated by the small drawing in the middle. On the right, our solar system is scaled up four times. Both inner and outer belts have similar proportions. Credit: NASA/JPL-Caltech

Check out the layout of Vega’s belts. Back at home, the main asteroid belt is kept in place by the interplay of gravity between Jupiter and the inner planets, while the outer Kuiper Belt was fashioned by the giant outer planets. Although we can’t see them yet, there are almost certainly planets at play in maintaining Vega’s belts, too. Ain’t gravity fun?

Arcturus, auger of spring, comes up around midnight below the handle of the Big Dipper.

Last night while out checking on a supernova in a galaxy in Leo, a bright spark of ruby light caught my eye low in the northeastern sky. I almost didn’t recognize it, but a second later it hit me -  Arcturus. The time was midnight and already the sky offered this taste of spring.

Arcturus is a brilliant ruddy star that stands high in the south come May. Because of its prominence in late spring and early summer, it’s imbued with memories of warm nights and green grass. In January, Arcturus still slumbers below the eastern horizon until shortly before midnight. Seeing it poke between the trees warmed me up … just a little.

The sun at 10:30 a.m. CST Jan. 10, 2013 photographed by the Solar Dynamics Observatory. The pair of sunspots at left, region 1654, is big enough to see with the naked eye using a safe solar filter. This group harbors the potential for significant solar flares. Credit: NASA

Nicer yet was the sun, which burned away in a blue sky this morning. Lots of sunspot groups, including two large new spots that have recently rounded the sun’s eastern limb, have increased the chance for solar flares in the coming days.

I don’t know about you but I miss the aurora. The last one good show in northern Minnesota happened in November. Let’s hope we won’t have to wait much longer.

Travel through time with the Summer Triangle

Aurora over Finland last night photographed by Ole Solomonsen

Always comes down to timing, doesn’t it?  Most of us never saw the auroras that arrived yesterday in the wake of last week’s solar eruption. They happened alright, but the show didn’t start until after sunrise and continued through daylight hours for North America. Siberians and Scandinavians were luckier. They had dark skies at the right time and got a real treat.

“After hours of waiting for the big aurora to show from the CME, and waiting for clouds to go away, I was about to give up. Then suddenly a spark on the horizon, which just grew, and grew and grew!”, wrote Ole Salomonsen who watched a beautiful aurora borealis unfold overhead from deep within a forest in northern Finland.

By the time darkness arrived in the U.S. Midwest, the northern lights had run out of steam. I looked – maybe you did too – but it was a no-show through midnight. Don’t give up! There’s still a chance tonight plus more goodies from the sun are on the way. NOAA space forecasters predict additional CME (coronal mass ejection) blasts both tomorrow and Thursday.

The brightest stars in the constellations Lyra (the Harp), Cygnus (the Swan) and Aquila (the Eagle) form a huge asterism in the sky called the Summer Triangle. Instead of distances, I’ve labeled the stars with the year the light you see tonight left each one. Created with Stellarium

One of late summer’s little astronomy joys is lying on your back and looking straight up at the Summer Triangle. You can do this with ease in early September when the three bright stars that form the triangle – Vega, Deneb and Altair – are due south as soon as the sky gets dark. Now tuck your hands back behind your head and join me for some time travel.

It takes just over 8 minutes for sunlight to travel the 150 million kilometers (93 million miles) to Earth. Credit: Wiki

Whenever we gaze at a celestial object we’re looking back in time. Even traveling at the unimaginable speed of 186,000 miles per second, light from distant objects takes time to reach our eyes. Moonlight needs 1 1/4 seconds old to get to Earth while sunlight takes just over 8 minutes. We might as well be watching a time-delayed TV program when we look up at the night sky.

Mars is 15 minutes away by light and the nearest star beyond the sun, Alpha Centauri, is 4.4 light years away. The light we see tonight departed its fiery surface in early 2008. No doubt about it – the stars are time machines of the imagination.

Cygnus the Swan and Lyra the Harp as seen from a mythological point of view. Credit: Urania’s Mirror

Let’s return to the Summer Triangle. Vega is almost directly overhead and a little off to the right (west) when darkness falls. It’s bright not only because it’s intrinsically luminous but also because it’s only 25 light years away. We see it as it shone in 1987 when a gallon of gas in the U.S. cost 89 cents, the home computer revolution was just getting underway and there were 5 billion humans on the planet. Today that number is over 7 billion.

Shifting your gaze to Deneb in the Northern Cross  – formally known as Cygnus the Swan – we peer much further back in time. Deneb is an extremely large and bright star, the reason it’s still a standout despite its whopping distance of 1,425 light years. That takes us to 587 A.D. when the Polynesian peoples first settled Hawaii and Tahiti. Europe was still dealing with deadly plagues in the 6th century while the Visigoth king in Spain converted to Christianity. It was a time of continuing conquests and wars following the end of the Roman Empire. So long ago, yet Deneb’s twinkle tweaks them back to life.

Altair sits near the head of Aquila (AK-will-uh) the Eagle. Credit: Urania’s Mirror

Altair lies at the base of the Summer Triangle and offers only a 17-year hop into the past. What were you doing in 1995 when there was no International Space Station to watch pass overhead at night?

Back then the brightest satellite was the Russian Mir space station, and we looked forward to its regular sweeps across the northern sky. On TV you’d see a lot of President Clinton and nearly as much of the O.J. Simpson trial.

Care to go back further back? The center star in the Cross, an easy naked-eye star called Gamma Cygni, is 1,800 light years from Earth, taking us back to 212 A.D., when the Chinese were inventing gunpowder and Emperor Elagabagus instituted sun worship in the Roman empire.

Since stars serve as such useful markers of our past, why not mix a little constellation study with history in the schools? Thanks to tireless efforts by astronomers and more recent measurements by the Hipparcos Space Astrometry Mission, we know the distances and look-back times of thousands of stars.  These tiny lights serve as reminders of  humanity’s long journey to the present.

The star Capella returns with a message

No matter how bright the moonlight, if you’re out in late summer, the star Capella still catches the eye. This picture was taken last night. Photo: Bob King

The eye of winter is upon us these late summer nights. I was out last night with my dog Sammy enjoying a walk in the almost-Blue Moon moonlight. Since my dog has mostly black fur, the extra light helps me keep track of where she’s sniffing around. Without the moon, she’s a phantom. Finding a black dog under a dark sky is similar to spotting a snowman in a blizzard.

Looking up in the bright moonlight, I noticed how few stars there were in the sky. With the moon nearly full and high in the south, its overpowering light simply washed out most of the them. Especially at first glance. Looking more closely I could see Cassiopeia, the Great Square of Pegasus and a few others, but the one star undiminished by the moon’s reflective power was Capella. It caught my attention more than Vega and the luminaries of the Summer Triangle simply because it lay straight ahead in my field of vision. I didn’t have to toss back my neck and crane upward to catch sight of it.

In bright “Blue Moon” moonlight the Big Dipper, riding low in the northwestern sky, is faint and take a little effort to find. Capella in the constellation Auriga the Charioteer is easy to see in the northeastern sky around 11 p.m. Created with Stellarium

Capella’s the brightest star in Auriga, a constellation more closely associated with mid-winter than late summer, but every season contains the seeds of the next. The star begins its ascent in the northeastern sky in late July when no one’s paying attention. By the end of August, you’ll see it twinkling around 20 degrees high (two fists held at arm’s length) around 11 p.m.

If Capella seems to be winking at you slyly, you’re right. It’s as if the star knows it cannot be denied. Come January, Capella shines from nearly overhead on the coldest nights of the year. When the mid-winter full moon glares down from above, I’ll probably be looking to the northeast once again, watching for Capella’s counterpart Vega to give me hope that spring will come.

Stars do that for you. They’re messengers with news of what’s to be, which is why it’s good to get to know them.

You say VAY-guh, I say VEE-guh, let’s just call it Vega

Vega raises its head above the trees, still leafless in Duluth, around 10 o'clock. Photo: Bob King

When I was a kid and supposed to be in bed sleeping, I’d stand up on the mattress and look out the north window of my bedroom on clear nights. The North Star was always there, but during March and April Vega twinkled low in the northeastern sky above the leafless trees. The star has been a steady friend ever since and a reminder that summer’s coming soon.

I still smile inside as an adult when I watch it return every April. This tiny explosion of light brings in the new season. Another reason for its warm persona is its position in the Summer Triangle, a group of three bright stars that dominate the southern sky from July through September. Vega is the brightest of the three and the first to rise in the east for northern hemisphere sky watchers.

While you’re out tonight hoping for a glimpse of the northern lights or waiting for a fireball to deliver a bundle of meteorites in your front yard, see if you can spot this stellar star.

Vega comes up around 9:30-10 p.m. in the northeast, well below the Big Dipper. Created with Stellarium

It’s as easy as facing northeast around 10 o’clock. Vega is the only bright white star low in the sky. Don’t be surprised if you see it twinkling. Low altitude means the star has to pass through the bottom of our atmosphere where the air is denser and more turbulent compared to straight above. Vega’s light gets pushed this way and that, making it spark and sputter.

Vega is the Alpha star in the constellation Lyra the Harp. Created with Stellarium

Vega’s other name is Alpha Lyrae. “Alpha”tells us it’s the brightest star in the constellation of Lyra the Harp. The small, rather faint group is shaped like a perfect parallelogram and represents the lyre or harp belonging to the great musician Orpheus of ancient Greek myth.

Vega is the 5th brightest star in the sky and at 25 light years from Earth, one of the closest. As you read this, the sun is moving in Vega’s direction at 43,000 miles an hour, so we’ll be even closer buds in the future.

Most people who’ve heard of the star pronounce it VAY-guh. I’ve always known it as VEE-guh. Either is correct. The name derives from Arabic and means “swooping eagle”, the reason it’s also known as the Eagle Star. Vega is about twice as massive as the sun but rotates much more rapidly (170 miles per second) compared to the sun’s slovenly 30 mps. Because it’s not a solid body like a planet, its speedy spin causes the star to flatten at the poles and bulge at the equator. Vega’s a giant jellybean!

Vega is younger, hotter and larger than the sun. It also rotates so rapidly it's oval shaped. From our point of view on Earth, we stare straight down at one of the star's poles. Credit: R.J. Hall

Back in 1983, astronomers using the Infrared Astronomical Satellite discovered that Vega is surrounded by a disk of warm dust. More recent observations with the larger and more powerful Spitzer Space Telescope reveal that the disk is likely supplied with material generated from asteroid collisions.

Gravity from a possible Jupiter-sized planet orbiting within the dust disk is suspected of creating thicker clumps of dust that may congeal into planets someday. Astronomers believe Vega’s disk may be similar to the one that surrounded the sun in the early solar system when planets were first forming.

Two views at different colors of infrared light of the dust disk around Vega photographed with the Spitzer Space Telescope. Credit: NASA

Vega is one of hundreds of stars surrounded by dusty disks or halos. When you’re building planets, you’ve got to start with what’s on hand.  The universe is flush with dust and gas. It’s a wonder that worlds as diverse as Earth and Saturn were fashioned from such unassuming bits.

Starts as starlight, becomes something wonderful

Tiny reflections of the sun created by the contact points of legs and water between two mating water striders. Photo: Bob King

Sunlight and starlight are transformed in wonderful ways by our environment. For a half hour this weekend I sat by a creek and watched water striders, those spidery-looking insects with long legs that scoot across a creek or pond in search of food. The tiny points of contact between their legs and water dimpled the surface without breaking it. They also focused the sun into minute images that reflected back to my eyes. When several striders by chance came together, the “sun spots” looked like a constellation of stars.

Time exposure of a flare from the Iridium 31 satellite last night from Duluth, Minn. The flare started at left and faded to the right. At far right is the star Arcturus. Photo: Bob King

Last night you might have seen a flare from an Iridium satellite similar to what we saw in Duluth just after 10 o’clock. Since satellites aren’t equipped with lights like airplanes, we see them only by the sunlight that reflects from their shiny parts. It’s the same reason the moon and planets are visible. A portion of the sunlight they receive is reflected back to our eyes.

Brilliant Vega and a host of neighboring stars rise through tree branches last night around 11 p.m. Photo: Bob King

Later yesterday evening the bright star Vega and a rich entourage of stars appeared in the northeastern sky. They glittery crew hung from bare branches like tiny flickering Christmas tree lights. The sight of stars mingled with trees has always been one of my favorites. They can transform a thicket of weed trees into a wonder of the night.

Frost crystals refract or bend sunlight into its many colors this morning. The picture was intentionally shot slightly out of focus to emphasize the colors, which show well to the eye but not when shot in focus with a digital camera. Photo: Bob King

This morning a heavy frost splintered sunlight into every color of the rainbow on my front lawn. Ice crystals took the sunlight and refracted it into its component colors. Moving my head this way and that, the colors continually shifted as the angle between my eyes, the crystals and sun changed. It was Isaac Newton who first demonstrated that a prism could refract or spread light into its component colors, but frost has been at it all along.

Forrest Overby of Duluth fishes for trout as sunlight glints off waves coming to shore on Lake Superior this morning at the mouth of the Sucker River. Photo: Bob King

While on assignment today for the newspaper, I came across a man fishing in Lake Superior for trout. He was enveloped in pure sunlight glinting off the waves as they crashed ashore. I love how moving water profoundly affects the light that travels to our eyes. Glass shards, perfect reflections, writhing underwater snake-streaks, millions of tiny suns – it’s all there and more in one of the most familiar substances on Earth.

I’ve heard that when we die we see a bright light at the end of a tunnel. I hope so. Light in its many forms has been a source of wonder all my life. How appropriate for it be there at the final train stop.

The Summer Triangle rides again

The Summer Triangle appears in the eastern sky at nightfall in late June, rising ever higher through the night. The band of the Milky Way slices diagonally through the figure coursing from southeast to northeast. Created with Stellarium

Now that we’ve finally bridged the solstice and embarked on our journey into summertime, it seems fitting to get re-acquainted with the Summer Triangle. I noticed it last night when my younger brother and I stepped out to watch the space station pass by.

As you might expect for a triangle, three stars join forces to create the huge figure in the eastern sky at nightfall. The brightest and one of the first stars to come out during twilight is Vega in the constellation Lyra the Harp. All Lyra’s stars are dim, but Vega more than compensates with a radiance as pure and white as burning magnesium. You can’t miss it about halfway up the eastern sky at nightfall.

All three look like points of light, but if we could see them up close, we'd discover that Altair (17 light years distant) is about twice the diameter of the sun, Vega (25 light years) about three times and Deneb (~2600 light years) is a supergiant star 200 times as big. Altair and Vega rotate rapidly causing them to bulge out at their equators. Illustration: Bob King

To find Deneb, the brightest star in Cygnus the Swan or Northern Cross, reach your balled fist to the sky and look ‘two fists’ to the lower left of Vega. Altair in Aquila the Eagle is way down to the lower right. Three-plus fists will get you there. Being first magnitude or brighter, Vega, Deneb and Altair are all easy to see; city and suburban observers should have little difficulty in finding them.

An additional treat awaits the eyes of rural observers or those who make a drive to the country. The Summer Triangle hosts a bright section of the Milky Way, and with moonless skies the entire week ahead, it’s a most impressive sight. This is especially true for those living in mid-northern latitudes. The lower half of the Milky Way in Sagittarius, while equally amazing, never gets high enough above the horizon haze to grab your attention the way the northern half does. Many a night I’ve stood back and watched the Summer Triangle and its strands of starry haze waft overhead accompanied by the gentle clatter of leaves in the breeze. The vastness of it all becomes palpable.

Let Vega whisk you into spring and beyond

Spring and robins are inseparable. Credit: Wiki/mdf

A week ago I only heard them, but on Wednesday I finally saw my first robins. Many of us look forward to the change of seasons and anticipate signs of their arrival.

Seasonal changes usually start slowly – a bare spot of ground opens on an otherwise snowy road or we hear the first toot-toots of a saw-whet owl at night – but they can reach a tipping point in a surprising hurry. Today, robins are everywhere and our yard is nearly free of snow.

In a similar way, we anticipate seeing certain stars in the nighttime sky. Stars that are associated with the seasons. I thoroughly enjoy watching Orion climb the eastern sky on November nights, reminding me that winter will soon be getting down to business. Mid-April nights see the decline of Orion in the southwest and the introduction of new stars in the eastern sky. We’ve met a few already – Arcturus, Spica and one non-star celebrity, the planet Saturn.

Vega comes up around 10 o'clock in the northeast, well below the Big Dipper. By 10:30 p.m., it's 10 degrees high or a fist held at arm's length. Created with Stellarium

Let me introduce you to Vega, a star that walks the line between spring and summer. Like the robins, you have to hunt a little to see it now, but before you know it, it’ll be right in your face.

Start with our dependable friend, the Big Dipper, and follow the arc of its handle southward to the first bright star you see. That’s Arcturus. Next, shoot a line from Arcturus about four fists in length straight toward the northeast horizon. If your view is unobstructed, you can’t miss Vega. It’s the brightest, twinkliest star in the region.

Stars are classified according to brightness or luminosity (left side of graph) versus temperature (bottom). The sun and Vega fall right in the middle. Giant stars are at upper right while the faint but hot white dwarfs are at lower left. Credit: ESO

Vega is dimmer than Arcturus by a hair, but the most noticeable difference between them is color. Arcturus is an orange giant with a cooler surface temperature (7,250 degrees F) compared to Vega’s 16,650 degrees. Whiter means hotter and redder means cooler when it comes to stars.

Vega is similar to the sun in star type, being a member of what astronomers call the main sequence. These stable stars ‘burn’ hydrogen in their blazingly-hot cores to create energy, starshine and leftover helium ‘ash’. Most of the stars in the sky belong to the main sequence.

As stars age, they leave the main sequence to become giant and supergiant stars that burn through additional elements to create energy. Arcturus burns its helium ash into carbon and oxygen. Changing fuel type changes a star’s equilibrium, causing it to expand into a stellar giant. Main sequence stars that were once sun-like in size balloon out, cool and redden as they age.

Vega in the constellation Lyra the Harp catches your eye in the northeast on mid-April nights. Photo: Bob King

Both the sun and Vega will switch over to helium burning in the distant future. As they do, astronomers expect them to evolve into big orange puffballs much like Arcturus. Will the sun grow large enough to fry the Earth to a crisp? Do you really want to know? The answer: most likely. Not to get too concerned yet. That unhappy day is still almost five billion years in the future.