Hold my hand as we peer into the Bootes Void

The Big Dipper, the brightest part of the constellation Ursa Major the Great Bear, is followed down into the northwestern sky by twinkling orange Arcturus and the constellation Bootes, the Bear Guard. Stellarium

Most of us would consider Bootes the Bear Guard a spring constellation. That’s when it first appears in the eastern sky, following the tail of Ursa Major the Great Bear as the snow drifts recede. Come fall, Bootes (Boh-OH-tease) and its bright luminary Arcturus recline in the west within spitting distance of the Dipper.

Every evening I look up to check on the condition of the sky. Arcturus is either flashing happily or gone missing, hidden by clouds. Gazing up from Arcturus, it’s easy to trace out the remaining points of starlight that form the kite-like figure of Bootes. Like a kite let go, Bootes drifts away to the west as the night deepens.

The next clear night, follow the arc of the Dipper’s Handle to Arcturus and then work your way up and around to pick out the constellation’s fainter stars. If you now direct your gaze to a blank spot between Bootes and the end of the Dipper’s handle, you’ll be staring at the center of a remarkable nothingness, the Bootes Void.

Map of the Bootes Void showing it alongside other dense superclusters of galaxies. Credit: Richard Powell

Normally we talk about the presence of something in the sky in this blog, but today we’ll focus on absence. The Void, a roughly spherical realm of space 250 million light years in diameter, is virtually empty. Space is already empty enough. If the sun were shrunk down to the size of a grapefruit, the nearest star system, Alpha Centauri, would be 2,000 miles away. From there, it’s another 1,000 miles to the next closest, Barnard’s Star.

American astronomer Robert Kirschner discovered the void in 1981 as part of a survey to measure how fast distant galaxies were fleeing from one another as the fabric of space expands in the ever-widening wake of the Big Bang. Six years later, Kirschner and team turned up 8 galaxies in this vast volume of space centered 700 million light years from Earth. By the late ’90s only 60 galaxies were known, making the Void not as devoid of galaxies as originally thought.

Still, the wind blows through it like a ghost town. Considering that the average distance between galaxies in typically a few million light years, the Void should contain some 10,000 inhabitants. Where have they fled?


The Millenium Simulation will give you a feel for the large-scale structure of the universe. Enjoy the ride!

Galaxies are vast assemblages of stars, clusters, gas clouds and planets thousands of light years across. Their mass gives them considerable gravitational might, so they’re attracted to one another. Over the lifetime of the universe, galaxies congregate into strands, clumps and clusters. The surrounding space empties out like a parking lot at closing time and becomes a void.

The Bootes Void is no ordinary emptiness. It’s HUGE. Too big to have formed with the current lifetime of the universe say astronomers. That’s why it’s thought to have agglomerated from smaller voids that merged together to form one of the largest voids in the known universe, a so-called supervoid.

Millenium Simulation of the large-scale structure of the universe shows a sponge-like texture of filaments of galaxies threading empty voids of space. The galaxies – each too tiny to see individually at this huge scale – clump around invisible dark matter and each other. Credit: Millenium Simulation

Galaxy clumping has amazing consequences for the large-scale structure of the universe. Astronomers think the visible matter of the universe clustered around clumps of dark matter, which makes up 73% of all the ‘stuff’ out there, shortly after the Big Bang. Once galaxies formed, they continued their clustering ways up to the present day. Instead of a random distribution of matter across space, the universe looks like a sponge where hundreds of billions of galaxies swirl in filaments and nodes around the comparatively empty voids.

Funny how the biggest things in the universe can be so surprisingly close to home. Look up toward the Big Dipper and Arcturus in the western sky after sundown and think of where you are.

Magnificent Mars and a celestial lightsaber

Face southeast around 10:30 p.m. local time and you’ll be pleasantly surprised at the line of bright “stars” there. The brightest is the planet Mars. Photo taken March 24, 2014 at 10:30 p.m. Credit: Bob King

Last night Mars blazed in the treetops. I’m still amazed at how bright the planet’s become in the past few weeks. Paired up with the bright, blue-white star Spica in Virgo, it’s unmistakable. The two clear the southeastern horizon together around 9:30 and become very obvious an hour later.

The magnitude scale. Negative magnitudes are brighter than positive ones. Credit: Univ. Nebraska-Lincoln

Reach your arm toward Mars and move “two fists” to its upper left and you’ll spot Arcturus, the brightest star in the constellation Bootes the Herdsman. Together the three form a striking “lightsaber” of luminaries.

Looking more closely, you’ll notice that each is a different brightness. Thanks to fortunate circumstance, they differ from each other by almost exactly one magnitude, the standard unit of measurement astronomers use to measure star brightness.

First magnitude stars are 2.5 times brighter than second magnitude stars, which are 2.5 times brighter than stars of third magnitude and so on.

Mars rules the roost at magnitude -1.2, Arcturus is next at 0 and Spica at 1.0. If you’ve ever wondered what a magnitude of difference between celestial objects looks like, check this convenient live demonstration the next clear evening.

Arcturus and Spica will remain fixed in their brightness – at least for thousands of years – but the light of Mars and the other planets vary depending on their distance from Earth. In astronomy, there’s a simple rule: when close, objects appear brighter than when farther away. Mars’ magnitude varies more than most of the planets with extremes of -3.0 when nearest to 1.6 when most distant. That’s a difference of nearly 100 times.

Because Mars’ orbit is more elliptical than Earth’s, distances between the two planets are vary significantly, causing the planet to vary greatly in brightness. Credit: Wikipedia with additions Bob King

These large variations directly relate to Mars’ more elliptical (oval) orbit. When the Red Planet is on the far end of its elliptical orbit at the same time Earth’s on the opposite side of the sun, it’s farthest and faintest. When on the far end of its orbit on the same side of the sun as our planet, it handily outshines every star and planet in the sky except Venus.

Mars on March 19, 2014 with some of its more prominent features marked. Hellas and Syrtis Major are relatively easy to see. The north polar cap is quite small now. Credit: Damian Peach

Even if you don’t give two shakes about magnitudes, make sure you take in a view of all three of these night sky gems. If you have a telescope and are observing from the western hemisphere, this is the best week to see the bright false south polar cap.

The “cap” is really Hellas, the largest crater on Mars, covered in frost and bedecked with clouds during southern hemisphere winter.

Look for a bright lens-shaped spot on the planet’s south end around midnight early this week and closer to 1-2 a.m. next weekend. It’ quite obvious in 6-inch and larger telescopes in steady air.

Don’t miss this Saturday’s Saturn-moon conjunction

The big picture in the southern sky this Saturday morning at dawn shows the moon just a degree below Saturn with Mars at upper right in the south and Venus very low in the southeastern sky. Stellarium

A very nice, close pairing of Saturn and the waning 3rd quarter moon will happen Saturday morning at dawn. With late sunrises still the rule, this should be a very easy event to catch even through a parted window shade.

At closest, the two will be just two moon widths or 1 degree apart. Saturn’s in Libra the Scales, a dim constellation that precedes the brighter, more picturesque Scorpius the Scorpion. You can see part of the scorpion to the lower left of the duo. In particular, look for the bright red supergiant star Antares.

Both Libra and Scorpius are late spring-early summer constellations, visible at nightfall in May when the butterflies fly. It’s thoughts like these that lift our spirits on cold winter nights. I had the same feeling two nights ago when I happened to be out observing around 11:30 p.m. and caught sight of a “new” star flashing in the northeastern sky – Arcturus. If there were ever a vanguard of spring, this star is it. Arcturus creeps higher every frigid night until the snow is gone, the leaves turn out and jackets are shed.

Mobile phone shot of Venus in twilight Monday morning. Credit: Sean Cassidy

While you’re out enjoying Saturday’s conjunction (by the way, Saturday’s named for the Roman god Saturn) stay out a little longer to enjoy the reappearance of Venus low in the southeastern sky about 40 minutes before sunrise. Sean’s photo will help you know what to expect.

Think pink for spring – Arcturus is back!

This map shows the sky around 10 p.m. local time in facing east tonight Feb. 24. Arcturus, the brightest star in the constellation Bootes the Herdsman, is well below the Big Dipper. The nearly full moon joins the scene a short distance from Leo’s brightest star Regulus. Maps created with Stellarium

I was startled two nights ago when I turned down the road and spied pink Arcturus scintillating low in the eastern sky. With snow all around and more on the way, my psyche was steeped in winter. So what was this big, bright spring star doing staring me in the face?

Find Arcturus using the old adage “Arc to Arcturus” by sliding down the arc of the Big Dipper’s handle.

After the sun, Arcturus is the 4th brightest star in the sky. It pokes up around 10 o’clock in late February. You’ll find it with ease simply by following the curve of the Big Dipper’s handle downward toward the eastern horizon. Its name comes from the ancient Greek word “arktos” for bear and means “Guardian of the Bear”. Appropriate considering it rides herd on Ursa Major the Great Bear, the brightest part of which is the Big Dipper.

The calendar notwithstanding, Arcturus is a true “spring star”. Come May, when the first mosquitos begin to whine, you’ll find it perched high in the southern sky lording over the landscape much as Orion does now during the early evening hours.

Right now the Bear Watcher is hunkered down in the east, sparking through tree branches and over neighborhood rooftops. Twinkling, most obvious in the brighter stars, is caused by shifting air currents that are more pronounced at lower altitudes.

Arcturus, an orange giant star some 21 million miles in diameter, compared to the sun, Jupiter and other familiar stars.

Funny that the atmosphere can jiggle the light of such a massive star about as if it were as flighty a thing as a dandelion seed. Arcturus is an orange giant star 25 times larger than the sun, but all that girth is reduced to a trembling point of light 36 light years (216 trillion miles) from Earth. Its true brilliance is likewise masked by distance. Put in place of the sun, Arcturus would dazzle 113 times brighter and cover an area of sky half as big as the Big Dipper. As for color, it looks pinkish to my eye. Others see it as red-orange.

Watch this flush-faced star loft higher and higher in the east in the coming weeks with the return of the spring season. There’s a special bonus if you go out tonight. The moon, on its way to becoming the Full Snow Moon tomorrow night, will shine near Leo the Lion’s brightest star Regulus.

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.

Solar blowout and a wicked star-planet alignment

Sunspot group 1476 "blemishes" the sun this morning as it rose over Lake Superior in Duluth, Minn. Photo: Bob King

It’s always worth getting up to see a sunrise. Sure, you can’t concentrate and your eyes weigh a pound a piece by afternoon, but it’s worth the lift you feel watching a star rise out of a lake. I saw the sun slowly ease out of Lake Superior in Duluth this morning, and for a few minutes it was safe enough to take pictures with a telephoto lens.

I enjoy imperfections. Matter of fact, I’m built on flaws both inherited and accumulated over the years. Once the solar disk freed itself from the horizon, I could see it also had a blemish, a piece of crud that wouldn’t wipe off. A monster sunspot!

That spot group was plainly visible in the camera once the sun was up. An hour later I easily saw it from home with the naked eye from behind a pair of eclipse glasses.

The sun photograhed this morning through a 3-inch refractor with solar filter later this morning. The big group is 1476; smaller 1477 is at bottom. Photo: Bob King

Now spanning more than 12 Earths, the group is magnificent to view in a small telescope. The main spot has a long string of followers and reminds me of mother goose and her goslings.  Exquisitely small black umbral spots contrasted with the pale, encircling penumbra around the main or lead spot in the group. The photo only hints at the beauty and complexity of the group.

Because the sun rotates on its axis about once every four weeks, we can watch the evolution of this group with each passing day.

In active sunspot groups like 1476, new spots form and evolve quickly. Some expand rapidly and last days or weeks. Others appear and disappear in just a day. Day to day changes are obvious through a small telescope and show us just how dynamic a star can be. As always, you’ll need a safe filter to look directly at the sun. Here’s a link to a recent blog listing good sources.


Must-see video of last night’s M5.7 flare from Region 1476. The best part is the audio. Crank it up!

At 11:18 p.m. Central time last night, sunspot region 1476 blasted off a significant M5-class flare. Though large, it’s not directed toward Earth. For the moment, none of the more powerful X-class flares have made an appearance.

All the activity with more to come is because 1476 is a delta group, where positive and negative magnetic fields (north and south poles) are packed so close together, there’s great potential for instability and the release of energy in the form of solar flares. While there’s only a small chance of auroras for the far north this evening from effects not related to these spots, let’s cross our fingers for possible weekend auroras related to the big group.

From top to bottom: Arcturus, Saturn and Spica form a straight line in the sky last night. Photo: Bob King

Last night when members of our local astronomy club departed the planetarium after the monthly meeting, we instinctively all looked up. Aha! The sky was clear. High up in the southeast was a most striking arrangement: Arcturus, Saturn and Spica all lay in a straight line.

Being humans, we can’t help but be drawn to patterns, and this one you couldn’t miss. Try spying it yourself the next clear night. Go out from 9:30 p.m. on and look well up in the southeastern sky. Arcturus is the bright, orange-red star; below it you’ll find the duo of Saturn and Spica. It’s just cool.

The line will remain straight for about the next several nights. After that, Saturn’s motion to the right (west) will break the pattern. When will you first notice this?

Arc to Mars-turus

Jupiiter pokes out from between "cloud streets" high in the southern sky around 6:30 p.m. on a recent evening. Photo: Bob King

Amazing how quickly the stars and planets slide by. A few months ago you had to stay up late to get a good look at Jupiter. Now it’s front and center (due south) at dinnertime. Everything celestial moves up from the east, peaks at maximum elevation in the southern sky and then eases down into the west. And it’s all because we live on an unstoppable planet traveling 18.5 miles a second around the sun.

You wouldn’t expect the landscape to remain unchanged while looking out the window of a car traveling at 65 mph. Scenes shift by the minute. It’s the same with Earth. As we gaze out into the night sky, starscapes change over days, week and months as we speed ever onward in our orbit. The Summer Triangle’s replaced by the Great Square of Pegasus, which is replaced by Orion, which is replaced by Leo and on and on it goes. The one difference between a fast car and Earth is that the same starry scenes repeat year after year because we travel in a closed loop around the sun, not a straight line.

With night after night of clear skies, January’s Full Wolf Moon got a lot of lookers in the Duluth region earlier this week. Last night through clouds, I could still see enough of the moon to tell it had changed shape. It’s beyond full now and in waning gibbous phase. Looked like an egg to me. And since the angle between the moon, Earth and sun is narrowing, less and less of the moon is illuminated by sunlight with each passing night. We’ll be watching it wane from gibbous to 3rd quarter and finally morning crescent in the next 10 days. The moon also rises later and later as its orbital motion carries it ever eastward.

A grand arc connect the moon-Regulus pair, Mars, Saturn-Spica and Antares in Scorpius tomorrow morning just before dawn. Created with Stellarium

For those of you up around 6 a.m. tomorrow morning (Jan. 12), take a look across the full breadth of the southern sky. The moon will be in conjunction with and directly below Leo’s brightest star Regulus. Now let your gaze slide eastward and you’ll soon bump into fiery orange Mars. Continuing down and left, you’ll soon arrive at the attractive pair of “eyes” formed by Spica and Saturn and finally ruddy Antares low above the southeastern horizon.

Above this grand arc, high in the south, shines the brilliant orange-hued Arcturus. Mars and Arcturus are a near perfect match in color and brightness at the moment. Do their colors look the same to your eye or are they different? Mars is officially at magnitude 0.0 and Arcturus is listed at -0.04, ever so slightly brighter. Can you see this tiny difference? There’s at least one way they should stand apart from one another. I’ll give you a hint: it has to do with our atmosphere. Go out for a look and let us know what you see.

The ghost of Comet Elenin haunts the morning sky

Comet Elenin is a very faint, elongated streak as photographed through a 4-inch refracting telescope early this morning from the GRAS network in New Mexico. The picture covers about 2 degrees from side to side. Credit: Rolando Ligustri

For those of you who checked yesterday’s blog, you already know that the German ROSAT (Roentgen X-ray satellite) burned up in the atmosphere last night between 8:45 and 9:15 p.m. CDT. To the best of my knowledge, after digging around various websites, it appears to have come down over the Indian Ocean north of the coral atoll Diego Garcia. Too bad there’s so much water on this planet otherwise we’d have lots more satellite parts and meteorites in our collections.

I wanted to share the most recent pictures of Comet Elenin with you. Amateur astronomers have been busy the past few mornings losing sleep photographing and trying to see the comet through their telescopes. The moon is out of the way and Elenin is presently high up in a dark sky after about 3 a.m. These are the conditions we’ve been waiting for for months! And finally, enough pictures have been taken to confirm that the comet is really there.

Another view of Comet Elenin taken this morning with a 10-inch wide-field telescope in Austria. Credit: Michael Jäger

The photos show a faint, elongated cloud of spreading comet dust, the last gasp of what was to be fall’s best bet for a bright comet. Its ghostly appearance hints at how difficult it’s been to see with one’s own eyes in a telescope. To date, only one observer – Juan Jose Gonzalez – has spotted this wispy remnant from his mountaintop observing site in northern Spain using an 8-inch telescope. Jacob Cerny of the Czech Republic is the second person to observe it, but it was so challenging, he listed his observation as “uncertain”.

Take a look at Elenin’s morphology or form. It reminds me of the Headless Horseman from The Legend of Sleepy Hollow. Indeed, the head of the comet is no longer a separate entity as it was before the August breakup. All is one galloping streak of light.

Comet Elenin will continue along its orbit as it slowly moves farther from Earth with each passing day, fading and expanding as it does and likely to never return. Even though this demure object has been wrongly credited with causing earthquakes and other mayhem, the bright side has been a lively discussion of comets and other topics astronomical. These are good things.

Several readers have mentioned or made reference to Arcturus in recent days. I thought it would be an opportune time to give the star – the 4th brightest in the sky after Sirius, Canopus and Alpha Centauri – one last evening farewell before we get up 11 hours later at dawn to welcome it back. What?

Use the handle of the Dipper to "arc" your way to Arcturus during the early evening. This map shows the sky facing northwest around 7:30 p.m. local time. Maps created with Stellarium

Arcturus, an orange giant star with a distinctive warm tint, hovers low in the northwestern sky off the handle of the Big Dipper on late October evenings. It’s best to catch it an hour or so after sunset during evening twilight when the star is high enough to see relatively easily. As dusk melts into darkness, try looking two outstretched “fists” directly above Arcturus for the little horseshoe-shaped constellation Corona Borealis the Northern Crown.

If you have an open view to the northeast during early dawn, you can watch Arcturus return to view - truly, a star for all seasons! This map shows the sky facing northeast around 6:15 a.m. tomorrow morning.

Arcturus makes its first evening appearance in late winter in the northeastern sky. By May and June, it’s high in the south at twilight’s end; its warm light has come to be associated with warming temperatures and the arrival of summer. In fall, the star drops off into the northwest and finally sets, but because nights are better than 12 hours long in late October, Earth’s rotation carries it back into view for observers in mid-northern latitudes. Watch for its winking red light in the northeast at dawn. In a sense, we never lose Arcturus.

The star’s northern location on the celestial sphere is also responsible for its continuous visibility. The closer a star is to the North Star – the pivot-point star due north that remains in one spot in the sky – the longer it remains visible. All stars within a circle with a radius the same as your latitude never set at all. They’re called circumpolar stars because they circle around the North Star day and night without ever touching the horizon. While Arcturus is not quite circumpolar for Duluth, Minn., the fortuitous combination of northerly location and long nights allow it to be seen every month of the year.

Bootes – the constellation nobody can say right

Bootes the Herdsman is well placed for viewing during early evening hours in late May. He keeps two dogs which represent the neighboring constellation Canes Venatici. Credit: Urania’s Mirror

Some constellation names are easy to pronounce at first sight like Leo, Hydra and Cygnus but then there’s Bootes. On first encountering the word as a young teen, I still remember calling it ‘booties’. That’s what it looks like after all. ‘Boots’ is another variation I’ve heard many times since. And yet somehow you know the ancients wouldn’t have created a cultural myth based on a pair of galoshes.

It’s really pronounced ‘Boe-OH-teez’ and represents a herdsman. The word’s origin isn’t certain but it may come from the Greek word for ‘noisy’ and refer to the herdman’s shouts to his animals. Or it might be rooted in the ancient Greek word for ‘ox driver’. The nearby constellation of Ursa Major (the Great Bear) was sometimes depicted as a cart pulled by oxen.

The cone-shaped constellation Bootes extends north of the bright star Arcturus, an orange giant star 37 light years from Earth. This map shows the sky facing south around 10 p.m. in late May. Maps created with Stellarium

In the 21st century I’ll often refer to it as the ‘ice cream cone constellation’ because Bootes’ outline resembles a sugar cone topped by a single scoop. Whatever it is, it’s not hard to see, because the group contains the fourth brightest star in the sky, Arcturus.

Face south at nightfall and you’ll see two bright ‘stars’ halfway up in the southern sky. Those are Saturn and Spica and they’re separated by one fist held at arm’s length. Now tip your head back and gaze off high and to their left to spy a  brilliant orange-pink star. That’s Arcturus, a Greek word for ‘bear guard’. If you’re crazy enough to tip your head even further back and risk falling over, you’ll understand the name’s origin. Arcturus follows the Big Dipper, part of the Great Bear, which is nearly overhead.

Arcturus forms a large, temporary figure in the late spring-early summer sky sometimes referred to as the Spring Triangle. The ice cream cone part of Bootes is composed of a handful of stars extending two fists to the north or above Arcturus. Two little ‘antennae’ poke out on either side of the brilliant star to complete the constellation’s outline. That wasn’t too hard, was it?

 

M3 forms a right triangle with Arcturus and the star Eta or a nice equilateral triangle with Arcturus and Rho. The cluster is about two binocular fields of view away from Arcturus. Both M3 and the marked star are 6th magnitude. Stars are shown to magnitude 7.5.

Next we’ll use your new-found knowledge of Bootes to visit one of spring’s most outstanding star clusters, the globular cluster M3 in nearby Canes Venatici. For this you’ll need a pair of binoculars – even small ones will do. Once your eyes are adapted to the darkness, point your binoculars at Arcturus and the fainter star Eta Bootis to its right. The cluster is about two binocular fields of view directly above Eta and forms a right triangle with Eta and Arcturus.

M3 will look like a bright, ‘fuzzy’ star right next to a similarly-bright but real star. It’s most convenient the two are next door to each other because the star helps us tell the two apart.

M3 shows its true colors as one the sky’s finest globular star clusters in this photo made with a 32″ telescope. It’s 33,900 light years away and 180 light years across. Globular clusters are rich, spherical collections of stars in the outer halo of our Milky Way galaxy that revolve around the galaxy’s core. Credit: Jim Misti

“Magnificent” will probably not be the first word to pop out of your mouth upon seeing M3, but we are using binoculars after all. In truth, there are a half million stars packed into that tiny undistinguished spot. To get a sense of this cluster’s true beauty, a modest 6-inch telescope and dark skies are required. They you’ll begin to tease out dozens upon dozens of tiny stellar points winking like fireflies around M3′s radiant core. Larger scopes provide a most impressive view that will keep an observer glued to the eyepiece for many minutes.

M3 was discovered by Charles Messier on May 3, 1764 and added to his catalog – the Messier catalog – of fuzzy objects not to be confused with his favorite quarry, comets.

There are two main types of clusters in our sky – the wider, spread-out variety like the Seven Sisters (Pleiades) called open clusters and the densely-packed, spherical globular clusters. Open clusters populate the Milky Way’s spiral arms and are generally much younger than the globulars, which occupy a great halo of space around the center of galaxy. They’re the mighty ancients of the universe with ages of 10 to 12 billion years. In contrast, most open clusters break apart into individual stars after several 100 million years.

When you look at M3, whether by telescope or binoculars, it’s hard to imagine its size and star density. 500,000 stars gathered into a sphere that spans five times the distance between Earth and the star Arcturus. Just think of that. What human imagination could have ever conceived of the wonder that nature rolls out with casual ease on warm May evenings.

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.