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Binocular Universe: Let’s Go Fly a Kite

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Binocular Universe: Let’s Go Fly a Kite

June 2015

Phil Harrington

The kite-shaped pattern of stars that we know as Boötes (pronounced Boh-oh-teez) is one of the oldest constellations in the entire sky.  Some say that it dates back to ancient Babylon, when they were used to depict the god Enlil, patron god of farmers.  Others trace it to Sumeria, where it represented "The Man Who Drove the Great Cart" (our Big Dipper).

Homer was first to use the name Boötes (in Greek, Βοώτης) in the classic The Odyssey, although the tie-in to Greek mythology has never been well established. Many mythology scholars believe that Boötes represents Philomenus, a plowman who legend has it drove oxen.  Like the Sumerian link, the "Big Dipper" was portrayed as a cart being pulled by Philomenus' oxen.

Actually seeing a herdsman or a plowman among his stars can prove just as challenging as trying to establish the exact origin of Boötes.  Our 21st-century imaginations usually find it easier to trace out a kite or an ice cream cone in this region rather than a human form, as our ancestors did.


Above: Spring star map from Star Watch by Phil Harrington.
Click the chart to open a printable PDF version in a new window.


Above: Finder chart for this month's Binocular Universe.

Chart adapted from Touring the Universe through Binoculars Atlas (TUBA)
Click the chart to open a printable PDF version in a new window.

There is no mistaking the identity of the constellation's brightest star, Arcturus.  Arcturus, shining at a dazzling magnitude +0.04, is the brightest star north of the celestial equator and fourth brightest in the entire sky.  Its distinctive orangish hue is instantly apparent through a telescope, binoculars, or the naked eye. The orange color tells us that Arcturus is cooler than our sun. Technically, it is a type K0 III orange giant, with a luminosity 110 times greater than the sun. Spectroscopic studies reveal that all of the fusible hydrogen in its core has been depleted, having been converted to helium. The core is shrinking and becoming hotter, but it has not yet reached conditions to support helium fusion; instead, Arcturus’ energy comes from hydrogen fusion occurring in a shell surrounding the core.

Arcturus is only 37 light years away, making it one of our Sun's more impressive neighbors. That means the starlight we are seeing tonight left Arcturus in 1978, the year that my wife and I met at college! What were you doing 37 years ago? Maybe dancing to that year’s #1 song on the Billboard charts, "Shadow Dancing" by Andy Gibb, or watching the year’s highest grossing movie, Grease. (Kids, ask your parents or grandparents!)  Maybe you weren't even a twinkle in your future parents' eyes!  Whatever it was, that’s when the light we are seeing tonight left Arcturus.

Although Boötes lacks any attention-getting deep-sky objects, the Herdsman has gathered a few interesting targets that often go missed.

For instance, there's one that hides just 40 arc-minutes south of Arcturus. With steadily support binoculars, a transparent sky, and sharp eyes, look an arc or chain of seven stars right at the brink of visibility.  The French amateur astronomer Fulbert Picot is credited with coining the group's name, Napoleon's Hat, for its likeness to the emperor's chapeau. Napoleon's Hat is centered at R.A. 14h 14.0m, Dec. +18° 33'. Typical 7x to 10x binoculars will have a tough time spotting all seven of the stars here, as they range in brightness from 9th to 11th magnitude, but my 16x70 giants show them quite plainly.

Above: The asterism Napoleon's Hat lies just south of Arcturus.

Chart adapted from Touring the Universe through Binoculars Atlas (TUBA)

As long as we are going for big game, let's try for a real challenge. Boötes holds a lone globular cluster just inside its western border adjacent to Canes Venatici. NGC 5466 shines at only 9th magnitude, and is a taxing test for 4- and 6-inch telescopes depending on sky conditions. But if you wait for that special night, it just might pop out in 50-mm binoculars.  You'll need to support your binoculars steadily for this one, and use all the tricks of the trade, such as averted vision.  Look for its ethereal glow, only a dim round smudge of gray light, just to the west of a 7th-magnitude star.

If NGC 5466 proved to be just too taxing, but it left you hungering for a globular cluster, then salvation lies just 5° to the west. Crossing quickly into Canes Venatici, we find M3, one of the best of its kind in the entire sky. Charles Messier discovered M3 on May 3, 1764. You can discover it for yourself by aiming at the halfway point between Arcturus and the star Cor Caroli in Canes Venatici. Keep an eye out for a right triangle of three dim stars pointing toward the southeast. Spot it? Take a closer look at the point marking the right angle itself. Notice how it is not a perfect point of light, but rather a tiny, fuzzy blob?  That's M3.

When we look toward M3, our gaze is crossing nearly 34,000 light years. Right away, knowing the cluster's overall brightness as well as that extreme distance tells you that M3 is no ordinary globular. Indeed, studies show that it is one of the largest members of the Milky Way's family of globular clusters, perhaps containing more than half a million stars.

Back into Boötes, let's ascend the "ice cream cone" to Delta Boötis. Delta is a binary system made up of two type-G stars. The primary shines at magnitude 3.5, making it an easy naked-eye find. Its companion, which is separated by 104", shines dimly at magnitude 7.8. The system's primary star is a type G8 III yellow giant that, like Arcturus, is evolving toward the red giant phase of life. The less massive companion is a type G0 V main sequence star, making it very similar to our own G3 V Sun.

Further northeast, we have Mu Boötis, another binary worthy of note.  Mu is also known as Alkalurops, from the Greek word kalaurops, meaning “the shepherd’s staff.” With our binoculars, we can easily make out that Mu is a binary star. Its 6.5-magnitude secondary star lies 108" of arc away from the 4.3-magnitude primary.

But wait, there's more.  A close look through a telescope shows that the companion is actually two closely spaced type G stars separated by a scant 1.5 arc-seconds, and labeled Mu-B and Mu-C. They orbit a common center once every 260 years and are separated from one another by about 54 Astronomical Units. Together, they are more than 4,000 AU distant from Mu-A, and take at least 125,000 years to complete an orbit.

With your eyes alone, look toward the northwestern corner of Boötes, just east of Alkaid (Eta Ursae Majoris) marking the end of the Big Dipper’s handle. See a faint glow there? Now, swing your binoculars that way and take another look. You’ll discover that naked-eye patch is actually a field of more than half a dozen stars scattered around Kappa and Iota Boötis.

The Iota Boötis system is made up of a 5th-magnitude primary and a 7.5-magnitude secondary. They appear separated by 39" of arc, which is right at the edge of resolution through 7x and 8x binoculars on nights of steady seeing. An unrelated 6th-magnitude star to the pair's east may mistakenly give the impression that Iota is actually a triple star system, but it is not.  Kappa is also a binary star, but with its two components separated by only 13.5”, we had best leave them to telescopes.

Kappa and Iota, along with Theta Boötis to their east are often portrayed as the Herdsman’s outstretched hand.  A smattering of fainter adjacent stars in northern Boötes and nearby Draco were once part of the now defunct constellation Quadrans Muralis, the wall-mounted quadrant. First created by French astronomer Joseph Jerome de Lalande in 1795, Quadrans Muralis was drawn from ten stars shining between 5th and 7th magnitudes. Despite Johann Bode later depicting it in his Uranographia star atlas of 1801, the constellation was never widely adapted. Yet, we acknowledge Lalande’s wall-mount quadrant every January when we gaze toward the radiant of the annual Quadrantid meteor shower.

Above: Quadrans Muralis, as depicted on Johann Bode's Uranographia star atlas of 1801.

The late spring sky has plenty to offer binocularists who wait for the sky to darken fully. Here are other targets within Boötes that are worth visiting this month.

Until we meet again next month, remember that two eyes are better than one.

About the Author:
Phil Harrington has written 9 books on astronomy, including Star Ware, Star Watch, and Touring the Universe through Binoculars.  Visit his web site, www.philharrington.net, for more information.


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