Diamond of Virgo

It has been said that diamonds are a girl’s best friend. Now any girl with her feet firmly planted on the ground knows for a fact that a girl’s best friends are Rocky Mountain Chocolate Factory truffles and control-top pantyhose.

But if I were to allow myself a brief indulgence in the alternate reality espoused by DeBeers and Tiffany’s, I would set my sights a little higher. Give me the Diamond of Virgo.

The Diamond of Virgo is a wonderful four-star, spring-into-summer asterism that, when spotted, reveals the location of four constellations. Please step into my showroom.

1) About an hour after sunset, face the western horizon, that is, toward the direction in which the sun set earlier.

Star maps created with Your Sky

2) Look high in the sky, a little towards the north, for the large, distinctive seven-star asterism (star pattern) known as the Big Dipper. In its current orientation, its handle will be sticking up above its bowl. Extend the curve of the handle in an imaginary line away from the bowl, until you reach a very bright star. This is Arcturus, the first point of our stellar diamond. Arcturus (ark-TOUR-uss) is an orange giant star, the brightest star in the constellation Bootes (boh-OH-teez) the Herdsman, and the fourth brightest star in the sky.

The Diamond of Virgo asterism

3) Now continue that same imaginary curving line toward the southwestern horizon until you reach the next bright star: Spica, brightest star in the constellation Virgo the Maiden and the second point of our diamond. Spica (SPY-kuh) is a blue-white dwarf star, and not as bright as Arcturus. Take a moment to compare Spica to Arcturus in order to see the subtle color difference. Can you discern the orange or golden color of Arcturus now, as compared to the blue to blue-white light streaming from Spica?

4) Below Arcturus and Spica, that is, closer to the western horizon, look for the shape of the constellation Leo the Lion. Our fearless feline dives after the setting sun. His head is marked by the Sickle asterism, which looks like a backwards question mark. His tail, higher in the sky than the head, is marked by a right-triangle asterism. The star in the right triangle that is highest above the western horizon is Denebola, the third star in our celestial gemstone. Denebola (denn-EBB-oh-luh) is a white dwarf star, and it’s dimmer than either Arcturus or Spica.

5) Mining our sky diamond has been fairly easy up to now. The fourth and final star is the most challenging, because it’s dimmer than the other three.

Our quarry is Cor Caroli (core CARE-oh-lye), brightest star in the constellation Canes Venatici (KAY-neez vee-NATT-uh-sigh). It lies to the right (or north) of the other three diamond points, and it lies between Spica and the handle of the Big Dipper, closer to the handle. To aid in finding it, draw an imaginary line between Denebola and the star at the end of the Big Dipper’s handle. That line will cross the white dwarf star Cor Caroli, which is a bit dimmer than Denebola.

If you can’t spot it, you may need to try again at a darker location, as an absence of light pollution is a big plus when hunting dimmer stars.

Cor Caroli is Latin for Heart of Charles and commemorates Charles II, King of England from 1630 to 1685. It was astronomer Edmond Halley (of Halley’s Comet fame) who honored the king—40 years after his death—with this designation, although it may have been Charles’s court physician who first suggested the heavenly namesake.

The Heavenly Herdsman

The name Bootes (boh-OH-teez) is believed to derive from ancient Greek words for ox and driver. Translation into other languages rendered ox-driver as herdsman, and so we’ve come to know this prominent spring constellation as Bootes the Herdsman.

You won’t find the Herdsman’s oxen in the sky. He was, however, associated with the nearby Big Dipper, what the Greeks called “the wagon.” It is this wagon that was reportedly being pulled by Bootes’ celestial oxen.

In a number of classical star atlases, Bootes is depicted as holding the leashes of a pair of hunting dogs: the constellation known as Canes Venatici (KAY-neez vee-NATT-uh-sigh). The hunting dogs are straining at the end of their leashes as they pursue nearby Ursa Major (ER-suh), the Big Bear. The Big Dipper is the central asterism (recognizable star pattern) in the constellation of Ursa Major.

Bootes and the Hunting Dogs in John Flamsteed's 1729 star atlas
Courtesy of Linda Hall Library of Science, Engineering and Technology

During spring and summer, when Bootes is prominent in the sky, you’ll notice that he and his dogs, well, dog the Big Bear across the sky as it circles the North Star counterclockwise. The Big Bear is one of the circumpolar constellations, which means it circles the North Celestial Pole, the imaginary fixed point in the sky that the Earth's axis would intersect, were it extended northward. The North Star, Polaris, just happens to lie at the North Celestial Pole, which is why the circumpolar constellations appear to circle the North Star.

Let’s follow the herd.

1) About an hour after your local sunset time, face south. If you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west. Stand with your right shoulder to the west, and you’ll be facing approximately south.

Arc to Arcturus
Star maps created with Your Sky

2) Tilt your head all the way back and look up at the zenith, the point directly overhead. Locate the Big Dipper, a little north of the zenith. Following the curve of its handle, arc to Arcturus, the brightest star in Bootes.

Big and brilliant, the orange giant star Arcturus is 25 times the diameter of our Sun and 113 times as luminous. Arcturus is Greek for guardian of the bear, a reference to the star’s ancient association with— and apparent trailing of— neighboring Ursa Major. Can you discern its golden or copper hue?

3) Now that you’ve found Arcturus, you can trace out one of my favorite asterisms: the Ice Cream Cone. I’ve a profound weakness for ice cream, so locating this delicious asterism is a sort of guilt-free indulgence.

Ice Cream Cone asterism in Bootes

Most of the bright stars in Bootes form the Ice Cream Cone. Arcturus is the bottom of the pointed cone. Moving north from the point, you’ll come to two stars that form the top of the cone. The one on the left (east) is the orange giant Izar, the second brightest star in Bootes. Izar (EYE-zahr) is from the Arabic for loin cloth. The one on the right (west) has no traditional name, so we call it Rho (ROE) for its star catalog designation. Like Arcturus and Izar, Rho is an orange giant star.

4) Continuing north, we are rewarded with a mound of sweet, cold confection bounded by the stars Delta, Nekkar, and Seginus, moving from east to west. Delta is the star catalog designation for this yellow giant with no traditional name. Nekkar (NECK-ahr) is from the Arabic for ox-driver. Nekkar is another yellow giant star.

Did you ever play the group game “Telephone” when you were a kid? The first kid in a line or circle of kids would whisper a phrase to the kid next to him. That kid would whisper it to the next kid, and so on. The last kid would say out loud the phrase she’d heard. By the time it got to the end of the line, the phrase was invariably garbled, sometimes beyond recognition.

That’s sort of what happened with our third ice-cream-mound star, the white giant Seginus. Believe it or not, the name Seginus (segg-EEN-uss) started out as the Greek name Bootes! It was first mangled in translation by the Arabs. Then the Arabic wrong name was corrupted again by the Romans into a Latinized form. So the name that filtered down into modern times, Seginus, is pretty much meaningless.

Except of course to us, because we know it’s just Telephonese for ox-driver.






Astronomy Essential: Hydrogen is the most abundant element in the universe.

Hydrogen is estimated to make up a whopping 75% of the visible matter in the universe.

Hydrogen is the simplest chemical element. A hydrogen atom is composed of just one proton at the nucleus (core) and one electron in orbit around the nucleus. A proton is a particle with a positive electrical charge, while an electron is a particle with a negative electrical charge.

Stable hydrogen nuclei are believed to have formed only three minutes after the Big Bang. It took another 700,000 years or so for the nuclei to collect their electrons and become stable atoms. Hydrogen was the most abundant element in the universe back then, too.

Hydrogen is the fuel that powers stars. Hydrogen burns into helium in the cores of stars, and this nuclear reaction produces energy in the form of heat and light.

After oxygen and carbon, hydrogen is the third most common element in the human body. It is a primary component of water, and our bodies are composed of more than 50% water. Without hydrogen, human life as we know it could not exist.

Arc to Arcturus

If you can locate the Big Dipper, you can easily locate the brightest star in our summer sky, Arcturus (ark-TOUR-uss). One of the first memory prompts that beginning stargazers learn is “arc to Arcturus.” Just extend the curve of the Big Dipper’s handle to the next star in that line that's brighter than the end star of the handle, and you’ll arc to Arcturus.

Chart created with Your Sky

Right now, Arcturus is also easy to spot if you simply face west one hour after sunset. Arcturus will be the brightest object in the western sky. At that time, planet Jupiter will be the only object in the sky that’s brighter; it’s the blazing star-like object in the southeast, over your left shoulder, so you shouldn’t confuse the two.

Arcturus is the fourth brightest star in the night sky, after Sirius (SEER-ee-uss), Canopus (kuh-NOPE-uss), and Alpha Centauri (senn-TARR-ee). Sirius is a winter star, and Canopus and Alpha Centauri are Southern Hemisphere stars. So, in the summer sky of the Northern Hemisphere, Arcturus rules.

Big and brilliant, Arcturus is 25 times the diameter of our Sun and 113 times as luminous. This orange giant star is the brightest luminary in the constellation of Bootes (Boh-OH-teez) the Herdsman. Arcturus is Greek for “guardian of the bear,” a reference to the star’s ancient association with its neighboring constellation Ursa Major (ER-suh). Ursa Major is the Great Bear, and the Big Dipper is the central star pattern or asterism of Ursa Major. Arcturus appears to trail the Great Bear, which moves counterclockwise around Polaris, the North Star. So you can see how fitting it is that we arc to Arcturus from the Big Dipper.

Arcturus lies 37 light years from Earth. A light year is the distance light travels in one Earth year, nearly six trillion miles. When you observe Arcturus, what hits your eyes is light that departed the star 37 years ago. You are receiving vintage starlight from 1971--starlight that began its journey the year that:

- China was admitted to the United Nations
- the voting age in the U.S. was lowered to 18
- Walt Disney World opened in Florida
- cigarette advertising ended on television
- Jim Morrison, lead singer of The Doors, was found dead in Paris
- Intel released the world’s first microprocessor
- Idi Amin took control of Uganda
- pocket calculators, floppy disks, and e-mail were invented
- the films Love Story and The French Connection were in the theaters
- Federal Express and Greenpeace were launched
- platform shoes and crushed velvet hot pants were all the rage

Stars are time capsules, and Arcturus is seriously retro.