The Snake Handler

We continue our exploration of the prominent summer constellation Ophiuchus the Snake Handler (oh-fee-YOO-kuss) with a closer look at the stars that make up its central asterism, the Coffin.

Asterisms are recognizable star patterns that help us navigate around the sky and figure out which constellation we’re in. The Big Dipper is an example of a more well-known asterism; it’s a star pattern within the constellation of Ursa Major the Big Bear.

Although the largest summer constellation, Ophiuchus is virtually unknown except among seasoned sky observers. Perhaps its difficult spelling and pronunciation have something to do with that. Perhaps it pales in comparison to neighboring constellations Scorpius the Scorpion and Sagittarius the Archer, which are each favored with brighter stars and more distinctive star patterns that really jump out at the observer. And perhaps it’s a conspiracy perpetrated by astrologers.

OK, just kidding on that last one. But it is interesting to note that Ophiuchus is, in effect, the thirteenth sign of the zodiac. The zodiac is the daisy chain of constellations that encompasses the paths the Sun, Moon, and planets take across the sky, as seen from Earth. In addition to the 12 conventionally-known zodiacal constellations, the Sun, Moon, and planets travel through Ophiuchus. And there have certainly been babies born while the Sun was in Ophiuchus. Yes, there are some Snake Handlers out there masquerading as Archers and Scorpions.

The band of the zodiac
Diagram by Dr. Guy Worthey

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.

Looking south to Scorpius and Ophiuchus
Star maps created with Your Sky

2) Locate the distinctive curve of the scorpion’s body, just above the southern horizon. Ophiuchus essentially rides on the back of the scorpion. So look north of the scorpion for the large Coffin asterism, which comprises the brightest stars in Ophiuchus. It’s known as the Coffin because it resembles an old-fashioned casket with a pointed head.

The stars of the Coffin asterism

3) The brightest star in Ophiuchus marks the pointed top of the Coffin. Its name, Rasalhague, comes from the Arabic for head of the serpent collector. Rasalhague (RAH-sahl-hayg) is a white giant star, as much as four times more massive than our Sun.

4) Moving counterclockwise around the Coffin from Rasalhague, we next come to Cebalrai, an orange giant star. Cebalrai (SEH-buhl-rye) is from the Arabic for the shepherd’s dog, a reference to an ancient Arabic tradition that saw that part of the sky as a pasture.

5) Next we come to Sabik, at the base of the Coffin. Sabik (SAH-bick) is the second brightest star in Ophiuchus, and its name is from the Arabic for the leading one. Sabik is a binary, that is, two stars in orbit around each other. In this case, both stars are white and of nearly the same brightness. Although we are seeing the combined light of two stars when we look at Sabik, it appears to the naked eye as one star.

6) The star in the middle of the Coffin’s base has no traditional name, so we call it Zeta after its star catalog designation. Zeta is a blue-white dwarf star. The next Coffin star, marking the western corner of the base, is Yed Prior. Yed Prior, a combination of Arabic and Latin, means the foremost hand. This star marks the left hand of the snake handler, the one that grasps the snake’s head. Yed Prior is a red giant star.

7) Finally, we complete the Coffin back up at the pointed end with Kappa, another star with no traditional name and known only by its star catalog designation. Kappa is a white star.

For a look at a few of the Snake Handler’s deep-sky delights for binocular and telescope viewing, visit my previous post and the one before that.

Ophiuchus in John Flamsteed’s 1729 star atlas
Courtesy of Linda Hall Library of Science, Engineering and Technology

Those of you in the health care field may be interested to know that in Greek mythology, Ophiuchus was identified with Aesculapius (ess-kyoo-LAY-pee-yus), the god of medicine. Perhaps there is an ancient connection between Ophiuchus/Aesculapius and his sinuous snake, and the caduceus (kuh-DOO-shuss)— the staff with two entwined snakes that has come to symbolize a physician.

A caduceus
Drawing by Rama and Eliot Lash

Astronomy Essential: One fifth of the world’s population can’t see the Milky Way.

Light pollution— excessive and inappropriate use of artificial night lighting— has impacted humankind’s view of the night sky. One-fifth of the world’s population can no longer see the glowing band of the Milky Way, because the sky is washed out by artificial light, much of it directed upwards. This phenomenon is at its worst in the United States, where two out of three residents cannot be inspired and awed by a view of their home galaxy.

Using properly shielded light fixtures that direct light only onto the ground, where it is needed for safety and security, is one effective solution to the problem.

Gobs of Globs

Note: There will be no August 6 post so that I may prepare for a She Is An Astronomer outreach event. Enjoy the July 30 post or browse my older posts. I'll be back with a new post on August 13.

Last week we looked at a bright open cluster in the summer constellation Ophiuchus the Snake Handler. Now let’s look at a different type of star cluster of which Ophiuchus contains a plethora: the globular cluster.

Globular clusters, or “globs” as they are commonly known, are dense balls of gravitationally bound stars. There are at least 150 known globs in our home galaxy, the Milky Way. Globs contain tens of thousands to millions of stars.

A number of the brighter globs that can be spotted from the Northern Hemisphere are found in the Messier catalog (MESS-ee-yay). This is the catalog of deep-sky objects compiled by the famed 18th century French astronomer Charles Messier, who observed from the rooftops of Paris. The Messier catalog contains some of the finest binocular and telescope objects in the night sky and is widely used by amateur astronomers as an observing list.

With seven each, Ophiuchus (oh-fee-YOO-kuss) and Sagittarius contain more Messier globular clusters than any other constellation.

If you’re not sure how to locate Ophiuchus, read last week’s post. The map below shows the locations of the Messier globs that call the Snake Handler “home.” Try spotting them with binoculars from a dark site, orienting from the Coffin asterism in Ophiuchus. Most should be visible as small fuzzy balls in modest-sized binoculars like 7x35s or 7x50s. The globs M9 and M107 will be tough to impossible, so don‘t bother with those. Use the binocular targeting tip I’ve discussed before.

The Messier catalog globular clusters in Ophiuchus
Star maps created with Your Sky

Now try observing them all with a telescope, if you have one. Depending on how much aperture (diameter of your primary lens or mirror) you have, you’ll either see a larger, brighter fuzzy ball or you’ll begin to resolve the cluster, that is, separate the stars into distinct points of light. Once resolved, you’ll see why I call globular clusters “galactic sugar piles.”

One theory among astronomers is that globs are the cores of ancient galaxies that collided with the Milky Way. All the outer stellar material was ripped from the galaxies and shredded by our home galaxy's powerful gravitational force. What remains are the densely star-packed galactic cores, studding the Milky Way like trophies on a hunter’s wall.

It’s a jungle out there.

Astronomy Essential: There is gravity in space.

There is gravity everywhere, since it's produced by all objects with mass in the universe. Its force, however, decreases with distance.

The “weightlessness” or “Zero G” (zero gravity) that an astronaut experiences in space is caused by the balancing act between the centrifugal force on his body and the gravitational force on his body.

In other words, Earth’s gravity— although a little weaker at that distance— is still pulling him towards the planet. However, the centrifugal force of his orbiting spacecraft propels him outward, away from the center of rotation (Earth), thus canceling out the effect of the gravity.

Caroline and the Cluster

If you ask an amateur astronomer to name a famous female astronomer, the first one who leaps to mind will most likely be Caroline Herschel (1750 to 1848). Sister to the renowned astronomer and Uranus discoverer William Herschel, she was an accomplished observer in her own right.

Although born in Germany, William and Caroline emigrated to England, where William became the royal astronomer to King George.

Caroline’s discoveries included eight comets; in fact she was the first woman to discover a comet. She also discovered 14 deep-sky objects, and she catalogued many stars and nebulas. The diminutive Caroline’s primary instrument was a modest-sized reflecting telescope, around four inches in diameter.

Let’s take a look at the brightest deep-sky object she discovered: the open cluster IC 4665 in Ophiuchus the Snake Handler. It is appropriate that we search for it in July, as she discovered it on July 31, 1783.

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.

Looking south to Scorpius and Ophiuchus
Star maps created with Your Sky

2) Locate the distinctive curve of the scorpion’s body, just above the southern horizon. Ophiuchus (oh-fee-YOO-kuss) is a large constellation that essentially rides on the back of the scorpion. So look north of the scorpion for a large asterism (star pattern) known as the Coffin, which comprises the brightest stars in Ophiuchus. It’s known as the Coffin because it resembles an old-fashioned casket with a pointed head. We’ll take a closer look at the Coffin stars in a future post.

The Coffin asterism of Ophiuchus with open cluster IC 4665

3) Point your binoculars or small-aperture telescope just above the star Cebalrai (SEH-buhl-rye) near the top of the Coffin. You don’t want to use a large-aperture (large-diameter) telescope or a lot of magnification for an object like this with a large apparent size (the amount of sky it covers from our perspective on Earth).

Can you spot the open cluster IC 4665? An open cluster is a loose collection of stars that formed around the same time in the same nebula (gas and dust cloud). You might want to think of an open cluster as a sort of family group. IC 4665 has around 30 members in its family.

Open cluster IC 4665

Image credit: Digital Sky Survey

Hats off and a tip of the teapot to Caroline Herschel, astronomer.

Astronomy Essential: Shooting stars are meteors.

The phenomenon we call a “shooting star” is actually a bit of space rock or dust called a meteoroid burning up as it enters Earth’s atmosphere. The streak of light produced as the meteoroid is incinerated is called a meteor. Most meteoroids are very small: the size of grains of sand or grains of rice. It is the high entry velocity of the particles that produces the lovely light show.

Occasionally, larger meteoroids will survive their high-speed encounter with Earth’s atmosphere and hit the ground; these rocks are known as meteorites.