Tea Party

Last week we located the Teapot, the picturesque asterism (star pattern) in the constellation of Sagittarius the Archer, and the nearby spot that marks the center of our Milky Way galaxy.

Now let’s take a closer look at the stars that make up the Teapot pattern.

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.

Star maps created with Your Sky

2) Look for the teapot shape low over the southern horizon and a little bit northeast of the Scorpion’s stinger. The Teapot is oriented with its curving handle on the eastern (left) side and the spout pointing toward the Scorpion on the right.

3) Let’s start at the top of the Teapot’s pointed lid. The star marking that spot is Kaus Borealis (KOWSS bore-ee-AL-iss), a blend of Arabic and Latin that means the northern bow, a reference to the Archer's weapon of choice. Kaus Borealis is an orange giant star.

Continuing clockwise around the Teapot, we next come to Kaus Media (KOWSS MAY-dee-yuh), Arabic and Latin for the central bow. Kaus Media is also an orange giant star.

4) Next in line is Alnasl, at the point of the spout. Alnasl (all-NAH-zull) is from the Arabic for the arrow’s point. And you may recall from my previous post that Alnasl points the way to the galactic center. Do you get my point?

5) At the bottom right corner of the Teapot’s base is Kaus Australis, the brightest star in Sagittarius. Kaus Australis (KOWSS aw-STRAH-liss) is Arabic and Latin for the southern bow. Kaus Australis is extremely bright, around 375 times more luminous than our Sun. There is some debate about its color; it may be either a blue or a white giant star.

Now you know the trinity of stars (Kaus Borealis, Media, and Australis) that delineates the curve of the Archer’s bow. But this is no ordinary two-legged archer. The ancient figure of Sagittarius is a bow-and-arrow-wielding centaur; a centaur is a mythological four-legged creature that’s half human, half horse.

Sagittarius in Johann Bode’s 1801 star atlas
Courtesy of Linda Hall Library of Science, Engineering and Technology

6) The bottom left corner of the Teapot’s base is marked by Ascella (uh-SELL-uh), Latin for armpit. Ascella is a binary system, that is, two stars in orbit around each other. Both of Ascella’s component stars are white stars of nearly the same brightness. With the naked eye, we see their combined light as one star.

7) The lower star on the Teapot’s handle has no traditional name, so we call it Tau for its Greek-lettered star catalog designation. The upper star, however, is Nunki, the second brightest star in Sagittarius. The name Nunki (NUNN-kee) is of Sumerian origin, and it may have something to do with a holy city in the sky. Nunki is a blue-white dwarf star.

Finally, where the upper end of the handle attaches to the Teapot is Phi, another star with no traditional name.





8) Do you take milk with your tea? If so, you’re in luck. Just connect the dots of Ascella, Tau, Nunki, Phi, and Kaus Borealis to make the asterism known as the Milk Dipper.

And to stir your fragrant libation, use the Teaspoon, the dainty four-star asterism that looks like a spoon viewed from the side. It’s floating northeast of the Teapot’s handle, at the ready.

Astronomy Essential: Massive stars die in supernova explosions.

Stars much more massive than our Sun typically die in cataclysmic explosions called supernovas.

A massive star evolves through nuclear fusion into an onion-like structure of layered, increasingly heavy elements terminating with an iron core. Eventually, the iron core collapses and violently rebounds, creating a shock wave that blasts the surrounding stellar material outward.

The resulting cloud of gas and dust— which contains the elements necessary for human life— expands into space and is eventually recycled into new stars.

The Center of the Galaxy

Of the many naked-eye, binocular, and telescopic treasures to be found in the summer constellation Sagittarius the Archer, none fires the imagination like the one we can’t actually see.

Just off the spout of the Archer’s central asterism, the Teapot, lies the spot that marks the direction of the center of the Milky Way, our home galaxy. An asterism is a recognizable star pattern, and the Teapot is a prime example of why amateur astronomers use asterisms to navigate the sky, not ancient, obscure constellation patterns.

I defy anyone to spot a centaur sporting a bow and arrow in the jumble of stars that is Sagittarius. But happily, the brighter stars in that region of the sky collectively resemble a teapot, an object with which we are perhaps a bit more familiar. The softly glowing billows of the Summer Milky Way intersect with the Teapot in a way that suggests steam vigorously issuing from the spout.

We can’t see the center of our galaxy in visible light because of the obscuring dust that lies between us and the galactic core. However, astronomers use cameras that operate in the infrared and radio wavelengths of light in order to “see” past that dust.

Composite image of the center of the Milky Way, in visible and infrared wavelengths
Credits: NASA, ESA, Q.D. Wang (University of Massachusetts, Amherst), Jet Propulsion Laboratory, and S. Stolovy (Spitzer Science Center/Caltech)

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.

Try to observe from a dark site, away from urban light pollution, so you can enjoy the picturesque “steam” rising from the Teapot.

2) Look for the teapot shape low over the southern horizon and a little bit northeast of the Scorpion’s stinger. The Teapot is oriented with its curving handle on the eastern (left) side and the spout pointing toward the Scorpion on the right.

Star map created with Your Sky

3) The galactic center lies in the glowing band of the Milky Way, our edgewise view of our platter-shaped galaxy. As shown on the star map, the Teapot’s spout points the way.

Since our eyes aren’t up to the task of penetrating the thick dust separating us from our quarry, we’ll just have to use our imagination. We can imagine the massive cluster of stars that congregate at the bustling galactic core. We can imagine the star-strewn pinwheel-shaped arms of our spiral galaxy radiating out from that core. And if we squint, perhaps we can even imagine the supermassive black hole that lurks at the heart of our home galaxy, a reassuringly distant 26,000 light years away.

Astronomy Essential: Visible light is just a small portion of the electromagnetic spectrum.

Light is a form of energy that travels in different wavelengths. Collectively, these different wavelengths of light are called the electromagnetic spectrum. Separately, we know them as gamma rays, X-rays, ultraviolet or UV, visible light, infrared, microwave, and radio. Gamma rays have the shortest wavelength and radio has the longest wavelength, up to several miles in length.

Notice that visible light, what we humans can see, represents just one wavelength on the electromagnetic spectrum. That is why astronomers use cameras with special detectors to capture data from the other wavelengths— the ones that remain hidden to our eyes.

Can you imagine a species that could see in all wavelengths of light?!

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.