Thursday, August 27, 2009

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.