Thursday, January 29, 2009

Kids, More Kids, and Something Fishy

Last week we located the constellation of Auriga the Charioteer and explored its central asterism (recognizable star pattern), the Pentagon.

Now let’s take a closer look and see if we can spot three smaller, quirkier asterisms.

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

1) About an hour after sunset, locate the Pentagon. Consult last week’s post if you need help finding it.

The Pentagon of Auriga
Star maps created with
Your Sky

2) Just south of bright Capella is a small triangle of stars. This is the asterism known as the Kids, a reference to the two baby goats being cradled by the ancient figure of the Charioteer. The three stars are all dimmer than any of the five stars of the Pentagon.

The brightest of the three is Almaaz, which is Arabic for he-goat. (Do you recall which star in Auriga has a name that means she-goat?) Almaaz is a yellow-white supergiant that undoubtedly will expire someday in a cataclysmic explosion called a supernova.

The other two dimmer stars of the Kids asterism are called the Haedi, Latin for the kids.

Asterisms in Auriga

3) Hoofing it across the Pentagon, south of Menkalinan, look for another small triangle of stars that resembles the Kids, if the Kids were dimmer and upside down. This is the asterism called the Little Kids.

4) Finally, look inside the Pentagon, down toward its “base.” If you’re in a dark location, free of light pollution, you’ll see an elongated patch of light. This is the combined light from a string of four naked-eye stars plus a couple dimmer ones, and this is the asterism known as the Minnow. Can you see the silvery flash of its scales as it navigates the currents of the Milky Way?

Astronomy Essential: Polaris, the North Star, is NOT the brightest star in the night sky.

Many beginning stargazers have trouble picking out Polaris (poe-LAIR-uss) because they figure the North Star must be really bright and flashy. But on the scale of cosmic bling, it’s not much of a sparkler. In fact, it’s number 48 on the brightest-stars hit parade.

The importance of Polaris lies in its location, not its magnitude of brightness. It lies very close to the North Celestial Pole, the imaginary fixed point in the sky that the Earth’s axis would intersect, were it extended from the North Pole into space. Therefore, if you locate Polaris and face it, you’ll be facing geographic north, also known as true north.

To learn how to locate Polaris using the Big Dipper, visit this post.

By the way, the brightest star in the night sky is Sirius, aka the Dog Star, found in the winter constellation of Canis Major, the Big Dog.

Thursday, January 22, 2009

The Purloined Pentagon

Just north of Orion the Hunter and the horns of Taurus the Bull lies a distinctive pentagon of stars. You may recall from murky memories of high school geometry that a pentagon is a five-sided closed figure. This starry pattern is an irregular pentagon, since its five sides are not equal in length.

The celestial Pentagon is an asterism (recognizable star pattern) containing the brightest stars in the constellation Auriga the Charioteer (aw-RYE-guh). Let’s take a closer look.

1) About an hour after sunset, 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) Locate the Hourglass asterism of Orion, rising in the southeastern sky. Above it are the business ends of Taurus’s deadly horns. Keep going north past them to locate the Pentagon.

3) The brightest star in the Pentagon is a tad brighter than both Betelgeuse and Rigel, the two brightest stars in the Orion hourglass. This is Capella, the sixth brightest star in the entire night sky as seen from Earth. Capella (kuh-PELL-luh) is from the Latin for she-goat. It’s a yellow-white star, only 42 light years away.

4) Next to Capella, moving counterclockwise around the Pentagon, is the second brightest star in Auriga, Menkalinan (menn-KAH-lih-nan). Its name is from the Arabic for shoulder of the rein-holder. Menkalinan is a white star.

5) The second brightest star in the Pentagon is not Menkalinan, and it’s not in Auriga. To make the Pentagon shape, we must purloin a star from Taurus. This star is Elnath, the tip of Taurus’s northern horn. Elnath (EL-noth) is from the Arabic for butting with the horns. Elnath is a blue-white giant star.

We’ll continue our exploration of Auriga in more depth next week. See you then!

Astronomy Essential: There is no dark side of the Moon.

Pink Floyd megahit notwithstanding, there is no such thing. The Moon has no side that is always dark. The entire surface of the Moon is illuminated by the Sun at one time or another during its month-long orbit around the Earth. However, only half of the Moon’s sphere can be illuminated by the Sun at any given time (shine a flashlight at a baseball, and you'll get the idea).

Although the Moon has no dark side, it does have a far side that always faces away from Earth. Because the Moon’s rotation (spin around its axis) is in lockstep with its revolution (orbit around the Earth), the same lunar hemisphere always faces us earthbound viewers.

If you could instead perch on the Sun awhile to observe the Earth/Moon system, you’d watch Moon circling Earth, turning just enough on its axis to keep the same face toward Earth as it went around. And from your vantage point on the Sun, you’d notice that— over the course of a month— your view of the Moon’s surface continually changed until you had seen it all.

Thursday, January 15, 2009


The meridian is the imaginary line in the sky that runs from north to south, passing through the zenith (the point directly above your head). This construct is useful because at any given time we can then say a particular star or other celestial object is “east of the meridian” or “west of the meridian.” If it’s west of the meridian, then we know it’s moving toward the western horizon or “setting.” If it’s east of the meridian, we know it’s “rising” or moving towards the meridian.

The exceptions to this are the stars and objects of the circumpolar constellations, the ones that—instead of rising and setting—endlessly circle Polaris, the North Star, counterclockwise. We’ll take a closer look at their motions relative to the meridian another time.

When an object crosses the meridian, we say that it is culminating. We might say, for example, “such-and-such galaxy culminates at 11:00 p.m.” This tells any astronomy geeks within earshot that that’s the time they want to drag their telescopes outside to look at that object. This is because an object’s culmination is the highest altitude it can attain above the horizon, as seen from a particular observing location on Earth.

Generally speaking, the higher an object is above the horizon, the better our view of it will be. This is because Earth’s atmosphere has a distorting effect on the object’s light as it travels to our eyes. When the object’s higher in the sky, we're looking through less of that distorting atmosphere.

An object’s culmination varies according to the observer’s latitude. For example, someone observing an object from Tucson, Arizona would see it culminate higher above the horizon than someone observing in Davenport, Iowa.

Triangle as tool in Bayer's 1603 star atlas
Courtesy of Linda Hall Library of Science, Engineering and Technology

Currently, about an hour after sunset, you can find one of the five smallest constellations in the northern hemisphere on or near the meridian. The pennant-shaped asterism (star pattern) at the heart of the constellation Triangulum the Triangle is a scalene triangle, having three sides of different length. Its distinctive shape has been known since antiquity, when it was associated with the fourth letter of the Greek alphabet, the triangular Delta. A number of classical star atlases depict the constellation as a drafting tool.

1) To find it, 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) In a dark site, away from bright lights, tilt your head back until you’re looking at the zenith. Triangulum will be near the zenith or slightly south of the zenith. It is east of the Great Square of Pegasus and southeast of the two star chains of Andromeda. Before hunting for it, note on the star map above how small it is compared to the Great Square.

3) The second brightest star in Triangulum marks the pointed end of the pennant and is the only one with a traditional name. This yellow-white star is called Mothallah (muh-THAH-luh), Arabic for triangle.

The brightest star, Beta, is a white subgiant surrounded by a disk of cool dust, which suggests it may have planets orbiting it. At the third point of the triangle is third brightest Gamma, a white dwarf rotating at least 100 times faster than our Sun.

4) Can you spot Triangulum Minus, a three-star asterism just south of the scalene triangle? With two sides the same length, it resembles an isosceles triangle. For over a century, Triangulum Minus was considered a constellation, but it was subsequently demoted by astronomers. These stars are pretty dim, with two of them approaching the limit of what the average person can see naked-eye, under dark skies.

Pinwheel Galaxy, M33

5) Although considered a minor constellation, Triangulum hosts one of the finest spiral galaxies in the night sky: the Pinwheel Galaxy, or M33. M33 is short for Messier (MESS-ee-yay) 33, the object’s number in the catalog of the famed 18th century French comet-hunter Charles Messier.

At a dark-sky location, you’ll be able to spot it even in binoculars, although you won’t see any detail. In a reflector telescope with six inches or more of diameter—assuming a dark location and good sky conditions—you should begin to see structure in the fuzzy mass. The more aperture (mirror diameter) you give this object, the more you’ll see.

It’s gorgeous (which, whenever possible, I like to say with a Hayley Mills/Pollyanna accent).

Astronomy Essential: Astronomy and astrology are NOT the same thing.

An astounding number of people use these terms interchangeably. Well-educated, degreed people, no less. Which is why I feel compelled to include this as an astronomy essential, to clarify the difference.

Astronomy is the scientific study of objects outside the Earth’s atmosphere. Astronomy is a science.

Astrology is the belief that celestial objects influence human beings and events, as well as the practice of divining this influence based on the positions of the celestial objects. Horoscopes, commonly seen in many newspapers and magazines, are astrological forecasts.

Thursday, January 8, 2009

Spock's Star

What exciting times we live in, cosmologically speaking. Last year, astronomers using the Spitzer Space Telescope’s infrared cameras discovered evidence of three giant Jupiter-like planets and two asteroid belts (in other words, a solar system) orbiting the star Epsilon Eridani (EPP-sill-ahn ee-RIDD-uh-nigh). At a distance of only 10.5 light years, this is the closest known solar system to ours.

Fans of Star Trek trivia may recall that Mr. Spock’s fictional home planet, Vulcan, was said to orbit either the star Epsilon Eridani or the star 40 Eridani. Both candidates for Spock’s Star are visible to the naked eye. Let’s see if we can spot them.

1) About two hours after sunset, 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.

2) You'll need a fairly dark location, away from bright lights. The bright Moon may interfere with your search since we’re approaching Full Moon on Saturday the 10th. If so, you may want to try again in the middle of next week when the Moon is rising later each night.

Star maps created with Your Sky

3) First locate the distinctive hourglass shape of the constellation Orion the Hunter, rising in the southeast. Draw an imaginary line between the two bright stars at the bottom of the hourglass, Saiph and Rigel. Then extend that line twice its length past Rigel. Make a right angle turn from that line and go south a short ways to the next fairly bright star. This is Zaurak (ZAW-rahk), Arabic for boat. Quite apropos, since we are now in the constellation Eridanus the River (ee-RIDD-uh-nuss). Zaurak is a little bit dimmer than Saiph.

4) Now look towards the two o’clock position from Zaurak, and you’ll see a pair of stars, side by side. The left star is Delta Eridani, and the slightly dimmer right star is none other than Epsilon Eridani, our first candidate for Spock’s Star and the site of the newly discovered solar system.

5) To find 40 Eridani, look towards the eleven o’clock position from Zaurak but a little farther in distance than Epsilon. You should come to a diagonal pair of stars that are close together, about half as far apart as the other pair, Delta and Epsilon. The star on the right is Beid (BEED), Arabic for eggs. The star on the left is 40 Eridani, our second candidate for Spock's Star. 40 Eridani’s traditional name is Keid (KEED), Arabic for eggshells. Beid and Keid are both dimmer than Epsilon.

We can only hope that, if a rocky Earth-like planet is discovered orbiting either Epsilon Eridani or 40 Eridani, astronomers will have enough good humor to officially name it “Vulcan.”

Astronomy Essential: The Sun is a star.

Maybe you already knew this. Maybe not. Or maybe you heard it once a long time ago, and then forgot all about it. Our experience of the Sun— how it fills our days with heat and light and makes our lives possible— is so different from our experience of the distant twinkle lights in the night sky. Perhaps then we may be forgiven if we sometimes forget that our Sun is just another star.

In its physical nature, it’s no different from the stars you see at night. It’s simply a whole lot closer. If we lived light years away on another planet orbiting a different star in the Milky Way, when we looked back at our Sun, we would see that it’s one star among many.

Our Sun is considered a yellow dwarf, because it shines with a yellow light and it’s smallish on the cosmic scale of star size. Although critically important to us Earthlings, and although we couldn’t do without it, the Sun is, well, average.

Thursday, January 1, 2009

The Universe, Yours to Discover

Welcome to the International Year of Astronomy (IYA). At long last, 2009 is here! Finally, those of us who bumble about in our backyards at all hours of the night, squinting at the night sky, can hold our heads up high. Even if we are wearing a combination of long johns, nightgown, and winter coat.

We-the-cosmically-curious uphold a 400-year-old tradition inaugurated by none other than the pioneering Italian astronomer Galileo Galilei. Every stargazer who strives to see more through binoculars or telescopes, every amateur telescope maker who grinds glass, every artist who sketches sunspots or moon craters at the eyepiece— they all walk in Galileo’s footsteps. He was the big kahuna who got this star party started.

Crayon portrait of Galileo by Leoni

In 1609, just one year after the invention of the refractor telescope, the enterprising do-it-yourselfer Galileo turned one of his own home-made instruments skyward. He became the first person to use a telescope to make a set of celestial observations, and he quickly made a series of remarkable discoveries. This was the birth of modern astronomy.

Four hundred years later, the International Astronomical Union, the United Nations, and 135 countries around the globe are launching a year-long celebration of the quadricentennial of the astronomical telescope and Galileo’s far-reaching discoveries. You can start your search for events and activities in your area on the IYA U.S. site: just click here.

For my part, I’ll be paying tribute to Galileo and the transformational power of astronomy by focusing my blogging efforts this year on cosmic literacy. In addition to pointing the way to interesting night-sky objects in the Milky Way, each post in 2009 will include a brief explanation— in plain English— of an astronomy fact that every Earthling should know. If you stick with me, at the end of the IYA, we’ll know quite a bit about both the night sky and the universe in which we live. We’ll begin next week.

So onward, fellow sky-watchers, into the International Year of Astronomy and beyond the wild blue yonder. And the next time the sheriff shows up to investigate your neighbor’s report of suspicious nighttime activity in your backyard, you can confidently assure him that your midnight muttering and puttering is sanctioned by the United Nations. As for your flannel cow-print pajamas, not to worry. The fashion police generally knock off at five.

Trifid Nebula, Milky Way