Once in a Blue Moon

Four hundred years ago, in Galileo’s time, a once-in-a-blue-moon event would occur, well, never, as the phrase referred to something so absurd as to be nonexistent. It would occur with the same frequency as, for example, hell freezing over.

In the 20th century, the expression came to mean a very rare event that, nonetheless, could actually happen. Astronomically speaking, Blue Moon came to refer to the second Full Moon in a calendar month, which typically occurs every two and a half years.

The Full Moon, with a few drops of artificial color

Tonight, on New Year’s Eve, as we leave behind the “oughts” of our brave new century and enter the “tens,” we can enjoy a view of a Blue Moon: the second Full Moon this month and the first Blue Moon to occur on New Year’s Eve since the close of 1990, nearly twenty years ago. Tonight the brilliant Moon waxes poetic, in what seems a perfect close to 2009, the International Year of Astronomy.

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Once in a blue moon, those of us who evangelize for astronomy get an opportunity to wear our hearts on our sleeves and have it fully sanctioned by such august bodies as the International Astronomical Union and the United Nations. The International Year of Astronomy, the quadricentennial of Galileo’s achievement, was certainly such an opportunity--if you seized it.

As I take stock of this past year, I feel gratitude for having been able to participate in communicating astronomy to the public during IYA--for having had the time, the resources, and the invaluable support of others in order to do so. It was an unforgettable adventure.

With a little help from my friends, I co-instructed weekend workshops in astronomy at a National Wildlife Refuge; gave slide show presentations at libraries; taught astronomy to gun-slinging women at an NRA facility; gave people views through my telescope at museums and public spaces; co-organized a free public astronomy event for girls; conceptualized a nonprofit science education organization which will launch next year; and began writing a second astronomy-related book (because working on one wasn’t challenging enough?!) I indulged myself in paying my passion forward, for whatever it may be worth.

Thank you to all who patronize my blog, especially those gracious individuals who leave comments. Thank you to my fellow astronomy enthusiasts who generously offered topic suggestions for this year’s “Astronomy Essentials” feature: Aileen O’Catherine, Barry Spletzer, Bob Havlen, David Nelson Blair, and Linda Hixon.

And thank you to everyone who this year said to me, “This is the first time I’ve looked through a telescope!” or “I never understood before what the Moon’s phases were!” or “Wow, look at those craters!”

Once in a blue moon, your heart is full.

Astronomy Essential: The Moon is visible during the day, nearly every day.

We tend to think of the Moon as a nighttime object, probably because its brightness is amplified against the dark backdrop of the night sky.

But, if you remember to look for it, you can find the Moon in the daytime sky. It’s visible with the naked eye for part of each day, nearly every day. The only times during its month-long cycle that the Moon doesn’t grace the daytime sky are: 1) Full Moon, when the Moon rises at sunset and sets at sunrise, and 2) a day or two surrounding New Moon, when it’s too close to the Sun in the daytime sky and is masked by the Sun’s glare. (Never ever look directly at the Sun!)

We see the Moon during the day both because it is so bright and close, and because it is in orbit around us and its “window of visibility” is always shifting relative to Earth’s day/night cycle.

Island Universe

Four hundred years ago, in 1609, the Italian astronomer Galileo Galilei turned his homemade telescope skyward and began a series of astronomical observations that would redefine human horizons. Among his discoveries was the realization that the Milky Way is a horde of stars too numerous and faint to be resolved with the naked eye. Before that telescopic revelation, the nature of the Milky Way--the name given to the hazy band of light stretching across the sky--was not known.

Over a century later, the German philosopher Immanuel Kant postulated that the Milky Way was a vast, disk-shaped collection of stars. He further suggested that the faint, fuzzy celestial clouds seen through telescopes and known as “nebulas” were large, distant collections of stars similar to the Milky Way. He called these nebulas island universes.

Although proof of the distance and separate nature of these island universes would not be acquired until Edwin Hubble’s work in the 1920s, Kant was correct. We merely had to wait another 150-plus years for our horizons to be again redefined: to learn that the Milky Way, our home galaxy, was not home to many of the so-called nebulas. The Milky Way was not the whole enchilada. There were other galaxies, other island universes, out there.

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When you look at the sky on a clear night from a dark location, at any given time you can see about 2500 stars with the naked eye. A telescope can reveal millions more. Regardless of whether you’re observing with the naked eye or the aided eye, every star you can see is in the Milky Way Galaxy. Essentially, you look out at the cosmos through the vast starfield of your home galaxy, your own island universe.

But you can also see beyond. In fact, there’s an island universe visible to the naked eye, if you observe from a dark site. Originally called the Great Andromeda Nebula, Hubble’s work confirmed its galactic nature, and it became known as the Andromeda Galaxy. At an estimated 2.5 million light years away, it is the most distant object that the average person can see naked-eye. It is the nearest spiral galaxy to the Milky Way, and it’s comparable to our home galaxy in size and mass. Looking at the Andromeda Galaxy is a bit like looking in the mirror, that is, on a galactic scale.

Andromeda Galaxy

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 the Great Square and the Chains of Andromeda
Star maps created with Your Sky

2) First, locate the Great Square asterism (star pattern) in Pegasus, high in the southern sky, on or near the meridian.











3) Next, find the Chains of Andromeda, the two strands of stars that arc upward and to the left of the star that marks the Square’s upper left corner. Now look above the middle star of the upper chain for a faint, fuzzy patch. A Persian astronomer of the 10th century called it the “little cloud,” an apt description.

If you can’t see it, you may need to try again at a darker site with less light pollution. Additionally, your sky transparency, or atmospheric clarity, can be negatively impacted by the presence of clouds, haze, dust, or humidity. This could impact your ability to see a faint object like the Andromeda Galaxy. If this is the case, you should try again when conditions are improved.

It’s worth a little extra effort for the thrill of seeing, with your own eyes, a world beyond your galactic neighborhood: an island universe where perhaps other curious skywatchers are turning their eyes toward you, and wondering.









Astronomy Essential: The universe has a dark side.

By studying gravity’s influence on the gas that exists between galaxies in galaxy clusters--gas that can only be seen in X-ray wavelengths of light--astronomers can determine how much matter there is in the cluster. Interestingly, these measurements show that there is far more mass present than can be accounted for by the ordinary matter in the cluster.

From these results, astronomers have deduced the presence of another type of matter that can’t be observed directly (at least not yet). They call this dark matter.

Discoveries in the 1990s that the expansion of the universe is speeding up and in 2003 that the universe is flat suggest to astronomers the presence of yet another substance in the universe, in the form of energy. They call this dark energy. Like dark matter, dark energy is not directly observable, but dark energy would account for the density needed to maintain both a flat universe and a universe whose expansion is accelerating.

Current estimates for the structure of the cosmos indicate that the ordinary matter with which we‘re familiar--matter made of atoms, such as trees, rocks, people, air, planets, and stars--constitutes less than 5% of the universe! The rest is mysterious, unseen dark matter and dark energy. Understanding their nature is one of the key areas of exploration in astronomy today.

Whale's Tail

Note: There will be no December 17 post. Enjoy this post or browse my older posts. I'll be back with a new post on December 24.

The brightest star in the autumn constellation Cetus the Whale is known by two traditional names: Deneb Kaitos (DENN-ebb KYE-tohs) and Diphda (DIFF-duh). The former is Arabic for whale’s tail, as the star marks the position of the celestial sea creature’s tail. The latter is more commonly used by amateur observers, and it’s from an Arabic phrase meaning second frog. The “first frog” is the nearby--and noticeably brighter--star Fomalhaut in Piscis Australis the Southern Fish.

Thar she blows!

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 the Great Square and Cetus
Star maps created with Your Sky

2) First, locate the Great Square asterism (star pattern) in Pegasus, high in the southern sky, on or near the meridian.

3) Now, let’s starhop. Using the two easternmost stars in the Square as pointers, draw an imaginary line between them and extend it towards the southern horizon. Traveling a little more than twice the distance between the two pointer stars, you’ll come to the bright star Diphda.

Can you discern a golden hue in the star’s light? Diphda is an orange giant star, nearly 150 times as luminous as our Sun. Of course, from our perspective nearly 100 light years away, it’s just another twinkle light in the autumn night sky. After all, one light year is nearly six trillion miles! So we can be forgiven if we think our Sun has more star power.

4) Reacquaint yourself with the “first frog,” Fomalhaut, to compare it to Diphda in color and brightness. Use the two westernmost stars in the Great Square as pointers this time. Draw an imaginary line between them and extend it towards the southern horizon. Traveling a little more than three times the distance between the two pointer stars, you’ll come to bright Fomalhaut, which will be closer to the southern horizon than Diphda.

Since Fomalhaut is a white star, try comparing the two, which may enhance Diphda’s subtle golden color. Fomalhaut’s brightness as seen from Earth, also known as apparent magnitude, is about two and a half times greater than Diphda’s, so you should discern a difference.

Astronomy Essential: The Milky Way is a barred spiral galaxy.

Our home galaxy was first determined to be a pinwheel-shaped spiral galaxy by radio astronomers in the 1950s, who began the on-going process of creating detailed maps of our galaxy’s structure. The curved “arms” of spiral galaxies--which radiate out from a dense galactic core--are regions of active star formation, which is why they are detectable in a variety of wavelengths and able to be mapped.

In 2005, new surveys of the galaxy in infrared light--conducted with the Spitzer Space Telescope--revealed a dense, bar-like congregation of stars cutting across the galaxy’s center. Extraterrestrial observers in other galaxies, positioned so as to have a face-on telescopic view of the Milky Way, would immediately recognize it as a barred spiral type.

Gibbous Moon

Note: There will be no December 3 post. Enjoy the November 26 post or browse my older posts. I'll be back with a new post on December 10.

The night sky is dominated right now by a waxing gibbous Moon, that is, a Moon that is more than half illuminated and that is growing in percent illuminated. Put another way, it is the phase of the Moon that occurs between First Quarter (also known as “Half Moon”) and Full Moon.

Once Full Moon occurs, our nearest celestial neighbor will enter its waning gibbous phase, when it is more than half illuminated and shrinking in percent illuminated. In other words, the waning gibbous Moon is the phase that occurs between Full Moon and Last Quarter (the other “Half Moon” phase).

If you’re curious about the etymology of these terms, as I was, you’ll find the following of interest.

“Wax” means to increase in size or intensity, and comes from the Old English weaxan, meaning to increase. “Wane” means to diminish in size or intensity, and comes down to us from the Old English wan, meaning deficient, and the Latin vanus, meaning empty. Finally, “gibbous” means marked by swelling, or humpbacked, and comes from the Latin gibbus, meaning hump.

Phases of the Moon
Credit: http://starchild.gsfc.nasa.gov/

So if the Moon appears humpbacked, it is gibbous. If the western--or right--side of the humpbacked Moon is illuminated, it’s waxing gibbous. If the eastern--or left--side of the swollen Moon is illuminated, it’s waning gibbous.

And if the slithy toves gyre and gimble in the wabe, it's plain gibberish.

Astronomy Essential: Stars do not twinkle.

Stars sometimes appear to blink on and off rapidly, dim and brighten wildly, and scintillate in a variety of colors. This “twinkling” is merely an optical distortion caused by the turbulence of Earth’s atmosphere, through which starlight must travel to reach our eyes. The starlight is “bent” in many random directions as it travels through atmospheric layers and pockets of different density and temperature. Our eyes interpret this bending or refraction of the light as twinkling.

This effect is usually most pronounced near the horizon, because the light from a star near the horizon must travel a longer path through the atmosphere to reach our position than it would if the star were positioned directly above us.

The next time you notice stars near the horizon twinkling, check the stars directly above you to see if they are in fact twinkling less or not twinkling at all.

Tropical Fish

There’s a third fish in the autumn sky, less heralded than the Pisces duo and--in the Northern Hemisphere--best seen from warmer latitudes such as the southern U.S. and Mexico. Considered a Southern Hemisphere constellation, this tropical creature is Piscis Austrinus the Southern Fish.

One would have to travel well south of the equator to, say, Santiago, Chile or Sydney, Australia in order to see Piscis Austrinus at the zenith, directly overhead. However, many northerners with a clear view of the southern horizon should be able to locate it easily because its brightest star is among the top twenty brightest stars in the night sky. Folks in far northern latitudes, such as Fargo, North Dakota, will have a bit more of a challenge because the star sits only about a fist-width above the southern horizon. A fist-width is the width of your fist, held at arm’s length against the sky, and measured across the knuckles.

Piscis Austrinus (PIE-siss aw-STRY-nuss) swims solo, south of Aquarius. In fact, the stream of water from the Water Bearer’s Water Jar has traditionally been depicted as pouring into the open mouth of Piscis Austrinus.

Piscis Austrinus (under Aquarius) in John Flamsteed’s 1729 star atlas
Courtesy of Linda Hall Library of Science, Engineering and Technology

I’m ready for a dip in warm, tropical waters. How about you?

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 Fomalhaut in Piscis Austrinus
Star maps created with Your Sky

2) Look south to find the Southern Fish, floating just east of the meridian. You can use the Bandanna of Capricornus to locate it, especially this year while the Bandanna is occupied by brilliant Jupiter. Jupiter is the brightest “star” you’ll see in the southern sky and the first celestial landmark to become visible after sunset.

3) The luminary you’re looking for is the only bright star in the Northern Fish and the only one with a traditional name: Fomalhaut. Fomalhaut (FOAM-uh-lott) is from the Arabic for mouth of the fish, and it marks the gaping maw of the oddly thirsty fish.

Only 25 light years away, this seemingly ordinary white star is surrounded by an emerging solar system four times the diameter of ours. A planet several times larger than Jupiter has been imaged in orbit around Fomalhaut.

It’s difficult to mistake Fomalhaut for any other star, since there are no other bright stars near it. In fact, Fomalhaut has been characterized by a number of writers as “lonely.” Once you spot it and take in the oceanic expanse of dark sky and dim stars around it, you’ll understand why its alternate classical name was Piscis Solitarius--the Solitary Fish.

Astronomy Essential: The zodiac is the band of 12 constellations that lie along the ecliptic.

The ecliptic is the imaginary line that represents the path the Sun appears to take across the sky, as seen from Earth. Because the Earth, the Moon, and the planets all lie in roughly the same plane as they orbit the Sun, the ecliptic can also be said to represent the plane of the solar system. This is why the Sun, Moon, and planets all appear to move along the ecliptic and through the constellations of the zodiac.

Although conventionally we say the Sun, Moon, and planets move “through” the zodiac, we need to remember that the stars of the zodiacal constellations are much farther away than the Sun, Moon, and planets. In essence, they form the backdrop for those solar system bodies.

The constellations of the zodiac are: Aries the Ram, Taurus the Bull, Gemini the Twins, Cancer the Crab, Leo the Lion, Virgo the Maiden, Libra the Scales, Scorpius the Scorpion, Sagittarius the Archer, Capricornus the Sea Goat, Aquarius the Water Bearer, and Pisces the Fishes.

The Ties That Bind

Last week, we located the most recognizable asterism (star pattern) in the constellation Pisces the Fishes: the Circlet. The Circlet marks the body of the Western Fish, the fish that points westward.

The other fish in the Pisces (PIE-seez) pair is the Northern Fish, the fish that points northward. Starting at the Circlet, let’s see if we can reel in the other fish on our line.

The Northern Fish (left) and the Western Fish (right) of Pisces
Courtesy of Linda Hall Library of Science, Engineering and Technology

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.

2) First, locate the Circlet. If you need help, consult last week’s post.

Looking south to Pisces

Star map created with Your Sky

3) Heading east from the Circlet is a streamer of eight naked-eye stars. This is the string binding the Western Fish. The terminal star--and the brightest in the string-- is called Alrescha. Alrescha (ahl-RESH-uh) is Arabic for the cord. It is also known as the Knot Star, because it marks the knot that binds the two strings--and the two fishes--together.

Alrescha is a binary star, that is, a system of two stars in orbit around each other. In Alrescha’s case, both are white dwarf stars. Because of their close proximity from our vantage point, we see their combined light as one star.

4) Heading northwest from Alrescha is the binding cord for the Northern Fish. From Alrescha, look for two bright stars spaced an equal distance apart. The second one, and the brighter of the two, is Kullat Nunu. It’s a little brighter than Alrescha. Kullat Nunu is Babylonian for cord of the fish. It’s a yellow giant and the brightest star in Pisces.

Beyond Kullat Nunu, the Northern Fish disintegrates into a jumble of not very bright stars with no readily apparent pattern to pick out. Suffice it to say that the ancients imagined a second succulent fish tethered there, ready for the fire.

Pass the tartar sauce, please.

Astronomy Essential: There are stars in the daytime sky.

If you could turn off the Sun during daylight hours--like you would turn off a light bulb--you would see a star-filled sky appear.

As the Earth spins, we are always looking out at the Milky Way and its legions of stars. During the day, those stars form a backdrop to the Sun. Consequently, they are--for the most part--not visible due to the Sun’s glaring brightness.

Ambitious amateur astronomers challenge themselves by trying to spot the brighter stars during the day, using a telescope as well as precise coordinates so they know where to point it. Popular daytime targets include: Castor and Pollux, the Gemini Twins; Rigel and Betelgeuse, brightest stars in Orion; Sirius, brightest star in our sky (after the Sun); and even not-so-bright Polaris, the North Star.

Circling the Circlet

Like Aquarius, Pisces the Fishes is another faint constellation that’s a little difficult to spot. But if you can find the Great Square of Pegasus, you can locate an asterism (recognizable star pattern) in Pisces and thereby orient yourself to the fishy constellation.

On classical star atlas maps, Pisces is typically represented as two fishes, each tied with a string at the tail, and the two strings joined with a knot. One fish heads west, and the other fish heads north.

Pisces is a constellation of the zodiac. The zodiac is a band of twelve constellations that straddles the ecliptic. The ecliptic is the imaginary line that represents the path the Sun appears to take across the sky, as seen from Earth. Because the Earth, the Moon, and the planets all lie in roughly the same plane as they orbit the Sun, the ecliptic can also be said to represent the plane of the solar system. This is why the Sun, Moon, and planets all appear to move along the ecliptic and through the constellations of the zodiac.

Pisces in Johann Bode’s 1782 star atlas
Courtesy of Linda Hall Library of Science, Engineering and Technology

Let’s circle our quarry.

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 the Circlet
Star maps created with Your Sky

2) First, locate the Great Square asterism in Pegasus, high in the southeastern sky.

3) Now look under the Great Square for a circular arrangement of five naked-eye stars. If you don’t see it, you’ll need to try again at a darker site, away from urban and suburban light pollution. This is the Circlet asterism, the most recognizable star pattern in Pisces. It lies a little east of the Water Jar asterism in Aquarius. The Circlet marks the body of what is known as the Western Fish, the fish that points westward.

The Circlet of Pisces

4) The stars in the Circlet do not have traditional names, but just west of the Circlet is Fum al Samakah, which is Arabic for fish’s mouth, and which marks the gaping mouth of the Western Fish. Fum al Samakah is a blue-white dwarf star, nearly 500 light years away (one light year is nearly six trillion miles).

Next time, we’ll locate the Northern Fish. Then you’re all invited to the fish fry.







Astronomy Essential: There are planets around other stars.

Thus far, astronomers have discovered over 350 planets orbiting stars other than our Sun. These are known as exoplanets. It seems the familiar eight planets of our solar system are not unique in the universe.

Astronomers use a number of methods to detect the presence of planets around distant stars. Orbiting planets can make stars wobble a bit, and that wobble can be measured to confirm the existence of a planet that can’t be directly observed. The periodic dimming of a star when an orbiting planet passes in front of it--that is, transits it from our perspective on Earth--can be measured. And in rare cases, exoplanets can be directly imaged.

The exoplanets found thus far are primarily gas giants and ice giants. The holy grail of current exoplanet detection research is to find terrestrial planets--rocky planets like Earth--orbiting in the habitable zone of their suns where, potentially, liquid water and life might exist.

The Water Jar

Between the Great Square of Pegasus and the Bandanna of Capricornus lies the rather nondescript constellation of Aquarius the Water Bearer.

Aquarius was traditionally depicted as a man upending an urn and pouring water into the mouth of a fish. A bizarre, inscrutable image, perhaps, but nevertheless, the way the ancients imagined it.

Saving the Aquarius constellation from obscurity are two bright stars and a little asterism (recognizable star pattern). Let’s see if we can spot them.

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

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 Aquarius the Water Bearer
Star maps created with Your Sky

2) First, locate the Great Square asterism in Pegasus, high in the sky, just east of the meridian, and the Bandanna asterism of Capricornus, low in the sky, just west of the meridian.

3) Now look between the Great Square and the Bandanna for two bright stars, Sadalsuud and Sadalmelik. Sadalsuud (sah-dull-suh-OOD), from the Arabic for the luckiest of all, is the brightest star in Aquarius. Sadalmelik (sah-dull-MELL-ick), from the Arabic for the luck of the king, is the number two Aquarian. Both stars are yellow supergiants, which is a relatively rare star type.

Don’t confuse them with nearby Enif, the nose of the winged horse Pegusus. Enif is a little brighter than the best and brightest of Aquarius.

4) Just east of Sadalmelik is a little “Y” of four fainter stars. This is the Water Jar asterism, which marks the position of the upended urn in the ancient star picture. If you can’t spot all four, you’ll need to try again at a darker site.

The Water Jar asterism of Aquarius

Of the four stars, only one has a traditional name: Sadachbia. Sadachbia (sah-DUCK-bee-yah), from the Arabic for luck of the tents, is a white star. We call the other three stars Eta, Zeta, and Pi, for their star catalog designations. Zeta, in the center, is the brightest star in the asterism.

Although Sadachbia is not the brightest of the Water Jar quartet, it clearly had enough significance to the ancients to be named and to be considered lucky like Sadalsuud and Sadalmelik. Perhaps whenever the early Arabs thanked their lucky stars, they had Aquarius in mind.

Astronomy Essential: We don’t see celestial objects the way cameras do.

Beginning stargazers are sometimes disappointed by their first telescopic view of a deep-sky object such as a galaxy, nebula, or star cluster. They expect the technicolor, high-resolution panoramas seen in Hubble Space Telescope images, which have become part of our public consciousness.

Instead they get small, fuzzy, black-and-white blobs.

What technology-savvy newcomers don’t realize is that human eyes are limited instruments. Collecting and integrating the faint light from distant objects— light that has traveled many trillions of miles to reach us— pushes our eyes to the limits of their ability. And in low-light situations, we don’t see color well. Compare that to the ability of an ultra-sensitive camera chip to detect extraordinarily faint light and integrate it over a long exposure time. Add to that the ability of specialized image-processing computer software to “stack” multiple images of an object, as well as color-correct the composite to approximate the color signatures of the chemical elements found in each celestial object.

What we can’t accomplish at the telescope eyepiece, we can accomplish at the computer keyboard.

At the end of the day, however, there is no substitute for looking at an astronomical object with your own eyes, collecting on your retinas those faint photons of light that have traveled many years to reach you, and discerning an image of a far-away world in real time, live, under your own power.

The Little Horse Head

Tucked between Pegasus the Winged Horse and Delphinus the Dolphin is the second smallest constellation in the sky: Equuleus the Foal. Equuleus (ee-KWOO-lee-yuss) is in fact the smallest constellation that can be seen from most latitudes in the Northern Hemisphere.

Like neighboring Pegasus, Equuleus is not a whole horse. Although the entire front half of Pegasus— head, front legs, torso, and wings— soars overhead, poor Equuleus must make do with a disembodied head. Make that an inverted disembodied head. Like Pegasus, Equuleus is upside down in the sky.

First mentioned by the Egyptian astronomer Ptolemy in the second century CE, the origin of the little horse head in the sky is unknown.

Pegasus, Equuleus, and Delphinus in J. Middleton’s 1842 star atlas
Courtesy of Linda Hall Library of Science, Engineering and Technology

You won’t need a carrot or a sugar cube to coax the stellar foal into view. You will, however, need a dark-sky location and you’ll need to be dark adapted, because his stars are not terribly bright.

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 Equuleus the Foal
Star maps created with Your Sky

2) First locate the Great Square of Pegasus asterism (star pattern) high in the southeast, and jutting out from it to the west, the right angle asterism that represents the neck and head of Pegasus. The star at the end of the right angle is Enif (EE-niff) which is from the Arabic for nose. Enif marks the snout of Pegasus.

3) Next locate the Dolphin asterism, the prominent star pattern in the little constellation of Delphinus the Dolphin (dell-FINE-uss). The head of Pegasus, punctuated by Enif, points to the Dolphin, which is currently on or near the meridian about an hour after sunset.

4) Now that you have your two celestial landmarks identified, look midway between Enif and the Dolphin— and then slightly south— to locate the four-star quadrilateral asterism that comprises the brightest stars in Equuleus. This asterism is known as the Horse’s Head.

5) The brightest of the four stars is Kitalpha (kitt-AL-fuh), from the Arabic for section of the horse. Kitalpha is a binary star, that is, a system of two stars in orbit around each other. In Kitalpha’s case, the two stars are a yellow giant and a white dwarf. Because of their close proximity from our vantage point, we see their combined light as one star. These two are so close, you won’t even be able to split them in a telescope.

6) The other three stars have no traditional name, so we call them (moving clockwise around the quadrilateral from Kitalpha) Beta, Delta, and Gamma for their star catalog designations. Delta is interesting in that it is also a binary star, with its two components a yellow-white dwarf and a yellow dwarf, the latter quite like our Sun. If you have a telescope, try splitting the two components.

Delta and Gamma mark the snout of the upside-down foal‘s head. He surely must be related to Pegasus. He’s a chip off the old block.

Astronomy Essential: The universe is 13 billion years old.

Currently the best estimate as to the age of our universe is 13 billion years (and change). In other words, 13 billion years have elapsed since the Big Bang.

Astronomers calculate this primarily by: 1) determining the age of the oldest stars, and 2) measuring the rate at which the universe is expanding and then extrapolating that back to the compressed state of the Big Bang.

In turn, identifying and dating the oldest stars is dependent upon what astronomers’ have learned thus far about star mass and about the life cycles of stars.

Measuring the universe’s rate of expansion is dependent upon astronomers’ knowledge of the current density and composition of the universe. In addition, they can peer back in time by observing and mapping the cosmic microwave background radiation, the afterglow of the Big Bang and the oldest light in the universe.

Get Out Your Bandannas

Note: There will be no October 15 post. Enjoy the October 8 post or browse my older posts. I'll be back with a new post on October 22.

Let’s wrap up our exploration of Capricornus the Sea Goat with a telescopic look at one of my favorite deep-sky objects: the globular cluster Messier 30.

Globular clusters, or “globs” as they are called in the astronomy community, are dense balls of gravitationally bound stars. There are at least 150 known globs scattered about 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 110 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.

Globs are my favorite type of deep-sky object, and Messier 30— or M30 as it is commonly known— is one of my favorites because of its irregular shape. I find the globs that are a bit asymmetric, rather than perfectly spherical, to have the most visual appeal.

Use the star map below to locate M30, just to the left (east) of the Bandanna asterism. If you have a dark sky (Moon-free and light pollution-free), try spotting it with binoculars first. If successful, you’ll see a small fuzzy ball, something like the end of a Q-tip.

Messier 30 in Capricornus
Star maps created with Your Sky

But honestly, M30 is one of those objects that is best examined in a telescope. Depending on your aperture (diameter of the primary optical element)— which dictates your telescope’s ability to collect light from faint celestial objects— you may begin to resolve the cluster. If so, the stars in the cluster will begin to separate into distinct points of light, and you’ll be able to truly appreciate M30’s endearing quirkiness.

Once you’ve located M30 with a low-power eyepiece (high mm number), switch to a high-power eyepiece (low mm number) and pump up the volume. This object warrants the most magnification you can muster.

Globular cluster M30
Source: NASA/ESA

Honk if you love globs. Or just wave your bandanna.

Astronomy Essential: Human eyes can adapt to the dark.

Seasoned night-sky observers typically go through a ritual called dark adaptation prior to embarking on an evening of stargazing. Dark adapting involves avoiding all white-light sources for 20 to 30 minutes, which prepares their eyes for enhanced seeing in the dark.

In a dark environment, first the human eye responds with pupil dilation. Next, chemical changes occur in our retinas’ receptors: the rods and cones. The rods become super-sensitized to light, thereby enabling us to see in low-light conditions.

As you can imagine, dark adapting— and then avoiding bright light once adapted— results in greater success seeing faint celestial objects through binoculars or telescopes, as well as with the naked eye. Astronomers maintain their dark adaptation by using red-light flashlights, since red light does not interfere with night vision.

The Sea Goat Revisited

In my previous post I introduced you to Capricornus the Sea Goat and its defining asterism (star pattern), the Bandanna.

This time, let’s take a look at the more prominent stars of the Bandanna— the ones with traditional names. They all lie along the top of the Bandanna. If you need help locating Capricornus, review my previous post.

The top left corner of the Bandanna is marked by Deneb Algedi, from the Arabic for tail of the goat. Deneb Algedi (DENN-ebb uhl-JEDD-ee), the brightest star in Capricornus, is a white star that lies about 39 light years away. A light year is the distance light travels in one Earth year, nearly six trillion miles.

The Bandanna of Capricornus
Star maps created with Your Sky

Moving right (or west), the next bright star is Nashira (nah-SHEE-rah). Its precise meaning in Arabic is unclear, but it references “luck.” Nashira is also a white star, but it lies nearly 100 light years farther away than Deneb Algedi.

Traveling across the top of the Bandanna toward the upper right corner, we next come to Dabih. Dabih (DAH-bee) is from the Arabic for luck of the slaughterer, a reference to the seasonal sacrifice made by Arabs when Dabih first appeared in the dawn sky before sunrise. Dabih is a binary system, that is, two stars in orbit around one another. The brighter of the pair is an orange giant, and the companion star is a blue-white giant. You should be able to “split” Dabih, that is, separate the two component stars, using binoculars.

The upper right corner of the Bandanna is marked by Algedi, Arabic for goat. Algedi is also two stars, but unlike Dabih, the two components are not gravitationally associated. They simply appear close together by line of sight from Earth. This type of double star is called an optical double. Coincidentally, both components of Algedi are yellow stars, similar in temperature to our Sun.

If you have keen eyesight, you should be able to split Algedi with the naked eye. If this proves difficult, the magnification provided by a pair of binoculars will bring you certain success.

Astronomy Essential: Constellations are three-dimensional.

We experience the night sky as if it’s an upside-down bowl, painted black, with an artistic sprinkle of luminous white dots. In other words, we experience it as a two-dimensional plane.

The connect-the-dot star pictures of the ancients, persisting across the centuries, do nothing to disabuse us of this notion.

We stargazers must, therefore, make a conscious effort to remember that the constellations and asterisms we use to navigate the sky are three-dimensional. Although we perceive a particular star pattern in two dimensions, the stars of that pattern are distributed in three dimensions. Some of the stars are relatively close to us, and some are relatively far from us.

If we could fly out into space and “through” a particular constellation, we would experience this first-hand. Zipping past each star in turn, we would finally see the third dimension— the depth— of space. We would finally understand that constellations and asterisms and any other patterns our brain seeks to make from random star positions are simply the artificial constructs of Earth-bound life forms with active imaginations.

The Sea Goat

Last night the cats fought over who would sleep under the blankets against human warmth and in the sheepskin-lined cat bed. It was a frantic feline version of musical chairs, and when the music stopped, it was every cat for him-or-herself.

This was my first clue that the first nip of autumn was in the air and that flannel sheet season was nigh. My second clue was the “prime time” prominence of fall constellation Capricornus the Sea Goat, which can be seen approaching the meridian from the east about an hour after sunset, when the sky’s just gotten good and dark. It will soon dislodge Sagittarius the Archer— just leaving the meridian, heading west— from its summertime domination of our view to the south.

Capricornus (kapp-rih-KORN-uss) is one of the twelve constellations of the zodiac. This band of constellations is significant because it straddles the ecliptic, the imaginary line that represents the path the Sun appears to take across the sky, as seen from Earth. Because the Earth, Moon, and planets all lie in roughly the same plane as they orbit the Sun, we see the Moon and the planets stick close to the ecliptic as they cross our sky.

You might say the ecliptic represents the plane of our platter-shaped solar system. But I like to think of it, and the zodiacal constellations that encompass it, as the celestial parade route upon which I’m sure to see a procession of planets float by.

Case in point: there are currently two planets passing through Capricornus, Jupiter and Neptune. Jupiter is easily seen with the naked eye; it’s the blazing “star” in the southeastern sky and the first luminary that pops out at you after sunset. Right now you can use Jupiter to help pinpoint the location of Capricornus, should you be unfamiliar with its star pattern.

Viewing Neptune (not a naked-eye object) requires a star map or software application that shows current planet positions, and large binoculars or a telescope.

Star map created with Your Sky

About an hour after your local sunset time, locate bright Jupiter. Using the map above and the relative position shown for Jupiter, trace out in the sky the star pattern shown. This is the asterism (recognizable star pattern) known as the Bandanna, and it contains the brightest stars in Capricornus.

Capricornus in Johannes Hevelius's 1690 star atlas
Courtesy of Linda Hall Library of Science, Engineering and Technology

Trust me, you’re far more likely to learn to recognize a stellar bandanna than a sea goat. I like Mesopotamian and Greek mythology— and tales of animal metamorphosis— as much as the next person. But honestly, what sort of perverse storyteller would find it necessary to graft a fish’s tail onto the head and body of a goat? It's so grotesque as to defy understanding, so perhaps we should just wave the white bandanna of surrender.

~ ~ ~ ~ ~

Here in the valley of the Rio Grande, the first nip of autumn means sweet relief from stifling summer heat along with the sweet smell of roasting New Mexican chiles. It also means I’ll be harvesting one of my favorite deep-sky objects from the telescopic depths of Capricornus. More on that later. Right now, I’ve got to air out my cozy flannel sheets and clean my high-power eyepiece.

Sweet.

Astronomy Essential: The four gas giant planets don’t have solid surfaces.

It’s hard to comprehend that no interplanetary traveler of the future will ever step out onto the surface of Jupiter or Saturn— even with the right protective space suit. Those gas giants are, as the name suggests, composed of gasses: primarily the elements hydrogen, helium, methane, ammonia, and oxygen.

On the two gas giants farthest from the Sun, Uranus and Neptune, the normally gaseous elements are believed to take liquid or semi-solid form. Gas-infused slush and frigid “seas” of liquid hydrogen, helium, methane, and ammonia make these two ports of call no less inhospitable than their vaporous neighbors.

Cassie's Cluster

Note: There will be no September 17 post so that I may prepare for the STAR-HOPPERS weekend workshop in astronomy for grandparents & grandkids. Enjoy the September 10 post or browse my older posts. I'll be back with a new post on September 24.

Messier 52 in the constellation Cassiopeia the Queen is one of my favorite open clusters. I like its rich star field and its somewhat fan-shaped appearance. I also consider it a big plus that it’s easy to find.

An open cluster is a loose collection of stars that formed around the same time in the same nebula (cloud of gas and dust). You might think of an open cluster as a sort of family group.

Messier 52, or M52 as it is commonly known, is one of the 110 celestial objects in the catalog of famed 18th century French astronomer and comet-hunter Charles Messier (pronounced MESS ee yay). This catalog is used extensively by amateur astronomers as an observing list, since it contains some of the “best and brightest” deep-sky objects in the night sky. Messier discovered M52 in 1774, while “chasing” a nearby comet.

M52 is easy to find because you can use the distinctive Lazy W asterism (star pattern) of Cassiopeia to locate it. Grab your binoculars, and let’s take a look at Cassie’s cluster.

1) About an hour after your local sunset time, face north. 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 left shoulder to the west, and you’ll be facing approximately north.

Looking north to Cassiopeia's Lazy W
Star maps created with Your Sky

2) Look for a W-shaped group of stars east of the meridian. This is the central asterism of Cassiopeia, the Lazy W. Cassiopeia is a circumpolar constellation, one that circles the North Celestial Pole, the imaginary fixed point in the sky directly above the North Pole. Luckily for us, there is a star extremely close to that point in the sky, which serves as a navigational marker. This is Polaris, the North Star.

Cassiopeia and the other circumpolar constellations appear to make a complete counterclockwise circuit around the North Star, over the course of one day. But they’re not really spinning around the North Star. This apparent motion, or the way they appear to move in our sky, is caused by the rotation of the Earth, as it spins on its axis like a top, 24/7.






3) From Shedar (SHEDD-er), the lower right star of the W, draw an imaginary line through Caph (KAFF), the upper right star of the W. Then extend that line the same distance again past Caph, plus a skosh. Train your binoculars on that spot, and you should see a fuzzy patch. With a small telescope, you’ll be able to resolve the stars in the cluster, that is, they’ll separate into distinct points of light.

M52 lies around 5,000 light years from Earth. One light year is the distance light travels in one Earth year, nearly six trillion miles. The cluster is estimated to contain 200 members.

The open cluster M52
Credit: AURA/NOAO/NSF

Two hundred family members in one place at the same time makes for quite a reunion. Pass the potato salad, please.







Astronomy Essential: The universe began with the Big Bang.

The Big Bang is a widely accepted scientific theory of the origin of the universe. It postulates that about 13.7 billion years ago, the visible universe was extremely dense and extremely small— about the size of a dime. This singularity suddenly expanded to create the large-scale universe, which continues to expand today.

Many astronomers accept that a Big Bang event is the best current explanation for some key observable features of the universe, such as: its continuing expansion from a smaller, denser state; the microwave radiation “glow” that is present throughout the universe; a consistent abundance of simple elements such as hydrogen and helium throughout the universe, even in the oldest objects; and a limit on the age of stars in the cosmos.

Horse Trade

In addition to the center of the galaxy, the spout of the Teapot asterism in the constellation of Sagittarius the Archer points to a whimsical naked-eye object in the Summer Milky Way. This object requires a dark sky to see it, but it’s worth a trip away from city lights.

The object is actually a two-fer, two objects in one economical package. Both are dark nebulas, and they lie across the “star river” of the Milky Way from the Teapot, in neighboring Ophiuchus the Snake Handler.

Dark nebulas (NEBB-yoo-luhs) were once thought to be empty areas in the sky where no stars existed. Now we know they are areas of thick dust— dust so dense it obscures the light of the stars behind it. Dark nebulas are sometimes named for the objects they resemble. It is human nature, after all, to attribute patterns or meaning to random visual events, for example, seeing animals or faces in clouds. This practice even has a name: pareidolia (pronounced pear-eye-DOH-lee-uh).

The first of our two objects is a dark nebula called the Pipe Nebula. You can see from the image below that it looks like the stem and bowl of a smoker’s pipe. This will be the easier of the two shapes to pick out.

For our second object, the Pipe becomes the hindquarters of a horse, and his front half extends away from the Milky Way, as shown in the next image. This is commonly known as the Prancing Horse Nebula.

You should be able to make out the equine's torso and head, as well as his raised front leg.

Here in the American Southwest, this object is more commonly known as the Burro Nebula, or simply the Burro. Burro is derived from the Spanish word for donkey and usually refers to the undomesticated version of that animal. There’s a wild burro population of about 3,800 in the American West. These animals are the descendants of those first introduced into the desert Southwest by the Spanish in the 1500s.

The Burro, with lowered head and upraised leg on the right, hindquarters on the left.

The glowing star cloud above him makes it look as though he is carrying a pack.
© T. Credner & S. Kohle, AlltheSky.com

You can have your prancing horse. I’ll stick with my burro. He eats a lot less.

Astronomy Essential: The Earth’s magnetic field protects us from the solar wind.

The Earth is a magnetic object, that is, it acts like a magnet, because it has an iron core. As with any magnet, the Earth generates a magnetic field that surrounds it. This magnetic field is called the magnetosphere.

The magnetosphere deflects the solar wind generated by the Sun. The solar wind is a stream of charged particles traveling at over one million miles per hour. Without the magnetosphere to protect it, Earth’s atmosphere would be vaporized by the solar wind.

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.