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.