The Kids Are Far Out - part three

The final set of questions from the kids of Cosmic Carnival may be last, but they’re certainly not least. In fact, I think these three budding scientists asked questions which we should all consider. To do so is to begin to have some understanding of our place in the universe.

Ryan from Albuquerque, age 9, pondered this:

“I was wondering how thick the atmosphere is on Earth.”

A real brain teaser of a question, Ryan! There is no straightforward answer to this question because our atmosphere does not have clearly defined borders. As we go up in altitude, Earth’s atmosphere very gradually becomes thinner and thinner until it merges with outer space. So we could say the answer is 800 miles thick if we include the outermost layer, the exosphere, where the air is extremely thin.

Or we could use the altitude where space is officially considered to begin: 62 miles (100 kilometers) above sea level. So, the answer could also be 62 miles thick, since around 99% of the mass of our atmosphere is found below this point. You can read more about Earth’s atmosphere here.

The layers of Earth's atmosphere, bottom to top:
Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere

Image source: NOAA/National Weather Service

Scott from Rio Rancho, age 8, posed this question:

“How does the Earth spin around the Sun?”

Scott, we generally say that Earth spins (or rotates) on its axis, the way a top spins. We also say it orbits (or revolves) around the Sun. 24 hours a day, 7 days a week, our home planet is spinning like a top and traveling in an orbit around the Sun, at the same time.

Whenever you look east (the direction of the rising Sun), you are looking in the direction toward which the Earth is spinning, as well as the direction in which Earth is traveling as it circles the Sun.


Sophie from Albuquerque, age 9, was looking way beyond the solar system when she asked:

“If we’re in the Milky Way, how do we have pictures of the Milky Way?”

It’s a puzzle, isn’t it, Sophie? It’s true: we do reside in the Milky Way galaxy. In fact, every star you see in the night sky is in the Milky Way galaxy.

If you go stargazing out in the country, away from city lights, you will probably see what looks like a long, glowing cloud arching overhead from horizon to horizon. It’s actually a collection of billions of stars too numerous and faint to be resolved (separated into distinct points of light) with the naked eye, so we see it as a hazy band of light. We call this object the “Milky Way” too, even though it’s just part of our home galaxy. This is probably what you have seen in photographs, as it’s a popular target for astrophotographers.

The glowing “cloud” is an edge-wise view of the star-packed spiral arms of our platter-shaped galaxy. Even though we are in one of those arms (the Orion Arm), we can look across space at neighboring arms. The diagram below will give you a better picture of your place in space.

Diagram of the spiral arms of the Milky Way

Image source: Richard Powell

In conclusion, I have to admit that I seriously doubt I could have formulated any of these questions at the tender age of 8 or 9. I was a science ignoramus for my entire childhood and, indeed, much of my adult life. So, I am awed and inspired by the far-out kids I met at Cosmic Carnival, who are already looking up and wondering about the universe in which they live. I hope they never lose that sense of wonder.

Have you looked?

Carpe Cosmos

The universe waits for no one. Celestial events and phenomena are occurring all the time, some with more frequency than others. Astronomical objects are coming in and out of view— monthly, seasonally, cyclically.

None of these occur on your schedule or my schedule. They occur on their own schedule, on a cosmic schedule. It is up to us to make ourselves available to witness them, to be at the right place at the right time, so to speak.

You don’t necessarily need a pile of high-priced equipment to seize the cosmic moment. In fact, some of these spectacles are best viewed with the naked eye. A selection of my favorites are listed below. Pencil a few into your datebook, won’t you?

1) Total Lunar Eclipses. Lunar eclipses occur only at Full Moon. When the Sun, Earth, and Moon are aligned such that the Sun casts Earth’s shadow on the Full Moon, we experience a lunar eclipse. A lunar eclipse may be partial or total, depending upon the alignment of the three bodies. When all three line up so that the Moon is entirely within Earth’s shadow, it's called a total lunar eclipse, and the Moon turns red. Really! It’s a phenomenon that’s even visible in the city, and you won’t soon forget the eerie sight.

The next total lunar eclipse will occur on December 21, 2010. Totality begins at 12:40 a.m. Mountain Time (adjust for your time zone) and ends at 1:53 a.m. Mountain Time. It will be visible throughout North America.

You can practice with a partial lunar eclipse on June 26, 2010. This one’s pretty well placed for the continental U.S., with the exception of the East Coast. You’ll need to get up in the wee hours on the 26th and watch the Moon setting, just prior to sunrise. This is when you’ll see a portion of the Moon in shadow— at greatest eclipse, about 50 percent.

2) Meteor Showers. Comets leave behind clouds of debris when their orbits take them near the Sun. Subsequently, when Earth, on its orbit around the Sun, plows through one of these debris clouds, we experience a meteor shower.

The Perseids (PURR-see-yidds) are a reliable shower active from mid-July through the end of August. This year, they peak on the morning of August 12, 2010. The peak date, as well as a day before and a day after, are all good times to plan to view them. You’ll need to watch for them between midnight and dawn. This year should be optimum viewing, as the waxing crescent Moon will set before midnight and therefore won’t wash out the sky.

You won’t see many “shooting stars” in the city, so find yourself a dark site away from urban light pollution. A meteor shower is Mother Nature’s fireworks show. Don’t miss out.

3) Planetary Alignments. Because the planets all travel at different speeds around the Sun, they periodically catch up to one another. From our vantage point on Earth, the naked-eye planets can sometimes appear to be close to one another in the sky, as they pass. In addition, they may happen to be nicely placed near a crescent Moon, since the Moon is always changing position in our sky over the course of a month.

These picturesque groupings are called alignments, and the combination of bright objects makes an easy observing target even for city dwellers. Here are some nice upcoming alignments to watch for:

Looking west after sunset on July 31
Star maps created with Your Sky

On July 31, about a half hour after sunset, look west for a trio of bunched-up planets: Venus (the brightest), Mars (reddish-colored), and Saturn (golden-colored). Mercury is there too, but hanging low over the western horizon, so it will be a challenge.

Looking west after sunset on August 13

On August 13, about a half hour after sunset, look west for the aforementioned trio with the crescent Moon now joining them.

4) Milky Way. You might call this one the “main event,” as the Milky Way is our home galaxy. How wicked cool is it that we can look up at the night sky any time of the year and see an edge-on view of the spiral arms of our platter-shaped galaxy? Well, that is, if we get away from city lights. Unfortunately, 20 percent of the world’s population can’t see the Milky Way from where they live, due to light pollution.

Naked eye, we see what looks like a long filmy cloud stretching across the sky, but we know it’s composed of billions of distant stars. Yes, billions! If you haven’t experienced it, get yourself out to the country immediately if not sooner, and look up. You won’t be sorry.

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.

The Way

There are an estimated 100 billion galaxies in the universe, and we occupy just one of them, the Milky Way.

It was the great 20th century American astronomer Edwin Hubble who determined that many mysterious telescopic objects thought to be emerging solar systems were in fact galaxies— immense star systems lying beyond the Milky Way. The Milky Way was not, it seemed, the whole enchilada. This discovery expanded our cosmic horizons and gave us our first inkling of just how immense the universe was.






Since Hubble’s landmark discovery, we’ve learned quite a bit about our cosmic 'hood. We now know that the Milky Way is a barred spiral type of galaxy. A spiral galaxy is shaped somewhat like a pinwheel, with curved arms radiating out from a center that is densely packed with stars. In a barred spiral, the center has an elongated shape.

We also know that there’s a supermassive black hole lurking at our galaxy's center. A black hole is an object so dense that nothing— not even light— can escape from its gravitational field.

Courtesy NASA/JPL-Caltech

In addition, we’ve learned that the Milky Way contains around 400 billion stars. We know it’s around 200,000 light years in diameter; one light year is the distance light travels in one Earth year, nearly six trillion miles. Knowing these numbers doesn’t necessarily mean we mere mortals can fully grasp the size and distance involved. The implication for a short-lived species such as Homo sapiens is that space travel to other parts of our galaxy would require thousands of successive generations of people on each pioneering space ship.

However, like all the generations of our species that came before us, we can see the Milky Way on most any night. If we look skyward from a dark site away from urban light pollution, we can enjoy an edge-on view of the star-packed arms of our platter-shaped galaxy. Because the Milky Way is a horde of stars too numerous and faint to be resolved (separated into distinct points of light) with the naked eye, we see it as a hazy band of light arching across the sky. Some folks seeing the Milky Way for the first time mistake it for a long, lingering cloud.

The poetic name for our home galaxy comes to us from the Latin Via Lactea (Milky Way), which in turn derived from the Greek word for milk. A number of other cultures also saw the band of light as a stream of milk. But around the world, there have been numerous names given to this distinctive celestial object. Here are just a few:

- Silver River
- Winter Street
- Path of White Ashes
- Birds’ Way
- Straw Road
- Pilgrims’ Road
- Great Serpent
- River of Heaven
- Heavenly Girdle
- Road of Souls
and my personal favorite, from the Polynesians:
- Long Blue Cloud-Eating Shark

My pet name for the Milky Way is simply “the Way,” because it represents for me a way of being and a way of seeing. I learned an important lesson a number of years ago on a camping and observing trip in southern Arizona. I had spent the better part of a night glued to the eyepiece of my telescope, hunting various galaxies, globular clusters, and nebulas on an observing list and methodically ticking off those “faint fuzzies” as I found them. Straightening up from the eyepiece to stretch my back, I faced south and audibly gasped. The woods south of the clearing where I and my partner were observing were on fire!

After a few heart-pounding seconds, I noticed that the raging firestorm licking the sky above the trees was black-and-white. Black-and-white flames? Then it dawned on me that what I thought was a forest fire was the Summer Milky Way, which had risen in all its magnificence while I was attached like a barnacle to my telescope.

Because I am fortunate to live and observe in New Mexico, which has excellent observing conditions, I thought I had seen the Milky Way. But I had never seen it like I saw it that night. The combination of superb transparency (atmospheric clarity) and a deep, dark, black-as-the-ace-of-spades sky background made every tendril and wisp of the Way pop out in blazing, 3D relief.

I almost missed the finest view of the night, a deeply satisfying naked-eye spectacle that flickered across my retinas and seared itself into my memory. And here’s the strange lesson: sometimes even serious sky observers have to remember to just look up.

Giving Thanks

These are a few of my favorite things.


Dance of the Planets
Watching the naked-eye planets (Mercury, Venus, Mars, Jupiter, Saturn) rhythmically huddle and disperse is like watching an intricate dance. These planetary alignments are the result of our earthbound view of the naked-eye planets moving in their respective orbits around the Sun. Some are traveling faster than Earth; some are traveling slower. The resulting variety of configurations gives us a sense of the “clockwork of the universe” and reminds us that everything is in motion.

Solar system diagram created with Solar System Live

Be sure to look southwest after sunset on Monday, December 1, when Venus, Jupiter, and the crescent Moon will bunch up in the twilit sky. Venus will be the brighter of the two star-like objects you see, and Jupiter the fainter. The waxing (growing) crescent Moon will be about 15 percent illuminated.

While you're enjoying the alignment, look for earthshine on the Moon. Earthshine is sunlight reflecting off the surface of the Earth and illuminating the dark part of the Moon. Even though the bright crescent is the only part of the Moon’s face being directly illuminated by the Sun, if you look carefully, you’ll see that the rest of the Moon’s face is glowing faintly with reflected glory: earthshine.

Shooting Stars
Wishing on a “falling star” is one of the guilty pleasures of the stargazer. Even after you know that falling stars, aka "shooting stars," are meteors, you can still appreciate this charming holdover from early folkloric traditions.

A meteor is the streak of light we see in the sky when a bit of dust or space debris hits Earth’s atmosphere at high velocity. A meteor shower occurs when Earth encounters a stream of debris left behind by a comet’s close approach to the Sun. Sporadics are meteors not associated with a particular shower.

Meteor showers occur reliably around the same time every year, as Earth returns to the point in its orbit where the debris field lies. Whenever you like, you can find out what meteor showers are currently active by visiting this website and scrolling down to the Meteor Shower Calendar.

Meteor storm - 1889 engraving by Adolf Vollmy

If you’re lucky, you might someday see a meteor storm, a very intense meteor shower with a high frequency of meteors. One of my top ten stargazing experiences ever was viewing the 2001 Leonid meteor storm. The meteors came so fast and furious, it was a bit like watching a fireworks show. I was with a large group of fellow amateur astronomers at a dark-sky site, and the oohs and aahs from the crowd as particularly fine meteors blazed across the sky just added to the ambiance of the event. We all knew we were seeing something rather spectacular.

Cosmic Dust Bunnies
Interplanetary space is not empty. Our solar system contains a vast number of minute particles, some left over from the time of planet formation and some ejected from passing comets or asteroid collisions. Light from our Sun illuminates the myriad particles lying in the solar system plane, and sometimes we see the reflected sunlight as a luminous pillar of light called the zodiacal light.

The zodiacal light (zoh-DYE-uh-kull) is a large, roughly triangular or cone-shaped glow in the night sky, extending upwards from either the eastern or western horizon. The base of the triangle or cone— the widest part of the glow— is at the horizon. The zodiacal light is typically seen in the spring above the western horizon after sunset and in autumn above the eastern horizon before sunrise.

If you're fortunate enough to view the zodiacal light when transparency (atmospheric clarity) is good and the sky is inky black, you may notice the light pillar has a yellowish cast. Our Sun is, after all, a yellow star, so it shines with a golden light.

Cone-shaped glow of zodiacal light above sunset glow
Image source: ESO

The zodiacal light is subtle and can be quite challenging for the beginner to spot. A dark site away from urban and suburban night lighting is critical for success, as is avoidance of a moonlit night.

Believe me, this phenomena is worth a little extra effort. It’s quite a rush when you spot it, especially when you then start thinking about what you’re looking at— vintage dust from when the solar system formed. The goofy image that always pops into my head is the Sun as a clean freak with a big flashlight, showing us what lurks under the furniture.


The Way
My personal pet name for our home galaxy, the Milky Way, is simply “the Way,” because it represents for me a way of being and a way of seeing. I learned an important lesson a number of years ago on a camping and observing trip in southern Arizona. I had spent the better part of a night looking through the eyepiece of my telescope, hunting various galaxies, globular clusters, and nebulas on an observing list and methodically ticking off those “faint fuzzies” as I found them. Straightening up from the eyepiece to stretch my back, I faced south and audibly gasped. The woods south of the clearing where I and my partner were observing were on fire!

To be continued…