Thursday, September 23, 2010

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?

Thursday, September 16, 2010

The Kids Are Far Out - part two

As a rule, kids like planets, and the kids at the recent Cosmic Carnival event were no exception.

Phillip from Albuquerque, age 8, commented on his favorite planet:

“I like Neptune because I think there might be life there.”

Phillip, that’s as good a reason to like a planet as I’ve ever heard! Wouldn’t it be exciting to discover evidence of extraterrestrial life in our own solar system?

Image source: NASA

Along with Jupiter, Saturn, and Uranus, Neptune is one of the gas giant planets, which means it has no solid surface on which we could walk. Its thick atmosphere has 1,000-mile-an-hour winds and a bone-chilling temperature of minus 350 degrees Fahrenheit. Brrrrr! Beneath the harsh atmosphere is a hot “ocean” of water, ammonia, and methane, and perhaps a small core of rock and ice.

It’s safe to say any life form that can survive on Neptune is pretty darn tough.

Julia from Rio Rancho, age 9, asked:

“Why did Jupiter become a moon?”

Thanks for your question, Julia. Jupiter is actually a planet, not a moon. In fact, Jupiter is the biggest planet in our solar system!

The planets to scale
Left to right: Outer edge of Sun, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
Image source: NASA

A planet is a celestial body with a nearly round shape that orbits the Sun. A moon, on the other hand, is a celestial body that orbits a planet. Jupiter has over 60 moons going around it! The four largest ones were discovered by the famous Italian astronomer Galileo. You can read more about Jupiter here.

Melissa from Albuquerque, age 12, wondered:

“How long does a day last on Pluto? How long does it take for it to orbit around the Sun?”

A great pair of questions, Melissa! Although distant Pluto has been reclassified by professional astronomers as a dwarf planet, we still love it, don’t we?

A day on Pluto, that is, the time it takes for Pluto to complete one rotation around its axis, is a little more than 6 Earth days. A year on Pluto, that is, the time it takes for Pluto to complete one orbit around the Sun, is 248 Earth years.

Life on Pluto is life is the slow lane.

Thursday, September 9, 2010

The Kids Are Far Out - part one

To turn kids on to science and astronomy was the reason we all gathered at the annual Cosmic Carnival outreach event held at the Albuquerque International Balloon Museum this past Sunday, September 5.

The joint was jumping!

Dave Dooling of the National Solar Observatory deflates the Sun.

Len Duda of Sandia National Labs inspires a future engineer.

I met some “far out” kids (and adults) who like astronomy and stargazing, and invited them to write a comment or pose a question to be published on my blog. Liam from Albuquerque, age 10, had this to say:

“My favorite constellation is ‘o-Ryann.’ My stepsister’s name is Ryann. She is three months younger than me. Sometimes we get into arguments, but most of the time I like her. I find Orion easy to recognize.”

Ditto, Liam! That distinctive hourglass shape, along with the three diagonal Belt stars in the middle, makes Orion the Hunter quite easy to spot in the winter sky, even if you’re a beginner. Read more here.

Wow, how lucky are the kids who call Dara from Albuquerque, age 40, “Mom.” She shared this story:

“Each time we take our sons camping, they are a little older and can pick out more things in the night sky. This summer our 5 year old spent hours looking for his favorite constellation, but never found it (must be the wrong time of year for Delphinus). But we had a great time counting shooting stars and naming our own constellations.”

Right you are, Dara. The delightful little constellation of Delphinus the Dolphin leaps its way into our hearts in autumn. Starting in late September, look for it after sunset, just west of the Great Square of Pegasus. Read more here.

Finally, a young lady named Vaidehi from Lone Tree, Colorado, age 8, posed this question:

“Why do the stars change over a year?”

Excellent question, Vaidehi! Many adults don’t know the answer to that question either. So, why do we say that Orion is a “winter constellation” and Delphinus is an “autumn constellation?” And why can we see Scorpius the Scorpion in the summer, but not in the winter? In other words, why are the stars seasonal?

The Earth is in orbit around the Sun 365 days a year, right? Because we’re always moving along this path around the Sun, each night when we spin around to face the night sky, we don’t have exactly the same view we had the night before. Although it won’t be obvious to you, the night sky and its star patterns have shifted slightly to the west, or right. This is because the Earth has moved slightly eastward in its orbit, or toward the left.

This continuous westward shifting of the stars will become more noticeable to you as the months pass and seasons change. For example, you might notice that the constellations you enjoyed in summer are moving farther and farther to the west in autumn, until finally they are below the western horizon after sunset and no longer visible.

The diagram below shows an example of this, using the constellations of the zodiac. If we were standing on the Earth shown in the diagram (the black circle), at night we would look out at the constellation Pisces the Fishes. But six months later in its orbit, when Earth was on the other side of the Sun, we would look out at the constellation Virgo the Maiden at night.

Diagram by Dr. Guy Worthey

Because we’re always in motion, we’re always looking out at different “slices” of the night sky.

Thursday, September 2, 2010

Why Is the Moon So Bright?

The brightest object in the nighttime sky is, by far, the Moon. In fact, it can seem blindingly bright, particularly when compared to other celestial objects. With its face only half illuminated, a First Quarter or Last Quarter Moon (sometimes called a “Half Moon”) is still around 250 times brighter than the next brightest celestial object, the planet Venus.

The Moon does not emit its own light, but rather shines by reflecting light from the Sun. And as reflective surfaces go, it’s just not that impressive. The reflectivity of a body or surface is known as its albedo (al-BEE-doh), a term derived from the Latin word for white. The Moon’s albedo is around 0.12, meaning that it reflects an average of only 12 percent of the sunlight reaching its surface.

The rest of the sunlight is absorbed by the Moon’s regolith (REGG-uh-lith), the loose surface layer of broken rock and dust covering the lunar bedrock.

So, if it’s reflecting only a small fraction of the sunlight that’s striking it, why does the Moon—even a slender crescent Moon—look so darn bright? The fact is our Sun is so bright that even a fraction of its light reflected is still a lot of light. Add to that the relatively close proximity of our Moon (about a quarter of a million miles away), which gives it a large apparent size, that is, the amount of sky it covers as seen from Earth.

Now consider this: planet Earth’s albedo, or reflectivity, is 0.37. Can you imagine how bright a “Full Earth” would look if you were standing on the Moon?