Using the Sky

Lucky for Us, Our Ancestors Did Just That

My friend Ed Krupp and I once got into a discussion about “using” the  sky. This was while I was working on exhibits for the Griffith Observatory (which Ed directs). Our conversation got started when I was writing some copy about the relationship early people had with the sky.

I wanted to make some statement about attaching mystical meaning to the sky and Ed warned me not to read too much into everything I might see about ceremonial sunrise rites and so on. Now, Ed’s an expert on various ancient cultures and the relationships they had with the stars, Sun, planets, and Moon. He’s traveled all over the place, examining temples and markers that were likely used to determine all kinds of iterative sky phenomena (stuff that happens regularly). And, he’s written widely respected books on the subject of early astronomers and their practices (you can find his book Skywatchers, Shamans and Kings in my online bookstore).  So, I listened and learned.

He pointed out that first and foremost, it’s important to know that people USED the sky. We still do, although not to the extent our earliest cultures did. For early people, the sky was a survival tool. While there was some element of mysticism attached to sky motions (and this is understandable, given that people in early times didn’t know what we do about the sky and we have this human disposition to attach mystical meaning to things we don’t understand), the practical, utilitarian use of the sky was at the root of everything  these people needed. They used it to know the time of day, the day and date, the seasons and the years.

To USE the sky, people had to WATCH the sky. They became intimately familiar with the objects and motions they observed, and that watchfulness is the root of astronomy. Now some early cultures made a real commotion about sky objects and motions. The Egyptians come to mind, as do the Aztec, Maya, the Chinese, the Polynesians, the earliest North American cultures, and many tribes in Africa. Whatever mystical meaning those people attached to the sky was secondary to the actual practice of watching the sky and charting the motions of the Sun, Moon, and planets and then using the knowledge gained to improve (and sustain) life and culture. In time, they began noting down what they saw in the sky (the pictograph in the image above is at Chaco Canyon in New Mexico, and is thought to depict the supernova of 1054 A.D. (courtesy Ron Lussier)).

There’s a direct connection between those ancient people and us today. It’s called survival. What they learned helped keep them alive. Knowing when the seasons would come helped them know when to plant, or till the soil, or harvest their crops, or stalk the wild game at the right time. If they hadn’t, human culture might never have taken root around the globe. Or, perhaps it would have rooted differently, with consquences that we’d feel today. For them,it was a matter of survival to know the sky. We should be grateful to those early humans for the very practical knowledge they used to keep themselves alive and thriving.

Stellar Family Portraits

They Tell us About the Process of Star Birth

Stars are born in messy litters that spread themselves across the sky for hundreds of thousands of light-years. If you look at one of these creches, you can see bright stars still embedded in the clouds that formed them. You can also see the “seeds” of stars — that is, regions where gas and dust is still wrapped so tightly around newly forming stars that they can’t yet be seen.

What starts a cloud of as and dust down the path of starbirth?  If the cloud just sits there with no outside forces acting on it, it will just stay a cloud. But, give it a little push, say from the strong wind of a nearby massive star (which shoves material along ahead of it), or even a supernova blast, and the cloud starts clumping together and swirling around. Eventually the material in the center, which is being compressed by the motion, will heat up. If this happens long enough and there’s enough material to keep the clumping going, a star will eventually form.  This is a very simple explanation for a complex set of processes that take hundreds of thousands of years to start a cloud down the path of starbirth.

The Spitzer Space Telescope (and other observatories) have long studied starbirth regions to understand the star-and-cloud interactions that seem to trigger the births of new stars. The latest picture from Spitzer (NASA/JPL-Caltech/Harvard-Smithsonian CfA) was just released last week  to help celebrate this infrared observatory’s fifth year on orbit. It shows multiple generations of stars all gathered in a big molecular cloud “family home” — a region called W5. This cloud complex is so big that it spans an area of sky about the size of four full moons. W5 lies about 6,500 light-years away from us in the constellation Cassiopeia.

In this image, the blue dots in the centers of the two hollow cavities are the older stars of the W5 stellar family (other blue dots are background and foreground stars not associated with the region). Younger stars line the rims of cavities in the cloud that were carved out by winds from the most massive stars in the area. Some of the younger stars can be seen as pink dots at the tips of the elephant-trunk-like pillars. The white knotty areas are where the youngest stars in the family are forming. Red shows heated dust that is scattered throughout the cavities. The densest clouds are colored green (and, this is a false-color image; the color-coding is there simply to help astronomers separate various regions and structures in the starbirth region).

This image contains some of the best evidence yet for the triggered star-formation theory. And, it’s a stunningly beautiful illustration of just how much we’ve learned about the births of multiple generations of stars by using some of the most advanced telescopes on and off the planet!