Tonight's Sky
Sun
Sun
Moon
Moon
Mercury
Mercury
Venus
Venus
Mars
Mars
Jupiter
Jupiter
Saturn
Saturn

Tonight's Sky — Change location

OR

Searching...

Tonight's Sky — Select location

Tonight's Sky — Enter coordinates

° '
° '

How dense are giant gas clouds like the "Pillars of Creation"?

Dave Sorrell, Waverly, Iowa
Eagle-Nebula
The Eagle Nebula appears to contain nearly solid pillars of gas, but these structures are actually much less dense than air on Earth. NASA/ESA/STScI/J. Hester and P. Scowen (Arizona State University)
The biggest pillar in the classic Hubble Space Telescope picture of the Eagle Nebula (also known as the “Pillars of Creation”) measures about 3 light-years. The pillars are about half a light-year thick. The image leads us to believe that the contrast between the pillars and the space between them is large — the pillars look almost solid. However, the amount of material we are looking through, rather than the density of the gas, determines this contrast.

The terrestrial analog is looking into a fog bank. What we call “dense fog” is not actually denser; it is just a larger cloud of material — more water droplets suspended in the air along our line of sight obscure our view. And so it is with these types of nebulae. Because we’re looking a half light-year through the pillars, we can see sharp edges and apparently dense structures — even though the material is quite tenuous.

In the Eagle Nebula, the density of material within the columns is about 4,000 particles per cubic centimeter. Air density at sea level has more than 1019 particles per cubic centimeter — that’s a factor of 10 million billion times more dense than in the pillars. The 4,000 particles per cubic centimeter density is far lower than that of the best vacuum we can achieve on Earth. So, it is the vast scales of these nebulae that give them the appearance of solid structures. — Paul Scowen, Arizona State University, Tempe
0

JOIN THE DISCUSSION

Read and share your comments on this article
Comment on this article
Want to leave a comment?
Only registered members of Astronomy.com are allowed to comment on this article. Registration is FREE and only takes a couple minutes.

Login or Register now.
0 comments
ADVERTISEMENT
FREE EMAIL NEWSLETTER

Receive news, sky-event information, observing tips, and more from Astronomy's weekly email newsletter. View our Privacy Policy.

ADVERTISEMENT
ADVERTISEMENT
Apollo_RightRail
A chronicle of the first steps on the Moon, and what it took to get there.
Find us on Facebook