On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs." --San Antonio Express-News
Cool images from Hubble! Astronomers have used the Hubble Space Telescope’s entire suite of instruments to produce spectacular new multi-wavelength images of two planetary nebulae, stars that for some reasons not yet entirely understood are surrounded by breath-taking jets and cloud-formations of all shapes and sizes.
The two images are to the right, cropped and reduced to post here.
Planetary nebulas, whose stars shed their layers over thousands of years, can turn into crazy whirligigs while puffing off shells and jets of hot gas. New images from the Hubble Space Telescope have helped researchers identify rapid changes in material blasting off stars at the centers of two nebulas — causing them to reconsider what is happening at their cores.
In the case of NGC 6302, dubbed the Butterfly Nebula, two S-shaped streams indicate its most recent ejections and may be the result of two stars interacting at the nebula’s core. In NGC 7027, a new cloverleaf pattern — with bullets of material shooting out in specific directions — may also point to the interactions of two central stars. Both nebulas are splitting themselves apart on extremely short timescales, allowing researchers to measure changes in their structures over only a few decades.
This is the first time both nebulas have been studied from near-ultraviolet to near-infrared light, a complex, multi-wavelength view only possible with Hubble.
The press release suggests that the most likely and popular explanation for the formation of planetary nebula is the interaction of two closely orbiting stars. While this might be true, it remains only one theory among many, all of which explain some of what we see and none of which explain everything. As I noted in my November 2014 cover story about planetary nebulae for Sky & Telescope:
The problem [with the binary star theory] is that, according to recent data, only about half of all planetary nebulae are binaries in a tight enough orbits to do the job. For the remainder, something else must produce the nebulae’s complicated shape.
Some scientists have proposed that the star’s magnetic field might help sculpt the nebula. The problem here is that the amount of magnetic energy used to fashion the cloud would in only a few decades suck the angular momentum from the star. Something else is required to replenish that energy.
Most recently, some astronomers have begun considering the possibility that exoplanets might help solve this problem. The angular momentum the star gains from swallowing a Jupiter-sized exoplanet could be sufficient to replenish the energy of its magnetic field. As Wouter Vlemmings (Chalmers University of Technology) said recently at a planetary nebula conference, “In principle a planet could handle it.”
It is also quite possible that — instead of one single overarching theory of formation — each planetary nebulae is formed in its own unique way. Some develop as they do because they are binaries. Others because they have a strong magnetic field and exoplanets. Many because the outer cloud has its own unique shape which helps guide the later fast winds coming from the evolving star.
And finally, some planetary nebulae might form because of a combination of ALL these factors.
In essence, what we have here is a classic example of the uncertainty of science. We have a phenomenon but our data is insufficient to explain it. We can only make educated guesses.
We are now in the third week of my annual July fund-raiser for Behind the Black. My deep thanks to everyone who has so far donated or subscribed. The response this year has been wonderful.
We are not done yet. This monthly fund-raiser is now half over, and I am hoping the second half will result in as many donations as the first half did. If it does, I will remain free to continue my writing as I see fit, unblemished by the efforts of others to squelch my perspective in this increasingly intolerant world.
This year's fund-raising drive is also significant in that it celebrates the 10th anniversary of this website's founding. It is hard to believe, but I have been doing this for a full decade, during which I have written more than 22,000 posts, of which more than 1,000 were essays and almost 2,600 were evening pauses.
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