Archive for the 'Astronomy/astrophysics' category

Repost: The solstice (in a two-sphere cosmos).

As I'm still barricaded in the Cave of Grading, and as the Winter Solstice may be upon us before I can emerge, victorious, here's a seasonal post from last December:

Here in the Northern Hemisphere (of Earth), today marks the Winter Solstice. Most people have some understanding that this means today is the day of minimum sunlight, or the longest night of the year. Fewer people, I think, have a good astronomical sense of why that is the case.

So, in honor of the solstice, let's do some old school astronomy. Really old school.

Let's consider the two-sphere cosmos:

TwoSpheres.jpg

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Friday Sprog Blogging: Kids Day at SLAC 2010 hazards and mitigations.

Longtime friend of the Free-Rides LO has been instrumental in hooking the Free-Ride offspring up with Kids Day @ SLAC. Finally the year has come when the younger Free-Ride offspring meets the age requirements to join the elder Free-Ride offspring. As is our practice, we prepared by reviewing the safety information:

Dr. Free-Ride: So, we're talking about Kids Day @ SLAC. I'm showing you the logo for this year's Kids Day @ SLAC. There seems to be some sort of -- I don't know if that's a laser beam or something. Looks interesting. But, the part we need to discuss has to do with the safety information. "All children must wear long pants, Kids Day T-shirts" -- which you guys will get from LO and put on when you get there -- "closed-toe shoes, no jewelry, and long hair must be pulled back. Please review the hazards and mitigation information on the workshops." Younger offspring, let's look at workshop B.

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The solstice (in a two-sphere cosmos).

Here in the Northern Hemisphere (of Earth), today marks the Winter Solstice. Most people have some understanding that this means today is the day of minimum sunlight, or the longest night of the year. Fewer people, I think, have a good astronomical sense of why that is the case.

So, in honor of the solstice, let's do some old school astronomy. Really old school.

Let's consider the two-sphere cosmos:

TwoSpheres.jpg

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9 responses so far

When collaboration ends badly.

Back before I was sucked into the vortex of paper-grading, an eagle-eyed Mattababy pointed me to a very interesting post by astronomer Mike Brown. Brown details his efforts to collaborate with another team of scientists who were working on the same scientific question he was working on, what became of that attempted collaboration, and the bad feelings that followed when Brown and the other scientists ended up publishing separate papers on the question.
Here's how Brown lays it out:

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Physical phenomena, competing models, and evil.

Over at Starts with a Bang, Ethan Siegel expressed exasperation that Nature and New Scientist are paying attention to (and lending too much credibility to) an astronomical theory Ethan views as a non-starter, Modified Netwonian Dynamics (or MOND):

[W]hy is Nature making a big deal out of a paper like this? Why are magazines like New Scientist declaring that there are cracks in dark matter theories?
Because someone (my guess is HongSheng Zhao, one of the authors of this paper who's fond of press releases and modifying gravity) is pimping this piece of evidence like it tells us something. Guess what? Galaxy rotation curves are the only thing MOND has ever been good for! MOND is lousy for everything else, and dark matter -- which is good for everything else -- is good for this too!
So thanks to a number of people for bringing these to my attention, because the record needs to be set straight. Dark matter: still fine. MOND: still horribly insufficient. Now, maybe we can get the editors and referees of journals like this to not only do quality control on the data, but also on the reasonableness of the conclusions drawn.

In a comment on that post, Steinn took issue with Ethan's characterization of MOND:

Ethan - this is not a creationism debate.
Hong Sheng is a top dynamicist and he knows perfectly well what the issues are. The whole point of science at this level is to test models and propose falsifiable alternatives.
MOND may be wrong, but it is not evil.
Cold Dark Matter is a likelier hypothesis, by far, but it has some serious problems in detail, and the underlying microphysics is essentially unknown and plagued with poorly motivated speculation.
MOND has always approached the issue from a different perspective: that you start with What You See Is What You Get, and then look for minimal modifications to account for the discrepancies. It is a phenomenological model, and makes little attempt to be a fundamental theory of anything. Observers tend to like it because it gives direct comparison with data and is rapidly testable.
I think Leslie Sage knew what he was doing when he published this paper.

In a subsequent post, Ethan responded to Steinn:

Yes, Steinn, it is evil to present MOND as though it is a viable alternative to dark matter.
It is evil to spread information about science based only on some tiny fraction of the available data, especially when the entire data set overwhelmingly favors dark matter and crushes MOND so as to render it untenable. It isn't evil in the same way that creationism is evil, but it is evil in the same way that pushing the steady-state-model over the Big Bang is evil.
It's a lie based on an unfair, incomplete argument. It's a discredited theory attacking the most valid model we have at -- arguably -- its only weak point. Or, to use a favorite term of mine, it is willfully ignorant to claim that MOND is reasonable in any sort of way as an alternative to dark matter. It's possibly worse than that, because it's selectively willful ignorance in this case.
And then I look at the effect it has. It undermines public understanding of dark matter, gravity, and the Universe, by presenting an unfeasible alternative as though it's perfectly valid. And it isn't perfectly valid. It isn't even close. It has nothing to do with how good their results as scientists are; it has everything to do with the invalid, untrue, knowledge-undermining conclusions that the public receives.
And yes, I find that incredibly evil. Do you?

I have no strong views on MOND or Cold Dark Matter, but given that my professional focus includes the methodology of science and issues of ethics in science, I find this back and forth really interesting.

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Friday Sprog Blogging: revisiting Pluto.

There's been a continuing discussion, in various online venues (including this blog), of Unscientific America, a book which notes the "demotion" of Pluto as an instance where the lessons the American public drew from the scientists' decisions may have diverged widely from the lessons the scientists would want the public to draw -- if they even thought about the possibility that the public was paying attention.
So, since the Free-Ride offspring were paying attention as the Pluto saga unfolded, I thought I should double back and see what their current thinking about it is.

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Announcing your findings (but not really).

Over at Cosmic Variance, Julianne Dalcanton describes a strategy for scientific communication that raises some interesting ethical issues:

Suppose you (and perhaps a competing team) had an incredibly exciting discovery that you wrote up and submitted to Nature.
Now suppose that you (and the competing team) simultaneously posted your (competing) papers to the ArXiv preprint server (which essentially all astronomers and physicists visit daily). But, suppose you then wrote in the comments "Submitted to Nature. Under press embargo".
In other words, you wrote the equivalent of "Well, we've submitted this to Nature, but they won't accept it or publish it if the news gets into the press, so can all of you reading this just not actually, you know, tell anyone? Oh, but can you make sure that you give us credit for the discovery, instead of the competing team? Thx!"
So, instead of blogging about the Incredibly Exciting Discovery (which I'd loooove to talk about), I'm writing about what a ridiculous fiction the authors are asking us all to participate in, for the sake of the authors' potentially getting a publication accepted to Nature. The authors advertised a paper to thousands of interesting, engaged scientists, who are then supposed to keep their mouths shut so that the authors can get a paper into a particular journal -- one that is not noticeably more influential in astrophysics (i.e. the difference between Nature and non-Nature is not nearly as big a deal as it is in biology).

The authors in this case are kind of announcing their findings to other scientists in their field -- but, owing to the embargo on their results, they kind of aren't.
What's going on here?

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Movie review: Orphans of Apollo.

OrphansOfApollo.jpg
I've mentioned before that I grew up in a family that was fairly captivated by the U.S. space program, especially the Apollo program that brought humans to the Moon. But as impressive as those manned missions to the Moon were, what did the Apollo program accomplish? Where are our moon-bases?
Orphans of Apollo, a documentary film by Michael Potter, explores what one group of space exploration enthusiasts did when NASA's commitment to the space age seemed to falter. By the mid-1970s, the Apollo program that put Americans on the moon was done, with two planned Apollo missions cancelled. The U.S. had beaten the U.S.S.R. to the moon and brought back some moon rocks for study but what, really, had been accomplished? Had the moon landings left a lasting impact on human culture that was more than superficial?
The impact was anything but superficial on a generation of kids whose imagination was captured by the Apollo program. As these kids grew up, dreaming of a human future in space, NASA's visions and priorities shifted. This generation that assumed space travel and exploration almost as an American birthright felt orphaned by the American space agency.
But, as Orphans of Apollo tells it, a group of them found each other and started figuring out how to get a foothold in space. If NASA couldn't establish colonies on the moon or manned space stations, maybe the private sector could.

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Book review: Maria Mitchell and the Sexing of Science.

MariaMitchell.jpg
Maria Mitchell and the Sexing of Science: An Astronomer among the American Romantics
by Renée Bergland
Boston: Beacon Press
2008

What is it like to be a woman scientist? In a society where being a woman is somehow a distinct experience from being an ordinary human being, the answer to this question can be complicated. And, in a time and place where being a scientist, being a professional -- indeed, even being American -- was still being worked out, the complexities of the answer can add up to a biography of that time, that place, that swirl of intellectual and cultural ferment, as well as of that woman scientist.
The astronomer Maria Mitchell was not only a pioneering woman scientist in the early history of the United States, but she was one of the nation's first professional scientists. Renée Bergland's biography of Mitchell illuminates a confluence of circumstances that made it possible for Mitchell to make her scientific contributions -- to be a scientist at all. At the same time, it tracks a retrograde cultural swing of which Mitchell herself was aware: a loss, during Mitchell's lifetime, of educational and career opportunities for women in the sciences.

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Friday Sprog Blogging: a song with secret science content?

This week, in SprogCast #4, the younger Free-Ride offspring sings and then suggests that the song bears on the planetary subject of the very first Friday Sprog Blogging entry, which also involved singing.
You can download the sound file for the a cappella performance and the discussion that follows. The transcript is included below.

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