How Far Are Stars?

Photo by Michael J. Bennett

This week’s post is a bit of a distraction from the usual business, based on a question I wondered about. Rather than ask Google, I dug in like a nerd to get a more complete picture.

One of my frequent spiels is about the vastness of space, in the context that we can dismiss fantasies about humans traveling to the stars. I do throw in an old-school calculation at the end to reinforce this point, but until then we’ll entertain ourselves with a sense for the scale of the sky we see with our eyes.

When we consider a scale model in which the sun is reduced to the size of a sand grain (about 1 millimeter), the closest neighbor star is about 30 km away. One light year at this scale is about 7 km. But how typical is this yawning gulf in our region of the galaxy? And how far away are the stars we lay eyes on in the night sky, typically?

Before getting to those questions, just how many stars can we see, naked-eye? It depends on the darkness of your sky. According to the Hipparcos catalog, rounding apparent visual magnitudes to the nearest integer, there are two −1 magnitude stars: Sirius and Canopus. Eight more join at magnitude zero; 12 at first magnitude; 71 at second; 192 at third; 622 at fourth; 1909 at fifth; and 5976 at sixth—at which point our eyes run out of steam. A suburban sky might allow fourth magnitude, or roughly 1,000 stars (not all at once, since only half are up at a time). At fifth magnitude, we get about 3,000 (all-sky). At the limit, we tally about 9,000 stars. About half this number would be above the horizon at any given time.

Incidentally, going to space hardly does a thing to improve visibility: the atmosphere is pretty impressively transparent at visible wavelengths (only “eating” about a tenth of a magnitude). I was excited to see the night sky from Mauna Kea on my first observing trip there as a graduate student. Being above 40% of the Earth’s atmosphere, it’s the closest I had been to space. The thing is, low oxygen levels impair visual sensitivity, so when I first went outside it really sucked: I could barely see a thing (eventually dark-adapted, but way slower than at lower elevations). Space is even worse on the oxygen front.

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The Anthropic Biodiversity Principle

When I proposed ten tenets of a new “religion” around life a few months back, the first tenet on the list said:

The universe is not here for us, or because of us, or designed to lead to us. We are simply here because we can be. It would not be possible for us to find ourselves in a universe in which the rules did not permit our existence.

While simply stated—perhaps to the point of being obvious—it is shorthand for a fundamental principle that has become a wedge issue among professionals who seek to understand the nature of the universe we live in, and the rules by which it operates. In this post, I will elaborate on the meaning and the controversy behind this deceptively simple statement.

The Schism

As a form of entertainment accompanying my journey through astrophysics, I witnessed a schism develop at the deepest roots of physics and cosmology. In brief, many physicists pursue a common quest to elucidate the one logically self-consistent set of rules by which the universe works: a Theory of Everything (ToE), so to speak. In other words, every mystery such as why the electron has the mass that it does, why the fundamental forces have the behaviors and relative strengths they do, why we have three generations of quarks and of leptons, etc. would all make sense someday as the only way the universe could have been.

An opposing camp allows that some of these properties may be essentially random and forever defy full understanding. Those in the ToE camp see this attitude as defeatist and point out that holding such a belief might have prevented discovery of the underlying (quantum) order in atomic energy levels, the unification of electricity and magnetism, reduction of a veritable zoo of particles into a small set of quarks, or any number of other discoveries in physics. Having self-identified in the “defeatist” camp, I knew for sure that the purists were just plain wrong about my position stifling curiosity to learn what we could. Our end goals were just different. I was content to describe the amazing universe—figuring out how rather than why it worked—and didn’t need to find a “god” substitute in an ultimate Theory of Everything (a big ToE).

The counter-cultural viewpoint I hold sometimes goes by the name The Anthropic Principle, simply because it acknowledges the fact that we humans are here—so that whatever form physics takes, it is constrained by this simple and incontrovertible observation to produce conditions supporting life. It amounts to a selection effect that would be insane to pretend isn’t manifestly true.

Scientists are perhaps too well trained to remove humans from the “equation,” and I can definitely get behind the spirit of this practice. After all, the history of science has involved one demotion after another for human importance: Earth is not the center of creation; the sun is not the center of the universe (the universe doesn’t even have a center)—or even the center of our galaxy; moreover, our galaxy is not special among the many billions. Ironically, even through the Anthropic moniker seems to attribute special importance to humans, the core idea is actually the opposite, translating to the ultimate cosmological demotion: our universe isn’t even special: a random instance among myriad possibilities. Yet, I suspect the name itself is a barrier for many scientists, as it seems superficially to describe an idea built around humans—which is a non-starter for many.

I can definitely sympathize with this reaction, as an avowed hater of human supremacy—a sworn enemy of the Human Reich. Don’t get me wrong: I’m not a misanthrope. I love humans, just not all at once on a destructive, self-aggrandizing rampage. Yet for all my loathing of anthropocentrism, I am fond of the Anthropic Principle. What gives?

Basically, I have to ignore the unfortunate label. A rose by any other name is still a rose. I propose using a less problematic name that gets to the same fundamental point: The Biodiversity Principle. I’ll explain what the principle is (by any name), and eventually how it relates to modernity and the meta-crisis as a compatible foundation for long-term sustainability.

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Don’t Look Surprised

planet-killer impact

From Pixabay/Comfreak.

I just watched Don’t Look Up! on Netflix. While the movie has a number of flaws, on the whole I recommend it for the insights it contains in its parody of human attention deficit disorder.

The premise is that astronomers discover a comet on a direct collision course with Earth, due to hit in six months’ time. The world has difficulty assimilating this information, quickly polarizing into the all-too-familiar pattern of believers and deniers. Moneyed interests, techno-optimism, and old-fashioned failures (by non-Americans, of course) thwart mitigation efforts, leaving the entire globe in mortal peril.  Even at a public event dedicated to the planet-killing crisis, the highlight was a pop star’s performance featuring dazzling lights and costumes. How ’bout them priorities!

Yes, it’s complete fiction, so we need to be careful about drawing lessons from the storyline—just as I would caution against forming opinions of space travel from the big screen. Aside from a list of technical nitpicks, I suspect that something as predictable/certain as a comet slamming into Earth would be taken far more seriously and be more universally accepted than are the more nebulous threats we currently face like limits to growth, climate change, and even COVID-19.

This post lacks a single overarching message, but explores a few worthy themes that the movie brings up for me.

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Life Found on Mars


No, life has not yet been found on Mars, but imagine waking up to that headline. How would you react? The headline’s font would be huge on print newspapers—maybe one word per page, occupying the first four pages. Some bold papers might even put one letter per page and go so far as to have blank pages for the spaces. The point is, it would be big news.

So I ask again, what would this stir for you?

For me, the swirl would be thick with competing thoughts and feelings, tripping over themselves to get out. First would be the raft of questions stemming from pure curiosity. Is it DNA-based? Is it a separate start, or do we share some ancient microbial ancestor—possibly shuttled from one body to the other following a meteoric impact? What lessons can we learn about how life forms? Can we get the discovered lifeforms to call us Mama or Dada? Will they make good pets?

One can imagine the discovery team, whether at NASA or elsewhere, ecstatic with joy. The entire exploration establishment around the planet would likely be giddy. SETI folks would probably be unable to chew for a while, wearing fixed grins.

I would share many of these same reactions, for the pure joy of discovery and the novel opportunity to re-examine what it means to be a part of life on Earth. But then it dawns on me just how devastating the news might actually be for the human race.

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Prolonged Absence

The cessation of regular blog posts has prompted a number of folks to ask if I still live and breathe. Several reasons contribute to the silence. Primarily, most of what I set out to do and say on Do the Math has been covered. How many times can I calculate total tidal power available? I’ve expressed views on our precarious trajectory with respect to finite resources, touched on the psychology of major change and sacrifice, and shared personal explorations in reducing energy/resource footprints at home. While some of this continues (look for a post on nickel-iron batteries soon), for the most part it’s already all there.

The second factor is that the research, education, and administration components of my life (i.e., my job) are demanding significant attention. This has generally been true all along, but the administrative burden has skyrocketed of late due to my role as vice chair of the physics department at UCSD since July 2013. Perhaps as I climb up the learning curve, I’ll find more “hobby” time in the months ahead.

While I am sharing personal news, two things of note: 1) My efforts to write and speak about energy and resource use to a broad audience has resulted in UCSD awarding me the Outstanding Faculty Sustainability Award for 2014. This despite the fact that I don’t know what sustainability means (suspecting that none of us really do), and that very little of my efforts have been directed at the UCSD campus.  All the same, I am as pleased as I am surprised by the recognition.  2) While not related to Do the Math, I encourage you to check out this stunning photo taken by Dan Long capturing our recent laser ranging efforts during the April 15 lunar eclipse.  This is a real photo, taken through a C-11 telescope with a focal reducer (700 mm, f/2)—the outgoing laser beam has not been artificially superimposed. Normally it is really difficult to get a picture of our faint beam heading toward the Moon, because the Moon is so glaringly bright. The eclipse provided a great photo-op, and also a means to test the hypothesis of dusty reflectors. To me, this shot is just gorgeous. But I have more invested in it than the average Joe: this picture serves as a visual representation of a key focus in my life over the last 14 years—so of course I’m enamored.

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Survey the People

The futuristic survey (covered in last post) has attracted about 1300 respondents, 900 from DtM, 300 from the Energy Bulletin (now, and a smattering from other places.

I will ultimately be sharing the results, but the habitual readers of the aforementioned sites are perhaps not representative of the population at large.

Thus I would like your help in pushing this out to a broader population.  See if you can get your friends and family members to take the survey, and perhaps even pass the link on to their friends, etc.  I’ve never done this sort of thing before, so do not know what to expect.  But let’s give it a try, yeah?

Here’s the link you want to pass on in whatever form (paste into e-mail, Twitter, link on FaceBook, whatever works):

Thanks for your help—should be very interesting.

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Futuristic Physicists?

One day, sitting around with a group of undergraduate physics students, I listened as one made the bold statement: “If it can be imagined, it can be done.” The others nodded in agreement. It sounded like wisdom. It took me all of two seconds to violate this dictum as I imagined myself jumping straight up to the Moon. I may have asked if the student really thought what he said was true, but resisted the impulse to turn it into an impromptu teaching moment. Instead, I wondered how pervasive this attitude was among physics students and faculty. So I put together a survey and in this post report what I found. The overriding theme: experts say don’t count on a Star Trek future. Ever.

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Supermoon Disappointment

Putting on my astronomer hat, as one whose main research focus involves measuring the distance between the Earth and Moon, I feel compelled to “speak out” about the “supermoon” hype that crops up periodically.

Last night’s full moon was touted to be a “supermoon”—larger than normal.  As a result, many folks made it a point to watch the Moon rise.  I love the fact that people are paying attention to the Moon, getting outside, and enjoying the serene experience of watching the Moon creep over the horizon.  What I don’t like is that the hype leads to an overall sense of disappointment in many.  Is the campaign a net positive, or a net negative?  I don’t know.

In this post, we’ll look at the numbers and see just how special the supermoon is.

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