Notes from the Astronomy Underground: Unappreciated Topics in Astronomy Part I

August 29, 2008, 1:23 pm
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Black Holes. Gamma-ray bursts. The hunt for extrasolar planets. Cosmology and the grandest scales of the cosmos. These are the fields of astronomy with the glitter and sweeping majesty of The Big Picture; sexy fields so infested with the most impressive contemporary buzzwords that NSF funding will chase you down like a pack of rabid ferrets should you show the slightest desire to work in them. But what about the other fields and attendant scientists, the ones that prefer to linger in relative obscurity, the ones to whom you could imagine all the other astronomers awkwardly crooning Bette Midler’s Wind Beneath My Wings?

Well, don’t actually imagine that. Trust me, it gives you really weird nightmares.

Anyway, it’s in honor of these thankless men and women of science I present:

Unappreciated Topics in Astronomy Part I: Standard Stars and Magnitude Calibrations

Ah, magnitudes. Perhaps nothing embodies our noble science’s absurd affinity for nonsensical units of measurement like this archaic, backwards, and nonlinear scale for categorizing apparent stellar brightnesses. Maybe it’s because we like to confuse irritable physicists, but for some reason astronomers have stuck with this bizarre system since Hipparchus trained his eyes to the sky Back in the Day.

Author’s note: Back in the Day = 2100 years ago.

Or maybe it’s because we’re always eager to classify things before we have any idea what’s actually going on. How else do you explain why there are predominantly early-type stars in late-type galaxies, and vice versa? Yeah, it takes a while to get used to.

But these numbers don’t just come out of nowhere, right? Well, actually, they do. Magnitudes are an arbitrary numerical description of a star’s brightness as seen from earth, but it’s a self-consistent, arbitrary system that has to reference both the physical reality of the star and the telescope, camera, CCD array, filter set, llama, whatever, that you’re using.

But just for the record, llamas make terrible astronomical detectors. They get spit everywhere.


The Job Description

Establishing a magnitude system requires a network of standard stars to which you can compare your observations. We like to start with Vega- it’s big, pretty, and according to Carl Sagan, it’s prime real estate for extraterrestrial communications industries. Only problem here is that, not only do you need to take your detector’s response to starlight into account for looking at this star (which, if you observed in the era where polio was all the rage, was probably frustratingly nonlinear and a real pain to figure out), but you need to carefully measure the continuum of Vega against some conditioned laboratory standard. Which means you need to know every little seemingly trivial technical aspect of this other apparatus as well. What’s even worse is that Vega may be a low-level variable, dust-enshrouded star with a correspondingly schizophrenic continuum. Not to mention there’s that whole “atmosphere” thing that gets between you and whatever you’re looking at. Getting rid of this in your measurement involves a tricky slew of wavelength-dependent factors like the star’s output flux, the airmass blocking your view, turbulence and weather-related problems, etc.

That’s especially important for the secondary star network I mentioned before, where the amount of air in your way and its extinction properties depend on where you look in the sky. Yet another issue lies in selecting the right stars for this business. Not every star is the same, and differences in composition and the absorption lies that come out in their spectra make a huge difference.

This is all well and good, but you just can’t stare at something and expect to get anything really interesting out of it (unless it’s a rerun of the old Adam West Batman series… I just realized Burgess Meredith was the Penguin! That’s pretty awesome). You have to sample the light in a couple of different parts of the spectrum with some filters, and compare results in each measurement. Producing filters to represent physically important phenomena is an equally a daunting challenge as transforming measurements made in one system to an entirely different one. This process is not exactly comparing apples to oranges, but rather comparing apples to other apples made half-way around the world with different soil, water, amounts of sunlight, everything. And you have to have faith the other guys (or their clueless, bumbling grad students, most likely) didn’t screw up some minute detail along the way.

Why No One likes it

In my opinion, doing this research is about as exciting as watching paint dry. But unfortunately, this would be the kind of paint that’s so undeniably important that, if someone doesn’t watch it, it’ll erupt into leaping flames and take out twelve city blocks. Your community is razed to a dystopian landscape of desolate, inhospitable ruin for decades, all because no one wanted to do one mind-numbingly boring task.

For astronomy, any measurement of any kind of perceived brightness (which for us is every measurement), be it from a star, galaxy, quasar, or what have you, would be rendered utterly worthless. And all our explanations of the underlying physics in all these objects would follow suit. No spitting llama telescope could circumvent this disaster.

Who Does this Stuff?

So what kind of person could possibly be attracted to such a thankless existence so fraught with agonizing observational minutia? Have you ever taken a class from someone who took off an inordinate amount of points on a homework assignment just because you dropped the eighth decimal place, or ignored some superficial process that contributes a measly 0.5% error? Yeah- it’s That Guy. But That Guy, as absolutely grating as his single-minded devotion to superhuman degrees of mathematical precision may seem, is the backbone of the angry, charging emu that is observational astronomy.

Or spitting llama, whatever.

And it is to the valiant men and women in this overlooked field that I dedicate this blatant rip-off of Budweiser’s Real Men of Genius laudatory ballad (feel free to sing the italicized backup vocals yourselves).

So many thanks, That Guy, you obsessive compulsive, passionate mess of firing neurons.

High signal-to-noise goin’ on in your brain…

Without your overwhelming zeal for effective wavelengths, extinction curves, and detector sensitivities, all of astronomy would crumble at your feet.

Sorry, cleaning it up is a union job…

Sure, your papers will get cited fairly often, but those authors just want to apply your hard work and sacrifice to their own nefarious schemes (seriously, it’s what I do). They’d just as soon cite a chimp if it had any capacity for your difficult work.

But then everything would be in units of bananas…

They don’t care about the hours you spent poring over your setup, your equipment, your data, massaging every last bit of useful information you could from the noise, the systematic and random errors that so often threaten to paralyze your achievements.

Yeah! No more ridiculous animal analogies todaaay…

We salute you, expert photometrist and unwavering bastion of astronomy.



Mullan, B. (2008). Notes from the Astronomy Underground: Unappreciated Topics in Astronomy Part I. Retrieved from


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