Tag: astronomy

Spectrometer

Posted on by Brian Garthwaite
Spectrometer and sodium lamp.
Rainbows!

Astronomy is roughly 98% figuring out how to look at stuff better than our eyes can do it.

Gathering more light with large-aperture lenses and reflectors. Gathering more light with long camera exposures. Using detectors for light outside the visible spectrum, from radio waves to gamma rays. Launching telescopes a million miles into space to get away from our pesky atmosphere. Splitting the broadly blended colors we perceive into their component wavelengths.

That last one’s the easiest to accomplish in a student lab setting, and it’s a broadly useful scientific tool across many disciplines. Turns out that certain particular constraints caused by quantum physics make all sorts of other observations possible. Who knew?

Pictured above is a low-pressure sodium lamp, just like the ones that once illuminated nighttime streets around the world with their flattening orange glow. Looks orange to our eyes, but it’s primarily a mix of red, orange, and yellow wavelengths. If you measure those carefully enough, you can discern a certain “fingerprint” on a spectrum of light that would tell you if sodium is or isn’t present in what you’re observing.

Same applies to hydrogen and helium. Nitrogen and oxygen. Argon and neon. Carbon dioxide. Water. Every atom and molecule – including different ionized states, which is a particularly useful bit of information for astronomers – has its own unique spectrum of light it emits. You just need to look at it in the right way.

Even if it’s millions of light-years distant.

Adapters

Posted on by Brian Garthwaite
Extruded aluminum telescope pier.
Expensive equipment goes on here.

A great many jobs in the daily work of a shop consist of riffs on this: can you make item A connect to item B? It might be physical connections, electronic and/or digital signals, or even the relatively abstract interpretation of transitioning a lab space over from one experiment to the next without disruption. The simplest ones are when someone can’t locate the proper connector cable. (There are so many different kinds!) Less simple are those times when two things are supposed to fit, but don’t.

Just straight-up don’t.

At the Tressler lab, we have the luxury of permanently-installed piers which support our telescope mounts. For our purposes, this is an excellent improvement over the default, a very stable yet heavy tripod. Now in the process of upgrading our mounts, we find that the tapped mounting holes on the pier don’t match the drilled and counterbored corresponding holes on the custom-made mount adapters. By 1/8″ or more in some cases. Sounds small. Is actually huge. Is will-not-fit-even-with-brute-force huge.

Note: not made in-house. We could try to guess where the error might have arisen, but our job is to fix it.

Also note: the previous mounting plate was not precisely machined to the proper dimensions, either, but was close enough that it was fastened by brute force. Sensing a theme here, which is this: precise measurements are crazy hard.

Pier with adapter plate.
Fix holes with more holes.

Getting to the adapter-for-the-adapter called for more than one CNC-milled plastic prototype. Measure, mill, test. Rinse, repeat. Polyethylene, as one might imagine, is cheap stuff.

A few test runs later, we have a custom-machined (in-house!) sheet of 1/2″ aluminum to connect to the 5/16″-18 tapped holes on the pier, which then sets up a new series of 1/4″-20 holes in this plate and the mount adapter to hold everything rock solid. Holes drilled and tapped, counterbored for a clean surface with all of those socket screws.

And all carefully measured and aligned on the milling machine to within 0.001″.

Telescope mount adapter, in place.
No one notices the unused holes in the dark.

You don’t appreciate the precision of reliable machinery and sharp tooling until the pieces slip together effortlessly. Whoa! Goosebumps!

Best part? The adapter is functionally invisible for anyone who doesn’t know to look for it. Few things feel as rewarding as solving a problem before (almost) anyone else realizes it’s there.

SkyCam

Posted on by Brian Garthwaite
SkyCam on roof
View from slightly higher than most.

Astronomy can be awkward. By necessity, observation happens at night. (Mostly.) And outside, in whatever weather permits clear skies. Hot and humid or bitter cold, the telescopes only function when they’re at equilibrium with the air around. When the temperature drops so low that the grease in the motorized mounts thickens, we call it quits, but nights reaching down to about 20°F are fair game. Precipitation always shuts things down, as does substantial cloud cover.

What to do when you’re at home, all warm in your jammies, and not sure if it’s worth trekking out into the cold? Check the Bucknell University Sky Camera website, of course. If it looks like this:

Camera image, night
I see stars! And light pollution!

Visible stars, no serious cloud cover: you’re good to go. The bright spot in this particular image is probably Saturn, but you get the idea. If you can see it here, you can see it through a telescope. Checking the weather forecast is fairly reliable, although it gets dicey around those transition zones between “good enough” and “should have stayed home.” Forecasts also describe cloud cover in terms of percentage obscured, without a distinction between sparse-but-dense and widespread-and-gauzy.

Depending on what you want to accomplish, sometimes clouds are something you can work with. Astrophotography? Visual observation? Naked eye and constellations? Sometimes, here in a Pennsylvania river valley, you shrug and make it work.

(The alternate method is to walk outside and look up – quite reliable, that – but maybe not ideal if you’re in the aforementioned jammies.)

Camera image, day
Note: one particular star very visible.

The skycam can also be entertaining to check during the daytime. You can watch the sun track across the ecliptic and see the discrepancy between clock time and solar time during Daylight Saving Time. On a cloudy day, sometimes the clouds themselves are just plain neat. Raindrops. Snow accumulating. Snow melting. Birds and bugs and all sorts of things captured by intermittent photography.

Camera image, day
Whoa. Fisheye.

Including the occasional technician out on maintenance duty. Wave hi!

Planisphere

Posted on by Brian Garthwaite
Planisphere in lit room
A handy, adjustable star chart…

Astronomy at Bucknell is not just for the undergraduate students, but for the wider community, too. With a whole slew of telescopes to explore the skies, the department sometimes runs family nights and other outreach programs. Local families, summer camps, and others can – weather permitting – have the opportunity to explore constellations, deep sky objects, planets, and sometimes even the crater-riddled surface of the moon.

For those at home, an ordinary pair of binoculars works quite well for that last one. Pick a night when the moon is between new and full, and look to the transition zone between the light and dark sides. The light rays raking across the surface dramatically emphasize the texture. The full moon’s straight-on illumination is less compelling, and, well, there’s not much to see on the new moon.

In order to help explain the skies to the public, the Observatory has a planisphere, built by one of the University’s Presidential Fellowship students with the help of the shop techs. A flattened portion of the celestial sphere rotates, enabling a view of the major constellations at any day and time throughout the year. Polaris, at the center, stays steady while the rest of the sky spins about.

For added excitement, a series of colorful LED lights ring the perimeter, making the stars and imaginary constellation lines glow in the etched acrylic.

Planisphere in dark room
…that really pops in the dark.

It’s pretty cool.