Too Many Internets

Two of the three objects that I showed tonight, the first night of UConn’s infamous Spring Weekend:

This is M53, a globular cluster in the constellation Coma Berenices. It presently spends most of the night climbing out of the eastern horizon, and looks something like a fuzzy pebble here at Storrs observatory. The very bright center of the cluster is just visible using averted vision.

[Photo grabbed from the Wikimedia project, located here, though it's in the public domain as it was captured by the Hubble.]

This is M44, also known as Praesepe (Latin for ‘manger’), also known as The Beehive Cluster. It’s an open cluster in the constellation Cancer. Something of a late-winter/Spring Pleiades, it makes for a beautiful binocular object and completely overflows even a low magnification telescope’s field of view. Open clusters tend to elicit the second-best response from students, after planets and just before nebulae. It’s especially powerful if I have the opportunity to show them an area just away from the cluster, and then bring the cluster in. The contrast between “a couple of stars” and “there’s so many stars!” is very nice.

I should mention that really only the bright stars in this photograph stand out when viewed from the ground.

[Photo grabbed from here, origin beyond that unknown.]

steven Upward astronomy, photos, SCIENCE

This spider web’s photons were captured by the brilliant kthread (Kristen Taylor), who is the kind of modern polymath I aspire to emulate. She’s a gifted photographer, skilled foodie and I gather well-versed in our New Media culture. She’s also consulted on a dinner party that I once co-hosted, so I’ll have to get her something nice if I ever have the pleasure of meeting her.

I grabbed this photo both to share its beauty, and because I’m excited by thin film diffraction.

See, each of the threads in the web is thin enough and spaced closely enough that the light from the other side is being bent (or diffracted) as it passes through. Light diffracted by the threads near the center has to travel a different distance than that near the edges, so that when they both reach your eyes (or your camera lens), the light waves from the different source locations are at different points in their oscillations (otherwise known as ‘out-of-phase’). This difference in distance travelled is called the path length difference.

The path length difference leads to wave interference: the waves are added together as they arrive and can appear brighter or darker than any individual wave. With lots of sources (like all of the threads and spaces in a spider web) there’s a lot of destructive interference happening, with waves mostly or totally canceling each other out. What’s left are bright peaks, the perceived color of which depends on the angle at which you’re viewing the web. This is because different colors have different wavelengths. Differences in wavelength changes the path length difference, in turn effecting where the bright maxima occur.

Since you see different parts of the web at different angles, it appears to shimmer kaleidoscopically, depending on which color is constructively interfering at that particular vantage point. This is ultimately the same phenomenon behind the rainbow of colors seen in gasoline spilled at the fill-up station, or the bands reflected on the back of a CD.

[Update! As E. J. points out in the comments below, if this is diffraction at all, it's likely due to reflection of the light rather than transmission through the web. The underlying principles of interference remain. However, it may also be that the camera wasn't capturing diffraction at all, but that the color is the result of Moiré patterns. This possibility didn't even occur to me, likely because I hadn't taught a lab on Moiré just two weeks ago.]

steven Studies in Repetition photos, SCIENCE

Though there have been a few times that the weather reached ‘pleasant’ here in Storrs, it wasn’t until today that I was able to go outside with a book and really enjoy the sunshine in the mid-60s. Unlike this child, though, I chose to spend my time far away from a field full of flowers because allergies, man, allergies.

Still, it makes a pretty picture.

[Photo grabbed from The Boston Globe's Big Picture feature, Signs of Spring entry. This image in particular is credited to Dan Kitwood, Getty Images.]

steven Studies in Repetition photos

The Pinwheel Galaxy (object #101 in Messier’s catalogue), a striking example of a spiral galaxy. It currently spends its time in Ursa Major, just a few clicks below Mizar (the middle star in the handle of the Big Dipper). Presently viewable in the northeast of the night’s sky, though you’re fortunate if you can make out anything more than a faint fuzziness with most amateur telescopes in most darkness situations.

Hooray for the Hubble!

(Image found today at NASA’s Astronomy Picture of the Day Site)

steven Upward astronomy, photos