Induquímica Laboratorios

Capturing Light from Long Ago

A “headless” Mac mini collects telescopic images under tough conditions.

A “headless” Mac mini collects telescopic images under tough conditions.

Terry’s iCCD program is all about transforming the raw science data into evocative images that spark the imagination. Some of the most abundant sources of this data are majestic spiral galaxies and fluorescent gaseous nebulae, which are actually the aftermath of dying stars’ final explosions. Terry wants non-scientists — artists, poets, and musicians — to be able to create stunning pictures. But doing so requires that iCCD’s interface be highly intuitive. “I’ve tried to make iCCD simple enough for even me to use,” says Terry with laugh. “I don’t believe in reading software manuals.”

Collecting and Processing Starlight on the Mac

On any given day (or night), Terry’s students run iCCD on at least four computers. Their main data-collection computer is a Mac mini. “It’s the perfect size,” says Terry. “It fits right on top of the telescope tripod and has more than enough power to collect images.” The Mac mini is one of the least costly pieces of the setup — much less expensive than the telescope, its motorized mount, or its CCD camera.

“I’m sure that’s not how Apple envisioned using a Mac mini: at -4° Celsius, outside, at 2:00 a.m., dripping wet!” says Terry. “But it’s been chugging away for about a year and a half without issues.” The Mac mini runs “headless” (no monitor attached), surrenders to network control, and sits in the dark grabbing image data.

“Being a big proponent of PowerPC-based computers, I was quite surprised to see the great performance of my iCCD application on the Intel Core Duo Macs. I had not expected that, to be quite honest. I was wrong, and I’m glad to be wrong. Speed is good!”

For image processing and stacking after the raw frames are captured, Terry’s crew generally turns to either a MacBook Pro (in the field) or the iMac with Intel Core Duo (in the lab). From time to time, Terry runs iCCD image processing on the lab’s Power Mac G5. He developed iCCD and ran it smoothly for years on his original PowerBook Titanium. “Being a big proponent of PowerPC-based computers, I was quite surprised to see the great performance of my iCCD application on the Intel Core Duo Macs,” Terry admits. “I had not expected that, to be quite honest. I was wrong, and I’m glad to be wrong. Speed is good!”

Student Science

But what are these images for? One stellar example is Terry’s recently launched program in which undergraduate students search for new supernova stars. ITT is located amidst Chicago’s light-polluted urban environment. But Terry’s students can remotely control their cameras and “ultimate telephoto lens” telescopes via the web using the VNC server built into Mac OS X. So it doesn’t really matter if the telescope is a meter away from the computer or thousands of kilometers away, under clear, dark skies. And the students like the fact that they can “stay out of range of mosquito dive bombers and out of the bitter cold,” says Terry.

After the students capture raw images, they must mine the data to determine whether they have discovered anything important. Supernovas can be seen in images of far away galaxies. But to find out whether they have captured one, students use iCCD to compare pairs of photos of target galaxies taken weeks — even years — apart. Thanks to Apple’s vImage engine, iCCD can easily rotate and register pairs of images to the same orientation. Students can then “blink” back and forth between before-and-after photos. This is when the supernova reveals itself.

Terry’s students are looking for a particular kind of supernova, the so-called type 1a. Because these supernovas flare with a known brightness, students can calculate their distances. This is important because it lets the student team look for answers to one of the most fundamental questions of our time: How fast is the universe expanding?

Whenever he can, Terry brings together students from different departments to focus on interdisciplinary astronomy projects. In spring 2003, such a group designed and built a 0.6m Newtonian telescope, then wrote Mac OS X-based software so they could control it with an iMac.

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Developing iCCD

To construct an application that would both automate image collection and facilitate easy processing in Apple’s document-based protocol, Terry turned to Objective-C. He likes the intuitive and direct way it builds objects out of the standard ANSI C language, and Objective-C’s clear and simple documentation made it painless to get the most out of Apple’s powerful Cocoa application environment.

“Cocoa is a great GUI writer,” Terry explains. “And GUIs are probably my weakest point as a programmer. But with Cocoa, it was easy. Everything came together rapidly and beautifully.”

As a scientist and engineer, Terry is no stranger to GUI-free command-line coding. He found Apple’s Xcode development package to be extremely helpful. Xcode, Apple’s integrated development environment, offers a graphical workbench of tools with which to build and debug iCCD. And with the Xcode compiler, each new revision of iCCD is native for both PowerPC-based and Intel Core Duo-based Macs.

Terry’s dedication to upgrading iCCD with each release of Mac OS X pays powerful dividends. “Apple continuously adds nice features to Mac OS X, and I love to take advantage of them,” he says. For instance, iCCD uses Apple’s built-in vImage routines to streamline picture-making tasks, particularly geometric transforms, such as rotating, cropping, and resizing images. Different types of telescopes flip the sky’s orientation. Objects might occupy only a portion of the frame or stretch across several frames. Aligning the frames is vital so that stars are registered (i.e., in the same relative positions). In addition, vImage can keep hierarchies of separate color channels for Luminance, Red, Green, Blue (LRGB) corresponding to separate astronomical filters.