Linux, Talon and Astronomy
Putting Talon to use requires a few initial calibration items. As with any telescope, you'll need to check and adjust the polar alignment—the physical location of the telescope in relation to celestial north.
With xobs in the boot.cfg script, the main Talon screen should open right after your desktop loads. From this main screen, select Find Homes (Figure 6). As noted, this routine finds the home mark on each encoder, RA, HA and Focus. From the pop-up window, select All. The telescope should move in all axes. Each axis skips past the home mark initially, backing up incrementally until it finds the mark again. This reduction of each move to the home mark ensures that the telescope ends up precisely on the mark.
The next step is to find limits. This routine locates the telescope's physical limit switches, which prevent the telescope from damaging itself by swinging too far through the travel of each axis. When the switches at both ends of travel are found in an axis, the software writes the location (in encoder counts) to the home.cfg file. You should need to complete the find limits routine only one time.
With the telescope calibrated and aligned, it's time to take some pictures. Open the camera and xephem applications from the command line. Enable telescope control in the xephem options. Select an object by right-clicking in the ephemeris, then select Point Telescope from the resulting pop-up. The telescope should slew to the new position. Click on the camera application and select Take One. With the proper connection to the camera, you'll hear the shutter trip. Within a few seconds, an image of the selected object renders on your screen.
To set up scheduled operations, use the telsched command. In the resulting window, select the size of the mesh, remembering that the tighter the mesh is, the more images taken. Set the time for the operations to start (in UT) and save the schedule file in the default directory. Then pop back out to the main Talon screen and select batch mode. You'll receive a confirmation window. When you select Yes, the Talon application slaves to auto mode. You can cancel auto mode from the main screen. You cannot, however, operate the telescope manually from the main screen while batch mode is in use.
The Talon program is rich with features, providing complete control over the operation of the telescope. Many of the finer features are outlined in the .pdf manual provided in the Talon .tgz file. It's worth a thorough read to understand the telescope interfaces to the control boards and to the software. The manual also contains in-depth information on image processing, solving for WCS solutions, automated and remote operations and finer calibration items that are beyond the scope of this article.
Talon represents a complete leap into the open-source world for astronomers, both professional and amateur. With the robust and networkable nature of Linux, Talon provides a stable platform from which we can do what we've been doing since the beginning of time—viewing, recording and discovering the heavens.
Tony Steidler-Dennison is the director of operations for Optical Mechanics, Inc., and the author of Lockergnome's Penguin Shell newsletter, a twice-weekly tome for Linux users. He maintains Talon on Sourceforge.net and the poli-tech blog “Frankly, I'd Rather Not” at www.steidler.net. He answers all e-mail sent to email@example.com.
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