User manual SBIG SEEING MONITOR

[. . . ] But more and more of our customers are mimicking professional observatory installations with remote observing sites and fully automated observing systems. Remote can mean anything from a few meters to a few thousand kilometers. No matter where one observes, it is often a time consuming matter to get ready for a nights imaging session. [. . . ] The lens and box is permanently pointed at Polaris by the user. It is assumed the user will mount posts in the ground outside his observatory or home for this purpose. Roof mounting is not recommended because small vibrations from the building may affect the monitor's measurements. When properly aligned, one will get an image of Polaris as shown in Figure Two. Of course, Polaris is not eactly at the pole. The field of view is just large enough that the entire orbit of Polaris about the north celestial pole can be captured no matter what time of night the measurements are taken with the camera set up on a fixed mount. Figure Three shows a sequence of images over a night superimposed. The position of the pole is now quite apparent. Figure Three: Sequence of 10 second Images Superimposed The streaks below Polaris in these images are due to the fact that the camera is shutterless and Polaris is exposing the CCD while it is being read out. This has no effect on the calculations for this application. Also, there is no need to take dark frmaes for such short exposures. This system is used to measure the seeing by measuring the hoizontal jitter in the position of Polaris at high speed. A set of equations then can be used to calculate the zenith Full Width Half Maximum (FWHM) that one will obtain in a long exposure image from the rms jitter. The jitter is measured by reading out the CCD while it is being exposed by the light from Polaris in Time Delay and Integration (TDI) mode. An example of the resulting image is shown in Figure Four. Figure Four: TDI Readout Image of Polaris Polaris leaves the bright streak on the right. [. . . ] The first, most common, clear night is a two to three hour period between sunset and the fog coming in from the ocean like a wall. The second is when we get "Santa Ana" winds off the mountains behind Santa Barbara, which is a hot wind characterized by really clear, but highly turbulent air. In Figure Five, below, a graph shows how good it got one night while monitoring with the seeing monitor. [. . . ]