Using RA and dec. (Right Ascension and declination) coordinates, it is possible to locate a faint target that might otherwise be difficult to see in your viewfinder. With an undriven mount, you are limited to relatively short exposures, but with a fast lens and high ISO setting, impressive night-sky images are certainly achievable.
The mount's RA axis must be aligned with Earth's axis of rotation, so you must adapt the downloadable plans to suit your latitude. At the North or South Poles, the RA axis would point vertically upwards, and at the equator it would be horizontal. For most of us, the angle between the RA disc and the ground is somewhere in between (90° minus your latitude).
Wrangle the angles
The dec. assembly pivots on the RA disc, but it is clampable with a wing nut when you're ready to take a photo. Similarly, the camera platform pivots on the dec. assembly, also with a clamp. The dec scale is glued so that it reads 90° when the camera is pointing directly at the Pole. As the night sky appears to rotate, the RA scale must be free to turn, so you can adjust it. A strong bulldog clip holds it still while you move the dec. assembly between targets.
To use the mount, it must firstly be polar aligned. Make sure the base is level, with the RA disc facing due north (in the Northern Hemisphere). To fine-tune the alignment, you can place a smartphone (with a planetarium app) on the RA disc and centre the displayed south celestial pole.
Esta historia es de la edición June 2023 de BBC Sky at Night Magazine.
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Esta historia es de la edición June 2023 de BBC Sky at Night Magazine.
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