Refracting telescopes won't need this hole. This allows the mask to rest against the corrector plate rim mounting or the vanes of the secondary spider. If necessary to stabilize the mask, cut a large central hole (shown in the diagram) to fit the mask over the secondary mirror mounting of a Schmidt Cassegrain telescope, or a smaller hole to pass the secondary adjustment knob on a Newtonian reflector. This hole can be in the center of the circle for a refractor, but must be to one side in a reflector to avoid the obstruction of the secondary mirror mounting.įor a more durable mask, an excellent material is the stiff plastic used to make real estate and business signs (sold in most hardware stores), but to cut this material you will need a utility knife or heavy shears and a strong hand. (2) Cut a single circular hole in the mask that is about 1/3 your aperture diameter or less, and no more than 80 mm in apertures larger than 200 mm. (1) Choose a suitably large piece of cardboard, matt board or thin foam core board, and cut it to a circular shape that will closely but not snugly fit inside your telescope tube or dew shield. This is easy to do by means of an aperture mask (diagram, below) that reduces the entrance pupil of a telescope and thereby enlarges the diffraction artifact for easier viewing. The first step in double star astronomy is to learn what the Airy disk and diffraction rings look like in their "pure" form, as they will appear under good seeing with sufficient magnification. But with the high magnification necessary to separate very close double stars, it defines the star image. This diffraction pattern is so tiny that the eye cannot distinguish it from a point when low magnification is used. Instead, due to the wave nature of light, they form a specific type of diffraction artifact: a circular, evenly bright Airy disk that (in bright stars) is encircled by one or more concentric diffraction rings. Recognize the Diffraction Artifactĭespite the preconception that stars appear to the observer as "point" light sources, stars never appear as points in an optical system. (See the page A Double Star Primer for an overview of double star astronomy.) 1. This page describes nine steps to develop your visual abilities, with information that can anchor your understanding of the visual challenges in double star astronomy. As observational targets they are robust against light pollution and poor seeing, within reach of telescopes of any aperture, and visible at all times of the year.ĭouble stars present unique challenges to the visual astronomer that require training the eye through knowledge and motivated practice. These gravitationally bound stellar systems combine all types of stars in an enormous variety of dynamic configurations, from matched binary suns to miniature star clusters.
Observing double stars is one of the great pleasures of visual astronomy. Double star astronomy: training the binary eyeĭouble Star Astronomy Part 2: Training the Binary EyeĨ.
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