Field of View

fov-bino   The field of view is the amount of sky you see using an optical aid. I do a lot of sky gazing using either 7×50 or 10×50 binoculars and one of the useful things to know about the binoculars is their respective field of view. In terms of degrees there is not much difference, only 1o between the 7×50 binoculars with an 8o field of view compared to the 10×50 binoculars with a 7o field of view. The greatest difference is the extra magnification the 10×50 binoculars provides.
   So how does this translate into something useful?
Star Hopping
   This is a technique for finding an object in the sky that is a known distance, in degrees, away from a more easily seen object. Typically this is done when using a telescope and the distances are the much smaller field of view for an eyepiece. Regardless of viewing with a telescope eyepiece or binoculars very often there will be a description of perhaps a faint object like an open star cluster, that is near a bright star. With a star chart you could determine which way and how many fields of view you would need to move your optical device. Then note an object across the field of view and re-aim so that the second object is now in the field of view on the side that the first object was. Repeat this until you come to the object being searched for. In this animated graphic a 7×50 binocular is used to view several Messier objects around the feet of the Gemini Twins, and the horns of Taurus the Bull by starting with the star El Nath in Taurus.
   If it Fits…
asterism-bino-ani   There are many small groupings of stars arranged in recognizable patterns like circlets, hexagons, triangles, squares, and so on. Many of these are known as asterisms, or star patterns that are not a constellation but rather are stars within one constellation making the pattern, or stars from more than one constellation sharing stars to form the asterism. Two easy to view are the ‘Y-shape’ in Aquarius the Water Bearer and the ‘Circlet’ in Pisces the Fishes.


Caution: Objects viewed with an optical aid are further than they appear.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

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