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    Re: Rising angle of stars
    From: Frank Reed
    Date: 2014 Oct 28, 16:52 -0700

    Hi Steve,

    Yes, that's right: Mintaka's dec is very near zero, which is unique for a star of that brightness. By the way, you weren't wrong. If you're listing a star's declination, and it's in degrees and minutes (sexagesimal notation), then you would normally indicate whether it's north or south by tagging it with a name, "N" or "S". So you would write 41° 30' S for a declination (or latitude). If you decimalize the angle, it's still OK to tag it with a name, but better yet, mark it negative if it's south. In this example, 41° 30' S would be -41.50°.

    For finding azimuth, Mintaka is a unique case. It rises within a fraction of a degree of due east and similarly sets within a fraction of a degree of due west. So if you see it in the sky in the east at a relatively low altitude, say between 3° (where it's minimally visible under excellent conditions) up to about 15°, you can "drag it" back to the horizon by imagining that rising angle, which in the case of a star so close to due east is equal to the latitude. A simple way to do this is to make a "V" with two of your fingers. One finger should point up, the other should point to Mintaka, and if the angle between your fingers is nearly equal to your latitude, then the base of the "V" at your hand on the horizon is due east. You can find (or make!) a protractor and do even better. The key here is that this "dragging" back to the horizon will work for an extended period of time. It takes over an hour for this star to travel from 3° to 15° altitude in mid-latitudes. Despite the fact that the star's actual azimuth may change significantly during that time, you can always find true east by knowing the rising angle.

    Consider a bright star with some other declination, like Capella or Sirius, both of which can be seen very low in the sky. You may not know its rising azimuth offhand, but you can get a "fixed point" on the horizon to steer by using its rising angle. Just trace it back to the horizon from whatever altitude it may have during the course of an hour or two as it climbs into the sky.

    -FER

     

       
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