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    Re: NASA and celestial navigation
    From: Sean C
    Date: 2018 Mar 6, 19:04 -0800

    "Often referred to as an octant, the instrument was truly a "point and shoot" device and is similar to the sextant in common use today."

    "Point and shoot", huh? Maybe I've misunderstood what that little button on the handle of my Astra is really for. ;) And to think I've been wasting all this time measuring index error, lining up the body and correcting for dip, etc.

    "By the 1700s, the most popular instrument was the Davis quadrant or back-staff. It was a major conceptual leap in seagoing celestial navigation because it provided a quantitative measurement in degrees of the altitude of Polaris or the sun and related this position to a geographic position. It could measure up to 90 degrees, or a quarter of a circle."

    Correct me if I'm wrong, but wasn't the backstaff limited to angles of around 45°? Also (and I'm being a little pedantic here), I don't think the backstaff itself related positions of Polaris or the Sun to anything. I thought that was the navigator's job.

    "...mirrors and prisms that could be used to observe the nighttime celestial bodies."

    Meh. Twilight and daytime, sure ... but nighttime?

    "Today, seafaring navigators use radar and radio beacons to find their way."

    Do they? I thought radar is primarily used for obstacle/ship avoidance and navigation is done almost exclusively with GPS. Granted, GPS satellites transmit their signals in radio waves, but this paragraph seems to suggest that systems like LORAN are still in widespread use.

    -Sean C.

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