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    Re: A Lunar Example: Sun and Moon vertically aligned
    From: Frank Reed
    Date: 2017 Dec 22, 10:57 -0800

    Ed, if you see that many moons, it may be time to put the bottle down...

    Ha! By the way, I will be replying to your various messages over the next couple of days. I need to set aside an hour or more to do that. Just wanted you to know I haven't forgotten you!

    One quick reply: to get the Sun and Moon on the same or opposite azimuths (both objects on the same vertical circle), plot the sub-Moon and sub-Sun points on the globe, also known as the "geographic positions" of the two bodies. Extend a great circle through those two locations. An observer anywhere along that great circle who can see both objects above the horizon will find them on the same vertical circle. Outside the arc between them, they're on the same azimuth. Inside the arc between them, they're on opposite azimuths. That's not how I set up the example I provided, because I was just playing around (more later), but this is the systematic way to create a vertically-aligned example. It would also be the systematic way to plan ahead to observe that setup.

    I need to write an essay "Crazy-Easy Lunars" to supersede the original "Easy Lunars" essay ...which is now nearly fourteen years old. Stay tuned.

    Frank Reed

       
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